Fix generator runtime assembly resolution for Abstractions and restore fluent source emission

[Copilot]

The source generator was failing at compile time with FileNotFoundException for MattSourceGenHelpers.Abstractions, which prevented generated partial method implementations from being emitted. This PR removes the fragile runtime coupling and updates fluent emission paths that became reachable once generator execution resumed.

• Generator runtime loading

  • Removed direct type coupling to MattSourceGenHelpers.Abstractions in generator runtime execution.
  • Switched to string-based lookup for:
    • assembly name (MattSourceGenHelpers.Abstractions)
    • runtime types (Generate, RecordingGeneratorsFactory)
    • reflected members (CurrentGenerator, LastRecord)
  • Normalized assembly resolution to load implementation assemblies (not ref assemblies) in AssemblyLoadContext.Resolving.

• Project dependency shape

  • Removed ProjectReference from MattSourceGenHelpers.Generators to MattSourceGenHelpers.Abstractions to avoid analyzer runtime dependency assumptions.

• Fluent generation edge handling

  • Extended fluent default-expression extraction to recognize WithBody(...).
  • For zero-parameter generated methods, emit direct return ...; instead of generating a switch over a synthetic argument.

// Before: compile-time coupling in generator assembly
Type? generatorStaticType = abstractionsAssembly.GetType(typeof(Generate).FullName!);

// After: runtime-decoupled lookup
private const string GenerateTypeName = "MattSourceGenHelpers.Abstractions.Generate";
Type? generatorStaticType = abstractionsAssembly.GetType(GenerateTypeName);

Original prompt

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This section details on the original issue you should resolve

<issue_title>Fix source generator</issue_title>
<issue_description>The project does not build, because the source generator fails with the following exception:

1>CSC: Warning CS8785 : Generator 'GeneratesMethodGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'FileNotFoundException' with message 'Could not load file or assembly 'MattSourceGenHelpers.Abstractions, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.'.

Fix it.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Fix source generator #15

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[Copilot]

Pull request overview

This PR fixes a FileNotFoundException that prevented the GeneratesMethodGenerator source generator from running, by removing the direct compile-time reference from MattSourceGenHelpers.Generators to MattSourceGenHelpers.Abstractions. It also restores fluent emission paths that were broken due to the generator not executing.

Changes:

• Removed the ProjectReference from MattSourceGenHelpers.Generators to MattSourceGenHelpers.Abstractions and replaced all direct type references with string-based constants for runtime reflection.
• Normalized assembly resolution in both AssemblyLoadContext.Resolving handlers to redirect ref assemblies to their implementation counterparts.
• Extended ExtractDefaultExpressionFromFluentMethod to recognize .WithBody(...) invocations, and added a zero-parameter early-return path in GenerateSwitchMethodSource to emit a direct return statement instead of a switch.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
MattSourceGenHelpers.Generators/MattSourceGenHelpers.Generators.csproj	Removes the ProjectReference to Abstractions that caused the analyzer runtime failure
MattSourceGenHelpers.Generators/GeneratesMethodExecutionRuntime.cs	Replaces direct Abstractions type references with string constants; applies ResolveImplementationAssemblyPath in Resolving handlers
MattSourceGenHelpers.Generators/GeneratesMethodPatternSourceBuilder.cs	Adds WithBody to fluent default-expression extraction; emits direct return for zero-parameter methods

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[Copilot]

The comment at line 18 is not indented, unlike all the members of the class that follow it. It starts at column 0 while the private constants below it are indented with 4 spaces. The comment should be indented to match the surrounding code members.

Suggested change

	// The Abstraction assembly cannot be referenced directly here, even though the IDE makes it look like it could. However, the source generation process will fail if it is.
	// The Abstraction assembly cannot be referenced directly here, even though the IDE makes it look like it could. However, the source generation process will fail if it is.

[Copilot]

The new zero-parameter direct-return path in GenerateSwitchMethodSource (lines 184–191) and the new WithBody recognition in ExtractDefaultExpressionFromFluentMethod (line 145) are not covered by any test in the test suite. There is an analogous ColorsClassFluent example in MattSourceGenHelpers.Examples that exercises this exact scenario (zero-parameter MethodImplementation<TReturnType>().WithBody(...)), but there's no corresponding test class in MattSourceGenHelpers.Tests verifying either the runtime output or the generated code for this pattern. A test similar to UnitTest1.cs / PiExampleFluentTests.cs should be added to confirm both paths work correctly.