fn extract_value(
cx: &mut AcceptContext<'_, '_>,
key: Symbol,
val: &NameValueParser,
span: Span,
out_val: &mut Option<(Symbol, Span)>,
failed: &mut bool,
)fn extract_value(
cx: &mut AcceptContext<'_, '_>,
key: Symbol,
val: &NameValueParser,
span: Span,
out_val: &mut Option<(Symbol, Span)>,
failed: &mut bool,
)