Fade unused directives, add "Remove unnecessary" code action and support Remove and Sort commands

[davidwengier]

Fixes a very large portion of #8548

This adds diagnostics and fading of unnecessary @using directives in Razor and MVC, and unnecessary @addTagHelper directives in Legacy. Also adds a "Remove unnecessary directives" code action whenever the cursor is in the block of directives. Looks like this:

Also needed a Roslyn bump so a couple of slight changes due to API differences, and I added a copilot skill so we can just ask copilot to do Roslyn bumps for us in future.

(redo of #12804 so I can keep working on the next phase)

[Copilot]

Pull request overview

Adds end-to-end support for detecting and fading unused Razor directives and offering a “Remove unnecessary directives” code action, leveraging Roslyn’s unused-imports diagnostics where possible and adding legacy @addTagHelper coverage.

Changes:

• Introduces unused-directive diagnostics plumbing (including caching) to power fading + removal code actions.
• Tracks directive → tag helper contributions during compilation to distinguish “unused in C#” vs “used for component/tag helper binding”.
• Adds cohost code action + diagnostics tests, updates resources, and bumps Roslyn dependency versions.

Reviewed changes

Copilot reviewed 43 out of 43 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CohostDocumentPullDiagnosticsTest.cs	Adds cohost diagnostics tests for unused @using and legacy @addTagHelper.
src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CodeActions/RemoveUnnecessaryDirectiveTests.cs	New tests validating the “Remove unnecessary directives” code action behavior.
src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CodeActions/CohostCodeActionsEndpointTestBase.cs	Extends code action test harness to optionally fetch real diagnostics before requesting code actions.
src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/CohostDocumentPullDiagnosticsTest.cs	Refactors diagnostics test helper and exposes a shared diagnostics-request helper for code action tests.
src/Razor/test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Cohost/CohostDocumentPullDiagnosticsTest.cs	Mirrors diagnostics helper refactor for VS cohost tests and adds shared diagnostics-request helper.
src/Razor/test/Microsoft.AspNetCore.Razor.Test.Common.Tooling/LanguageServer/CSharpTestLspServer.cs	Adjusts reflection invocation for Roslyn language server lifecycle calls after dependency/API changes.
src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/Diagnostics/RemoteDiagnosticsService.cs	Normalizes unused-import diagnostics to Razor’s RZ0005, sets unnecessary tags, caches unused directive line info, and adds legacy @addTagHelper unused diagnostics.
src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/CodeActions/RemoteServices.cs	Exports new OOP provider/resolver for remove-unnecessary-directives code action.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.zh-Hant.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.zh-Hans.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.tr.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.ru.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.pt-BR.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.pl.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.ko.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.ja.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.it.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.fr.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.es.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.de.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/xlf/SR.cs.xlf	Adds localized string entry for “Remove unnecessary directives”.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/SR.resx	Adds the new resource key/value for the code action title.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Protocol/LanguageServerConstants.cs	Adds RemoveUnnecessaryDirectives code action name constant.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/UsingDirectiveHelper.cs	Extracts reusable helper to compute the text edit for removing a directive line/span.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/RazorSyntaxTreeExtensions.cs	Adds helper to enumerate @addTagHelper directives.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/RazorSyntaxNodeExtensions.cs	Adds directive identification helper and span-trimming utility for directive ranges.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Diagnostics/UnusedDirectiveCache.cs	New cache for unused-directive line numbers keyed to a RazorCodeDocument.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Diagnostics/RazorTranslateDiagnosticsService.cs	Updates C# diagnostic filtering to handle unused-using diagnostics with Razor-specific usage semantics.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/CodeActions/Razor/RemoveUnnecessaryDirectivesCodeActionResolver.cs	New resolver that applies removal edits for all unused directive spans.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/CodeActions/Razor/RemoveUnnecessaryDirectivesCodeActionProvider.cs	New provider that offers the removal code action when selection is on a directive and cached unused directives exist.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/CodeActions/Razor/RazorCodeActionFactory.cs	Adds code action factory method, localized title, telemetry id, and ordering for the new action.
src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/CodeActions/Models/RemoveUnnecessaryDirectivesCodeActionParams.cs	New model carrying the unused directive spans to the resolver.
src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/RazorLifeCycleManager.cs	Updates lifecycle API surface (Shutdown signature change) for updated protocol/framework APIs.
src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/RazorCodeDocumentExtensions.cs	Adds imports-file detection and directive usage evaluation based on recorded contributions and referenced tag helpers.
src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/RazorCodeDocument.cs	Stores directive tag helper contribution data on the code document.
src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/DirectiveTagHelperContribution.cs	New record representing a directive’s contributed tag helpers.
src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/DefaultRazorTagHelperContextDiscoveryPhase.cs	Records per-directive contributions while discovering tag helpers/components.
src/Compiler/Microsoft.AspNetCore.Razor.Language/test/RazorCodeDocumentExtensionsTest.cs	Adds unit tests for directive contribution storage and directive usage evaluation.
src/Compiler/Microsoft.AspNetCore.Razor.Language/test/IntegrationTests/TagHelpersIntegrationTest.cs	Adds integration tests validating @addTagHelper directive usage tracking.
src/Compiler/Microsoft.AspNetCore.Razor.Language/test/IntegrationTests/ComponentDiscoveryIntegrationTest.cs	Adds integration tests validating @using directive usage tracking for components and fully-qualified tags.
eng/Version.Details.xml	Bumps Roslyn dependency versions/SHA and updates Arcade SDK toolset dependency.
eng/Version.Details.props	Updates Roslyn package version properties and Arcade SDK version property.
.github/skills/update-roslyn-version/SKILL.md	Adds a repo skill guide for performing Roslyn version bumps consistently.

Comments suppressed due to low confidence (2)

.github/skills/update-roslyn-version/SKILL.md:24

• The skill text is machine-specific (‘D:\NugetCache on this machine’). Since this lives in the repo and should be reusable, consider rewording step 5 to refer to the user’s NuGet cache generically (and keep the platform-specific paths in the Notes section).

5. **Get the commit hash**: After restore, find a `.nuspec` file for one of the restored Roslyn packages in the NuGet cache (`D:\NugetCache` on this machine). For example:

D:\NugetCache\microsoft.codeanalysis.common<NEW_VERSION>\microsoft.codeanalysis.common.nuspec

Parse the `<repository commit="...">` element from the nuspec to extract the commit SHA. All Roslyn packages share the same commit.

eng/Version.Details.xml:105

• This PR description calls out a Roslyn bump, but these changes also modify the Microsoft.DotNet.Arcade.Sdk toolset dependency (and appear to downgrade it from 10.0.0-beta.26123.2 to 10.0.0-beta.26110.1). If this isn’t intentional/required for the Roslyn update, consider reverting it or updating the PR description to explain why Arcade needs to change too.

    <Dependency Name="Microsoft.DotNet.Arcade.Sdk" Version="10.0.0-beta.26110.1">
      <Uri>https://github.com/dotnet/arcade</Uri>
      <Sha>4bf37ce670528cf2aef4d9b1cd892554b1b02d9d</Sha>

[davidwengier]

Have pushed changes for each comment. Ready for round 2.

[ToddGrun]

[davidwengier]

@chsienki would be good to get your sign-off on the compiler changes, just in case.