Go: cmd/go2go: panic if using a method on undefined type

[gertcuykens]

Follow up on https://github.com/golang/go/issues/39664

Did a git pull, but still find a way to let it panic by accident, I was trying to correct Robert version so it would compile but failed to do so.

package main

type T(type _) struct {}

func (e T(int)) m()

func _() {
    var x interface { m() }
    x = T(int){}
    _ = x
}

go tool go2go run hello.go2
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0x1211069]

goroutine 1 [running]:
go/go2go.(*translator).instantiateBlockStmt(0xc0001876f8, 0xc00010f3b0, 0x0, 0xc00011a280)
        /usr/local/go/src/go/go2go/instantiate.go:500 +0x29
go/go2go.(*translator).instantiateTypeDecl(0xc0001876f8, 0x0, 0xc00011a3a0, 0xc000128240, 0xc000108430, 0x1, 0x1, 0xc0001085a0, 0x1, 0x1, ...)
        /usr/local/go/src/go/go2go/instantiate.go:211 +0x64e
go/go2go.(*translator).translateTypeInstantiation(0xc0001876f8, 0xc000106480)
        /usr/local/go/src/go/go2go/rewrite.go:809 +0x4d8
go/go2go.(*translator).translateExpr(0xc0001876f8, 0xc000106480)
        /usr/local/go/src/go/go2go/rewrite.go:617 +0x3bb
go/go2go.(*translator).translateExpr(0xc0001876f8, 0xc000108440)
        /usr/local/go/src/go/go2go/rewrite.go:572 +0xf9
go/go2go.(*translator).translateExprList(0xc0001876f8, 0xc000108440, 0x1, 0x1)
        /usr/local/go/src/go/go2go/rewrite.go:694 +0x46
go/go2go.(*translator).translateStmt(0xc0001876f8, 0xc000106550)
        /usr/local/go/src/go/go2go/rewrite.go:495 +0x29d
go/go2go.(*translator).translateBlockStmt(0xc0001876f8, 0xc00010eb70)
        /usr/local/go/src/go/go2go/rewrite.go:456 +0x52
go/go2go.(*translator).translateFuncDecl(0xc0001876f8, 0xc0001065a0)
        /usr/local/go/src/go/go2go/rewrite.go:449 +0xc5
go/go2go.(*translator).translate(0xc0001876f8, 0xc000132180)
        /usr/local/go/src/go/go2go/rewrite.go:376 +0x391
go/go2go.rewriteAST(0xc000106240, 0xc00011f360, 0x0, 0x0, 0xc00011f5e0, 0xc000132180, 0x1a43a01, 0xc000106280, 0x140f7e0)
        /usr/local/go/src/go/go2go/rewrite.go:188 +0x109
go/go2go.rewriteFile(0xc0001700a0, 0x43, 0xc000106240, 0xc00011f360, 0x0, 0x0, 0xc00011f5e0, 0xc000170230, 0x4e, 0xc000132180, ...)
        /usr/local/go/src/go/go2go/rewrite.go:151 +0xb8
go/go2go.rewriteFilesInPath(0xc00011f360, 0x0, 0x0, 0xc0001700a0, 0x43, 0xc0001082e0, 0x1, 0x1, 0x0, 0x0, ...)
        /usr/local/go/src/go/go2go/go2go.go:104 +0xc11
go/go2go.rewriteToPkgs(0xc00011f360, 0x0, 0x0, 0xc0001700a0, 0x43, 0xc00010e050, 0xc0001700a0, 0x43, 0x7ffeefbff78e, 0xa)
        /usr/local/go/src/go/go2go/go2go.go:46 +0x165
go/go2go.Rewrite(...)
        /usr/local/go/src/go/go2go/go2go.go:30
main.translate(0xc00011f360, 0xc0001700a0, 0x43)
        /usr/local/go/src/cmd/go2go/translate.go:15 +0x47
main.main()
        /usr/local/go/src/cmd/go2go/main.go:53 +0xb0f

[griesemer]

Thanks. The type-checker is happy with this, but the translator is not. ~Possibly it has trouble with the receiver of m declaring an int type parameter.~

Edited: The problem is the missing method body.

[zeebo]

This looks like the same bug as https://github.com/golang/go/issues/39634#issuecomment-645630176 which is caused by the method not having a body (the top frame in the stack trace is instantiateBlockStmt).

[griesemer]

Indeed. It has nothing to do with the receiver, it's that the method doesn't have a body. Will be fixed in the translator.

[gopherbot]

Change https://golang.org/cl/238761 mentions this issue: [dev.go2go] go/go2go: don't crash on functions/methods with no body

[ianlancetaylor]

Thanks. Fixed on the dev.go2go branch.