feature: Do not emit generated code if no Refit interfaces

[martincostello]

Is your feature request related to a problem? Please describe.

As part of investigating coverlet-coverage/coverlet#1084 and the impact it is having on various projects I maintain trying to use Refit 6.0, I noticed that Refit is emitting a Generated class into each project that references Refit, even transitively, rather than only projects which explicitly define a Refit interface.

As a consequence this spreads the coverlet issue to the entire solution through the transitive reference(s) and breaks coverlet code coverage for all projects under test that reference Refit.

Unless there's a specific reason why this emitted code must always be present, it seems to me that it would be better not to emit the Generated class (or PreserveAttribute). As well as helping mitigate the problem in coverlet, it would also reduce the on-disk size of assemblies referencing Refit by not emitting unused types.

Would you accept a PR to adjust the generator in this way?

Describe the solution you'd like

Refit does not emit any generated code into an assembly referencing Refit if no Refit interfaces are present to generate code for.

Describe alternatives you've considered

None.

Describe suggestions on how to achieve the feature

Have the GenerateInterfaceStubs() method exit early if there are no Refit interfaces found.

refit/InterfaceStubGenerator.Core/InterfaceStubGenerator.cs

Line 45 in f6621d9

public void GenerateInterfaceStubs(GeneratorExecutionContext context)

Additional context

Screenshot of ILSpy showing a Generated class in three assemblies, where two are empty, despite only one containing a Refit interface.

The assemblies were generated from this repro project: https://github.com/martincostello/coverlet-refit-repro

[clairernovotny]

Totally valid -- we shouldn't be emitting code into projects where there aren't any interfaces.

[github-actions]

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