x/tools/gopls: bad completion insertion after syntax error

[muirdm]

In this code

package foo

func foo() {
	foo(a ...interface{})
	f<>
}

Completing "f" to "foo" ends up inserting "ffoo" instead of "foo". This is because the syntax error on the previous line completely obscures the "f" *ast.Ident, so we don't detect it properly as the prefix. Perhaps if we are in a BadExpr we could "manually" detect the surrounding identifier so completion still works to some degree?

/cc @stamblerre

[gopherbot]

Change https://golang.org/cl/195039 mentions this issue: internal/lsp: fix completion prefix detection with syntax errors