[release/10.0] Fix ModelMetadata null reference exception in emitted XMLComment transformers #23

tomerqodo · 2026-01-22T00:35:14Z

Summary by CodeRabbit

Release Notes

New Features
- XML documentation comments are now integrated into generated OpenAPI documents, enriching API documentation with summaries, parameter descriptions, examples, and response details.
Bug Fixes
- Added null-safety checks to prevent potential null reference exceptions when processing parameter metadata.
Tests
- Extended test coverage for route parameter documentation in controller-based APIs.

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…ment transformers When a route parameter does not have a bound model it would case a null reference exception because the ModelMetadata on the ParameterDescriptor was null. This is fixed by adding a null reference check Fixes dotnet#63757

As I think this was the encoding before my change

coderabbitai · 2026-01-22T00:35:55Z

Walkthrough

A new test method validates route parameter descriptions from controller actions. Multiple test snapshot files are updated with null-checks before accessing metadata properties. One substantial snapshot file introduces comprehensive XML comment support infrastructure for the OpenAPI source generator, including transformers, documentation ID helpers, and caching logic.

Changes

Cohort / File(s)	Summary
Test Method Addition `src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/OperationTests.Controllers.cs`	Adds `SupportsRouteParametersFromControllers()` test method to validate that controller route parameters with descriptions are correctly included in generated OpenAPI documents.
Null-Check Guards in Snapshot Files `src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/AddOpenApiTests...#OpenApiXmlCommentSupport.generated.verified.cs`, `AdditionalTextsTests...#OpenApiXmlCommentSupport.generated.verified.cs`, `CompletenessTests...#OpenApiXmlCommentSupport.generated.verified.cs`, `OperationTests.SupportsXmlCommentsOnOperationsFromControllers...#OpenApiXmlCommentSupport.generated.verified.cs`, `OperationTests.SupportsXmlCommentsOnOperationsFromMinimalApis...#OpenApiXmlCommentSupport.generated.verified.cs`, `SchemaTests.SupportsXmlCommentsOnSchemas...#OpenApiXmlCommentSupport.generated.verified.cs`, `SchemaTests.XmlCommentsOnPropertiesShouldApplyToSchemaReferences...#OpenApiXmlCommentSupport.generated.verified.cs`, `XmlCommentDocumentationIdTests...#OpenApiXmlCommentSupport.generated.verified.cs`	Adds null-check guards (`metadata is not null`) before accessing `MetadataKind`, `ContainerType`, and `PropertyName` in parameter description loops, preventing null reference exceptions when `parameterDescription.ModelMetadata` is null. Consistent pattern applied across 8 snapshot files.
Comprehensive XML Comment Support `src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsRouteParametersFromControllers#OpenApiXmlCommentSupport.generated.verified.cs`	New snapshot file introducing extensive XML comment integration: InterceptsLocationAttribute for method tagging; XmlComment, XmlParameterComment, and XmlResponseComment data contracts; XmlCommentCache for comment caching with GenerateCacheEntries method; DocumentationCommentIdHelper with doc ID generation and normalization; XmlCommentOperationTransformer and XmlCommentSchemaTransformer for applying comments to operations and schemas; JsonNodeExtensions for JSON parsing; GeneratedServiceCollectionExtensions for OpenAPI registration.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

🐰 Null checks dance through snapshot land,
Parameter guards, oh so grand!
XML comments now take their flight,
Making docs both rich and bright,
Route descriptions, clear and true—
OpenAPI thanks the testing crew! 🎉

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 30.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly identifies the primary change: fixing a ModelMetadata null reference exception in XMLComment transformers, which matches the core objective and multiple file changes.

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✨ Finishing touches

📝 Generate docstrings

🧹 Recent nitpick comments

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsRouteParametersFromControllers#OpenApiXmlCommentSupport.generated.verified.cs (1)

374-374: Unused variable parameterInfo.

The variable parameterInfo is assigned but never used. This appears to be in the generated code template. If this is intentional for future use, consider adding a comment; otherwise, the source generator template should be updated to remove it.

📜 Recent review details

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 2151ff6 and bd02708.

⛔ Files ignored due to path filters (1)

src/OpenApi/gen/XmlCommentGenerator.Emitter.cs is excluded by !**/gen/**

📒 Files selected for processing (10)

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/OperationTests.Controllers.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/AddOpenApiTests.CanInterceptAddOpenApi#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/AdditionalTextsTests.CanHandleXmlForSchemasInAdditionalTexts#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/CompletenessTests.SupportsAllXmlTagsOnSchemas#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsRouteParametersFromControllers#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsXmlCommentsOnOperationsFromControllers#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsXmlCommentsOnOperationsFromMinimalApis#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/SchemaTests.SupportsXmlCommentsOnSchemas#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/SchemaTests.XmlCommentsOnPropertiesShouldApplyToSchemaReferences#OpenApiXmlCommentSupport.generated.verified.cs
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/XmlCommentDocumentationIdTests.CanMergeXmlCommentsWithDifferentDocumentationIdFormats#OpenApiXmlCommentSupport.generated.verified.cs

🔇 Additional comments (10)

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/SchemaTests.XmlCommentsOnPropertiesShouldApplyToSchemaReferences#OpenApiXmlCommentSupport.generated.verified.cs (1)

437-441: Good null-guard before touching metadata.
Prevents NREs when parameters lack ModelMetadata (e.g., route-only params).

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/CompletenessTests.SupportsAllXmlTagsOnSchemas#OpenApiXmlCommentSupport.generated.verified.cs (1)

553-559: Null-check looks correct.
Keeps the parameter loop safe when ModelMetadata is absent.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/AdditionalTextsTests.CanHandleXmlForSchemasInAdditionalTexts#OpenApiXmlCommentSupport.generated.verified.cs (1)

455-461: Null-guard is a solid safety fix.
Protects against ModelMetadata being null in this path.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/XmlCommentDocumentationIdTests.CanMergeXmlCommentsWithDifferentDocumentationIdFormats#OpenApiXmlCommentSupport.generated.verified.cs (1)

427-434: Guarding ModelMetadata is the right fix.
Eliminates potential null dereference in the parameter loop.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/AddOpenApiTests.CanInterceptAddOpenApi#OpenApiXmlCommentSupport.generated.verified.cs (1)

426-433: Null-guard is appropriate here.
Keeps the transformer resilient when metadata is missing.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/OperationTests.Controllers.cs (1)

100-143: Nice coverage for route parameter descriptions.
This test directly exercises the regression scenario and validates the expected OpenAPI output.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsRouteParametersFromControllers#OpenApiXmlCommentSupport.generated.verified.cs (1)

427-433: Null check correctly prevents NRE when ModelMetadata is null.

This fix properly guards against null ModelMetadata on route parameters that don't have a bound model, addressing the upstream issue dotnet#63757. The pattern-matching approach with metadata is not null combined with the subsequent property checks is clean and idiomatic.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsXmlCommentsOnOperationsFromMinimalApis#OpenApiXmlCommentSupport.generated.verified.cs (1)

477-480: Null check correctly applied for minimal APIs scenario.

The null guard for metadata is consistently applied here, preventing potential NullReferenceException when processing parameter descriptions where ModelMetadata may be null.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/OperationTests.SupportsXmlCommentsOnOperationsFromControllers#OpenApiXmlCommentSupport.generated.verified.cs (1)

433-436: Null check correctly applied for controller route parameters.

This is the core fix for the PR - adding the null guard before accessing MetadataKind prevents the NullReferenceException when controller route parameters do not have a bound model (as referenced in dotnet#63757).

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.SourceGenerators.Tests/snapshots/SchemaTests.SupportsXmlCommentsOnSchemas#OpenApiXmlCommentSupport.generated.verified.cs (1)

459-462: Null check consistently applied in schema test snapshot.

The defensive null check is uniformly applied across all test snapshots, ensuring the fix is propagated to all scenarios where parameter metadata is accessed.

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desjoerd and others added 5 commits January 21, 2026 16:01

Change snapshots to utf-8 with bom

446105a

As I think this was the encoding before my change

Rename controller test to allow adding it for minimal api's as well

aa45c34

Fix whitespace difference in OpenApi XML Source generator snapshot

21795a4

update pr

bd02708

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[release/10.0] Fix ModelMetadata null reference exception in emitted XMLComment transformers #23

[release/10.0] Fix ModelMetadata null reference exception in emitted XMLComment transformers #23

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tomerqodo commented Jan 22, 2026 •

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[release/10.0] Fix ModelMetadata null reference exception in emitted XMLComment transformers #23

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Summary by CodeRabbit

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Walkthrough

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tomerqodo commented Jan 22, 2026 •

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