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[flutter_tools] Fix UNC path resolution in depfile parsing on Windows - #191265

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bkonyi:investigation/issue-43594
Aug 20, 2026
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auto-submit[bot] merged 3 commits into
flutter:masterfrom
bkonyi:investigation/issue-43594

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@bkonyi bkonyi commented Aug 18, 2026

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Normalize root-relative Windows UNC paths starting with \UNC\ in depfiles to standard UNC paths starting with \\. Also unify SourceVisitor depfile parsing to use DepfileService.

Fixes #43594

Pre-launch Checklist

On Windows, `Uri.toFilePath()` converts a UNC URI like `file:///UNC/server/share/file`
to a root-relative path `\UNC\server\share\file`. When parsed by the build system,
this path is resolved relative to the current drive (e.g., `U:\UNC\server\share\file`),
which does not exist.

This change detects root-relative UNC paths starting with `\UNC\` (case-insensitive)
and converts them to standard UNC paths starting with `\\` (e.g., `\\server\share\file`),
which are resolved correctly on Windows.

Also refactored `SourceVisitor` to use `DepfileService` for parsing depfiles,
eliminating redundant parsing logic and ensuring both paths benefit from this fix.

Fixes flutter#43594
@github-actions github-actions Bot added the tool Affects the "flutter" command-line tool. See also t: labels. label Aug 18, 2026
@bkonyi bkonyi added the CICD Run CI/CD label Aug 20, 2026
@bkonyi
bkonyi requested a review from dcharkes August 20, 2026 16:26
@bkonyi
bkonyi marked this pull request as ready for review August 20, 2026 16:26

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Code Review

This pull request refactors depfile parsing in SourceVisitor to utilize DepfileService and introduces support for handling Windows UNC paths within DepfileService._processList. It also adds comprehensive tests for parsing and writing various Windows UNC path formats. Feedback suggests optimizing the Windows UNC path detection in depfile.dart by checking the path length and lowercasing only the prefix substring rather than the entire path string to avoid unnecessary allocations.

Comment thread packages/flutter_tools/lib/src/build_system/depfile.dart Outdated
dcharkes
dcharkes previously approved these changes Aug 20, 2026
/// If the file is missing, this visitor is marked as [containsNewDepfile].
/// This is used by the [Node] class to tell the [BuildSystem] to
/// defer hash computation until after executing the target.
// depfile logic adopted from https://github.com/flutter/flutter/blob/7065e4330624a5a216c8ffbace0a462617dc1bf5/dev/devicelab/lib/framework/apk_utils.dart#L390

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So all of this is no longer relevant?

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Exactly — the parsing logic (_processList, _separatorExpr, _escapeExpr) was duplicate implementation of what DepfileService.parse already does (splitting inputs/outputs, unescaping spaces, and path normalization).

Delegating to environment.depFileService.parse eliminates the duplication and ensures SourceVisitor stays in sync with any depfile fixes (like this Windows UNC handling). I've restored the doc comment explaining the containsNewDepfile hash deferral mechanism for clarity.

@bkonyi bkonyi added the autosubmit Merge PR when tree becomes green via auto submit App label Aug 20, 2026
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auto-submit Bot added this pull request to the merge queue Aug 20, 2026
Merged via the queue into flutter:master with commit 5e5237a Aug 20, 2026
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@flutter-dashboard flutter-dashboard Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Aug 20, 2026
auto-submit Bot pushed a commit to flutter/packages that referenced this pull request Aug 22, 2026
Roll Flutter from c2437523d308 to 65c9a8dc60bc (195 revisions)

flutter/flutter@c243752...65c9a8d

2026-08-22 [email protected] Roll ICU from d578f2e8b7bd to 8cc91d9b6ab9 (1 revision) (flutter/flutter#191542)
2026-08-22 [email protected] Roll Skia from 666a9b3d5cf0 to ad2106c0bb64 (3 revisions) (flutter/flutter#191527)
2026-08-22 [email protected] Roll Fuchsia Test Scripts from KaOq3EE4qJ9fnaaaK... to 0iCv10IlKfiilEBOU... (flutter/flutter#191524)
2026-08-22 [email protected] [flutter_tools] Add tests for negative lookahead regex in test runner and batch entrypoints (flutter/flutter#191438)
2026-08-22 [email protected] Roll Skia from 0c37868737fa to 666a9b3d5cf0 (2 revisions) (flutter/flutter#191518)
2026-08-21 [email protected] Revert "[input] Migrate fuchsia.ui.pointerinjector to TouchSource (#190855) (flutter/flutter#191509)
2026-08-21 [email protected] Fixes windows gallery benchmarks by forcing mobile layout (flutter/flutter#191507)
2026-08-21 [email protected] [flutter_tools] Restrict WebAssetServer source resolution to source map extensions (flutter/flutter#191501)
2026-08-21 [email protected] Roll Skia from f6900c5b8439 to 0c37868737fa (2 revisions) (flutter/flutter#191504)
2026-08-21 [email protected] Refactor `FlutterDevice.connect` and VM service discovery (flutter/flutter#191221)
2026-08-21 [email protected] [flutter_tools] Fix crash when migrating flow-style exclude lists in analysis_options.yaml (flutter/flutter#191269)
2026-08-21 [email protected] [rules] Add packages/flutter_tools/gradle/AGENTS.md rules (flutter/flutter#191486)
2026-08-21 [email protected] [flutter_tools] refactor CLI argument architecture with typed option descriptors and bundles (PoC) (flutter/flutter#191018)
2026-08-21 [email protected] tools: Extract Dart SDK to temp directory before moving to final location (flutter/flutter#191263)
2026-08-21 [email protected] [web] Move CanvasKit fragment shader classes to canvaskit/fragment_shader.dart (flutter/flutter#191451)
2026-08-21 [email protected] Roll Fuchsia Linux SDK from GCQlmt6h-esJsNubS... to ic6GjOSn-KN508XyK... (flutter/flutter#191485)
2026-08-21 [email protected] [Widget Preview] Isolate PageStorage scope in widget preview group expansion tile (flutter/flutter#191378)
2026-08-21 [email protected] [flutter_tools] Deprecate --build and --no-build flags on flutter run (flutter/flutter#191358)
2026-08-21 [email protected] Roll Skia from 70988bed1b3b to f6900c5b8439 (2 revisions) (flutter/flutter#191481)
2026-08-21 [email protected] Roll Packages from 1785501 to 252bb33 (6 revisions) (flutter/flutter#191480)
2026-08-21 [email protected] Roll Fuchsia Linux SDK from 20IJas24bZiNmCZTK... to GCQlmt6h-esJsNubS... (flutter/flutter#191415)
2026-08-21 [email protected] Roll Skia from 2ba6971bd0d1 to 70988bed1b3b (2 revisions) (flutter/flutter#191476)
2026-08-21 [email protected] Roll Skia from 1d5f72537ba6 to 2ba6971bd0d1 (2 revisions) (flutter/flutter#191473)
2026-08-21 [email protected] Roll Skia from 2c25efd2e369 to 1d5f72537ba6 (1 revision) (flutter/flutter#191472)
2026-08-21 [email protected] Roll Skia from 09b1b810850a to 2c25efd2e369 (9 revisions) (flutter/flutter#191470)
2026-08-21 [email protected] [Impeller] fix position of cached single glyph text shadows (flutter/flutter#191325)
2026-08-21 [email protected] Roll Skia from abdf8821f313 to 09b1b810850a (15 revisions) (flutter/flutter#191458)
2026-08-21 [email protected] Document that programmatic TextEditingController changes do not run input formatters (flutter/flutter#190166)
2026-08-21 [email protected] Adds new gallery benchmarks to windows (skia and impeller) (flutter/flutter#191454)
2026-08-21 [email protected] iOS: Deprecate FlutterEngine.isGpuDisabled (flutter/flutter#191393)
2026-08-21 [email protected] Revert: [web] Unskip decoration image lerp tests (flutter/flutter#191462)
2026-08-20 [email protected] android_hardware_smoke_test: Improve reliability (flutter/flutter#191374)
2026-08-20 [email protected] Don't size or offset the Android platform view before it is laid out (flutter/flutter#190895)
2026-08-20 [email protected] [iOS][add2app] Skip building SwiftPM plugins when generating CocoaPods artifacts (flutter/flutter#190736)
2026-08-20 [email protected] Optimize JSONMessageCodec UTF-8 conversion (flutter/flutter#190529)
2026-08-20 [email protected] [FML] Replace deprecated wstring_convert with Win32 APIs (flutter/flutter#191394)
2026-08-20 [email protected] SliverFillRemaining extends beyond viewport size when fillOverscroll is true (flutter/flutter#191236)
2026-08-20 [email protected] [flutter_tools] Update argParser usageLineLength when --wrap-column is passed (flutter/flutter#191264)
2026-08-20 [email protected] [flutter_tools] Fix UNC path resolution in depfile parsing on Windows (flutter/flutter#191265)
2026-08-20 [email protected] [web] Unskip decoration image lerp tests (flutter/flutter#191426)
2026-08-20 [email protected] Do not inject 'type' and 'method' into service extension responses (flutter/flutter#190946)
2026-08-20 [email protected] [flutter_tools] Fix crash in symbolize command on stream error (flutter/flutter#191273)
2026-08-20 [email protected] [flutter_tools] Prevent deletion of shared native asset hooks outputs as stale (flutter/flutter#191272)
2026-08-20 [email protected] [flutter_tools] Support package wildcard assets in app pubspec (flutter/flutter#191266)
2026-08-20 [email protected] Add SliverClipRect and SliverClipRRect (flutter/flutter#179003)
2026-08-20 [email protected] [flutter_tools] Implement Diagnostics extension slice and doctor integration (flutter/flutter#191162)
...
@bkonyi bkonyi added the cp: stable cherry pick this pull request to stable release candidate branch label Aug 24, 2026
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Flutter build fails when project source is located on a mapped Samba Share (Network Drive Letter)

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