x/tools/gopls: gopls restart needed after changing build tags

[muirdm]

With gopls on master (9580c84), starting with:

-- foo.go --
package main

func main() {}
-- bar.go --
package main

func main() {}

1. Confirm you get "duplicate main" diagnostic
2. Add "//go:build ignore" to one of the files
3. Observe you still see the diagnostic until you restart gopls

[findleyr]

This is just a bug: changes to build tags should (and probably do) invalidate packages.

The likely nature of this bug is that we don't clear diagnostics when the file is dropped from a package. I will fix this.

[findleyr]

It looks like this bug is already fixed at tip. Bisecting.

[findleyr]

This was fixed by https://go.dev/cl/417576. I'll close this with a passing regression test.

But the regtest I wrote is failing in the "experimental" mode. Investigating why...

[gopherbot]

Change https://go.dev/cl/420537 mentions this issue: gopls/internal/regtest: add a test that ignoring a file resolves errors