x/tools/gopls: panic in FillStruct with invalid fields

[findleyr]

Filling S{} panics here:

type S struct {
  F int
  E
}

func_() {
  S{}
}

...due to S having invalid fields. Add tests and fix.

[Oguidan]

The problem is with "E" bro

[findleyr]

@Oguidan yes, E is not defined. The problem is that gopls panics. gopls should not panic, even when the code being edited is invalid.

[Oguidan]

But @findleyr , you know that Golang is garbage collector!

[gopherbot]

Change https://go.dev/cl/549116 mentions this issue: gopls/internal/analysis/fillstruct: don't panic with invalid fields