x/tools/gopls: "expected declaration, found 'package'" after cutting and pasting a file's contents

[stamblerre]

I've noticed that the go list empty file error message will sometimes reappear in this case. This needs both a fix and a regression test.

[segevfiner]

I'm seeing this issue. Looks like something like starting with an empty file or removing it's content, then typing the package statement, waiting a bit, and continuing on to write some other stuff in the file, like a func main. Is this the gopls in memory representation of the file getting messed up or something?

[gopherbot]

Change https://golang.org/cl/243577 mentions this issue: internal/lsp: handle deletion of file content