Source generated syntax trees should report IsGenerated

[chsienki]

We should add GeneratedKind.SourceGenerator and have any syntax trees added by a generator return this value.

We should also update the original bool version of the property to report true for this value.

[mavasani]

@chsienki Should we close out #48480?

[ericstj]

Will this impact the way the compiler raises diagnostics for generated code? I can imagine there are a set of compiler checks we'd want to be ignored for generated code to simplify code-generators (eg: style analyzers) where there are others that we would want to be honored (obsolete, nullable annotations). cc @AaronRobinsonMSFT

[jmarolf]

Will this impact the way the compiler raises diagnostics for generated code?

Each analyzer can choose whether it needs to analyze generated code or not via the ConfigureGeneratedCodeAnalysis method.

roslyn/src/Compilers/Core/Portable/DiagnosticAnalyzer/DiagnosticAnalysisContext.cs

Lines 214 to 219 in f52afd9

	/// <summary>
	/// Configure analysis mode of generated code for this analyzer.
	/// Non-configured analyzers will default to an appropriate default mode for generated code.
	/// It is recommended for the analyzer to invoke this API with the required <see cref="GeneratedCodeAnalysisFlags"/> setting.
	/// </summary>
	public virtual void ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags analysisMode)

Today all analyzers that come with the SDK that are required for code correctness (for example security analyzers) look at generated code.

[sharwell]

💭 It seems desirable to continue requiring source generators to emit the // <auto-generated/> header at the top of the file.

[eerhardt]

Looking at dotnet/runtime#53275, the change is appending the .g suffix to the file to indicate this is a generated file.

How many different ways are source generators supposed to mark their files as "generated"? So far I see:

1. emitting // <auto-generated/> header
2. naming the file .g.cs
3. calling ConfigureGeneratedCodeAnalysis
4. any more?

What are the recommendations for dotnet/runtime source generators should do to mark their code as "generated"?

[AaronRobinsonMSFT]

@sharwell Is the following the appropriate way to add the comment?

SyntaxFactory.Comment("<auto-generated/>").ToString()

[sharwell]

@AaronRobinsonMSFT SyntaxFactory.Comment would be more for cases where you are generating a SyntaxTree. For cases where you are generating a string, rather than use ToString() like that line you could just add "// <auto-generated/>" directly.

[333fred]

@chsienki can you fill out the API proposal template for this?

[chsienki]

Added #56810 to track the API