x/tools/gopls: consider supporting script directories with multiple programs

[stamblerre]

Currently, gopls only supports directories with a single main, no matter whether you open a single file or a directory. For single files, we load the entire directory, no matter what. Some users create directories with multiple mains, which they run using go run file.go. Should gopls support such directories? If so, how should it work?

[bcmills]

Most single files intended for use with go run should be tagged // +build ignore or similar, and they necessarily each declare a func main. Perhaps you could use unusual build constraints plus func main as a heuristic for which mode to use?

[myitcv]

Previous discussion: #33595

[myitcv]

Looking at the arguments against this, if someone can come up with a good enough name for the file that contains the build-ignore main package, they can use that name for a subdirectory ./internal/$NAME thereby obviating the need for any kind of single-file support in gopls.

The counter argument to this is that there is lots of preexisting code out there that does following the single-file approach.

[mvdan]

Perhaps you could use unusual build constraints plus func main as a heuristic for which mode to use?

I think this would work reasonably well. I think it would have covered nearly all the times I've encountered gopls to error in this way.

they can use that name for a subdirectory ./internal/$NAME thereby obviating the need for any kind of single-file support in gopls.

While I see the point, I disagree. There's nothing wrong with build-tag-ignored one-off programs being part of an existing package. An extra directory with just one file will be more verbose, and an oddity that has never been needed in Go before. Coming up to all those users and telling them they need to change their workflow just to please gopls, and objectively for no other good reason, seems like it won't end well :)

[quasilyte]

I don't think this idiom is very common, but apart from the build ignore tag there is also a pattern where you put your "scripts" under a "_" prefixed folder, like _scripts.

This excludes Go files as per-file ignore would, but still keeps them usable with go run ./_scripts/gendocs.go.

I haven't checked it with the newer versions of gopls, but ignore tag previously turned off most gopls features for the file. Or maybe it's a VSCode integration (plugin) issue.