Add Net Analyzer

Add or port a .NET code analysis (CA) rule

AGENTS.md maps the tree and carries the build/test commands and environment gotchas. Paths below are relative to $NA = src/Microsoft.CodeAnalysis.NetAnalyzers.

1. Confirm the rule is wanted

New CA rules are proposed and triaged before implementation — .NET API-related ones in dotnet/runtime under the code-analyzer label. If an API review already decided the category, severity, and whether a fixer is wanted, follow that decision and cite it in the PR rather than re-deriving one. Ask before diverging from it.

2. Allocate the diagnostic ID

DiagnosticCategoryAndIdRanges.txt records only merged work, so the "next" ID is routinely already claimed by an open PR or a concurrent branch. Run:

./.dotnet/dotnet .github/skills/add-net-analyzer/scripts/NextDiagnosticId.cs Performance

It scans forward from the end of the category's range until it finds an ID unclaimed in the working tree, on any local branch, and in any open dotnet/sdk PR, prints the exact range edit to apply, and reports anything it skipped. Exit 0 means every check ran, 1 means the ID is proposed but open PRs went unchecked, and 2 is a hard failure — including "every candidate in the scan window is already taken". The PR check matches titles and bodies rather than diffs, so treat it as a strong heuristic, not proof.

3. Implement the analyzer and fixer

Read references/authoring-patterns.md first.

The language-agnostic analyzer goes in $NA/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.<Group>.Analyzers/<Category>/<Name>.cs, the fixer in <Name>.Fixer.cs beside it. Derive C#/VB types only where you genuinely need syntax; those go at the same relative path inside $NA/src/Microsoft.CodeAnalysis.CSharp.NetAnalyzers/ or …VisualBasic.NetAnalyzers/. The folder is the rule group's category — the category: you report can differ, and comes from the DiagnosticCategory constants, never a raw string. Decisions that are yours rather than pattern-matching an existing rule:

• RuleLevel — IdeSuggestion unless you have a reason. IdeHidden_BulkConfigurable is the first level that tolerates any false positives, and BuildWarning additionally breaks builds under TreatWarningsAsErrors.
• Whether the fix preserves semantics — preserve them where doing so is trivial; where it is not, the fix may still change them but must say so ((may change semantics)).

4. Add the strings

Append to the resx for the rule group — e.g. $NA/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.NetCore.Analyzers/MicrosoftNetCoreAnalyzersResources.resx — one entry each for <Name>Title, <Name>Message, <Name>Description, plus <Name>CodeFixTitle if there is a fixer. Reference them via CreateLocalizableResourceString(nameof(<Name>Title)) with using static <Resources>; at the top of the namespace.

<Name>CodeFixTitle names the action the fix performs ("Extract to static readonly field"), not the problem the analyzer reports. Terms that must not be translated get <comment>{Locked="static readonly"}</comment>; multiple terms are adjacent braces with no separator.

Then regenerate the 13 .xlf files in the xlf/ subfolder beside it. Run the target against the project that owns the resx — passing /t:UpdateXlf to build.cmd fails with MSB4057, because Arcade applies the target to its own Build.proj rather than to the projects being built:

./.dotnet/dotnet msbuild src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.CodeAnalysis.NetAnalyzers.csproj /t:UpdateXlf

5. Record the rule in release tracking

Each of the three analyzer projects has its own AnalyzerReleases.Unshipped.md at its root; the row goes in the project that declares the descriptor, which for a language-agnostic rule is Microsoft.CodeAnalysis.NetAnalyzers. The RS2000/RS2001 meta-analyzers fail the build if you skip this, and they ship a code fix that writes the row for you.

Rule ID | Category | Severity | Notes
--------|----------|----------|-------
CA#### | Performance | Info | <Name>Analyzer, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca####)

Severity is the release-tracking severity for your RuleLevel, which is not always the descriptor's DiagnosticSeverity — a disabled rule carries Warning on the descriptor but tracks as Disabled:

The Documentation link must carry the same rule ID as the row it sits on, lowercased to match the help link DiagnosticDescriptorHelper derives for the descriptor. Nothing validates this, and a row copy-pasted from the one above keeps that rule's ID, quietly pointing readers at a different rule — check it by eye. The page itself 404s until your docs PR lands, which is expected; don't paper over it by linking an existing rule's page.

Rows move to AnalyzerReleases.Shipped.md at release time — don't move them yourself.

6. Write the tests

Tests go in $NA/tests/Microsoft.CodeAnalysis.NetAnalyzers.UnitTests/Microsoft.<Group>.Analyzers/<Category>/<Name>Tests.cs, mirroring the analyzer's folder. Full conventions are in references/authoring-patterns.md; the coverage bar:

• C# fully; VB at least mainline positive and negative, fully if any VB-specific code exists. Split by both behavior and language — a separate test method per language.
• When a fixer exists, write every test as a code-fix test, and include a trivia case. If the diagnostic can nest, add a nested case — that is what catches a broken fix-all.
• The negative cases you reasoned about while designing. Reviewers will ask for them.

7. Build and test

# ~10s incremental once .dotnet is provisioned; the first run provisions it.
./build.cmd -projects src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.CodeAnalysis.NetAnalyzers.slnx -c Debug

Then invoke the run-tests skill for src/Microsoft.CodeAnalysis.NetAnalyzers/tests/Microsoft.CodeAnalysis.NetAnalyzers.UnitTests/Microsoft.CodeAnalysis.NetAnalyzers.UnitTests.csproj with a filter for <Name>Tests. This project does not consume the assembled SDK, so the runner may skip its redist check.

Then git status and commit the regenerated files along with your change. ./build.sh on Linux/macOS; never pass -restore/-build alongside -projects.

8. Validate the rule against real code

Unit tests prove the rule fires; they say nothing about how often it is wrong, and that is the gate on RuleLevel. Every level from IdeSuggestion up requires no false positives, so before proposing one, run the built analyzer over a large real codebase (dotnet/runtime, dotnet/roslyn) and triage every hit. Report the result in the PR. docs/netcore-getting-started.md has the mechanics and the full definition of done.

9. Documentation

Each CA#### is auto-assigned the help link https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca####, backed by ca####.md in dotnet/docs. A docs PR is required within one week of the rule merging, or the implementation may be reverted — a condition of the rule landing, not an optional follow-up. Raise it with the user as outstanding work and leave the opening to them. Nothing in the build checks that the page exists — RulesMissingDocumentation.md is generated with the link check disabled and stays empty — so the docs PR is the only thing standing between the rule and a dead help link in every user's IDE.

Checklist

• Rule proposal reviewed and accepted, and the decision cited in the PR.
• ID unclaimed by any local branch or open PR, and the category's range extended to cover it.
• AnalyzerReleases.Unshipped.md row added, its Documentation link matching the row's own ID in lowercase.
• .resx edited and .xlf regenerated via /t:UpdateXlf — neither hand-edited.
• Regenerated .md / .sarif.template committed.
• Targeted test run passes, covering VB and the negative cases.
• Analyzer not narrowed to what the fixer handles, and no fix registered that leaves the document unchanged.
• Fix-all handles nesting (not the batch fixer), if the diagnostic can overlap or nest.
• Every shape the fix offers itself on produces compiling code.
• Rule run against a real codebase and hits triaged, at IdeSuggestion or stronger.
• dotnet/docs PR raised with the user as a condition of merging.