Suppress union ambiguity warning when a global classified is specified at compile time

[eiriktsarpalis]

Options-level type classifiers are emitted into JsonSerializerOptions.TypeClassifiers, but the source generator's union ambiguity diagnostic only checked JsonUnionAttribute.TypeClassifier. Treat a non-empty validated JsonSourceGenerationOptionsAttribute.TypeClassifiers list as configured classifier support so SYSLIB1227 isn't emitted in that case.

The existing source-generator diagnostic tests now cover both per-union and options-level classifier registration.

Validated with build.cmd clr+libs -rc release and all System.Text.Json test projects (130,518 executions, 0 failures; 17 existing skips).

Note

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[Copilot]

Pull request overview

Updates the System.Text.Json source generator’s union ambiguity warning logic so that global (options-level) type classifiers are treated as configured classifier support, and adjusts diagnostics tests accordingly.

Changes:

• Treat non-empty JsonSourceGenerationOptionsAttribute.TypeClassifiers as satisfying union classifier configuration (suppressing SYSLIB1227).
• Update the union ambiguity diagnostic unit test to validate no SYSLIB1227 is produced when options-level classifiers are present.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs	Initializes the “classifier configured” flag from options-level TypeClassifiers so union ambiguity diagnostics aren’t emitted when global classifiers are registered.
src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorDiagnosticsTests.cs	Updates/renames the relevant diagnostic test to assert SYSLIB1227 is not produced for options-level classifier registration.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorDiagnosticsTests.cs:819

• Now that this test expects the generator to produce no diagnostics, leaving disableDiagnosticValidation: true weakens the test by skipping compilation+generator severity validation in CompilationHelper.RunJsonSourceGenerator. Consider removing the flag so the helper asserts there are no warnings/errors anywhere, matching other "CompilesWithout..." tests in this file.

            Compilation compilation = CompilationHelper.CreateCompilation(source);
            JsonSourceGeneratorResult result = CompilationHelper.RunJsonSourceGenerator(compilation, disableDiagnosticValidation: true);

            Assert.Empty(result.Diagnostics);

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Suppressed comments (2)

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs:991

• hasUnionTypeClassifierSpecified is now initialized from options-level TypeClassifiers, but the name can be misread as only reflecting JsonUnionAttribute.TypeClassifier. Adding an inline comment here would make it clear that a non-empty context/options classifier list also opts a union into runtime classification and therefore suppresses ambiguity diagnostics.

                bool hasUnionTypeClassifierSpecified = options?.TypeClassifiers is { Count: > 0 };

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorDiagnosticsTests.cs:819

• Assert.Empty(result.Diagnostics) makes this test brittle and inconsistent with the neighboring union-ambiguity tests, which only assert that SYSLIB1227 is (not) produced. If any unrelated source-generator diagnostic is added in the future, this test will start failing even though the behavior under test (suppressing SYSLIB1227 when options-level TypeClassifiers are present) still works.

            Assert.Empty(result.Diagnostics);

[eiriktsarpalis]

/ba-g test failures are unrelated