rustc_ast_lowering/
expr.rs

1use std::mem;
2use std::ops::ControlFlow;
3use std::sync::Arc;
4
5use rustc_ast::*;
6use rustc_ast_pretty::pprust::expr_to_string;
7use rustc_data_structures::stack::ensure_sufficient_stack;
8use rustc_errors::msg;
9use rustc_hir as hir;
10use rustc_hir::def::{DefKind, Res};
11use rustc_hir::{HirId, Target, find_attr};
12use rustc_middle::span_bug;
13use rustc_middle::ty::TyCtxt;
14use rustc_session::errors::report_lit_error;
15use rustc_span::{ByteSymbol, DUMMY_SP, DesugaringKind, Ident, Span, Spanned, Symbol, respan, sym};
16use thin_vec::{ThinVec, thin_vec};
17use visit::{Visitor, walk_expr};
18
19use super::errors::{
20    AsyncCoroutinesNotSupported, AwaitOnlyInAsyncFnAndBlocks, ClosureCannotBeStatic,
21    CoroutineTooManyParameters, FunctionalRecordUpdateDestructuringAssignment,
22    InclusiveRangeWithNoEnd, MatchArmWithNoBody, NeverPatternWithBody, NeverPatternWithGuard,
23    UnderscoreExprLhsAssign,
24};
25use super::{
26    GenericArgsMode, ImplTraitContext, LoweringContext, ParamMode, ResolverAstLoweringExt,
27};
28use crate::errors::{InvalidLegacyConstGenericArg, UseConstGenericArg, YieldInClosure};
29use crate::{AllowReturnTypeNotation, FnDeclKind, ImplTraitPosition, TryBlockScope};
30
31pub(super) struct WillCreateDefIdsVisitor;
32
33impl<'v> rustc_ast::visit::Visitor<'v> for WillCreateDefIdsVisitor {
34    type Result = ControlFlow<Span>;
35
36    fn visit_anon_const(&mut self, c: &'v AnonConst) -> Self::Result {
37        ControlFlow::Break(c.value.span)
38    }
39
40    fn visit_item(&mut self, item: &'v Item) -> Self::Result {
41        ControlFlow::Break(item.span)
42    }
43
44    fn visit_expr(&mut self, ex: &'v Expr) -> Self::Result {
45        match ex.kind {
46            ExprKind::Gen(..) | ExprKind::ConstBlock(..) | ExprKind::Closure(..) => {
47                ControlFlow::Break(ex.span)
48            }
49            _ => walk_expr(self, ex),
50        }
51    }
52}
53
54impl<'hir> LoweringContext<'_, 'hir> {
55    fn lower_exprs(&mut self, exprs: &[Box<Expr>]) -> &'hir [hir::Expr<'hir>] {
56        self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
57    }
58
59    pub(super) fn lower_expr(&mut self, e: &Expr) -> &'hir hir::Expr<'hir> {
60        self.arena.alloc(self.lower_expr_mut(e))
61    }
62
63    pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
64        ensure_sufficient_stack(|| {
65            let mut span = self.lower_span(e.span);
66            match &e.kind {
67                // Parenthesis expression does not have a HirId and is handled specially.
68                ExprKind::Paren(ex) => {
69                    let mut ex = self.lower_expr_mut(ex);
70                    // Include parens in span, but only if it is a super-span.
71                    if e.span.contains(ex.span) {
72                        ex.span = self.lower_span(e.span.with_ctxt(ex.span.ctxt()));
73                    }
74                    // Merge attributes into the inner expression.
75                    if !e.attrs.is_empty() {
76                        let old_attrs = self.attrs.get(&ex.hir_id.local_id).copied().unwrap_or(&[]);
77                        let new_attrs = self
78                            .lower_attrs_vec(&e.attrs, e.span, ex.hir_id, Target::from_expr(e))
79                            .into_iter()
80                            .chain(old_attrs.iter().cloned());
81                        let new_attrs = &*self.arena.alloc_from_iter(new_attrs);
82                        if new_attrs.is_empty() {
83                            return ex;
84                        }
85                        self.attrs.insert(ex.hir_id.local_id, new_attrs);
86                    }
87                    return ex;
88                }
89                // Desugar `ExprForLoop`
90                // from: `[opt_ident]: for await? <pat> in <iter> <body>`
91                //
92                // This also needs special handling because the HirId of the returned `hir::Expr` will not
93                // correspond to the `e.id`, so `lower_expr_for` handles attribute lowering itself.
94                ExprKind::ForLoop { pat, iter, body, label, kind } => {
95                    return self.lower_expr_for(e, pat, iter, body, *label, *kind);
96                }
97                _ => (),
98            }
99
100            let expr_hir_id = self.lower_node_id(e.id);
101            let attrs = self.lower_attrs(expr_hir_id, &e.attrs, e.span, Target::from_expr(e));
102
103            let kind = match &e.kind {
104                ExprKind::Array(exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
105                ExprKind::ConstBlock(c) => hir::ExprKind::ConstBlock(self.lower_const_block(c)),
106                ExprKind::Repeat(expr, count) => {
107                    let expr = self.lower_expr(expr);
108                    let count = self.lower_array_length_to_const_arg(count);
109                    hir::ExprKind::Repeat(expr, count)
110                }
111                ExprKind::Tup(elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
112                ExprKind::Call(f, args) => {
113                    if let Some(legacy_args) = self.resolver.legacy_const_generic_args(f, self.tcx)
114                    {
115                        self.lower_legacy_const_generics((**f).clone(), args.clone(), &legacy_args)
116                    } else {
117                        let f = self.lower_expr(f);
118                        hir::ExprKind::Call(f, self.lower_exprs(args))
119                    }
120                }
121                ExprKind::MethodCall(box MethodCall { seg, receiver, args, span }) => {
122                    let hir_seg = self.arena.alloc(self.lower_path_segment(
123                        e.span,
124                        seg,
125                        ParamMode::Optional,
126                        GenericArgsMode::Err,
127                        ImplTraitContext::Disallowed(ImplTraitPosition::Path),
128                        // Method calls can't have bound modifiers
129                        None,
130                    ));
131                    let receiver = self.lower_expr(receiver);
132                    let args =
133                        self.arena.alloc_from_iter(args.iter().map(|x| self.lower_expr_mut(x)));
134                    hir::ExprKind::MethodCall(hir_seg, receiver, args, self.lower_span(*span))
135                }
136                ExprKind::Binary(binop, lhs, rhs) => {
137                    let binop = self.lower_binop(*binop);
138                    let lhs = self.lower_expr(lhs);
139                    let rhs = self.lower_expr(rhs);
140                    hir::ExprKind::Binary(binop, lhs, rhs)
141                }
142                ExprKind::Unary(op, ohs) => {
143                    let op = self.lower_unop(*op);
144                    let ohs = self.lower_expr(ohs);
145                    hir::ExprKind::Unary(op, ohs)
146                }
147                ExprKind::Lit(token_lit) => hir::ExprKind::Lit(self.lower_lit(token_lit, e.span)),
148                ExprKind::IncludedBytes(byte_sym) => {
149                    let lit = respan(
150                        self.lower_span(e.span),
151                        LitKind::ByteStr(*byte_sym, StrStyle::Cooked),
152                    );
153                    hir::ExprKind::Lit(lit)
154                }
155                ExprKind::Cast(expr, ty) => {
156                    let expr = self.lower_expr(expr);
157                    let ty = self
158                        .lower_ty_alloc(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Cast));
159                    hir::ExprKind::Cast(expr, ty)
160                }
161                ExprKind::Type(expr, ty) => {
162                    let expr = self.lower_expr(expr);
163                    let ty = self
164                        .lower_ty_alloc(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Cast));
165                    hir::ExprKind::Type(expr, ty)
166                }
167                ExprKind::AddrOf(k, m, ohs) => {
168                    let ohs = self.lower_expr(ohs);
169                    hir::ExprKind::AddrOf(*k, *m, ohs)
170                }
171                ExprKind::Let(pat, scrutinee, span, recovered) => {
172                    hir::ExprKind::Let(self.arena.alloc(hir::LetExpr {
173                        span: self.lower_span(*span),
174                        pat: self.lower_pat(pat),
175                        ty: None,
176                        init: self.lower_expr(scrutinee),
177                        recovered: *recovered,
178                    }))
179                }
180                ExprKind::If(cond, then, else_opt) => {
181                    self.lower_expr_if(cond, then, else_opt.as_deref())
182                }
183                ExprKind::While(cond, body, opt_label) => {
184                    self.with_loop_scope(expr_hir_id, |this| {
185                        let span =
186                            this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
187                        let opt_label = this.lower_label(*opt_label, e.id, expr_hir_id);
188                        this.lower_expr_while_in_loop_scope(span, cond, body, opt_label)
189                    })
190                }
191                ExprKind::Loop(body, opt_label, span) => {
192                    self.with_loop_scope(expr_hir_id, |this| {
193                        let opt_label = this.lower_label(*opt_label, e.id, expr_hir_id);
194                        hir::ExprKind::Loop(
195                            this.lower_block(body, false),
196                            opt_label,
197                            hir::LoopSource::Loop,
198                            this.lower_span(*span),
199                        )
200                    })
201                }
202                ExprKind::TryBlock(body, opt_ty) => {
203                    self.lower_expr_try_block(body, opt_ty.as_deref())
204                }
205                ExprKind::Match(expr, arms, kind) => hir::ExprKind::Match(
206                    self.lower_expr(expr),
207                    self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
208                    match kind {
209                        MatchKind::Prefix => hir::MatchSource::Normal,
210                        MatchKind::Postfix => hir::MatchSource::Postfix,
211                    },
212                ),
213                ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
214                ExprKind::Use(expr, use_kw_span) => self.lower_expr_use(*use_kw_span, expr),
215                ExprKind::Closure(box Closure {
216                    binder,
217                    capture_clause,
218                    constness,
219                    coroutine_kind,
220                    movability,
221                    fn_decl,
222                    body,
223                    fn_decl_span,
224                    fn_arg_span,
225                }) => match coroutine_kind {
226                    Some(coroutine_kind) => self.lower_expr_coroutine_closure(
227                        binder,
228                        *capture_clause,
229                        e.id,
230                        expr_hir_id,
231                        *coroutine_kind,
232                        *constness,
233                        fn_decl,
234                        body,
235                        *fn_decl_span,
236                        *fn_arg_span,
237                    ),
238                    None => self.lower_expr_closure(
239                        attrs,
240                        binder,
241                        *capture_clause,
242                        e.id,
243                        *constness,
244                        *movability,
245                        fn_decl,
246                        body,
247                        *fn_decl_span,
248                        *fn_arg_span,
249                    ),
250                },
251                ExprKind::Gen(capture_clause, block, genblock_kind, decl_span) => {
252                    let desugaring_kind = match genblock_kind {
253                        GenBlockKind::Async => hir::CoroutineDesugaring::Async,
254                        GenBlockKind::Gen => hir::CoroutineDesugaring::Gen,
255                        GenBlockKind::AsyncGen => hir::CoroutineDesugaring::AsyncGen,
256                    };
257                    self.make_desugared_coroutine_expr(
258                        *capture_clause,
259                        e.id,
260                        None,
261                        *decl_span,
262                        e.span,
263                        desugaring_kind,
264                        hir::CoroutineSource::Block,
265                        |this| this.with_new_scopes(e.span, |this| this.lower_block_expr(block)),
266                    )
267                }
268                ExprKind::Block(blk, opt_label) => {
269                    // Different from loops, label of block resolves to block id rather than
270                    // expr node id.
271                    let block_hir_id = self.lower_node_id(blk.id);
272                    let opt_label = self.lower_label(*opt_label, blk.id, block_hir_id);
273                    let hir_block = self.arena.alloc(self.lower_block_noalloc(
274                        block_hir_id,
275                        blk,
276                        opt_label.is_some(),
277                    ));
278                    hir::ExprKind::Block(hir_block, opt_label)
279                }
280                ExprKind::Assign(el, er, span) => self.lower_expr_assign(el, er, *span, e.span),
281                ExprKind::AssignOp(op, el, er) => hir::ExprKind::AssignOp(
282                    self.lower_assign_op(*op),
283                    self.lower_expr(el),
284                    self.lower_expr(er),
285                ),
286                ExprKind::Field(el, ident) => {
287                    hir::ExprKind::Field(self.lower_expr(el), self.lower_ident(*ident))
288                }
289                ExprKind::Index(el, er, brackets_span) => hir::ExprKind::Index(
290                    self.lower_expr(el),
291                    self.lower_expr(er),
292                    self.lower_span(*brackets_span),
293                ),
294                ExprKind::Range(e1, e2, lims) => {
295                    span = self.mark_span_with_reason(DesugaringKind::RangeExpr, span, None);
296                    self.lower_expr_range(span, e1.as_deref(), e2.as_deref(), *lims)
297                }
298                ExprKind::Underscore => {
299                    let guar = self.dcx().emit_err(UnderscoreExprLhsAssign { span: e.span });
300                    hir::ExprKind::Err(guar)
301                }
302                ExprKind::Path(qself, path) => {
303                    let qpath = self.lower_qpath(
304                        e.id,
305                        qself,
306                        path,
307                        ParamMode::Optional,
308                        AllowReturnTypeNotation::No,
309                        ImplTraitContext::Disallowed(ImplTraitPosition::Path),
310                        None,
311                    );
312                    hir::ExprKind::Path(qpath)
313                }
314                ExprKind::Break(opt_label, opt_expr) => {
315                    let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
316                    hir::ExprKind::Break(self.lower_jump_destination(e.id, *opt_label), opt_expr)
317                }
318                ExprKind::Continue(opt_label) => {
319                    hir::ExprKind::Continue(self.lower_jump_destination(e.id, *opt_label))
320                }
321                ExprKind::Ret(e) => {
322                    let expr = e.as_ref().map(|x| self.lower_expr(x));
323                    self.checked_return(expr)
324                }
325                ExprKind::Yeet(sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
326                ExprKind::Become(sub_expr) => {
327                    let sub_expr = self.lower_expr(sub_expr);
328                    hir::ExprKind::Become(sub_expr)
329                }
330                ExprKind::InlineAsm(asm) => {
331                    hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
332                }
333                ExprKind::FormatArgs(fmt) => self.lower_format_args(e.span, fmt),
334                ExprKind::OffsetOf(container, fields) => hir::ExprKind::OffsetOf(
335                    self.lower_ty_alloc(
336                        container,
337                        ImplTraitContext::Disallowed(ImplTraitPosition::OffsetOf),
338                    ),
339                    self.arena.alloc_from_iter(fields.iter().map(|&ident| self.lower_ident(ident))),
340                ),
341                ExprKind::Struct(se) => {
342                    let rest = match se.rest {
343                        StructRest::Base(ref e) => hir::StructTailExpr::Base(self.lower_expr(e)),
344                        StructRest::Rest(sp) => {
345                            hir::StructTailExpr::DefaultFields(self.lower_span(sp))
346                        }
347                        StructRest::None => hir::StructTailExpr::None,
348                        StructRest::NoneWithError(guar) => hir::StructTailExpr::NoneWithError(guar),
349                    };
350                    hir::ExprKind::Struct(
351                        self.arena.alloc(self.lower_qpath(
352                            e.id,
353                            &se.qself,
354                            &se.path,
355                            ParamMode::Optional,
356                            AllowReturnTypeNotation::No,
357                            ImplTraitContext::Disallowed(ImplTraitPosition::Path),
358                            None,
359                        )),
360                        self.arena
361                            .alloc_from_iter(se.fields.iter().map(|x| self.lower_expr_field(x))),
362                        rest,
363                    )
364                }
365                ExprKind::Yield(kind) => self.lower_expr_yield(e.span, kind.expr().map(|x| &**x)),
366                ExprKind::Err(guar) => hir::ExprKind::Err(*guar),
367
368                ExprKind::UnsafeBinderCast(kind, expr, ty) => hir::ExprKind::UnsafeBinderCast(
369                    *kind,
370                    self.lower_expr(expr),
371                    ty.as_ref().map(|ty| {
372                        self.lower_ty_alloc(
373                            ty,
374                            ImplTraitContext::Disallowed(ImplTraitPosition::Cast),
375                        )
376                    }),
377                ),
378
379                ExprKind::Dummy => {
380                    ::rustc_middle::util::bug::span_bug_fmt(e.span,
    format_args!("lowered ExprKind::Dummy"))span_bug!(e.span, "lowered ExprKind::Dummy")
381                }
382
383                ExprKind::Try(sub_expr) => self.lower_expr_try(e.span, sub_expr),
384
385                ExprKind::Paren(_) | ExprKind::ForLoop { .. } => {
386                    {
    ::core::panicking::panic_fmt(format_args!("internal error: entered unreachable code: {0}",
            format_args!("already handled")));
}unreachable!("already handled")
387                }
388
389                ExprKind::MacCall(_) => {
    ::core::panicking::panic_fmt(format_args!("{0:?} shouldn\'t exist here",
            e.span));
}panic!("{:?} shouldn't exist here", e.span),
390            };
391
392            hir::Expr { hir_id: expr_hir_id, kind, span }
393        })
394    }
395
396    pub(crate) fn lower_const_block(&mut self, c: &AnonConst) -> hir::ConstBlock {
397        self.with_new_scopes(c.value.span, |this| {
398            let def_id = this.local_def_id(c.id);
399            hir::ConstBlock {
400                def_id,
401                hir_id: this.lower_node_id(c.id),
402                body: this.lower_const_body(c.value.span, Some(&c.value)),
403            }
404        })
405    }
406
407    pub(crate) fn lower_lit(&mut self, token_lit: &token::Lit, span: Span) -> hir::Lit {
408        let lit_kind = match LitKind::from_token_lit(*token_lit) {
409            Ok(lit_kind) => lit_kind,
410            Err(err) => {
411                let guar = report_lit_error(&self.tcx.sess.psess, err, *token_lit, span);
412                LitKind::Err(guar)
413            }
414        };
415        respan(self.lower_span(span), lit_kind)
416    }
417
418    fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
419        match u {
420            UnOp::Deref => hir::UnOp::Deref,
421            UnOp::Not => hir::UnOp::Not,
422            UnOp::Neg => hir::UnOp::Neg,
423        }
424    }
425
426    fn lower_binop(&mut self, b: BinOp) -> BinOp {
427        Spanned { node: b.node, span: self.lower_span(b.span) }
428    }
429
430    fn lower_assign_op(&mut self, a: AssignOp) -> AssignOp {
431        Spanned { node: a.node, span: self.lower_span(a.span) }
432    }
433
434    fn lower_legacy_const_generics(
435        &mut self,
436        mut f: Expr,
437        args: ThinVec<Box<Expr>>,
438        legacy_args_idx: &[usize],
439    ) -> hir::ExprKind<'hir> {
440        let ExprKind::Path(None, path) = &mut f.kind else {
441            ::core::panicking::panic("internal error: entered unreachable code");unreachable!();
442        };
443
444        let mut error = None;
445        let mut invalid_expr_error = |tcx: TyCtxt<'_>, span| {
446            // Avoid emitting the error multiple times.
447            if error.is_none() {
448                let mut const_args = ::alloc::vec::Vec::new()vec![];
449                let mut other_args = ::alloc::vec::Vec::new()vec![];
450                for (idx, arg) in args.iter().enumerate() {
451                    if legacy_args_idx.contains(&idx) {
452                        const_args.push(::alloc::__export::must_use({
        ::alloc::fmt::format(format_args!("{{ {0} }}", expr_to_string(arg)))
    })format!("{{ {} }}", expr_to_string(arg)));
453                    } else {
454                        other_args.push(expr_to_string(arg));
455                    }
456                }
457                let suggestion = UseConstGenericArg {
458                    end_of_fn: f.span.shrink_to_hi(),
459                    const_args: const_args.join(", "),
460                    other_args: other_args.join(", "),
461                    call_args: args[0].span.to(args.last().unwrap().span),
462                };
463                error = Some(tcx.dcx().emit_err(InvalidLegacyConstGenericArg { span, suggestion }));
464            }
465            error.unwrap()
466        };
467
468        // Split the arguments into const generics and normal arguments
469        let mut real_args = ::alloc::vec::Vec::new()vec![];
470        let mut generic_args = ThinVec::new();
471        for (idx, arg) in args.iter().cloned().enumerate() {
472            if legacy_args_idx.contains(&idx) {
473                let node_id = self.next_node_id();
474                self.create_def(node_id, None, DefKind::AnonConst, f.span);
475                let const_value =
476                    if let ControlFlow::Break(span) = WillCreateDefIdsVisitor.visit_expr(&arg) {
477                        Box::new(Expr {
478                            id: self.next_node_id(),
479                            kind: ExprKind::Err(invalid_expr_error(self.tcx, span)),
480                            span: f.span,
481                            attrs: [].into(),
482                            tokens: None,
483                        })
484                    } else {
485                        arg
486                    };
487
488                let anon_const = AnonConst {
489                    id: node_id,
490                    value: const_value,
491                    mgca_disambiguation: MgcaDisambiguation::AnonConst,
492                };
493                generic_args.push(AngleBracketedArg::Arg(GenericArg::Const(anon_const)));
494            } else {
495                real_args.push(arg);
496            }
497        }
498
499        // Add generic args to the last element of the path.
500        let last_segment = path.segments.last_mut().unwrap();
501        if !last_segment.args.is_none() {
    ::core::panicking::panic("assertion failed: last_segment.args.is_none()")
};assert!(last_segment.args.is_none());
502        last_segment.args = Some(Box::new(GenericArgs::AngleBracketed(AngleBracketedArgs {
503            span: DUMMY_SP,
504            args: generic_args,
505        })));
506
507        // Now lower everything as normal.
508        let f = self.lower_expr(&f);
509        hir::ExprKind::Call(f, self.lower_exprs(&real_args))
510    }
511
512    fn lower_expr_if(
513        &mut self,
514        cond: &Expr,
515        then: &Block,
516        else_opt: Option<&Expr>,
517    ) -> hir::ExprKind<'hir> {
518        let lowered_cond = self.lower_expr(cond);
519        let then_expr = self.lower_block_expr(then);
520        if let Some(rslt) = else_opt {
521            hir::ExprKind::If(
522                lowered_cond,
523                self.arena.alloc(then_expr),
524                Some(self.lower_expr(rslt)),
525            )
526        } else {
527            hir::ExprKind::If(lowered_cond, self.arena.alloc(then_expr), None)
528        }
529    }
530
531    // We desugar: `'label: while $cond $body` into:
532    //
533    // ```
534    // 'label: loop {
535    //   if { let _t = $cond; _t } {
536    //     $body
537    //   }
538    //   else {
539    //     break;
540    //   }
541    // }
542    // ```
543    //
544    // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
545    // to preserve drop semantics since `while $cond { ... }` does not
546    // let temporaries live outside of `cond`.
547    fn lower_expr_while_in_loop_scope(
548        &mut self,
549        span: Span,
550        cond: &Expr,
551        body: &Block,
552        opt_label: Option<Label>,
553    ) -> hir::ExprKind<'hir> {
554        let lowered_cond = self.with_loop_condition_scope(|t| t.lower_expr(cond));
555        let then = self.lower_block_expr(body);
556        let expr_break = self.expr_break(span);
557        let stmt_break = self.stmt_expr(span, expr_break);
558        let else_blk = self.block_all(span, self.arena.alloc_from_iter([stmt_break])arena_vec![self; stmt_break], None);
559        let else_expr = self.arena.alloc(self.expr_block(else_blk));
560        let if_kind = hir::ExprKind::If(lowered_cond, self.arena.alloc(then), Some(else_expr));
561        let if_expr = self.expr(span, if_kind);
562        let block = self.block_expr(self.arena.alloc(if_expr));
563        let span = self.lower_span(span.with_hi(cond.span.hi()));
564        hir::ExprKind::Loop(block, opt_label, hir::LoopSource::While, span)
565    }
566
567    /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_output(<expr>) }`,
568    /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_output(()) }`
569    /// and save the block id to use it as a break target for desugaring of the `?` operator.
570    fn lower_expr_try_block(&mut self, body: &Block, opt_ty: Option<&Ty>) -> hir::ExprKind<'hir> {
571        let body_hir_id = self.lower_node_id(body.id);
572        let new_scope = if opt_ty.is_some() {
573            TryBlockScope::Heterogeneous(body_hir_id)
574        } else {
575            TryBlockScope::Homogeneous(body_hir_id)
576        };
577        let whole_block = self.with_try_block_scope(new_scope, |this| {
578            let mut block = this.lower_block_noalloc(body_hir_id, body, true);
579
580            // Final expression of the block (if present) or `()` with span at the end of block
581            let (try_span, tail_expr) = if let Some(expr) = block.expr.take() {
582                (
583                    this.mark_span_with_reason(
584                        DesugaringKind::TryBlock,
585                        expr.span,
586                        Some(Arc::clone(&this.allow_try_trait)),
587                    ),
588                    expr,
589                )
590            } else {
591                let try_span = this.mark_span_with_reason(
592                    DesugaringKind::TryBlock,
593                    this.tcx.sess.source_map().end_point(body.span),
594                    Some(Arc::clone(&this.allow_try_trait)),
595                );
596
597                (try_span, this.expr_unit(try_span))
598            };
599
600            let ok_wrapped_span =
601                this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
602
603            // `::std::ops::Try::from_output($tail_expr)`
604            block.expr = Some(this.wrap_in_try_constructor(
605                hir::LangItem::TryTraitFromOutput,
606                try_span,
607                tail_expr,
608                ok_wrapped_span,
609            ));
610
611            this.arena.alloc(block)
612        });
613
614        if let Some(ty) = opt_ty {
615            let ty = self.lower_ty_alloc(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Path));
616            let block_expr = self.arena.alloc(self.expr_block(whole_block));
617            hir::ExprKind::Type(block_expr, ty)
618        } else {
619            hir::ExprKind::Block(whole_block, None)
620        }
621    }
622
623    fn wrap_in_try_constructor(
624        &mut self,
625        lang_item: hir::LangItem,
626        method_span: Span,
627        expr: &'hir hir::Expr<'hir>,
628        overall_span: Span,
629    ) -> &'hir hir::Expr<'hir> {
630        let constructor = self.arena.alloc(self.expr_lang_item_path(method_span, lang_item));
631        self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
632    }
633
634    fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
635        let pat = self.lower_pat(&arm.pat);
636        let guard = arm.guard.as_ref().map(|guard| self.lower_expr(&guard.cond));
637        let hir_id = self.next_id();
638        let span = self.lower_span(arm.span);
639        self.lower_attrs(hir_id, &arm.attrs, arm.span, Target::Arm);
640        let is_never_pattern = pat.is_never_pattern();
641        // We need to lower the body even if it's unneeded for never pattern in match,
642        // ensure that we can get HirId for DefId if need (issue #137708).
643        let body = arm.body.as_ref().map(|x| self.lower_expr(x));
644        let body = if let Some(body) = body
645            && !is_never_pattern
646        {
647            body
648        } else {
649            // Either `body.is_none()` or `is_never_pattern` here.
650            if !is_never_pattern {
651                if self.tcx.features().never_patterns() {
652                    // If the feature is off we already emitted the error after parsing.
653                    let suggestion = span.shrink_to_hi();
654                    self.dcx().emit_err(MatchArmWithNoBody { span, suggestion });
655                }
656            } else if let Some(body) = &arm.body {
657                self.dcx().emit_err(NeverPatternWithBody { span: body.span });
658            } else if let Some(g) = &arm.guard {
659                self.dcx().emit_err(NeverPatternWithGuard { span: g.span() });
660            }
661
662            // We add a fake `loop {}` arm body so that it typecks to `!`. The mir lowering of never
663            // patterns ensures this loop is not reachable.
664            let block = self.arena.alloc(hir::Block {
665                stmts: &[],
666                expr: None,
667                hir_id: self.next_id(),
668                rules: hir::BlockCheckMode::DefaultBlock,
669                span,
670                targeted_by_break: false,
671            });
672            self.arena.alloc(hir::Expr {
673                hir_id: self.next_id(),
674                kind: hir::ExprKind::Loop(block, None, hir::LoopSource::Loop, span),
675                span,
676            })
677        };
678        hir::Arm { hir_id, pat, guard, body, span }
679    }
680
681    fn lower_capture_clause(&mut self, capture_clause: CaptureBy) -> CaptureBy {
682        match capture_clause {
683            CaptureBy::Ref => CaptureBy::Ref,
684            CaptureBy::Use { use_kw } => CaptureBy::Use { use_kw: self.lower_span(use_kw) },
685            CaptureBy::Value { move_kw } => CaptureBy::Value { move_kw: self.lower_span(move_kw) },
686        }
687    }
688
689    /// Lower/desugar a coroutine construct.
690    ///
691    /// In particular, this creates the correct async resume argument and `_task_context`.
692    ///
693    /// This results in:
694    ///
695    /// ```text
696    /// static move? |<_task_context?>| -> <return_ty> {
697    ///     <body>
698    /// }
699    /// ```
700    pub(super) fn make_desugared_coroutine_expr(
701        &mut self,
702        capture_clause: CaptureBy,
703        closure_node_id: NodeId,
704        return_ty: Option<hir::FnRetTy<'hir>>,
705        fn_decl_span: Span,
706        span: Span,
707        desugaring_kind: hir::CoroutineDesugaring,
708        coroutine_source: hir::CoroutineSource,
709        body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
710    ) -> hir::ExprKind<'hir> {
711        let closure_def_id = self.local_def_id(closure_node_id);
712        let coroutine_kind = hir::CoroutineKind::Desugared(desugaring_kind, coroutine_source);
713
714        // The `async` desugaring takes a resume argument and maintains a `task_context`,
715        // whereas a generator does not.
716        let (inputs, params, task_context): (&[_], &[_], _) = match desugaring_kind {
717            hir::CoroutineDesugaring::Async | hir::CoroutineDesugaring::AsyncGen => {
718                // Resume argument type: `ResumeTy`
719                let unstable_span = self.mark_span_with_reason(
720                    DesugaringKind::Async,
721                    self.lower_span(span),
722                    Some(Arc::clone(&self.allow_gen_future)),
723                );
724                let resume_ty =
725                    self.make_lang_item_qpath(hir::LangItem::ResumeTy, unstable_span, None);
726                let input_ty = hir::Ty {
727                    hir_id: self.next_id(),
728                    kind: hir::TyKind::Path(resume_ty),
729                    span: unstable_span,
730                };
731                let inputs = self.arena.alloc_from_iter([input_ty])arena_vec![self; input_ty];
732
733                // Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
734                let (pat, task_context_hid) = self.pat_ident_binding_mode(
735                    span,
736                    Ident::with_dummy_span(sym::_task_context),
737                    hir::BindingMode::MUT,
738                );
739                let param = hir::Param {
740                    hir_id: self.next_id(),
741                    pat,
742                    ty_span: self.lower_span(span),
743                    span: self.lower_span(span),
744                };
745                let params = self.arena.alloc_from_iter([param])arena_vec![self; param];
746
747                (inputs, params, Some(task_context_hid))
748            }
749            hir::CoroutineDesugaring::Gen => (&[], &[], None),
750        };
751
752        let output =
753            return_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span)));
754
755        let fn_decl = self.arena.alloc(hir::FnDecl {
756            inputs,
757            output,
758            fn_decl_kind: hir::FnDeclFlags::default(),
759        });
760
761        let body = self.lower_body(move |this| {
762            this.coroutine_kind = Some(coroutine_kind);
763
764            let old_ctx = this.task_context;
765            if task_context.is_some() {
766                this.task_context = task_context;
767            }
768            let res = body(this);
769            this.task_context = old_ctx;
770
771            (params, res)
772        });
773
774        // `static |<_task_context?>| -> <return_ty> { <body> }`:
775        hir::ExprKind::Closure(self.arena.alloc(hir::Closure {
776            def_id: closure_def_id,
777            binder: hir::ClosureBinder::Default,
778            capture_clause: self.lower_capture_clause(capture_clause),
779            bound_generic_params: &[],
780            fn_decl,
781            body,
782            fn_decl_span: self.lower_span(fn_decl_span),
783            fn_arg_span: None,
784            kind: hir::ClosureKind::Coroutine(coroutine_kind),
785            constness: hir::Constness::NotConst,
786        }))
787    }
788
789    /// Forwards a possible `#[track_caller]` annotation from `outer_hir_id` to
790    /// `inner_hir_id` in case the `async_fn_track_caller` feature is enabled.
791    pub(super) fn maybe_forward_track_caller(
792        &mut self,
793        span: Span,
794        outer_hir_id: HirId,
795        inner_hir_id: HirId,
796    ) {
797        if self.tcx.features().async_fn_track_caller()
798            && let Some(attrs) = self.attrs.get(&outer_hir_id.local_id)
799            && {
    {
            'done:
                {
                for i in *attrs {
                    #[allow(unused_imports)]
                    use rustc_hir::attrs::AttributeKind::*;
                    let i: &rustc_hir::Attribute = i;
                    match i {
                        rustc_hir::Attribute::Parsed(TrackCaller(_)) => {
                            break 'done Some(());
                        }
                        rustc_hir::Attribute::Unparsed(..) =>
                            {}
                            #[deny(unreachable_patterns)]
                            _ => {}
                    }
                }
                None
            }
        }.is_some()
}find_attr!(*attrs, TrackCaller(_))
800        {
801            let unstable_span = self.mark_span_with_reason(
802                DesugaringKind::Async,
803                span,
804                Some(Arc::clone(&self.allow_gen_future)),
805            );
806            self.lower_attrs(
807                inner_hir_id,
808                &[Attribute {
809                    kind: AttrKind::Normal(Box::new(NormalAttr::from_ident(Ident::new(
810                        sym::track_caller,
811                        span,
812                    )))),
813                    id: self.tcx.sess.psess.attr_id_generator.mk_attr_id(),
814                    style: AttrStyle::Outer,
815                    span: unstable_span,
816                }],
817                span,
818                Target::Fn,
819            );
820        }
821    }
822
823    /// Desugar `<expr>.await` into:
824    /// ```ignore (pseudo-rust)
825    /// match ::std::future::IntoFuture::into_future(<expr>) {
826    ///     mut __awaitee => loop {
827    ///         match unsafe { ::std::future::Future::poll(
828    ///             <::std::pin::Pin>::new_unchecked(&mut __awaitee),
829    ///             ::std::future::get_context(task_context),
830    ///         ) } {
831    ///             ::std::task::Poll::Ready(result) => break result,
832    ///             ::std::task::Poll::Pending => {}
833    ///         }
834    ///         task_context = yield ();
835    ///     }
836    /// }
837    /// ```
838    fn lower_expr_await(&mut self, await_kw_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
839        let expr = self.arena.alloc(self.lower_expr_mut(expr));
840        self.make_lowered_await(await_kw_span, expr, FutureKind::Future)
841    }
842
843    /// Takes an expr that has already been lowered and generates a desugared await loop around it
844    fn make_lowered_await(
845        &mut self,
846        await_kw_span: Span,
847        expr: &'hir hir::Expr<'hir>,
848        await_kind: FutureKind,
849    ) -> hir::ExprKind<'hir> {
850        let full_span = expr.span.to(await_kw_span);
851
852        let is_async_gen = match self.coroutine_kind {
853            Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)) => false,
854            Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::AsyncGen, _)) => true,
855            Some(hir::CoroutineKind::Coroutine(_))
856            | Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _))
857            | None => {
858                // Lower to a block `{ EXPR; <error> }` so that the awaited expr
859                // is not accidentally orphaned.
860                let stmt_id = self.next_id();
861                let expr_err = self.expr(
862                    expr.span,
863                    hir::ExprKind::Err(self.dcx().emit_err(AwaitOnlyInAsyncFnAndBlocks {
864                        await_kw_span,
865                        item_span: self.current_item,
866                    })),
867                );
868                return hir::ExprKind::Block(
869                    self.block_all(
870                        expr.span,
871                        self.arena.alloc_from_iter([hir::Stmt {
                hir_id: stmt_id,
                kind: hir::StmtKind::Semi(expr),
                span: expr.span,
            }])arena_vec![self; hir::Stmt {
872                            hir_id: stmt_id,
873                            kind: hir::StmtKind::Semi(expr),
874                            span: expr.span,
875                        }],
876                        Some(self.arena.alloc(expr_err)),
877                    ),
878                    None,
879                );
880            }
881        };
882
883        let features = match await_kind {
884            FutureKind::Future if is_async_gen => Some(Arc::clone(&self.allow_async_gen)),
885            FutureKind::Future => None,
886            FutureKind::AsyncIterator => Some(Arc::clone(&self.allow_for_await)),
887        };
888        let span = self.mark_span_with_reason(DesugaringKind::Await, await_kw_span, features);
889        let gen_future_span = self.mark_span_with_reason(
890            DesugaringKind::Await,
891            full_span,
892            Some(Arc::clone(&self.allow_gen_future)),
893        );
894        let expr_hir_id = expr.hir_id;
895
896        // Note that the name of this binding must not be changed to something else because
897        // debuggers and debugger extensions expect it to be called `__awaitee`. They use
898        // this name to identify what is being awaited by a suspended async functions.
899        let awaitee_ident = Ident::with_dummy_span(sym::__awaitee);
900        let (awaitee_pat, awaitee_pat_hid) =
901            self.pat_ident_binding_mode(gen_future_span, awaitee_ident, hir::BindingMode::MUT);
902
903        let task_context_ident = Ident::with_dummy_span(sym::_task_context);
904
905        // unsafe {
906        //     ::std::future::Future::poll(
907        //         ::std::pin::Pin::new_unchecked(&mut __awaitee),
908        //         ::std::future::get_context(task_context),
909        //     )
910        // }
911        let poll_expr = {
912            let awaitee = self.expr_ident(span, awaitee_ident, awaitee_pat_hid);
913            let ref_mut_awaitee = self.expr_mut_addr_of(span, awaitee);
914
915            let Some(task_context_hid) = self.task_context else {
916                {
    ::core::panicking::panic_fmt(format_args!("internal error: entered unreachable code: {0}",
            format_args!("use of `await` outside of an async context.")));
};unreachable!("use of `await` outside of an async context.");
917            };
918
919            let task_context = self.expr_ident_mut(span, task_context_ident, task_context_hid);
920
921            let new_unchecked = self.expr_call_lang_item_fn_mut(
922                span,
923                hir::LangItem::PinNewUnchecked,
924                self.arena.alloc_from_iter([ref_mut_awaitee])arena_vec![self; ref_mut_awaitee],
925            );
926            let get_context = self.expr_call_lang_item_fn_mut(
927                gen_future_span,
928                hir::LangItem::GetContext,
929                self.arena.alloc_from_iter([task_context])arena_vec![self; task_context],
930            );
931            let call = match await_kind {
932                FutureKind::Future => self.expr_call_lang_item_fn(
933                    span,
934                    hir::LangItem::FuturePoll,
935                    self.arena.alloc_from_iter([new_unchecked, get_context])arena_vec![self; new_unchecked, get_context],
936                ),
937                FutureKind::AsyncIterator => self.expr_call_lang_item_fn(
938                    span,
939                    hir::LangItem::AsyncIteratorPollNext,
940                    self.arena.alloc_from_iter([new_unchecked, get_context])arena_vec![self; new_unchecked, get_context],
941                ),
942            };
943            self.arena.alloc(self.expr_unsafe(span, call))
944        };
945
946        // `::std::task::Poll::Ready(result) => break result`
947        let loop_node_id = self.next_node_id();
948        let loop_hir_id = self.lower_node_id(loop_node_id);
949        let ready_arm = {
950            let x_ident = Ident::with_dummy_span(sym::result);
951            let (x_pat, x_pat_hid) = self.pat_ident(gen_future_span, x_ident);
952            let x_expr = self.expr_ident(gen_future_span, x_ident, x_pat_hid);
953            let ready_field = self.single_pat_field(gen_future_span, x_pat);
954            let ready_pat = self.pat_lang_item_variant(span, hir::LangItem::PollReady, ready_field);
955            let break_x = self.with_loop_scope(loop_hir_id, move |this| {
956                let expr_break =
957                    hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
958                this.arena.alloc(this.expr(gen_future_span, expr_break))
959            });
960            self.arm(ready_pat, break_x, span)
961        };
962
963        // `::std::task::Poll::Pending => {}`
964        let pending_arm = {
965            let pending_pat = self.pat_lang_item_variant(span, hir::LangItem::PollPending, &[]);
966            let empty_block = self.expr_block_empty(span);
967            self.arm(pending_pat, empty_block, span)
968        };
969
970        let inner_match_stmt = {
971            let match_expr = self.expr_match(
972                span,
973                poll_expr,
974                self.arena.alloc_from_iter([ready_arm, pending_arm])arena_vec![self; ready_arm, pending_arm],
975                hir::MatchSource::AwaitDesugar,
976            );
977            self.stmt_expr(span, match_expr)
978        };
979
980        // Depending on `async` of `async gen`:
981        // async     - task_context = yield ();
982        // async gen - task_context = yield ASYNC_GEN_PENDING;
983        let yield_stmt = {
984            let yielded = if is_async_gen {
985                self.arena.alloc(self.expr_lang_item_path(span, hir::LangItem::AsyncGenPending))
986            } else {
987                self.expr_unit(span)
988            };
989
990            let yield_expr = self.expr(
991                span,
992                hir::ExprKind::Yield(yielded, hir::YieldSource::Await { expr: Some(expr_hir_id) }),
993            );
994            let yield_expr = self.arena.alloc(yield_expr);
995
996            let Some(task_context_hid) = self.task_context else {
997                {
    ::core::panicking::panic_fmt(format_args!("internal error: entered unreachable code: {0}",
            format_args!("use of `await` outside of an async context.")));
};unreachable!("use of `await` outside of an async context.");
998            };
999
1000            let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
1001            let assign =
1002                self.expr(span, hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span)));
1003            self.stmt_expr(span, assign)
1004        };
1005
1006        let loop_block = self.block_all(span, self.arena.alloc_from_iter([inner_match_stmt, yield_stmt])arena_vec![self; inner_match_stmt, yield_stmt], None);
1007
1008        // loop { .. }
1009        let loop_expr = self.arena.alloc(hir::Expr {
1010            hir_id: loop_hir_id,
1011            kind: hir::ExprKind::Loop(
1012                loop_block,
1013                None,
1014                hir::LoopSource::Loop,
1015                self.lower_span(span),
1016            ),
1017            span: self.lower_span(span),
1018        });
1019
1020        // mut __awaitee => loop { ... }
1021        let awaitee_arm = self.arm(awaitee_pat, loop_expr, span);
1022
1023        // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
1024        let into_future_expr = match await_kind {
1025            FutureKind::Future => self.expr_call_lang_item_fn(
1026                span,
1027                hir::LangItem::IntoFutureIntoFuture,
1028                self.arena.alloc_from_iter([*expr])arena_vec![self; *expr],
1029            ),
1030            // Not needed for `for await` because we expect to have already called
1031            // `IntoAsyncIterator::into_async_iter` on it.
1032            FutureKind::AsyncIterator => expr,
1033        };
1034
1035        // match <into_future_expr> {
1036        //     mut __awaitee => loop { .. }
1037        // }
1038        hir::ExprKind::Match(
1039            into_future_expr,
1040            self.arena.alloc_from_iter([awaitee_arm])arena_vec![self; awaitee_arm],
1041            hir::MatchSource::AwaitDesugar,
1042        )
1043    }
1044
1045    fn lower_expr_use(&mut self, use_kw_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
1046        hir::ExprKind::Use(self.lower_expr(expr), self.lower_span(use_kw_span))
1047    }
1048
1049    fn lower_expr_closure(
1050        &mut self,
1051        attrs: &[rustc_hir::Attribute],
1052        binder: &ClosureBinder,
1053        capture_clause: CaptureBy,
1054        closure_id: NodeId,
1055        constness: Const,
1056        movability: Movability,
1057        decl: &FnDecl,
1058        body: &Expr,
1059        fn_decl_span: Span,
1060        fn_arg_span: Span,
1061    ) -> hir::ExprKind<'hir> {
1062        let closure_def_id = self.local_def_id(closure_id);
1063        let (binder_clause, generic_params) = self.lower_closure_binder(binder);
1064
1065        let (body_id, closure_kind) = self.with_new_scopes(fn_decl_span, move |this| {
1066            let mut coroutine_kind =
1067                {
    'done:
        {
        for i in attrs {
            #[allow(unused_imports)]
            use rustc_hir::attrs::AttributeKind::*;
            let i: &rustc_hir::Attribute = i;
            match i {
                rustc_hir::Attribute::Parsed(Coroutine) => {
                    break 'done
                        Some(hir::CoroutineKind::Coroutine(Movability::Movable));
                }
                rustc_hir::Attribute::Unparsed(..) =>
                    {}
                    #[deny(unreachable_patterns)]
                    _ => {}
            }
        }
        None
    }
}find_attr!(attrs, Coroutine => hir::CoroutineKind::Coroutine(Movability::Movable));
1068
1069            // FIXME(contracts): Support contracts on closures?
1070            let body_id = this.lower_fn_body(decl, None, |this| {
1071                this.coroutine_kind = coroutine_kind;
1072                let e = this.lower_expr_mut(body);
1073                coroutine_kind = this.coroutine_kind;
1074                e
1075            });
1076            let coroutine_option =
1077                this.closure_movability_for_fn(decl, fn_decl_span, coroutine_kind, movability);
1078            (body_id, coroutine_option)
1079        });
1080
1081        let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
1082        // Lower outside new scope to preserve `is_in_loop_condition`.
1083        let fn_decl = self.lower_fn_decl(decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
1084
1085        let c = self.arena.alloc(hir::Closure {
1086            def_id: closure_def_id,
1087            binder: binder_clause,
1088            capture_clause: self.lower_capture_clause(capture_clause),
1089            bound_generic_params,
1090            fn_decl,
1091            body: body_id,
1092            fn_decl_span: self.lower_span(fn_decl_span),
1093            fn_arg_span: Some(self.lower_span(fn_arg_span)),
1094            kind: closure_kind,
1095            constness: self.lower_constness(constness),
1096        });
1097
1098        hir::ExprKind::Closure(c)
1099    }
1100
1101    fn closure_movability_for_fn(
1102        &mut self,
1103        decl: &FnDecl,
1104        fn_decl_span: Span,
1105        coroutine_kind: Option<hir::CoroutineKind>,
1106        movability: Movability,
1107    ) -> hir::ClosureKind {
1108        match coroutine_kind {
1109            Some(hir::CoroutineKind::Coroutine(_)) => {
1110                if decl.inputs.len() > 1 {
1111                    self.dcx().emit_err(CoroutineTooManyParameters { fn_decl_span });
1112                }
1113                hir::ClosureKind::Coroutine(hir::CoroutineKind::Coroutine(movability))
1114            }
1115            Some(
1116                hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _)
1117                | hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)
1118                | hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::AsyncGen, _),
1119            ) => {
1120                {
    ::core::panicking::panic_fmt(format_args!("non-`async`/`gen` closure body turned `async`/`gen` during lowering"));
};panic!("non-`async`/`gen` closure body turned `async`/`gen` during lowering");
1121            }
1122            None => {
1123                if movability == Movability::Static {
1124                    self.dcx().emit_err(ClosureCannotBeStatic { fn_decl_span });
1125                }
1126                hir::ClosureKind::Closure
1127            }
1128        }
1129    }
1130
1131    fn lower_closure_binder<'c>(
1132        &mut self,
1133        binder: &'c ClosureBinder,
1134    ) -> (hir::ClosureBinder, &'c [GenericParam]) {
1135        let (binder, params) = match binder {
1136            ClosureBinder::NotPresent => (hir::ClosureBinder::Default, &[][..]),
1137            ClosureBinder::For { span, generic_params } => {
1138                let span = self.lower_span(*span);
1139                (hir::ClosureBinder::For { span }, &**generic_params)
1140            }
1141        };
1142
1143        (binder, params)
1144    }
1145
1146    fn lower_expr_coroutine_closure(
1147        &mut self,
1148        binder: &ClosureBinder,
1149        capture_clause: CaptureBy,
1150        closure_id: NodeId,
1151        closure_hir_id: HirId,
1152        coroutine_kind: CoroutineKind,
1153        constness: Const,
1154        decl: &FnDecl,
1155        body: &Expr,
1156        fn_decl_span: Span,
1157        fn_arg_span: Span,
1158    ) -> hir::ExprKind<'hir> {
1159        let closure_def_id = self.local_def_id(closure_id);
1160        let (binder_clause, generic_params) = self.lower_closure_binder(binder);
1161
1162        let coroutine_desugaring = match coroutine_kind {
1163            CoroutineKind::Async { .. } => hir::CoroutineDesugaring::Async,
1164            CoroutineKind::Gen { .. } => hir::CoroutineDesugaring::Gen,
1165            CoroutineKind::AsyncGen { span, .. } => {
1166                ::rustc_middle::util::bug::span_bug_fmt(span,
    format_args!("only async closures and `iter!` closures are supported currently"))span_bug!(span, "only async closures and `iter!` closures are supported currently")
1167            }
1168        };
1169
1170        let body = self.with_new_scopes(fn_decl_span, |this| {
1171            let inner_decl =
1172                FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
1173
1174            // Transform `async |x: u8| -> X { ... }` into
1175            // `|x: u8| || -> X { ... }`.
1176            let body_id = this.lower_body(|this| {
1177                let (parameters, expr) = this.lower_coroutine_body_with_moved_arguments(
1178                    &inner_decl,
1179                    |this| this.with_new_scopes(fn_decl_span, |this| this.lower_expr_mut(body)),
1180                    fn_decl_span,
1181                    body.span,
1182                    coroutine_kind,
1183                    hir::CoroutineSource::Closure,
1184                );
1185
1186                this.maybe_forward_track_caller(body.span, closure_hir_id, expr.hir_id);
1187
1188                (parameters, expr)
1189            });
1190            body_id
1191        });
1192
1193        let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
1194        // We need to lower the declaration outside the new scope, because we
1195        // have to conserve the state of being inside a loop condition for the
1196        // closure argument types.
1197        let fn_decl =
1198            self.lower_fn_decl(&decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
1199
1200        if let Const::Yes(span) = constness {
1201            self.dcx().span_err(span, "const coroutines are not supported");
1202        }
1203
1204        let c = self.arena.alloc(hir::Closure {
1205            def_id: closure_def_id,
1206            binder: binder_clause,
1207            capture_clause: self.lower_capture_clause(capture_clause),
1208            bound_generic_params,
1209            fn_decl,
1210            body,
1211            fn_decl_span: self.lower_span(fn_decl_span),
1212            fn_arg_span: Some(self.lower_span(fn_arg_span)),
1213            // Lower this as a `CoroutineClosure`. That will ensure that HIR typeck
1214            // knows that a `FnDecl` output type like `-> &str` actually means
1215            // "coroutine that returns &str", rather than directly returning a `&str`.
1216            kind: hir::ClosureKind::CoroutineClosure(coroutine_desugaring),
1217            constness: self.lower_constness(constness),
1218        });
1219        hir::ExprKind::Closure(c)
1220    }
1221
1222    /// Destructure the LHS of complex assignments.
1223    /// For instance, lower `(a, b) = t` to `{ let (lhs1, lhs2) = t; a = lhs1; b = lhs2; }`.
1224    fn lower_expr_assign(
1225        &mut self,
1226        lhs: &Expr,
1227        rhs: &Expr,
1228        eq_sign_span: Span,
1229        whole_span: Span,
1230    ) -> hir::ExprKind<'hir> {
1231        // Return early in case of an ordinary assignment.
1232        fn is_ordinary(lower_ctx: &mut LoweringContext<'_, '_>, lhs: &Expr) -> bool {
1233            match &lhs.kind {
1234                ExprKind::Array(..)
1235                | ExprKind::Struct(..)
1236                | ExprKind::Tup(..)
1237                | ExprKind::Underscore => false,
1238                // Check for unit struct constructor.
1239                ExprKind::Path(..) => lower_ctx.extract_unit_struct_path(lhs).is_none(),
1240                // Check for tuple struct constructor.
1241                ExprKind::Call(callee, ..) => lower_ctx.extract_tuple_struct_path(callee).is_none(),
1242                ExprKind::Paren(e) => {
1243                    match e.kind {
1244                        // We special-case `(..)` for consistency with patterns.
1245                        ExprKind::Range(None, None, RangeLimits::HalfOpen) => false,
1246                        _ => is_ordinary(lower_ctx, e),
1247                    }
1248                }
1249                _ => true,
1250            }
1251        }
1252        if is_ordinary(self, lhs) {
1253            return hir::ExprKind::Assign(
1254                self.lower_expr(lhs),
1255                self.lower_expr(rhs),
1256                self.lower_span(eq_sign_span),
1257            );
1258        }
1259
1260        let mut assignments = ::alloc::vec::Vec::new()vec![];
1261
1262        // The LHS becomes a pattern: `(lhs1, lhs2)`.
1263        let pat = self.destructure_assign(lhs, eq_sign_span, &mut assignments);
1264        let rhs = self.lower_expr(rhs);
1265
1266        // Introduce a `let` for destructuring: `let (lhs1, lhs2) = t`.
1267        let destructure_let =
1268            self.stmt_let_pat(None, whole_span, Some(rhs), pat, hir::LocalSource::AssignDesugar);
1269
1270        // `a = lhs1; b = lhs2;`.
1271        let stmts = self.arena.alloc_from_iter(std::iter::once(destructure_let).chain(assignments));
1272
1273        // Wrap everything in a block.
1274        hir::ExprKind::Block(self.block_all(whole_span, stmts, None), None)
1275    }
1276
1277    /// If the given expression is a path to a tuple struct, returns that path.
1278    /// It is not a complete check, but just tries to reject most paths early
1279    /// if they are not tuple structs.
1280    /// Type checking will take care of the full validation later.
1281    fn extract_tuple_struct_path<'a>(
1282        &mut self,
1283        expr: &'a Expr,
1284    ) -> Option<(&'a Option<Box<QSelf>>, &'a Path)> {
1285        if let ExprKind::Path(qself, path) = &expr.kind {
1286            // Does the path resolve to something disallowed in a tuple struct/variant pattern?
1287            if let Some(partial_res) = self.get_partial_res(expr.id) {
1288                if let Some(res) = partial_res.full_res()
1289                    && !res.expected_in_tuple_struct_pat()
1290                {
1291                    return None;
1292                }
1293            }
1294            return Some((qself, path));
1295        }
1296        None
1297    }
1298
1299    /// If the given expression is a path to a unit struct, returns that path.
1300    /// It is not a complete check, but just tries to reject most paths early
1301    /// if they are not unit structs.
1302    /// Type checking will take care of the full validation later.
1303    fn extract_unit_struct_path<'a>(
1304        &mut self,
1305        expr: &'a Expr,
1306    ) -> Option<(&'a Option<Box<QSelf>>, &'a Path)> {
1307        if let ExprKind::Path(qself, path) = &expr.kind {
1308            // Does the path resolve to something disallowed in a unit struct/variant pattern?
1309            if let Some(partial_res) = self.get_partial_res(expr.id) {
1310                if let Some(res) = partial_res.full_res()
1311                    && !res.expected_in_unit_struct_pat()
1312                {
1313                    return None;
1314                }
1315            }
1316            return Some((qself, path));
1317        }
1318        None
1319    }
1320
1321    /// Convert the LHS of a destructuring assignment to a pattern.
1322    /// Each sub-assignment is recorded in `assignments`.
1323    fn destructure_assign(
1324        &mut self,
1325        lhs: &Expr,
1326        eq_sign_span: Span,
1327        assignments: &mut Vec<hir::Stmt<'hir>>,
1328    ) -> &'hir hir::Pat<'hir> {
1329        self.arena.alloc(self.destructure_assign_mut(lhs, eq_sign_span, assignments))
1330    }
1331
1332    fn destructure_assign_mut(
1333        &mut self,
1334        lhs: &Expr,
1335        eq_sign_span: Span,
1336        assignments: &mut Vec<hir::Stmt<'hir>>,
1337    ) -> hir::Pat<'hir> {
1338        match &lhs.kind {
1339            // Underscore pattern.
1340            ExprKind::Underscore => {
1341                return self.pat_without_dbm(lhs.span, hir::PatKind::Wild);
1342            }
1343            // Slice patterns.
1344            ExprKind::Array(elements) => {
1345                let (pats, rest) =
1346                    self.destructure_sequence(elements, "slice", eq_sign_span, assignments);
1347                let slice_pat = if let Some((i, span)) = rest {
1348                    let (before, after) = pats.split_at(i);
1349                    hir::PatKind::Slice(
1350                        before,
1351                        Some(self.arena.alloc(self.pat_without_dbm(span, hir::PatKind::Wild))),
1352                        after,
1353                    )
1354                } else {
1355                    hir::PatKind::Slice(pats, None, &[])
1356                };
1357                return self.pat_without_dbm(lhs.span, slice_pat);
1358            }
1359            // Tuple structs.
1360            ExprKind::Call(callee, args) => {
1361                if let Some((qself, path)) = self.extract_tuple_struct_path(callee) {
1362                    let (pats, rest) = self.destructure_sequence(
1363                        args,
1364                        "tuple struct or variant",
1365                        eq_sign_span,
1366                        assignments,
1367                    );
1368                    let qpath = self.lower_qpath(
1369                        callee.id,
1370                        qself,
1371                        path,
1372                        ParamMode::Optional,
1373                        AllowReturnTypeNotation::No,
1374                        ImplTraitContext::Disallowed(ImplTraitPosition::Path),
1375                        None,
1376                    );
1377                    // Destructure like a tuple struct.
1378                    let tuple_struct_pat = hir::PatKind::TupleStruct(
1379                        qpath,
1380                        pats,
1381                        hir::DotDotPos::new(rest.map(|r| r.0)),
1382                    );
1383                    return self.pat_without_dbm(lhs.span, tuple_struct_pat);
1384                }
1385            }
1386            // Unit structs and enum variants.
1387            ExprKind::Path(..) => {
1388                if let Some((qself, path)) = self.extract_unit_struct_path(lhs) {
1389                    let qpath = self.lower_qpath(
1390                        lhs.id,
1391                        qself,
1392                        path,
1393                        ParamMode::Optional,
1394                        AllowReturnTypeNotation::No,
1395                        ImplTraitContext::Disallowed(ImplTraitPosition::Path),
1396                        None,
1397                    );
1398                    // Destructure like a unit struct.
1399                    let unit_struct_pat = hir::PatKind::Expr(self.arena.alloc(hir::PatExpr {
1400                        kind: hir::PatExprKind::Path(qpath),
1401                        hir_id: self.next_id(),
1402                        span: self.lower_span(lhs.span),
1403                    }));
1404                    return self.pat_without_dbm(lhs.span, unit_struct_pat);
1405                }
1406            }
1407            // Structs.
1408            ExprKind::Struct(se) => {
1409                let field_pats = self.arena.alloc_from_iter(se.fields.iter().map(|f| {
1410                    let pat = self.destructure_assign(&f.expr, eq_sign_span, assignments);
1411                    hir::PatField {
1412                        hir_id: self.next_id(),
1413                        ident: self.lower_ident(f.ident),
1414                        pat,
1415                        is_shorthand: f.is_shorthand,
1416                        span: self.lower_span(f.span),
1417                    }
1418                }));
1419                let qpath = self.lower_qpath(
1420                    lhs.id,
1421                    &se.qself,
1422                    &se.path,
1423                    ParamMode::Optional,
1424                    AllowReturnTypeNotation::No,
1425                    ImplTraitContext::Disallowed(ImplTraitPosition::Path),
1426                    None,
1427                );
1428                let fields_omitted = match &se.rest {
1429                    StructRest::Base(e) => {
1430                        self.dcx().emit_err(FunctionalRecordUpdateDestructuringAssignment {
1431                            span: e.span,
1432                        });
1433                        Some(self.lower_span(e.span))
1434                    }
1435                    StructRest::Rest(span) => Some(self.lower_span(*span)),
1436                    StructRest::None | StructRest::NoneWithError(_) => None,
1437                };
1438                let struct_pat = hir::PatKind::Struct(qpath, field_pats, fields_omitted);
1439                return self.pat_without_dbm(lhs.span, struct_pat);
1440            }
1441            // Tuples.
1442            ExprKind::Tup(elements) => {
1443                let (pats, rest) =
1444                    self.destructure_sequence(elements, "tuple", eq_sign_span, assignments);
1445                let tuple_pat = hir::PatKind::Tuple(pats, hir::DotDotPos::new(rest.map(|r| r.0)));
1446                return self.pat_without_dbm(lhs.span, tuple_pat);
1447            }
1448            ExprKind::Paren(e) => {
1449                // We special-case `(..)` for consistency with patterns.
1450                if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
1451                    let tuple_pat = hir::PatKind::Tuple(&[], hir::DotDotPos::new(Some(0)));
1452                    return self.pat_without_dbm(lhs.span, tuple_pat);
1453                } else {
1454                    return self.destructure_assign_mut(e, eq_sign_span, assignments);
1455                }
1456            }
1457            _ => {}
1458        }
1459        // Treat all other cases as normal lvalue.
1460        let ident = Ident::new(sym::lhs, self.lower_span(lhs.span));
1461        let (pat, binding) = self.pat_ident_mut(lhs.span, ident);
1462        let ident = self.expr_ident(lhs.span, ident, binding);
1463        let assign =
1464            hir::ExprKind::Assign(self.lower_expr(lhs), ident, self.lower_span(eq_sign_span));
1465        let expr = self.expr(lhs.span, assign);
1466        assignments.push(self.stmt_expr(lhs.span, expr));
1467        pat
1468    }
1469
1470    /// Destructure a sequence of expressions occurring on the LHS of an assignment.
1471    /// Such a sequence occurs in a tuple (struct)/slice.
1472    /// Return a sequence of corresponding patterns, and the index and the span of `..` if it
1473    /// exists.
1474    /// Each sub-assignment is recorded in `assignments`.
1475    fn destructure_sequence(
1476        &mut self,
1477        elements: &[Box<Expr>],
1478        ctx: &str,
1479        eq_sign_span: Span,
1480        assignments: &mut Vec<hir::Stmt<'hir>>,
1481    ) -> (&'hir [hir::Pat<'hir>], Option<(usize, Span)>) {
1482        let mut rest = None;
1483        let elements =
1484            self.arena.alloc_from_iter(elements.iter().enumerate().filter_map(|(i, e)| {
1485                // Check for `..` pattern.
1486                if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
1487                    if let Some((_, prev_span)) = rest {
1488                        self.ban_extra_rest_pat(e.span, prev_span, ctx);
1489                    } else {
1490                        rest = Some((i, e.span));
1491                    }
1492                    None
1493                } else {
1494                    Some(self.destructure_assign_mut(e, eq_sign_span, assignments))
1495                }
1496            }));
1497        (elements, rest)
1498    }
1499
1500    /// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
1501    fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
1502        let e1 = self.lower_expr_mut(e1);
1503        let e2 = self.lower_expr_mut(e2);
1504        let fn_path = self.make_lang_item_qpath(hir::LangItem::RangeInclusiveNew, span, None);
1505        let fn_expr = self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path)));
1506        hir::ExprKind::Call(fn_expr, self.arena.alloc_from_iter([e1, e2])arena_vec![self; e1, e2])
1507    }
1508
1509    fn lower_expr_range(
1510        &mut self,
1511        span: Span,
1512        e1: Option<&Expr>,
1513        e2: Option<&Expr>,
1514        lims: RangeLimits,
1515    ) -> hir::ExprKind<'hir> {
1516        use rustc_ast::RangeLimits::*;
1517
1518        let lang_item = match (e1, e2, lims) {
1519            (None, None, HalfOpen) => hir::LangItem::RangeFull,
1520            (Some(..), None, HalfOpen) => {
1521                if self.tcx.features().new_range() {
1522                    hir::LangItem::RangeFromCopy
1523                } else {
1524                    hir::LangItem::RangeFrom
1525                }
1526            }
1527            (None, Some(..), HalfOpen) => hir::LangItem::RangeTo,
1528            (Some(..), Some(..), HalfOpen) => {
1529                if self.tcx.features().new_range() {
1530                    hir::LangItem::RangeCopy
1531                } else {
1532                    hir::LangItem::Range
1533                }
1534            }
1535            (None, Some(..), Closed) => {
1536                if self.tcx.features().new_range() {
1537                    hir::LangItem::RangeToInclusiveCopy
1538                } else {
1539                    hir::LangItem::RangeToInclusive
1540                }
1541            }
1542            (Some(e1), Some(e2), Closed) => {
1543                if self.tcx.features().new_range() {
1544                    hir::LangItem::RangeInclusiveCopy
1545                } else {
1546                    return self.lower_expr_range_closed(span, e1, e2);
1547                }
1548            }
1549            (start, None, Closed) => {
1550                self.dcx().emit_err(InclusiveRangeWithNoEnd { span });
1551                match start {
1552                    Some(..) => {
1553                        if self.tcx.features().new_range() {
1554                            hir::LangItem::RangeFromCopy
1555                        } else {
1556                            hir::LangItem::RangeFrom
1557                        }
1558                    }
1559                    None => hir::LangItem::RangeFull,
1560                }
1561            }
1562        };
1563
1564        let fields = self.arena.alloc_from_iter(
1565            e1.iter()
1566                .map(|e| (sym::start, e))
1567                .chain(e2.iter().map(|e| {
1568                    (
1569                        if #[allow(non_exhaustive_omitted_patterns)] match lang_item {
    hir::LangItem::RangeInclusiveCopy | hir::LangItem::RangeToInclusiveCopy =>
        true,
    _ => false,
}matches!(
1570                            lang_item,
1571                            hir::LangItem::RangeInclusiveCopy | hir::LangItem::RangeToInclusiveCopy
1572                        ) {
1573                            sym::last
1574                        } else {
1575                            sym::end
1576                        },
1577                        e,
1578                    )
1579                }))
1580                .map(|(s, e)| {
1581                    let span = self.lower_span(e.span);
1582                    let span = self.mark_span_with_reason(DesugaringKind::RangeExpr, span, None);
1583                    let expr = self.lower_expr(e);
1584                    let ident = Ident::new(s, span);
1585                    self.expr_field(ident, expr, span)
1586                }),
1587        );
1588
1589        hir::ExprKind::Struct(
1590            self.arena.alloc(self.make_lang_item_qpath(lang_item, span, None)),
1591            fields,
1592            hir::StructTailExpr::None,
1593        )
1594    }
1595
1596    // Record labelled expr's HirId so that we can retrieve it in `lower_jump_destination` without
1597    // lowering node id again.
1598    fn lower_label(
1599        &mut self,
1600        opt_label: Option<Label>,
1601        dest_id: NodeId,
1602        dest_hir_id: hir::HirId,
1603    ) -> Option<Label> {
1604        let label = opt_label?;
1605        self.ident_and_label_to_local_id.insert(dest_id, dest_hir_id.local_id);
1606        Some(Label { ident: self.lower_ident(label.ident) })
1607    }
1608
1609    fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
1610        let target_id = match destination {
1611            Some((id, _)) => {
1612                if let Some(loop_id) = self.resolver.get_label_res(id) {
1613                    let local_id = self.ident_and_label_to_local_id[&loop_id];
1614                    let loop_hir_id = HirId { owner: self.current_hir_id_owner, local_id };
1615                    Ok(loop_hir_id)
1616                } else {
1617                    Err(hir::LoopIdError::UnresolvedLabel)
1618                }
1619            }
1620            None => {
1621                self.loop_scope.map(|id| Ok(id)).unwrap_or(Err(hir::LoopIdError::OutsideLoopScope))
1622            }
1623        };
1624        let label = destination
1625            .map(|(_, label)| label)
1626            .map(|label| Label { ident: self.lower_ident(label.ident) });
1627        hir::Destination { label, target_id }
1628    }
1629
1630    fn lower_jump_destination(&mut self, id: NodeId, opt_label: Option<Label>) -> hir::Destination {
1631        if self.is_in_loop_condition && opt_label.is_none() {
1632            hir::Destination {
1633                label: None,
1634                target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition),
1635            }
1636        } else {
1637            self.lower_loop_destination(opt_label.map(|label| (id, label)))
1638        }
1639    }
1640
1641    fn with_try_block_scope<T>(
1642        &mut self,
1643        scope: TryBlockScope,
1644        f: impl FnOnce(&mut Self) -> T,
1645    ) -> T {
1646        let old_scope = mem::replace(&mut self.try_block_scope, scope);
1647        let result = f(self);
1648        self.try_block_scope = old_scope;
1649        result
1650    }
1651
1652    fn with_loop_scope<T>(&mut self, loop_id: hir::HirId, f: impl FnOnce(&mut Self) -> T) -> T {
1653        // We're no longer in the base loop's condition; we're in another loop.
1654        let was_in_loop_condition = self.is_in_loop_condition;
1655        self.is_in_loop_condition = false;
1656
1657        let old_scope = self.loop_scope.replace(loop_id);
1658        let result = f(self);
1659        self.loop_scope = old_scope;
1660
1661        self.is_in_loop_condition = was_in_loop_condition;
1662
1663        result
1664    }
1665
1666    fn with_loop_condition_scope<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
1667        let was_in_loop_condition = self.is_in_loop_condition;
1668        self.is_in_loop_condition = true;
1669
1670        let result = f(self);
1671
1672        self.is_in_loop_condition = was_in_loop_condition;
1673
1674        result
1675    }
1676
1677    fn lower_expr_field(&mut self, f: &ExprField) -> hir::ExprField<'hir> {
1678        let hir_id = self.lower_node_id(f.id);
1679        self.lower_attrs(hir_id, &f.attrs, f.span, Target::ExprField);
1680        hir::ExprField {
1681            hir_id,
1682            ident: self.lower_ident(f.ident),
1683            expr: self.lower_expr(&f.expr),
1684            span: self.lower_span(f.span),
1685            is_shorthand: f.is_shorthand,
1686        }
1687    }
1688
1689    fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
1690        let yielded =
1691            opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
1692
1693        if !self.tcx.features().yield_expr()
1694            && !self.tcx.features().coroutines()
1695            && !self.tcx.features().gen_blocks()
1696        {
1697            rustc_session::errors::feature_err(
1698                &self.tcx.sess,
1699                sym::yield_expr,
1700                span,
1701                rustc_errors::DiagMessage::Inline(std::borrow::Cow::Borrowed("yield syntax is experimental"))msg!("yield syntax is experimental"),
1702            )
1703            .emit();
1704        }
1705
1706        let is_async_gen = match self.coroutine_kind {
1707            Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _)) => false,
1708            Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::AsyncGen, _)) => true,
1709            Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)) => {
1710                // Lower to a block `{ EXPR; <error> }` so that the awaited expr
1711                // is not accidentally orphaned.
1712                let stmt_id = self.next_id();
1713                let expr_err = self.expr(
1714                    yielded.span,
1715                    hir::ExprKind::Err(self.dcx().emit_err(AsyncCoroutinesNotSupported { span })),
1716                );
1717                return hir::ExprKind::Block(
1718                    self.block_all(
1719                        yielded.span,
1720                        self.arena.alloc_from_iter([hir::Stmt {
                hir_id: stmt_id,
                kind: hir::StmtKind::Semi(yielded),
                span: yielded.span,
            }])arena_vec![self; hir::Stmt {
1721                            hir_id: stmt_id,
1722                            kind: hir::StmtKind::Semi(yielded),
1723                            span: yielded.span,
1724                        }],
1725                        Some(self.arena.alloc(expr_err)),
1726                    ),
1727                    None,
1728                );
1729            }
1730            Some(hir::CoroutineKind::Coroutine(_)) => false,
1731            None => {
1732                let suggestion = self.current_item.map(|s| s.shrink_to_lo());
1733                self.dcx().emit_err(YieldInClosure { span, suggestion });
1734                self.coroutine_kind = Some(hir::CoroutineKind::Coroutine(Movability::Movable));
1735
1736                false
1737            }
1738        };
1739
1740        if is_async_gen {
1741            // `yield $expr` is transformed into `task_context = yield async_gen_ready($expr)`.
1742            // This ensures that we store our resumed `ResumeContext` correctly, and also that
1743            // the apparent value of the `yield` expression is `()`.
1744            let desugar_span = self.mark_span_with_reason(
1745                DesugaringKind::Async,
1746                span,
1747                Some(Arc::clone(&self.allow_async_gen)),
1748            );
1749            let wrapped_yielded = self.expr_call_lang_item_fn(
1750                desugar_span,
1751                hir::LangItem::AsyncGenReady,
1752                std::slice::from_ref(yielded),
1753            );
1754            let yield_expr = self.arena.alloc(
1755                self.expr(span, hir::ExprKind::Yield(wrapped_yielded, hir::YieldSource::Yield)),
1756            );
1757
1758            let Some(task_context_hid) = self.task_context else {
1759                {
    ::core::panicking::panic_fmt(format_args!("internal error: entered unreachable code: {0}",
            format_args!("use of `await` outside of an async context.")));
};unreachable!("use of `await` outside of an async context.");
1760            };
1761            let task_context_ident = Ident::with_dummy_span(sym::_task_context);
1762            let lhs = self.expr_ident(desugar_span, task_context_ident, task_context_hid);
1763
1764            hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span))
1765        } else {
1766            hir::ExprKind::Yield(yielded, hir::YieldSource::Yield)
1767        }
1768    }
1769
1770    /// Desugar `ExprForLoop` from: `[opt_ident]: for <pat> in <head> <body>` into:
1771    /// ```ignore (pseudo-rust)
1772    /// {
1773    ///     let result = match IntoIterator::into_iter(<head>) {
1774    ///         mut iter => {
1775    ///             [opt_ident]: loop {
1776    ///                 match Iterator::next(&mut iter) {
1777    ///                     None => break,
1778    ///                     Some(<pat>) => <body>,
1779    ///                 };
1780    ///             }
1781    ///         }
1782    ///     };
1783    ///     result
1784    /// }
1785    /// ```
1786    fn lower_expr_for(
1787        &mut self,
1788        e: &Expr,
1789        pat: &Pat,
1790        head: &Expr,
1791        body: &Block,
1792        opt_label: Option<Label>,
1793        loop_kind: ForLoopKind,
1794    ) -> hir::Expr<'hir> {
1795        let head = self.lower_expr_mut(head);
1796        let pat = self.lower_pat(pat);
1797        let for_span =
1798            self.mark_span_with_reason(DesugaringKind::ForLoop, self.lower_span(e.span), None);
1799        let for_ctxt = for_span.ctxt();
1800
1801        // Try to point both the head and pat spans to their position in the for loop
1802        // rather than inside a macro.
1803        let head_span =
1804            head.span.find_ancestor_in_same_ctxt(e.span).unwrap_or(head.span).with_ctxt(for_ctxt);
1805        let pat_span =
1806            pat.span.find_ancestor_in_same_ctxt(e.span).unwrap_or(pat.span).with_ctxt(for_ctxt);
1807
1808        let loop_hir_id = self.lower_node_id(e.id);
1809        let label = self.lower_label(opt_label, e.id, loop_hir_id);
1810
1811        // `None => break`
1812        let none_arm = {
1813            let break_expr =
1814                self.with_loop_scope(loop_hir_id, |this| this.expr_break_alloc(for_span));
1815            let pat = self.pat_none(for_span);
1816            self.arm(pat, break_expr, for_span)
1817        };
1818
1819        // Some(<pat>) => <body>,
1820        let some_arm = {
1821            let some_pat = self.pat_some(pat_span, pat);
1822            let body_block =
1823                self.with_loop_scope(loop_hir_id, |this| this.lower_block(body, false));
1824            let body_expr = self.arena.alloc(self.expr_block(body_block));
1825            self.arm(some_pat, body_expr, for_span)
1826        };
1827
1828        // `mut iter`
1829        let iter = Ident::with_dummy_span(sym::iter);
1830        let (iter_pat, iter_pat_nid) =
1831            self.pat_ident_binding_mode(head_span, iter, hir::BindingMode::MUT);
1832
1833        let match_expr = {
1834            let iter = self.expr_ident(head_span, iter, iter_pat_nid);
1835            let next_expr = match loop_kind {
1836                ForLoopKind::For => {
1837                    // `Iterator::next(&mut iter)`
1838                    let ref_mut_iter = self.expr_mut_addr_of(head_span, iter);
1839                    self.expr_call_lang_item_fn(
1840                        head_span,
1841                        hir::LangItem::IteratorNext,
1842                        self.arena.alloc_from_iter([ref_mut_iter])arena_vec![self; ref_mut_iter],
1843                    )
1844                }
1845                ForLoopKind::ForAwait => {
1846                    // we'll generate `unsafe { Pin::new_unchecked(&mut iter) })` and then pass this
1847                    // to make_lowered_await with `FutureKind::AsyncIterator` which will generator
1848                    // calls to `poll_next`. In user code, this would probably be a call to
1849                    // `Pin::as_mut` but here it's easy enough to do `new_unchecked`.
1850
1851                    // `&mut iter`
1852                    let iter = self.expr_mut_addr_of(head_span, iter);
1853                    // `Pin::new_unchecked(...)`
1854                    let iter = self.arena.alloc(self.expr_call_lang_item_fn_mut(
1855                        head_span,
1856                        hir::LangItem::PinNewUnchecked,
1857                        self.arena.alloc_from_iter([iter])arena_vec![self; iter],
1858                    ));
1859                    // `unsafe { ... }`
1860                    let iter = self.arena.alloc(self.expr_unsafe(head_span, iter));
1861                    let kind = self.make_lowered_await(head_span, iter, FutureKind::AsyncIterator);
1862                    self.arena.alloc(hir::Expr { hir_id: self.next_id(), kind, span: head_span })
1863                }
1864            };
1865            let arms = self.arena.alloc_from_iter([none_arm, some_arm])arena_vec![self; none_arm, some_arm];
1866
1867            // `match $next_expr { ... }`
1868            self.expr_match(head_span, next_expr, arms, hir::MatchSource::ForLoopDesugar)
1869        };
1870        let match_stmt = self.stmt_expr(for_span, match_expr);
1871
1872        let loop_block = self.block_all(for_span, self.arena.alloc_from_iter([match_stmt])arena_vec![self; match_stmt], None);
1873
1874        // `[opt_ident]: loop { ... }`
1875        let kind = hir::ExprKind::Loop(
1876            loop_block,
1877            label,
1878            hir::LoopSource::ForLoop,
1879            self.lower_span(for_span.with_hi(head.span.hi())),
1880        );
1881        let loop_expr = self.arena.alloc(hir::Expr { hir_id: loop_hir_id, kind, span: for_span });
1882
1883        // `mut iter => { ... }`
1884        let iter_arm = self.arm(iter_pat, loop_expr, for_span);
1885
1886        let match_expr = match loop_kind {
1887            ForLoopKind::For => {
1888                // `::std::iter::IntoIterator::into_iter(<head>)`
1889                let into_iter_expr = self.expr_call_lang_item_fn(
1890                    head_span,
1891                    hir::LangItem::IntoIterIntoIter,
1892                    self.arena.alloc_from_iter([head])arena_vec![self; head],
1893                );
1894
1895                self.arena.alloc(self.expr_match(
1896                    for_span,
1897                    into_iter_expr,
1898                    self.arena.alloc_from_iter([iter_arm])arena_vec![self; iter_arm],
1899                    hir::MatchSource::ForLoopDesugar,
1900                ))
1901            }
1902            // `match into_async_iter(<head>) { ref mut iter => match unsafe { Pin::new_unchecked(iter) } { ... } }`
1903            ForLoopKind::ForAwait => {
1904                let iter_ident = iter;
1905                let (async_iter_pat, async_iter_pat_id) =
1906                    self.pat_ident_binding_mode(head_span, iter_ident, hir::BindingMode::REF_MUT);
1907                let iter = self.expr_ident_mut(head_span, iter_ident, async_iter_pat_id);
1908                // `Pin::new_unchecked(...)`
1909                let iter = self.arena.alloc(self.expr_call_lang_item_fn_mut(
1910                    head_span,
1911                    hir::LangItem::PinNewUnchecked,
1912                    self.arena.alloc_from_iter([iter])arena_vec![self; iter],
1913                ));
1914                // `unsafe { ... }`
1915                let iter = self.arena.alloc(self.expr_unsafe(head_span, iter));
1916                let inner_match_expr = self.arena.alloc(self.expr_match(
1917                    for_span,
1918                    iter,
1919                    self.arena.alloc_from_iter([iter_arm])arena_vec![self; iter_arm],
1920                    hir::MatchSource::ForLoopDesugar,
1921                ));
1922
1923                // `::core::async_iter::IntoAsyncIterator::into_async_iter(<head>)`
1924                let iter = self.expr_call_lang_item_fn(
1925                    head_span,
1926                    hir::LangItem::IntoAsyncIterIntoIter,
1927                    self.arena.alloc_from_iter([head])arena_vec![self; head],
1928                );
1929                let iter_arm = self.arm(async_iter_pat, inner_match_expr, for_span);
1930                self.arena.alloc(self.expr_match(
1931                    for_span,
1932                    iter,
1933                    self.arena.alloc_from_iter([iter_arm])arena_vec![self; iter_arm],
1934                    hir::MatchSource::ForLoopDesugar,
1935                ))
1936            }
1937        };
1938
1939        // This is effectively `{ let _result = ...; _result }`.
1940        // The construct was introduced in #21984 and is necessary to make sure that
1941        // temporaries in the `head` expression are dropped and do not leak to the
1942        // surrounding scope of the `match` since the `match` is not a terminating scope.
1943        //
1944        // Also, add the attributes to the outer returned expr node.
1945        let expr = self.expr_drop_temps_mut(for_span, match_expr);
1946        self.lower_attrs(expr.hir_id, &e.attrs, e.span, Target::from_expr(e));
1947        expr
1948    }
1949
1950    /// Desugar `ExprKind::Try` from: `<expr>?` into:
1951    /// ```ignore (pseudo-rust)
1952    /// match Try::branch(<expr>) {
1953    ///     ControlFlow::Continue(val) => #[allow(unreachable_code)] val,,
1954    ///     ControlFlow::Break(residual) =>
1955    ///         #[allow(unreachable_code)]
1956    ///         // If there is an enclosing `try {...}`:
1957    ///         break 'catch_target Residual::into_try_type(residual),
1958    ///         // Otherwise:
1959    ///         return Try::from_residual(residual),
1960    /// }
1961    /// ```
1962    fn lower_expr_try(&mut self, span: Span, sub_expr: &Expr) -> hir::ExprKind<'hir> {
1963        let unstable_span = self.mark_span_with_reason(
1964            DesugaringKind::QuestionMark,
1965            span,
1966            Some(Arc::clone(&self.allow_try_trait)),
1967        );
1968        let try_span = self.tcx.sess.source_map().end_point(span);
1969        let try_span = self.mark_span_with_reason(
1970            DesugaringKind::QuestionMark,
1971            try_span,
1972            Some(Arc::clone(&self.allow_try_trait)),
1973        );
1974
1975        // `Try::branch(<expr>)`
1976        let scrutinee = {
1977            // expand <expr>
1978            let sub_expr = self.lower_expr_mut(sub_expr);
1979
1980            self.expr_call_lang_item_fn(
1981                unstable_span,
1982                hir::LangItem::TryTraitBranch,
1983                self.arena.alloc_from_iter([sub_expr])arena_vec![self; sub_expr],
1984            )
1985        };
1986
1987        let attrs: AttrVec = {
    let len = [()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(self.unreachable_code_attr(try_span));
    vec
}thin_vec![self.unreachable_code_attr(try_span)];
1988
1989        // `ControlFlow::Continue(val) => #[allow(unreachable_code)] val,`
1990        let continue_arm = {
1991            let val_ident = Ident::with_dummy_span(sym::val);
1992            let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
1993            let val_expr = self.expr_ident(span, val_ident, val_pat_nid);
1994            self.lower_attrs(val_expr.hir_id, &attrs, span, Target::Expression);
1995            let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
1996            self.arm(continue_pat, val_expr, try_span)
1997        };
1998
1999        // `ControlFlow::Break(residual) =>
2000        //     #[allow(unreachable_code)]
2001        //     return Try::from_residual(residual),`
2002        let break_arm = {
2003            let residual_ident = Ident::with_dummy_span(sym::residual);
2004            let (residual_local, residual_local_nid) = self.pat_ident(try_span, residual_ident);
2005            let residual_expr = self.expr_ident_mut(try_span, residual_ident, residual_local_nid);
2006
2007            let (constructor_item, target_id) = match self.try_block_scope {
2008                TryBlockScope::Function => {
2009                    (hir::LangItem::TryTraitFromResidual, Err(hir::LoopIdError::OutsideLoopScope))
2010                }
2011                TryBlockScope::Homogeneous(block_id) => {
2012                    (hir::LangItem::ResidualIntoTryType, Ok(block_id))
2013                }
2014                TryBlockScope::Heterogeneous(block_id) => {
2015                    (hir::LangItem::TryTraitFromResidual, Ok(block_id))
2016                }
2017            };
2018            let from_residual_expr = self.wrap_in_try_constructor(
2019                constructor_item,
2020                try_span,
2021                self.arena.alloc(residual_expr),
2022                unstable_span,
2023            );
2024            let ret_expr = if target_id.is_ok() {
2025                self.arena.alloc(self.expr(
2026                    try_span,
2027                    hir::ExprKind::Break(
2028                        hir::Destination { label: None, target_id },
2029                        Some(from_residual_expr),
2030                    ),
2031                ))
2032            } else {
2033                let ret_expr = self.checked_return(Some(from_residual_expr));
2034                self.arena.alloc(self.expr(try_span, ret_expr))
2035            };
2036            self.lower_attrs(ret_expr.hir_id, &attrs, span, Target::Expression);
2037
2038            let break_pat = self.pat_cf_break(try_span, residual_local);
2039            self.arm(break_pat, ret_expr, try_span)
2040        };
2041
2042        hir::ExprKind::Match(
2043            scrutinee,
2044            self.arena.alloc_from_iter([break_arm, continue_arm])arena_vec![self; break_arm, continue_arm],
2045            hir::MatchSource::TryDesugar(scrutinee.hir_id),
2046        )
2047    }
2048
2049    /// Desugar `ExprKind::Yeet` from: `do yeet <expr>` into:
2050    /// ```ignore(illustrative)
2051    /// // If there is an enclosing `try {...}`:
2052    /// break 'catch_target FromResidual::from_residual(Yeet(residual));
2053    /// // Otherwise:
2054    /// return FromResidual::from_residual(Yeet(residual));
2055    /// ```
2056    /// But to simplify this, there's a `from_yeet` lang item function which
2057    /// handles the combined `FromResidual::from_residual(Yeet(residual))`.
2058    fn lower_expr_yeet(&mut self, span: Span, sub_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
2059        // The expression (if present) or `()` otherwise.
2060        let (yeeted_span, yeeted_expr) = if let Some(sub_expr) = sub_expr {
2061            (sub_expr.span, self.lower_expr(sub_expr))
2062        } else {
2063            (self.mark_span_with_reason(DesugaringKind::YeetExpr, span, None), self.expr_unit(span))
2064        };
2065
2066        let unstable_span = self.mark_span_with_reason(
2067            DesugaringKind::YeetExpr,
2068            span,
2069            Some(Arc::clone(&self.allow_try_trait)),
2070        );
2071
2072        let from_yeet_expr = self.wrap_in_try_constructor(
2073            hir::LangItem::TryTraitFromYeet,
2074            unstable_span,
2075            yeeted_expr,
2076            yeeted_span,
2077        );
2078
2079        match self.try_block_scope {
2080            TryBlockScope::Homogeneous(block_id) | TryBlockScope::Heterogeneous(block_id) => {
2081                hir::ExprKind::Break(
2082                    hir::Destination { label: None, target_id: Ok(block_id) },
2083                    Some(from_yeet_expr),
2084                )
2085            }
2086            TryBlockScope::Function => self.checked_return(Some(from_yeet_expr)),
2087        }
2088    }
2089
2090    // =========================================================================
2091    // Helper methods for building HIR.
2092    // =========================================================================
2093
2094    /// Wrap the given `expr` in a terminating scope using `hir::ExprKind::DropTemps`.
2095    ///
2096    /// In terms of drop order, it has the same effect as wrapping `expr` in
2097    /// `{ let _t = $expr; _t }` but should provide better compile-time performance.
2098    ///
2099    /// The drop order can be important, e.g. to drop temporaries from an `async fn`
2100    /// body before its parameters.
2101    pub(super) fn expr_drop_temps(
2102        &mut self,
2103        span: Span,
2104        expr: &'hir hir::Expr<'hir>,
2105    ) -> &'hir hir::Expr<'hir> {
2106        self.arena.alloc(self.expr_drop_temps_mut(span, expr))
2107    }
2108
2109    pub(super) fn expr_drop_temps_mut(
2110        &mut self,
2111        span: Span,
2112        expr: &'hir hir::Expr<'hir>,
2113    ) -> hir::Expr<'hir> {
2114        self.expr(span, hir::ExprKind::DropTemps(expr))
2115    }
2116
2117    pub(super) fn expr_match(
2118        &mut self,
2119        span: Span,
2120        arg: &'hir hir::Expr<'hir>,
2121        arms: &'hir [hir::Arm<'hir>],
2122        source: hir::MatchSource,
2123    ) -> hir::Expr<'hir> {
2124        self.expr(span, hir::ExprKind::Match(arg, arms, source))
2125    }
2126
2127    fn expr_break(&mut self, span: Span) -> hir::Expr<'hir> {
2128        let expr_break = hir::ExprKind::Break(self.lower_loop_destination(None), None);
2129        self.expr(span, expr_break)
2130    }
2131
2132    fn expr_break_alloc(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
2133        let expr_break = self.expr_break(span);
2134        self.arena.alloc(expr_break)
2135    }
2136
2137    fn expr_mut_addr_of(&mut self, span: Span, e: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
2138        self.expr(span, hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e))
2139    }
2140
2141    pub(super) fn expr_unit(&mut self, sp: Span) -> &'hir hir::Expr<'hir> {
2142        self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[])))
2143    }
2144
2145    pub(super) fn expr_str(&mut self, sp: Span, value: Symbol) -> hir::Expr<'hir> {
2146        let lit = hir::Lit {
2147            span: self.lower_span(sp),
2148            node: ast::LitKind::Str(value, ast::StrStyle::Cooked),
2149        };
2150        self.expr(sp, hir::ExprKind::Lit(lit))
2151    }
2152
2153    pub(super) fn expr_byte_str(&mut self, sp: Span, value: ByteSymbol) -> hir::Expr<'hir> {
2154        let lit = hir::Lit {
2155            span: self.lower_span(sp),
2156            node: ast::LitKind::ByteStr(value, ast::StrStyle::Cooked),
2157        };
2158        self.expr(sp, hir::ExprKind::Lit(lit))
2159    }
2160
2161    pub(super) fn expr_call_mut(
2162        &mut self,
2163        span: Span,
2164        e: &'hir hir::Expr<'hir>,
2165        args: &'hir [hir::Expr<'hir>],
2166    ) -> hir::Expr<'hir> {
2167        self.expr(span, hir::ExprKind::Call(e, args))
2168    }
2169
2170    pub(super) fn expr_struct(
2171        &mut self,
2172        span: Span,
2173        path: &'hir hir::QPath<'hir>,
2174        fields: &'hir [hir::ExprField<'hir>],
2175    ) -> hir::Expr<'hir> {
2176        self.expr(span, hir::ExprKind::Struct(path, fields, rustc_hir::StructTailExpr::None))
2177    }
2178
2179    pub(super) fn expr_enum_variant(
2180        &mut self,
2181        span: Span,
2182        path: &'hir hir::QPath<'hir>,
2183        fields: &'hir [hir::Expr<'hir>],
2184    ) -> hir::Expr<'hir> {
2185        let fields = self.arena.alloc_from_iter(fields.into_iter().enumerate().map(|(i, f)| {
2186            hir::ExprField {
2187                hir_id: self.next_id(),
2188                ident: Ident::from_str(&i.to_string()),
2189                expr: f,
2190                span: f.span,
2191                is_shorthand: false,
2192            }
2193        }));
2194        self.expr_struct(span, path, fields)
2195    }
2196
2197    pub(super) fn expr_enum_variant_lang_item(
2198        &mut self,
2199        span: Span,
2200        lang_item: hir::LangItem,
2201        fields: &'hir [hir::Expr<'hir>],
2202    ) -> hir::Expr<'hir> {
2203        let path = self.arena.alloc(self.make_lang_item_qpath(lang_item, span, None));
2204        self.expr_enum_variant(span, path, fields)
2205    }
2206
2207    pub(super) fn expr_call(
2208        &mut self,
2209        span: Span,
2210        e: &'hir hir::Expr<'hir>,
2211        args: &'hir [hir::Expr<'hir>],
2212    ) -> &'hir hir::Expr<'hir> {
2213        self.arena.alloc(self.expr_call_mut(span, e, args))
2214    }
2215
2216    pub(super) fn expr_call_lang_item_fn_mut(
2217        &mut self,
2218        span: Span,
2219        lang_item: hir::LangItem,
2220        args: &'hir [hir::Expr<'hir>],
2221    ) -> hir::Expr<'hir> {
2222        let path = self.arena.alloc(self.expr_lang_item_path(span, lang_item));
2223        self.expr_call_mut(span, path, args)
2224    }
2225
2226    pub(super) fn expr_call_lang_item_fn(
2227        &mut self,
2228        span: Span,
2229        lang_item: hir::LangItem,
2230        args: &'hir [hir::Expr<'hir>],
2231    ) -> &'hir hir::Expr<'hir> {
2232        self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args))
2233    }
2234
2235    pub(super) fn expr_lang_item_path(
2236        &mut self,
2237        span: Span,
2238        lang_item: hir::LangItem,
2239    ) -> hir::Expr<'hir> {
2240        let qpath = self.make_lang_item_qpath(lang_item, self.lower_span(span), None);
2241        self.expr(span, hir::ExprKind::Path(qpath))
2242    }
2243
2244    /// `<LangItem>::name`
2245    pub(super) fn expr_lang_item_type_relative(
2246        &mut self,
2247        span: Span,
2248        lang_item: hir::LangItem,
2249        name: Symbol,
2250    ) -> hir::Expr<'hir> {
2251        let qpath = self.make_lang_item_qpath(lang_item, self.lower_span(span), None);
2252        let path = hir::ExprKind::Path(hir::QPath::TypeRelative(
2253            self.arena.alloc(self.ty(span, hir::TyKind::Path(qpath))),
2254            self.arena.alloc(hir::PathSegment::new(
2255                Ident::new(name, self.lower_span(span)),
2256                self.next_id(),
2257                Res::Err,
2258            )),
2259        ));
2260        self.expr(span, path)
2261    }
2262
2263    pub(super) fn expr_ident(
2264        &mut self,
2265        sp: Span,
2266        ident: Ident,
2267        binding: HirId,
2268    ) -> &'hir hir::Expr<'hir> {
2269        self.arena.alloc(self.expr_ident_mut(sp, ident, binding))
2270    }
2271
2272    pub(super) fn expr_ident_mut(
2273        &mut self,
2274        span: Span,
2275        ident: Ident,
2276        binding: HirId,
2277    ) -> hir::Expr<'hir> {
2278        let hir_id = self.next_id();
2279        let res = Res::Local(binding);
2280        let expr_path = hir::ExprKind::Path(hir::QPath::Resolved(
2281            None,
2282            self.arena.alloc(hir::Path {
2283                span: self.lower_span(span),
2284                res,
2285                segments: self.arena.alloc_from_iter([hir::PathSegment::new(self.lower_ident(ident),
                hir_id, res)])arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2286            }),
2287        ));
2288
2289        self.expr(span, expr_path)
2290    }
2291
2292    pub(super) fn expr_unsafe(
2293        &mut self,
2294        span: Span,
2295        expr: &'hir hir::Expr<'hir>,
2296    ) -> hir::Expr<'hir> {
2297        let hir_id = self.next_id();
2298        self.expr(
2299            span,
2300            hir::ExprKind::Block(
2301                self.arena.alloc(hir::Block {
2302                    stmts: &[],
2303                    expr: Some(expr),
2304                    hir_id,
2305                    rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
2306                    span: self.lower_span(span),
2307                    targeted_by_break: false,
2308                }),
2309                None,
2310            ),
2311        )
2312    }
2313
2314    fn expr_block_empty(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
2315        let blk = self.block_all(span, &[], None);
2316        let expr = self.expr_block(blk);
2317        self.arena.alloc(expr)
2318    }
2319
2320    pub(super) fn expr_block(&mut self, b: &'hir hir::Block<'hir>) -> hir::Expr<'hir> {
2321        self.expr(b.span, hir::ExprKind::Block(b, None))
2322    }
2323
2324    /// Wrap an expression in a block, and wrap that block in an expression again.
2325    /// Useful for constructing if-expressions, which require expressions of
2326    /// kind block.
2327    pub(super) fn block_expr_block(
2328        &mut self,
2329        expr: &'hir hir::Expr<'hir>,
2330    ) -> &'hir hir::Expr<'hir> {
2331        let b = self.block_expr(expr);
2332        self.arena.alloc(self.expr_block(b))
2333    }
2334
2335    pub(super) fn expr_ref(&mut self, span: Span, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
2336        self.expr(span, hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, expr))
2337    }
2338
2339    pub(super) fn expr_bool_literal(&mut self, span: Span, val: bool) -> hir::Expr<'hir> {
2340        self.expr(span, hir::ExprKind::Lit(Spanned { node: LitKind::Bool(val), span }))
2341    }
2342
2343    pub(super) fn expr(&mut self, span: Span, kind: hir::ExprKind<'hir>) -> hir::Expr<'hir> {
2344        let hir_id = self.next_id();
2345        hir::Expr { hir_id, kind, span: self.lower_span(span) }
2346    }
2347
2348    pub(super) fn expr_field(
2349        &mut self,
2350        ident: Ident,
2351        expr: &'hir hir::Expr<'hir>,
2352        span: Span,
2353    ) -> hir::ExprField<'hir> {
2354        hir::ExprField {
2355            hir_id: self.next_id(),
2356            ident,
2357            span: self.lower_span(span),
2358            expr,
2359            is_shorthand: false,
2360        }
2361    }
2362
2363    pub(super) fn arm(
2364        &mut self,
2365        pat: &'hir hir::Pat<'hir>,
2366        expr: &'hir hir::Expr<'hir>,
2367        span: Span,
2368    ) -> hir::Arm<'hir> {
2369        hir::Arm {
2370            hir_id: self.next_id(),
2371            pat,
2372            guard: None,
2373            span: self.lower_span(span),
2374            body: expr,
2375        }
2376    }
2377
2378    /// `#[allow(unreachable_code)]`
2379    pub(super) fn unreachable_code_attr(&mut self, span: Span) -> Attribute {
2380        let attr = attr::mk_attr_nested_word(
2381            &self.tcx.sess.psess.attr_id_generator,
2382            AttrStyle::Outer,
2383            Safety::Default,
2384            sym::allow,
2385            sym::unreachable_code,
2386            span,
2387        );
2388        attr
2389    }
2390}
2391
2392/// Used by [`LoweringContext::make_lowered_await`] to customize the desugaring based on what kind
2393/// of future we are awaiting.
2394#[derive(#[automatically_derived]
impl ::core::marker::Copy for FutureKind { }Copy, #[automatically_derived]
impl ::core::clone::Clone for FutureKind {
    #[inline]
    fn clone(&self) -> FutureKind { *self }
}Clone, #[automatically_derived]
impl ::core::fmt::Debug for FutureKind {
    #[inline]
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        ::core::fmt::Formatter::write_str(f,
            match self {
                FutureKind::Future => "Future",
                FutureKind::AsyncIterator => "AsyncIterator",
            })
    }
}Debug, #[automatically_derived]
impl ::core::cmp::PartialEq for FutureKind {
    #[inline]
    fn eq(&self, other: &FutureKind) -> bool {
        let __self_discr = ::core::intrinsics::discriminant_value(self);
        let __arg1_discr = ::core::intrinsics::discriminant_value(other);
        __self_discr == __arg1_discr
    }
}PartialEq, #[automatically_derived]
impl ::core::cmp::Eq for FutureKind {
    #[inline]
    #[doc(hidden)]
    #[coverage(off)]
    fn assert_fields_are_eq(&self) {}
}Eq)]
2395enum FutureKind {
2396    /// We are awaiting a normal future
2397    Future,
2398    /// We are awaiting something that's known to be an AsyncIterator (i.e. we are in the header of
2399    /// a `for await` loop)
2400    AsyncIterator,
2401}
rustc_ast_lowering/expr.rs

rustc_ast_lowering/
expr.rs
