x/tools/gopls: extract(refactor) fails on anonymous structs

[KrzysztofJopek]

What version of Go are you using (go version)?

go version go1.20.6 darwin/amd64

golang.org/x/tools/gopls v0.12.4
    golang.org/x/tools/gopls@(devel)

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

darwin, amd64

What did you expect to see?

Refactor of code with anonymous struct completes successfully

What did you see instead?

parent nil error while extracting code with anonymous struct
I was able to reproduce the issue in both Neovim and VSCode.

On the demo below, you can see a successful refactor of named struct and then fail on anonymous struct.
https://github.com/golang/go/assets/27726430/f3096917-4158-4bf1-be52-4477863fa454

[adonovan]

Thanks for the bug report. I can reproduce it using the testcase below.

It includes a test case for a second bug that was obvious from inspection of the code, which not only doesn't distinguish local vars from field vars, but doesn't distinguish vars from types.

I suspect the fix will be more involved that we have time for at the moment.

$ cat  gopls/internal/regtest/marker/testdata/codeaction/extract_issue61496.txt
This test verifies extraction of a function
whose parameters include anonymous struct types.
It is a regression test for issue #61496.

-- go.mod --
module testdata
go 1.18

-- a.go --
package testdata

func _() {
	var x struct { y int }	//@ codeaction("refactor.extract", "var", end, anon)
	println(x.y)		//@ loc(end, ")")
}

-- @anon/a.go --
xxx

-- @localtype/b.go --
package testdata

func _() {
        type T int 
	var x T 		//@ codeaction("refactor.extract", "var", end, anon)
	println(x.y)		//@ loc(end, ")")
}

-- @localtype/b.go --
xxx