Update logging source generator to support generic methods

[Copilot]

Mirrors dotnet/runtime#124638. LOGGEN007 previously rejected all generic logging methods unconditionally. The restriction is narrowed to only block allows ref struct constraints, which can't be stored as fields in the generated state struct.

Changes

• Parser: Remove Arity > 0 → LOGGEN007. Populate LoggingMethod.TypeParameters from IMethodSymbol.TypeParameters, serializing all constraint kinds. Detect allows ref struct via reflection on ITypeParameterSymbol.AllowsRefLikeType (Roslyn 4.9+; no-ops on older Roslyn).
• Diagnostic: Rename LoggingMethodIsGeneric → LoggingMethodHasAllowsRefStructConstraint with updated message; update docs/list-of-diagnostics.md.
• Model: Add LoggingMethodTypeParameter (Name, Constraints); add TypeParameters list to LoggingMethod.
• Emitter: Emit <T1, T2, ...> and properly indented where T : ... clauses on the generated partial method signature. Use Out(char) for single-character output.
• Tests: MethodGeneric now expects success; add MethodGenericWithConstraints, MethodGenericMultipleTypeParams, MethodGenericWithAllowsRefStructConstraint (skips on Roslyn < 4.9), and GenericTestExtensions.cs for emitter validation.

Example

// Previously LOGGEN007 — now generates correct code
[LoggerMessage(0, LogLevel.Trace, "Received {Code} on {Channel}")]
public static partial void PacketReceived<TCode>(
    ILogger logger, TCode code, ConnectionChannel channel)
    where TCode : struct, Enum;

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[svick]

cc: @evgenyfedorov2

[Copilot]

Pull request overview

This PR updates the Microsoft.Gen.Logging source generator to allow generic logging methods, while keeping LOGGEN007 only for the C# 13 allows ref struct anti-constraint (which can’t be represented safely in the generated state).

Changes:

• Allow generic logging methods and model/serialize method type parameters + constraints during parsing.
• Rename LOGGEN007 descriptor/message to target only allows ref struct.
• Emit generic type parameters and where constraints on the generated partial method signatures; add test coverage for allowed and rejected cases.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/Generators/Microsoft.Gen.Logging/Unit/ParserTests.LogMethod.cs	Adds tests for generic logging methods, constraints, and allows ref struct rejection (skipping on older Roslyn).
test/Generators/Microsoft.Gen.Logging/TestClasses/GenericTestExtensions.cs	Adds representative generic logging methods for emitter/regression coverage.
src/Generators/Microsoft.Gen.Logging/Parsing/Resources.resx	Updates LOGGEN007 title/message to “allows ref struct” constraint wording.
src/Generators/Microsoft.Gen.Logging/Parsing/Resources.Designer.cs	Regenerates strongly-typed resource accessors for the renamed resource keys.
src/Generators/Microsoft.Gen.Logging/Parsing/Parser.cs	Removes generic-method rejection, adds type parameter capture + constraint formatting, and detects allows ref struct via reflection.
src/Generators/Microsoft.Gen.Logging/Parsing/DiagDescriptors.cs	Renames LOGGEN007 descriptor to LoggingMethodHasAllowsRefStructConstraint.
src/Generators/Microsoft.Gen.Logging/Model/LoggingMethodTypeParameter.cs	Introduces a model type for method type parameters + constraint text.
src/Generators/Microsoft.Gen.Logging/Model/LoggingMethod.cs	Adds TypeParameters collection to the logging method model.
src/Generators/Microsoft.Gen.Logging/Emission/Emitter.Utils.cs	Adds helper emission for <T...> and where T : ... clauses.
src/Generators/Microsoft.Gen.Logging/Emission/Emitter.Method.cs	Emits generic parameters/constraints in the generated partial method signature.

Files not reviewed (1)

• src/Generators/Microsoft.Gen.Logging/Parsing/Resources.Designer.cs: Language not supported

[Copilot]

GenTypeConstraints hardcodes 4 spaces (" where ...") instead of using the current indentation level. This will misalign where clauses when the generated method is inside nested types (indent > 1). After OutLn(), call OutIndent() and then write where ... without hardcoded spaces (or otherwise compute indentation from the current indent level).

Suggested change

	Out($" where {tp.Name} : {tp.Constraints}");
	OutIndent();
	Out($"where {tp.Name} : {tp.Constraints}");

[svick]

@copilot Fix this. Type constraints should be indented one more level than the surrounding code, since this is the common formatting convention.

[Copilot]

Fixed in 8ad114f. GenTypeConstraints now uses Indent()/OutIndent()/Unindent() so the where clause is indented one extra level beyond the method signature, regardless of nesting depth.