Add analyzer for OSCondition (MSTEST0059) #7015

Copilot · 2025-11-28T09:40:20Z

Adds a new code analyzer MSTEST0059 that detects usage of RuntimeInformation.IsOSPlatform with early return or Assert.Inconclusive in test methods and suggests using the [OSCondition] attribute instead.

Fixes #7011

Changes Made

Analyzer: Created UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer that detects:
- if (RuntimeInformation.IsOSPlatform(...)) { return; } patterns (suggests ConditionMode.Exclude)
- if (!RuntimeInformation.IsOSPlatform(...)) { return; } patterns (suggests ConditionMode.Include)
- Assert.Inconclusive calls within the if blocks
- Supports Windows, Linux, OSX, and FreeBSD platforms
Code Fixer: Created UseOSConditionAttributeInsteadOfRuntimeCheckFixer that:
- Adds [OSCondition] attribute with the appropriate ConditionMode and OperatingSystems value
- Removes the if statement from the method body
Infrastructure:
- Added diagnostic ID MSTEST0059 in DiagnosticIds.cs
- Added type name for RuntimeInformation in WellKnownTypeNames.cs
- Added resource strings and localization entries
Tests: Comprehensive unit tests covering:
- Negated and non-negated runtime checks
- Different platforms (Windows, Linux, OSX)
- Single statement vs block returns
- Assert.Inconclusive patterns
- Edge cases (else branches, non-test methods, other statements)
- Code fix behavior with trivias (leading/trailing/inline comments)

Original prompt

This section details on the original issue you should resolve

<issue_title>Add analyzer for OSCondition</issue_title>
<issue_description>## Summary

With #6994 merged an analyzer can help widespread the use of the new attribute.

</issue_description>

<agent_instructions>Add a new code analyzer that will detect in test methods the usage of early return or assert.inconclusive for calls to RuntimeInformation.IsOSPlatform and suggest instead to use [OSCondition] attribute. We should also handle !RuntimeInformation.... and also provide a codefix for this new analyzer.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes Add analyzer for OSCondition #7011

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Co-authored-by: Evangelink <[email protected]>

src/Analyzers/MSTest.Analyzers/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer.cs

...ests/MSTest.Analyzers.UnitTests/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzerTests.cs

Co-authored-by: Evangelink <[email protected]>

Copilot · 2025-11-28T13:25:49Z

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

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Co-authored-by: Evangelink <[email protected]>

src/Analyzers/MSTest.Analyzers/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer.cs

Evangelink

@copilot let's add some test cases with trivias to see how the code fix reacts. For example

// Skip on windows
if (RuntimeInformation.IsOSPLatform(OSPlatform.Windows)

or with trivias after the if block

Co-authored-by: Evangelink <[email protected]>

Copilot · 2025-11-28T15:01:42Z

@copilot let's add some test cases with trivias to see how the code fix reacts. For example

Added test cases with trivias in cbd04fa:

WhenRuntimeCheckWithLeadingComment_Diagnostic: Comment before the if statement
WhenRuntimeCheckWithTrailingComment_Diagnostic: Comment after the if block
WhenRuntimeCheckWithCommentInsideBlock_Diagnostic: Comment inside the if block

src/Analyzers/MSTest.Analyzers.CodeFixes/UseOSConditionAttributeInsteadOfRuntimeCheckFixer.cs

Youssef1313 · 2025-11-28T16:54:01Z

src/Analyzers/MSTest.Analyzers/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer.cs

+                return;
+            }
+
+            IMethodSymbol? isOSPlatformMethod = runtimeInformationSymbol.GetMembers("IsOSPlatform")


Do we also want to handle OperatingSystem.Is<OS> methods?

Youssef1313 · 2025-11-28T16:55:56Z

src/Analyzers/MSTest.Analyzers/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer.cs

+                blockContext.RegisterOperationAction(
+                    operationContext => AnalyzeIfStatement(operationContext, isOSPlatformMethod, assertSymbol),
+                    OperationKind.Conditional);


This will analyze conditions that appear anywhere in the method body. But if I have a test method like the following:

[TestMethod] public void MyTestMethod() { // arrange // some assertions // if windows, return // some other assertions that are non-Windows only. }

This shouldn't get flagged.

Youssef1313 · 2025-11-28T16:58:24Z

src/Analyzers/MSTest.Analyzers/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer.cs

+
+        // Check if it's an invocation of RuntimeInformation.IsOSPlatform
+        if (actualCondition is not IInvocationOperation invocation ||
+            !SymbolEqualityComparer.Default.Equals(invocation.TargetMethod.OriginalDefinition, isOSPlatformMethod))


Is accessing OriginalDefinition really needed here?

Youssef1313 · 2025-11-28T16:59:25Z

src/Analyzers/MSTest.Analyzers/UseOSConditionAttributeInsteadOfRuntimeCheckAnalyzer.cs

+            foreach (IOperation operation in blockOperation.Operations)
+            {
+                if (IsReturnOrAssertInconclusive(operation, assertSymbol))
+                {
+                    return true;
+                }
+            }
+
+            return false;


Is this correct? Shouldn't we only look at the first operation?

Youssef1313 · 2025-11-28T17:02:32Z

src/Analyzers/MSTest.Analyzers.CodeFixes/UseOSConditionAttributeInsteadOfRuntimeCheckFixer.cs

+        }
+
+        // Find the if statement to remove
+        IfStatementSyntax? ifStatement = diagnosticNode.FirstAncestorOrSelf<IfStatementSyntax>();


The diagnostic node here is what? Shouldn't it be the IfStatementSyntax in question already? Why do we need FirstAncestorOrSelf?

Initial plan

d23a3b4

Copilot AI assigned Copilot and Evangelink Nov 28, 2025

Copilot started work on behalf of Evangelink November 28, 2025 09:40 View session

Add analyzer and code fixer for OSCondition attribute

679b549

Co-authored-by: Evangelink <[email protected]>

Copilot AI changed the title ~~[WIP] Add analyzer for OSCondition usage in test methods~~ Add analyzer for OSCondition (MSTEST0059) Nov 28, 2025

Copilot AI requested a review from Evangelink November 28, 2025 10:28

Copilot finished work on behalf of Evangelink November 28, 2025 10:28

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Add missing using directive for RoslynAnalyzerHelpers namespace

a5c0841

Co-authored-by: Evangelink <[email protected]>

Copilot AI requested a review from Evangelink November 28, 2025 13:25

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Copilot started work on behalf of Evangelink November 28, 2025 13:26 View session

Fix pattern matching issue and unify test structure

155ccc3

Co-authored-by: Evangelink <[email protected]>

Copilot finished work on behalf of Evangelink November 28, 2025 13:31

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Copilot started work on behalf of Evangelink November 28, 2025 14:59 View session

Evangelink marked this pull request as ready for review November 28, 2025 15:00

Add test cases with trivias (comments) for code fix behavior

cbd04fa

Co-authored-by: Evangelink <[email protected]>

Copilot AI requested a review from Evangelink November 28, 2025 15:03

Copilot finished work on behalf of Evangelink November 28, 2025 15:03

Evangelink enabled auto-merge (squash) November 28, 2025 15:05

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Evangelink added 2 commits November 28, 2025 17:13

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Fix codefix and update tests

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Youssef1313 reviewed Nov 28, 2025

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Add analyzer for OSCondition (MSTEST0059) #7015

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Copilot AI commented Nov 28, 2025

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Copilot AI commented Nov 28, 2025 •

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