Expose registered project file extensions by JoeRobich · Pull Request #85106 · dotnet/roslyn

JoeRobich · 2026-08-31T16:10:03Z

Summary

Expose focused query APIs on ProjectFileExtensionRegistry for consumers that need to enumerate registered project extensions or resolve a language directly from an extension.

Existing project-path lookup retains file-based application compatibility; this PR only separates reusable registry queries from that behavior.

Stack

Depends on Centralize Language Server workspace folder tracking.

Validation

Analyzer-enabled Microsoft.CodeAnalysis.Workspaces.MSBuild build succeeded with 0 errors.

Microsoft Reviewers: Open in CodeFlow

azure-pipelines · 2026-08-31T16:10:14Z

Azure Pipelines: 2 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

Copilot

Copilot review overview

🟢 Approval recommended

Changes are small and low-risk, and the only feedback is minor clarity/documentation improvements rather than correctness issues.

Review tier: Lite
Findings: 3

New issues introduced by this change (1)

Severity	Finding
	`src/Workspaces/MSBuild/Test/NetCoreTests.cs` — This test change is specifically validating that leading-dot extensions are accepted/normalized.…

Pre-existing issues (2)

Severity	Finding
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — TryGetLanguageNameFromExtension() is a new query API but doesn’t document whether callers should… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This change adds new query APIs (GetRegisteredProjectFileExtensions/TryGetLanguageNameFromExtension)… View comment

Issues resolved since last review (1)

Severity	Finding
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — GetRegisteredProjectFileExtensions() returns dictionary key enumeration order, which is not… View resolved comment

Suppressed comments (1)

src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs:60

TryGetLanguageNameFromExtension is a newly exposed query API but doesn’t document the accepted extension format (leading '.' allowed/ignored) or the intent that it matches Path.GetExtension inputs. Adding an XML doc comment here would help internal consumers avoid re-learning the normalization rules.

    public bool TryGetLanguageNameFromExtension(string extension, [NotNullWhen(true)] out string? languageName)
    {

Copilot

Copilot review overview

🔵 Needs a closer look

The updated test drops coverage for the historically-supported non-dotted extension form and should validate both "cs" and ".cs" for backward compatibility.

Review tier: Lite
Findings: 3

Pre-existing issues (3)

Severity	Finding
	`src/Workspaces/MSBuild/Test/NetCoreTests.cs` — This test change is specifically validating that leading-dot extensions are accepted/normalized.… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — TryGetLanguageNameFromExtension() is a new query API but doesn’t document whether callers should… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This change adds new query APIs (GetRegisteredProjectFileExtensions/TryGetLanguageNameFromExtension)… View comment

Suppressed comments (1)

src/Workspaces/MSBuild/Test/NetCoreTests.cs:753

This test now only exercises the ".cs" form of AssociateFileExtensionWithLanguage(). Since the API historically accepted extensions without a leading dot, it would be good to cover both "cs" and ".cs" here to protect backward compatibility while also validating the new normalization behavior.

        using var workspace = CreateMSBuildWorkspace();
        workspace.AssociateFileExtensionWithLanguage(".cs", LanguageNames.CSharp);
        await workspace.OpenProjectAsync(sourceFilePath);

        // [Failure] Msbuild failed when processing the file 'Program.cs' with message:

Copilot

Copilot review overview

🟡 Changes recommended

WorkspaceFolderTracker now reads shared state without a synchronization/visibility mechanism, which can lead to stale workspace-folder sets being observed across threads.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Lite
Findings: 1 · 3

New issues introduced by this change (1)

Severity	Finding
	`src/LanguageServer/Protocol/Handler/WorkspaceFolderTracker.cs` — GetRequiredWorkspaceFolderPaths() now reads _workspaceFolderPaths without any synchronization, but…

Pre-existing issues (3)

Severity	Finding
	`src/Workspaces/MSBuild/Test/NetCoreTests.cs` — This test change is specifically validating that leading-dot extensions are accepted/normalized.… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — TryGetLanguageNameFromExtension() is a new query API but doesn’t document whether callers should… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This change adds new query APIs (GetRegisteredProjectFileExtensions/TryGetLanguageNameFromExtension)… View comment

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Copilot review overview

🟡 Changes recommended

Extension normalization currently treats the single-dot string "." as an empty extension, which is a subtle behavioral change worth fixing or explicitly deciding on before merge.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Lite
Findings: 1 · 4

New issues introduced by this change (2)

Severity	Finding
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — `RemoveLeadingDot` currently treats the single-dot string "." as an empty extension (it returns…
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This adds new query APIs (`GetRegisteredProjectFileExtensions` / `TryGetLanguageNameFromExtension`)…

Pre-existing issues (3)

Severity	Finding
	`src/Workspaces/MSBuild/Test/NetCoreTests.cs` — This test change is specifically validating that leading-dot extensions are accepted/normalized.… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — TryGetLanguageNameFromExtension() is a new query API but doesn’t document whether callers should… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This change adds new query APIs (GetRegisteredProjectFileExtensions/TryGetLanguageNameFromExtension)… View comment

Issues resolved since last review (1)

Severity	Finding
	`src/LanguageServer/Protocol/Handler/WorkspaceFolderTracker.cs` — GetRequiredWorkspaceFolderPaths() now reads _workspaceFolderPaths without any synchronization, but… View resolved comment

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1d6a35c4-0f49-4671-b352-8cac98e9eaa4

Copilot

Copilot review overview

🟡 Changes recommended

It introduces a couple of correctness/maintainability issues (notably an over-strong XML doc contract and a brittle test assertion) that should be addressed before merging.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Lite
Findings: 6

New issues introduced by this change (2)

Severity	Finding
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — The XML doc for GetRegisteredProjectFileExtensions() promises every returned extension has a…
	`src/Workspaces/MSBuild/Test/NetCoreTests.cs` — This test hard-codes the current number of default registered extensions (3), which makes it…

Pre-existing issues (4)

Severity	Finding
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This adds new query APIs (`GetRegisteredProjectFileExtensions` / `TryGetLanguageNameFromExtension`)… View comment
	`src/Workspaces/MSBuild/Test/NetCoreTests.cs` — This test change is specifically validating that leading-dot extensions are accepted/normalized.… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — TryGetLanguageNameFromExtension() is a new query API but doesn’t document whether callers should… View comment
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — This change adds new query APIs (GetRegisteredProjectFileExtensions/TryGetLanguageNameFromExtension)… View comment

Issues resolved since last review (1)

Severity	Finding
	`src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs` — `RemoveLeadingDot` currently treats the single-dot string "." as an empty extension (it returns… View resolved comment

JoeRobich · 2026-09-09T00:25:28Z

/azp run roslyn-CI

azure-pipelines · 2026-09-09T00:25:43Z

Azure Pipelines: Successfully started running 1 pipeline(s).

jasonmalinowski

Approved -- comments can be done in a mop-up.

JoeRobich requested a review from a team as a code owner August 31, 2026 16:10

dotnet-policy-service Bot added the VSCode label Aug 31, 2026

JoeRobich mentioned this pull request Aug 31, 2026

Add on-demand project loading #84591

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JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 4641429 to 288bc3c Compare August 31, 2026 16:38

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 288bc3c to 3bf7054 Compare August 31, 2026 16:53

akhera99 previously approved these changes Aug 31, 2026

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JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 3bf7054 to 639cc89 Compare August 31, 2026 17:06

dibarbet previously approved these changes Aug 31, 2026

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jasonmalinowski previously approved these changes Sep 1, 2026

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Comment thread src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs

Comment thread src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 639cc89 to cccc725 Compare September 1, 2026 22:36

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from cccc725 to 5e4077d Compare September 2, 2026 05:24

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 5e4077d to c5022f7 Compare September 2, 2026 20:25

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from c5022f7 to 9afef8b Compare September 2, 2026 22:27

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 9afef8b to 0c7bc7f Compare September 2, 2026 23:11

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 0c7bc7f to 602d180 Compare September 3, 2026 04:29

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 602d180 to 1bcb8dc Compare September 3, 2026 05:08

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 1bcb8dc to 4e2613c Compare September 3, 2026 05:15

Copilot AI reviewed Sep 4, 2026

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Comment thread src/Workspaces/MSBuild/Test/NetCoreTests.cs

Copilot AI review requested due to automatic review settings September 4, 2026 06:48

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 72170b9 to 3462c3a Compare September 4, 2026 06:49

Copilot started reviewing on behalf of JoeRobich September 4, 2026 06:50 View session

Copilot AI reviewed Sep 4, 2026

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jasonmalinowski approved these changes Sep 4, 2026

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Comment thread src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs Outdated

Copilot AI review requested due to automatic review settings September 8, 2026 17:20

Copilot started reviewing on behalf of JoeRobich September 8, 2026 17:22 View session

Copilot AI reviewed Sep 8, 2026

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Comment thread src/LanguageServer/Protocol/Handler/WorkspaceFolderTracker.cs Outdated

Copilot AI review requested due to automatic review settings September 8, 2026 18:11

Copilot started reviewing on behalf of JoeRobich September 8, 2026 18:12 View session

Base automatically changed from dev/jorobich/lsp-workspace-folder-tracker to main September 8, 2026 18:12

JoeRobich and others added 3 commits September 8, 2026 11:12

Expose registered project file extensions

a7c68f3

Simplify workspace folder change notifications

eb3254d

Change _workspaceFolderPaths to be volatile

ebe1514

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

JoeRobich force-pushed the dev/jorobich/project-extension-registry-apis branch from 75eda8e to ebe1514 Compare September 8, 2026 18:13

Copilot AI reviewed Sep 8, 2026

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Comment thread src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs Outdated

Comment thread src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs

Store registered project extensions with leading dots

1957b27

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1d6a35c4-0f49-4671-b352-8cac98e9eaa4

Copilot AI reviewed Sep 8, 2026

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Comment thread src/Workspaces/MSBuild/Core/MSBuild/ProjectFileExtensionRegistry.cs

Comment thread src/Workspaces/MSBuild/Test/NetCoreTests.cs

jasonmalinowski reviewed Sep 9, 2026

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Comment thread .github/instructions/IDE.instructions.md

jasonmalinowski reviewed Sep 9, 2026

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Comment thread src/LanguageServer/Protocol/Handler/IWorkspaceFolderTracker.cs

jasonmalinowski approved these changes Sep 9, 2026

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Comment thread src/LanguageServer/Protocol/Handler/WorkspaceFolderTracker.cs

JoeRobich mentioned this pull request Sep 9, 2026

Add on-demand project loading #85234

Open

This was referenced Sep 9, 2026

[release/11.0.1xx] Source code updates from dotnet/roslyn dotnet/dotnet#9210

Merged

[main] Source code updates from dotnet/roslyn dotnet/dotnet#9228

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dotnet-bot mentioned this pull request Sep 10, 2026

[Automated] PRs inserted in VS build main-12209.490 #85246

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dibarbet mentioned this pull request Sep 11, 2026

Update roslyn to 5.12.0-1.26461.1 dotnet/vscode-csharp#9751

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🟡 Changes recommended

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JoeRobich commented Aug 31, 2026 •

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