cmd/compile: cannot use .this ( type *T[interface{}]) as type T[go.shape.interface {}_0] in T[go.shape.interface {}_0].Method

[csgura]

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

$ go version
go version devel go1.18-07525e1 Fri Jan 7 00:15:59 2022 +0000 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

The gotip playground

What did you do?

https://gotipplay.golang.org/p/vuF7acfKTIv

What did you expect to see?

No Error.

What did you see instead?

# goerror
<autogenerated>:1: cannot use .this (type *fp.Seq[interface {}]) as type fp.Seq[go.shape.interface {}_0] in argument to fp.Seq[go.shape.interface {}_0].Append
<autogenerated>:1: cannot use .this (type *fp.Seq[interface {}]) as type fp.Seq[go.shape.interface {}_0] in argument to fp.Seq[go.shape.interface {}_0].Iterator
<autogenerated>:1: cannot use .this (type *fp.Seq[interface {}]) as type fp.Seq[go.shape.interface {}_0] in argument to fp.Seq[go.shape.interface {}_0].Size

If I remove ToSeq or Map method of Iterator, the error goes away.

[cuonglm]

Maybe related #50419 cc @danscales

[danscales]

Even though the gotip playground example is still failing, I can't seem to reproduce this locally. I create the module directory with main.go, go.mod, and fp/fp.go, and when I do 'go run main.go, everything runs fine. Everything runs fine locally at both 07525e1 and current tip 11b28e7 (and also the beta1 release becaeea). I also tried building with GOARCH=386 (since I thought the playground is sometimes a 32-bit machine), but that also worked fine. Is there something different about the gotip playground that I need to account for?

Can anyone else reproduce locally? I'm missing something.

@randall77 @cuonglm @ianlancetaylor

[danscales]

Oops, sorry about that, there was something mixed up in my local setup. Now I can reproduce it fine. Will take a look.

[danscales]

OK, I understand the issue and have a fix. (Not related to #50419, since that relates to the use of blanks for typeparams.)

[gopherbot]

Change https://golang.org/cl/377094 mentions this issue: cmd/compile: in typ0(), load base type before checking s.Def