# Plan #117

**Source:** Dart SDK 3.0.0
**Category:** Replacement / Migration
**Relevance Score:** 5
**Detected APIs:** Observatory

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## Release Note Entry

> - Observatory is no longer served by default and users should instead use Dart
>
> Context: DevTools. Users requiring specific functionality in Observatory should set

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## Migration Analysis

### What Changed

A better pattern or API is now available. The old approach still works but the new one is preferred.

### APIs Involved

- `Observatory`

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## Proposed Lint Rule

**Rule Type:** `prefer_replacement`
**Estimated Difficulty:** medium

### Detection Strategy

Detect old pattern and suggest the replacement

**Relevant AST nodes:**
- `MethodInvocation`
- `PropertyAccess`
- `SimpleIdentifier`

### Fix Strategy

Replace old API/pattern with the new recommended approach

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## Implementation Checklist

- [ ] Verify the API change in Flutter/Dart SDK source
- [ ] Determine minimum SDK version requirement
- [ ] Write detection logic (AST visitor)
- [ ] Write quick-fix replacement
- [ ] Create test fixture with bad/good examples
- [ ] Add unit tests
- [ ] Register rule in `all_rules.dart`
- [ ] Add to tier in `tiers.dart`
- [ ] Update ROADMAP.md
- [ ] Update CHANGELOG.md

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**Status:** Not started
**Generated:** From Dart SDK v3.0.0 release notes
