cmd/compile: cannot compile with alias type used in multiple files

[mandelsoft]

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

$ go version
go version go1.17.6 linux/amd64

Does this issue reproduce with the latest release?

yes

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="some path"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/contrib/inst/go1.17.6"
GOSUMDB="off"
GOTMPDIR=""
GOTOOLDIR="/usr/local/contrib/inst/go1.17.6/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.6"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3458372569=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I have two go file in a package, one with a type definitial and an alias declaration

package compilererror

type A struct {
	c C
}

type O  = A

and a second file with a used type and a using type

package compilererror

type Dummy interface {
//	Dummy(A)
}

type B interface {
	// cannot use O here, because compiler crashes
        // F0(*A)
	F1() (*O, error)
	F2() (*O, error)
}

type C interface {
	F3(*O) error
}

What did you expect to see?

Compiling this package succeeds.

What did you see instead?

Compiling this package results in a compiler error:

compilererror/c.go:21:6: internal compiler error: cannot handle alias type declaration (issue #25838): %!v(PANIC=Format method: runtime error: invalid memory address or nil pointer dereference)

Please file a bug report including a short program that triggers the error.
https://golang.org/issue/new

With go release 1.16 a similar error is reported but with a working error message (not the nil pointer exception) complaining about the type alias.

Possibilities to circumvent this problem.

There are several strange ways to avoid this compile error:

• add a dummy interface (as shown in b.go) USING the original type instead of the alias (just uncomment this line)
• replace the FIRST occurrence of the alias type (O) in a file by the original type (A) (or just uncomment F0)
• rename the file c.go to be alphabetically before b.c (or just e.g. a.go)
• put all the stuff in one file

[ianlancetaylor]

Thanks for the bug report. As the error message says, this is a dup of #25838. See also #50729. Closing as a dup.