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Suppress SYSLIB1227 for unions with custom converters - #133244
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eiriktsarpalis merged 1 commit intoSep 9, 2026
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Co-authored-by: Copilot App <[email protected]> Copilot-Session: 45c8108d-e1a0-493a-b9d3-6ffc8bd752d4
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🟡 Changes recommended
The new test can pass without actually exercising the intended scenario if the in-memory compilation fails, and it should assert compilation success (and/or align the test name with what is asserted).
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Pull request overview
This PR updates the System.Text.Json source generator’s union analysis so that when a type has a type-level [JsonConverter] (i.e., metadata will use the custom-converter contract path), the generator no longer discovers union case types and no longer emits the union ambiguity warning SYSLIB1227. It also adds a unit test covering the scenario.
Changes:
- Skip union case-type enqueueing/ambiguity diagnostics when a type-level
JsonConverterAttributeis present. - Add source-generator diagnostic test coverage ensuring
SYSLIB1227is not produced for an otherwise-ambiguous union when a custom converter is applied.
File summaries
| File | Description |
|---|---|
| src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs | Gated union case discovery/ambiguity diagnostics behind “no type-level JsonConverterAttribute” so custom-converter-owned contracts don’t trigger SYSLIB1227. |
| src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorDiagnosticsTests.cs | Adds a regression test for unions with a type-level custom converter to ensure SYSLIB1227 is not emitted. |
Review details
Suppressed comments (1)
src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorDiagnosticsTests.cs:749
- This test can pass vacuously if the in-memory compilation fails (since diagnostic validation is disabled and the test doesn't assert compilation success). Add a compilation diagnostic check so the test always exercises the generator with valid source.
Compilation compilation = CompilationHelper.CreateCompilation(source);
JsonSourceGeneratorResult result = CompilationHelper.RunJsonSourceGenerator(compilation, disableDiagnosticValidation: true);
Assert.DoesNotContain(result.Diagnostics, diagnostic => diagnostic.Id == "SYSLIB1227");
- Files reviewed: 2/2 changed files
- Comments generated: 1
- Review effort level: Lite
PranavSenthilnathan
approved these changes
Sep 8, 2026
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/backport to release/11.0 |
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Sep 10, 2026
…133475) Backport of #133244 to release/11.0 /cc @eiriktsarpalis ## Customer Impact - [x] Customer reported - [ ] Found internally Customer reported issue where the source generator will report a diagnostic about a union type requiring a type classifier even though it has been annotated with a `JsonConverterAttribute` which overrides all other serialization mechanisms. ## Regression - [ ] Yes - [x] No ## Testing Added unit testing covering the impacted scenario. ## Risk Low. Targeted product code fix adding a missing check. Co-authored-by: Eirik Tsarpalis <[email protected]> Copilot-Session: 45c8108d-e1a0-493a-b9d3-6ffc8bd752d4
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A type-level
[JsonConverter]makes generated metadata use the custom-converter path, but the source generator still analyzed the union cases first and emittedSYSLIB1227.Skip union case discovery and ambiguity diagnostics when a type-level converter owns the contract. Add source-generator coverage for an otherwise ambiguous union handled by a custom converter.
Fixes #133156.
Validated with:
build.cmd clr+libs -rc releaseNote
This pull request description was generated by GitHub Copilot.