Allow non-public constructors with a single parameter in a union declaration#83788
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…claration Align behavior with the spec.
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Pull request overview
This change updates C# compiler validation for union declarations so that only public explicitly-declared instance constructors with a single parameter are rejected, allowing non-public (for example, private/internal) single-parameter constructors as permitted by the language rules.
Changes:
- Restrict CS9374 (
ERR_InstanceCtorWithOneParameterInUnion) to public one-parameter instance constructors inuniondeclarations. - Update and extend
UnionsTeststo:- Make the invalid constructors explicitly
public(to keep testing CS9374). - Add coverage showing
private/internalone-parameter constructors are allowed when properly chained. - Add new negative cases showing non-public one-parameter constructors still must use the required
thisinitializer rule (CS9375).
- Make the invalid constructors explicitly
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol.cs | Changes the union-member validation to only report CS9374 for public one-parameter instance constructors (excluding synthesized union ctors). |
| src/Compilers/CSharp/Test/CSharp15/UnionsTests.cs | Adjusts expected diagnostics and adds test cases covering allowed non-public one-parameter constructors and required initializer diagnostics. |
RikkiGibson
approved these changes
May 19, 2026
Contributor
Author
|
@jjonescz, @dotnet/roslyn-compiler For a second review |
jjonescz
approved these changes
May 20, 2026
This was referenced May 20, 2026
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Align behavior with the spec.
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