proposal: cmd/fix: apply fixes from modernizers and gofix analyzers

[jba]

(This proposal is the second of a sequence of two; #73605 is the first. --adonovan)

Proposal Details

go fix should have a type of fix called modernize that applies modernizers.

As an example, running go fix would change all occurrences of interface{} to any, provided the identifier any is not shadowed.

For the current set of modernizers, see https://go.googlesource.com/tools/+/refs/heads/master/gopls/internal/analysis/modernize.

[adonovan]

Currently the go fix comment command is completely unrelated to the //go:fix inline annotation; it's just a grab-bag of syntax-only rewrites for very ancient features. I'm not sure whether anyone really uses it at all. At some point it might be worth rethinking it as a front-end for the go/analysis framework and the multichecker's -fix functionality.

[mvdan]

(I assume you meant "go fix command" above). I have yet to encounter a recent Go user (say, who started using Go after 2015 or so) who is aware of go fix or what it does. I suspect at this point the command could be redesigned to do whatever you feel like is most useful, as long as it can be safely run on large codebases without having to worry about any subtle breakages.

[adonovan]

I agree. A good step would be to add a telemetry counter to Go 1.25 for invocations of go fix so we can tell whether anyone is in fact still using it.
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