[http-client-csharp] Dedup operators between generated and customization partials

[Copilot]

Customization partials that declare ==, !=, or implicit/explicit operators on a type whose generated partial also emits those operators (e.g. extensible enums) trigger CS0111 because the dedup path in MethodSignatureBase.SignatureComparer never matches operator methods.

Root cause: the comparer's early Name equality check fails for operators because the two sides use different naming conventions:

Operator	Generated (ExtensibleEnumProvider / MrwSerializationTypeDefinition)	Customization (NamedTypeSymbolProvider via Roslyn ToDisplayString)
==, !=	"==", "!="	"operator ==", "operator !="
implicit operator T(...)	string.Empty	"T" (return type name)
explicit operator T(...)	"T"	"T"

Only the explicit-operator case happens to align, which is why MRW-serialization dedup tests pass while extensible-enum operators slip through.

Changes

• MethodSignatureBase.SignatureComparer.Equals — when both signatures carry the Operator modifier:
  • User-defined operators (==, !=, +, …): normalize the name by stripping a leading "operator " prefix before comparing, so "operator ==" matches "==" while == and != remain distinguishable.
  • Conversion operators (implicit/explicit): skip the Name comparison entirely. Modifiers + return type + parameter types fully identify a conversion operator (C# disallows duplicates).
  • Existing return-type and explicit-vs-implicit modifier checks are preserved.
• MethodSignatureComparerTests — new unit tests covering: == generated/customization name normalization, == vs != not equal, implicit-cast string.Empty matching customization return-type name, and implicit vs explicit not equal.
• NamedTypeSymbolProviderTests.ValidateOperatorSignaturesMatchGenerated — end-to-end test that uses the existing TestData/Helpers.GetCompilationFromDirectoryAsync() infrastructure to load a WithOperators customization partial, parse its operator signatures via NamedTypeSymbolProvider, and assert they match generated-side signatures (==, !=, implicit operator T(string)) through MethodSignatureBase.SignatureComparer.
• TypeProviderTests.CanonicalViewDedupesCustomOperators — end-to-end test that builds a generated TypeProvider with ==, !=, and implicit operator MethodProviders, loads a matching customization partial via TestData, and asserts that CanonicalView.Methods contains exactly the three operators all sourced from CustomCodeView (i.e., the generated copies are filtered out).

Example

// Generated partial (from ExtensibleEnumProvider)
public readonly partial struct MyEnum
{
    public static bool operator ==(MyEnum left, MyEnum right) => left.Equals(right);
    public static implicit operator MyEnum(string value) => new MyEnum(value);
}

// Customization partial — previously triggered CS0111 on both operators;
// now correctly suppresses the duplicates from the generated partial.
public readonly partial struct MyEnum : IEquatable<MyEnum>
{
    public static bool operator ==(MyEnum left, MyEnum right) => left.Equals(right);
    public static implicit operator MyEnum(string value) => new MyEnum(value);
}

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commit: c765004

[jorgerangel-msft]

@copilot lets also add a test in TypeProviderTests to validate that the resulting canonicalview of a generated type who was customized with operators only has the custom operators

[Copilot]

@copilot lets also add a test in TypeProviderTests to validate that the resulting canonicalview of a generated type who was customized with operators only has the custom operators

Added TypeProviderTests.CanonicalViewDedupesCustomOperators in c765004. It builds a TestTypeProvider named CustomOperatorType with generated ==, !=, and implicit operator MethodProviders, loads a customization partial (TestData/TypeProviderTests/CanonicalViewDedupesCustomOperators/CustomOperatorType.cs) that declares the same three operators, and asserts CanonicalView.Methods contains exactly the three operators all sourced from CustomCodeView (i.e., the generated copies are filtered out).