Move diagnostic generation from LibraryImportGenerator to LibraryImportDiagnosticsAnalyzer #123780

Copilot · 2026-01-29T22:59:01Z

Description

Moves diagnostic generation from the LibraryImportGenerator source generator to a new LibraryImportDiagnosticsAnalyzer, per Roslyn team recommendation.

Changes:

Added LibraryImportDiagnosticsAnalyzer.cs with infrastructure to run diagnostic logic
- Uses SymbolEqualityComparer to compare attribute types instead of string matching
- Returns early when ProcessLibraryImportAttribute returns null (invalid compilation)
Updated CSharpSourceGeneratorVerifier to accept a TAnalyzer type parameter for specifying which analyzer to run alongside a generator
Removed diagnostic reporting from LibraryImportGenerator:
- Removed all DiagnosticOr usage from the pipeline
- Added IsValidMethodForGeneration method that returns a boolean for filtering
- Methods are now filtered with Where directly before entering the pipeline
Updated diagnostic tests to use CSharpAnalyzerVerifier instead of CSharpSourceGeneratorVerifier:
- Tests now run only the analyzer without the generator
- Updated CSharpAnalyzerVerifier.Test to ignore compiler diagnostics since partial methods won't have implementations without the generator
Updated other test files to use two type parameters:
- LibraryImportGenerator tests use LibraryImportDiagnosticsAnalyzer
- Other generators use EmptyDiagnosticAnalyzer from Microsoft.CodeAnalysis.Testing as a placeholder

Current state: 672/703 tests pass (95%). The analyzer reports most diagnostics but doesn't yet handle all edge cases that the generator previously handled (e.g., InvalidStringMarshallingConfiguration validation, some MarshalAs field validations).

Next steps (future PRs):

Complete analyzer to handle all diagnostic edge cases
Apply pattern to ComInterfaceGenerator, JSImportGenerator, JSExportGenerator, DownlevelLibraryImportGenerator

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

… diagnostics Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

…itional analyzer loading Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

…till reports diagnostics) Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Mis-clicked approve

jkoritzinsky

@copilot address this review.

jkoritzinsky · 2026-01-30T00:18:04Z

...ime.InteropServices/gen/LibraryImportGenerator/Analyzers/LibraryImportDiagnosticsAnalyzer.cs

+
+            // Only analyze methods with LibraryImportAttribute
+            AttributeData? libraryImportAttr = null;
+            foreach (AttributeData attr in method.GetAttributes())
+            {
+                if (attr.AttributeClass?.ToDisplayString() == TypeNames.LibraryImportAttribute)
+                {
+                    libraryImportAttr = attr;
+                    break;
+                }
+            }
+
+            if (libraryImportAttr is null)
+                return false;


Use the LibraryImportAttribute type from the compilation (via GetBestTypeByMetadataName) instead of matching on name

Fixed in 6232571. Now uses GetBestTypeByMetadataName to get the LibraryImportAttribute type and compares using SymbolEqualityComparer.Default.Equals.

jkoritzinsky · 2026-01-30T00:18:32Z

...ime.InteropServices/gen/LibraryImportGenerator/Analyzers/LibraryImportDiagnosticsAnalyzer.cs

+
+            // Process the LibraryImport attribute
+            LibraryImportCompilationData libraryImportData =
+                ProcessLibraryImportAttribute(libraryImportAttr) ??


If ProcessLibraryImportAttribute returns null, we can stop handling diagnostics here. We already know we have an invalid compilation.

Fixed in 6232571. Now returns early with empty diagnostics when ProcessLibraryImportAttribute returns null.

jkoritzinsky · 2026-01-30T00:18:53Z

...raries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/DiagnosticOr.cs

+
+        /// <summary>
+        /// Filters the <see cref="IncrementalValuesProvider{TValue}"/> by whether or not the element has a value, discarding diagnostics.
+        /// Use this when diagnostics are reported by an analyzer instead of the generator.
+        /// </summary>
+        public static IncrementalValuesProvider<T> FilterWithoutReportingDiagnostics<T>(this IncrementalValuesProvider<DiagnosticOr<T>> diagnosticOrValues)
+        {
+            var (values, _) = diagnosticOrValues.Split();
+            return values;
+        }


We'll eventually remove usages of DiagnosticOr so we shouldn't need this helper anyway.

Removed in 6232571. Now uses Split() directly instead of a helper method.

jkoritzinsky · 2026-01-30T00:19:09Z

...aries/System.Runtime.InteropServices/tests/Common/Verifiers/CSharpSourceGeneratorVerifier.cs

+            protected override IEnumerable<DiagnosticAnalyzer> GetDiagnosticAnalyzers()
+            {
+                // Include the corresponding diagnostics analyzer when testing specific generators.
+                // Note: The analyzer is available alongside the generator but diagnostics are still
+                // reported by the generator for now. This will change as we migrate diagnostics to analyzers.
+                foreach (var analyzer in base.GetDiagnosticAnalyzers())
+                {
+                    yield return analyzer;
+                }
+            }
+


Instead of overriding GetDiagnosticAnalyzers(), update CSharpSourceGeneratorVerifier to have a TAnalyzer argument as well (and instantiate an instance of that analyzer here).

That should enable you to remove the diagnostics from the LibraryImportGenerator source generator's code.

…per review feedback Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

jkoritzinsky · 2026-01-30T00:50:30Z

...ibraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/LibraryImportGenerator.cs

            });

-            var methodsToGenerate = context.FilterAndReportDiagnostics(methodsWithDiagnostics);
+            // Filter methods but don't report diagnostics - the analyzer will handle that


@copilot Filter out the diagnostics earlier. I would like to not see DiagnosticOr used in the pipeline at all and instead have diagnostics dropped before they ever get into a step's output.

Fixed in 7a1d4df. Removed DiagnosticOr from the pipeline entirely. Methods are now filtered with Where directly using a new IsValidMethodForGeneration method that returns a boolean.

jkoritzinsky · 2026-01-30T00:51:28Z

...braries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Diagnostics.cs

@copilot since we're moving the diagnostics to be emitted by the analyzer, we can change these tests to not run the generator and only run the analyzer.

Fixed in 7a1d4df. Changed Diagnostics.cs to use CSharpAnalyzerVerifier<LibraryImportDiagnosticsAnalyzer> instead of running the generator. Updated the analyzer verifier to ignore compiler diagnostics since without the generator, partial methods don't have implementations.

…null, remove helper method Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

…analyzer only Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Initial plan

5ab07b3

Copilot AI assigned Copilot and jkoritzinsky Jan 29, 2026

github-project-automation bot added this to AppModel Jan 29, 2026

Copilot started work on behalf of jkoritzinsky January 29, 2026 22:59 View session

Copilot AI and others added 4 commits January 29, 2026 23:28

Add LibraryImportDiagnosticsAnalyzer and update generator to not emit…

87827dd

… diagnostics Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Fix duplicate diagnostics in LibraryImportDiagnosticsAnalyzer

4e3556e

Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Address code review feedback - fix RequiresAllowUnsafeBlocks and cond…

b0d4d92

…itional analyzer loading Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Add LibraryImportDiagnosticsAnalyzer alongside generator (generator s…

deaee03

…till reports diagnostics) Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Move diagnostic generation to analyzers alongside generators~~ Add LibraryImportDiagnosticsAnalyzer foundation for diagnostic migration Jan 29, 2026

Copilot AI requested a review from jkoritzinsky January 29, 2026 23:53

Copilot finished work on behalf of jkoritzinsky January 29, 2026 23:53

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Copilot started work on behalf of jkoritzinsky January 30, 2026 00:18 View session

jkoritzinsky reviewed Jan 30, 2026

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Update CSharpSourceGeneratorVerifier to use TAnalyzer type parameter …

f8ec08c

…per review feedback Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Copilot AI changed the title ~~Add LibraryImportDiagnosticsAnalyzer foundation for diagnostic migration~~ Move diagnostic generation from LibraryImportGenerator to LibraryImportDiagnosticsAnalyzer Jan 30, 2026

Copilot AI requested a review from jkoritzinsky January 30, 2026 00:47

Copilot finished work on behalf of jkoritzinsky January 30, 2026 00:47

Copilot started work on behalf of jkoritzinsky January 30, 2026 00:48 View session

jkoritzinsky reviewed Jan 30, 2026

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Address review feedback: use SymbolEqualityComparer, return early on …

6232571

…null, remove helper method Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Copilot AI requested a review from jkoritzinsky January 30, 2026 01:13

Copilot finished work on behalf of jkoritzinsky January 30, 2026 01:13

Copilot started work on behalf of jkoritzinsky January 30, 2026 01:14 View session

Filter diagnostics earlier in pipeline and run diagnostic tests with …

7a1d4df

…analyzer only Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Copilot finished work on behalf of jkoritzinsky January 30, 2026 01:39

Move diagnostic generation from LibraryImportGenerator to LibraryImportDiagnosticsAnalyzer #123780

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Move diagnostic generation from LibraryImportGenerator to LibraryImportDiagnosticsAnalyzer #123780

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Copilot AI commented Jan 29, 2026 •

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