Remove early return in GetCanonicalForm, always call System.IO.Path#13532
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JanProvaznik merged 3 commits intoApr 14, 2026
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Pull request overview
This PR fixes a behavioral inconsistency in Microsoft.Build.Framework.AbsolutePath.GetCanonicalForm() where some “already-canonical-looking” paths could bypass Path.GetFullPath and therefore fail to reject invalid path characters. The change aligns canonicalization behavior with the BCL so invalid paths are rejected consistently.
Changes:
- Removed the “skip
Path.GetFullPath” optimization branch inAbsolutePath.GetCanonicalForm()so it always callsPath.GetFullPath. - Updated XML docs to explicitly state invalid path characters are rejected.
- Added a unit test ensuring
GetCanonicalForm()throws the same exception type asPath.GetFullPathfor invalid characters.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/Framework/PathHelpers/AbsolutePath.cs | Ensures canonicalization always runs through Path.GetFullPath, fixing invalid-character validation gaps. |
| src/Framework.UnitTests/AbsolutePath_Tests.cs | Adds regression coverage verifying exception-type parity with Path.GetFullPath for invalid paths. |
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Review Summary
This PR removes the ChangeWave.Wave18_6 fast-path optimization from GetCanonicalForm() and always delegates to Path.GetFullPath. The intent — simpler code and consistent BCL behavior including invalid-character rejection — is reasonable, but there's a notable performance concern.
Key Finding
Performance regression on hot paths (Medium priority): The removed optimization avoided Path.GetFullPath for already-canonical paths (which is the common case). GetCanonicalForm() is called per-item in Copy, FindUnderPath, and AssignTargetPath — all with explicit performance annotations. The AssignTargetPath source code itself contains a PERF NOTE warning that Path.GetFullPath() "consumes a lot of memory, esp. when we have a lot of items."
If the motivation is rejecting invalid path characters, consider augmenting the existing fast-path with an invalid-character check rather than removing the optimization entirely. This would preserve the performance characteristics while gaining the correctness improvement.
Minor Items
- Redundant type assertion in the test (line 313) —
Should.Throwalready checks type - Manual try/catch could be simplified with
Record.Exception
Dimensions with No Issues
ChangeWave discipline (reverting to simpler behavior is fine), backwards compatibility (no new warnings/errors for valid paths), cross-platform correctness, null safety, concurrency, naming, API surface — all clean.
Note
🔒 Integrity filter blocked 2 items
The following items were blocked because they don't meet the GitHub integrity level.
- #13532
pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved". - #13532
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min-integrity: approved # merged | approved | unapproved | noneGenerated by Expert Code Review (on open) for issue #13532 · ● 2.2M
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…ullPath The optimization in GetCanonicalForm() that skipped Path.GetFullPath for paths without relative segments, separator issues, or consecutive separators caused invalid path characters to be silently accepted. This broke tasks that relied on Path.GetFullPath throwing for invalid characters. Simplify GetCanonicalForm() to always call Path.GetFullPath, ensuring consistent behavior with the BCL including rejection of invalid path characters. Add test verifying GetCanonicalForm() throws the same exception as Path.GetFullPath for paths containing invalid characters (null character). Fixes dotnet#13514 Co-authored-by: Copilot <[email protected]>
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Updated [Microsoft.Build](https://github.com/dotnet/msbuild) from 18.6.3 to 18.7.1. <details> <summary>Release notes</summary> _Sourced from [Microsoft.Build's releases](https://github.com/dotnet/msbuild/releases)._ ## 18.7.1 ## What's Changed * Fix TraceEngine file contention deadlock in multithreaded mode by @JanProvaznik in dotnet/msbuild#13446 * Remove duplicate test cases in MultithreadableTaskAnalyzer by @Youssef1313 in dotnet/msbuild#13483 * Ensure ThreadSafeTaskAnalyzer.Tests is considered as a unit test project by @Youssef1313 in dotnet/msbuild#13481 * Fix MSBuildTask0002 analyzer warnings in already-migrated tasks by @JanProvaznik in dotnet/msbuild#13466 * Fix race conditions in task host path resolution by @AR-May in dotnet/msbuild#13485 * Migrate ToolTask and Al task to TaskEnvironment API by @OvesN in dotnet/msbuild#13423 * Bump main to 18.7, add vs18.6 to merge flow by @MichalPavlik in dotnet/msbuild#13472 * Avoid allocations in GetHashCode implementations by @DustinCampbell in dotnet/msbuild#13475 * Add PATs rotation to agentic workflow(s) by @JanKrivanek in dotnet/msbuild#13496 * Fix ASP.NET WebSite projects to copy netstandard.dll facade when required by @JanProvaznik in dotnet/msbuild#13058 * Migrate AspNetCompiler to TaskEnvironment API by @OvesN in dotnet/msbuild#13424 * Add review workflow by @JanKrivanek in dotnet/msbuild#13503 * Strengthen reviewer skill: add step-back analysis dimensions by @JanProvaznik in dotnet/msbuild#13504 * Add 'Request Speedometer Perf Run' to VS experimental insertion build policies by @Copilot in dotnet/msbuild#13505 * Remove duplicate @ prefix from issueAuthor in GitOps by @akoeplinger in dotnet/msbuild#13492 * Improve review aw by @JanKrivanek in dotnet/msbuild#13510 * Migrates unit tests to use RoslynCodeTaskFactory to enable running tests under .NET Core by @jankratochvilcz in dotnet/msbuild#13500 * Fix cross-AppDomain TaskItem modifier cache regression by @DustinCampbell in dotnet/msbuild#13493 * Discourage review agent from approving PRs by @JanKrivanek in dotnet/msbuild#13512 * Stop trying to deploy ValueTuple by @rainersigwald in dotnet/msbuild#13507 * Ad-hoc re-sign bootstrap dotnet on macOS to prevent SIGKILL by @jankratochvilcz in dotnet/msbuild#13513 * RoslynCodeTaskFactory: Log MSB3753 when task class does not implement ITask by @jankratochvilcz in dotnet/msbuild#13517 * Update gh-aw (upon mcp policy changes) by @JanKrivanek in dotnet/msbuild#13526 * Eliminate XmlChildNodes allocations in GetXmlNodeInnerContents by @nareshjo in dotnet/msbuild#13509 * Fix telemetry allocation regression: per-engine collector ownership by @JanProvaznik in dotnet/msbuild#13516 * Migrate to xunit.v3 by @Youssef1313 in dotnet/msbuild#13482 * Fix stray brace in HandleBuildCancel trace string causing MSB1025 by @Copilot in dotnet/msbuild#13535 * Bumping to 10.0.4 runtime packages by @MichalPavlik in dotnet/msbuild#13533 * Remove early return in GetCanonicalForm, always call System.IO.Path by @OvesN in dotnet/msbuild#13532 * Do not overwrite GetCopyToOutputDirectoryItemsDependsOn, just add new… by @snechaev in dotnet/msbuild#13474 * Migrate GetReferenceAssemblyPaths task to TaskEnvironment API by @OvesN in dotnet/msbuild#13495 * Stabilize ToolTaskThatTimeoutAndRetry test by @rainersigwald in dotnet/msbuild#13489 * [automated] Merge branch 'vs18.6' => 'main' by @github-actions[bot] in dotnet/msbuild#13506 * Add extra test assertions around tests by @Youssef1313 in dotnet/msbuild#13536 * Add static eval for repo skills/agents via skill-validator by @JanKrivanek in dotnet/msbuild#13537 * Migrate SGen task to Task environment API by @OvesN in dotnet/msbuild#13457 * Fix TerminalLogger assert failure for metaproj files and cached project eval ID by @OvesN in dotnet/msbuild#13480 * Filter out approving review from pr-reviewer agent by @JanKrivanek in dotnet/msbuild#13553 * Use a unique task name per invocation to tabilize RoslynCodeTaskFactory_ReuseCompilation test by @huulinhnguyen-dev in dotnet/msbuild#13551 * Brief doc on feedback/logging/data systems by @rainersigwald in dotnet/msbuild#13554 * Localized file check-in by OneLocBuild Task: Build definition ID 9434: Build ID 13881982 by @dotnet-bot in dotnet/msbuild#13437 * Stage 3: Forward BuildProjectFile* callbacks from OOP TaskHost to worker node by @JanProvaznik in dotnet/msbuild#13350 * Enable TaskHost Callbacks by default by @JanProvaznik in dotnet/msbuild#13579 * Remove unactionable info from reviewer agent by @JanKrivanek in dotnet/msbuild#13578 * Enlighten RequiresFramework35SP1Assembly task for multithreaded mode by @jankratochvilcz in dotnet/msbuild#13575 * Make SdkResolver-provided environment variables take precedence over ambient environment by @Copilot in dotnet/msbuild#12655 * Add dotnet/skills marketplace and enable plugins by @Evangelink in dotnet/msbuild#13582 * The skills/agents check filters-in only touched files by @JanKrivanek in dotnet/msbuild#13586 * Fix skill-validation workflow failing when agents directory is deleted by @JeremyKuhne in dotnet/msbuild#13592 ... (truncated) Commits viewable in [compare view](dotnet/msbuild@v18.6.3...v18.7.1). </details> Signed-off-by: dependabot[bot] <[email protected]> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
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Fixes #13514
Context
AbsolutePath.GetCanonicalForm()silently accepted invalid path characters thatPath.GetFullPathwould reject. An optimization branch skipped callingPath.GetFullPathwhen the path had no relative segments, separator issues, or consecutive separators — causing invalid characters to never be validated.Changes Made
AbsolutePath.csGetCanonicalForm()that skipped callingPath.GetFullPathfor already-canonical-looking paths.GetCanonicalForm()now always callsSystem.IO.Path.GetFullPath.Testing
AbsolutePath_Tests.csGetCanonicalForm_InvalidPathCharacters_ShouldThrowSameAsPathGetFullPath— verifies thatGetCanonicalForm()throws the same exception type asPath.GetFullPathfor paths containing invalid characters.