x/tools/gopls: check for code after f.Fuzz

[suzmue]

Spin-off of #50198: our analysis of Fuzz targets can be improved by checking for code after a call to f.Fuzz

This analyzer is the last of the analyzers suggested in the original vet check proposal #46218

This could also possibly be split into several analyzers to check for:

• multiple calls to f.Fuzz
• calls to f.Add after the call to f.Fuzz

@ansaba

[zpavlinovic]

Perhaps a silly question, assuming this will also land in go vet, should this be a separate proposal or we can just add it to #46218?

[suzmue]

Not a silly question! This issue is primarily for milestone tracking for gopls development. The proposal already includes checking for code after f.Fuzz.

[timothy-king]

The border for whether a new type of diagnostic for an existing vet checker needs a proposal is slightly blurry. It requires a judgement call on how different it is from the existing checks and how risky it is for meeting the vet criteria. In this case, I think we are fine without a proposal as the check is very similar to the already accepted #46218 (straightforward extension in the same spirit) and the risk to fail to meet on of the vet criteria is low here.