internal compile error caused by function type alias

[mdavis-ciena]

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

$ go version
go version go1.13.5 linux/amd64

Does this issue reproduce with the latest release?

Yes (haven't tried 1.14beta1).

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/mdavis/.cache/go-build"
GOENV="/home/mdavis/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/mdavis/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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-build066272323=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Compile the following source using go build bug.go:

package pkg

type I interface {
    M(FT)
}

type S struct {
    F FT
}

type FT = func(S)

All of the shown components seem to be necessary. In particular, the compile error disappears if any of the following are done:

1. Remove the interface I, its method M or that method's argument (or change the argument type).
2. Remove the field F of S (or change its type).
3. Remove the argument of the function type (or change the argument's type).
4. Change the type alias to a type definition (remove the "=").

What did you expect to see?

Successful compilation (no output).

What did you see instead?

# command-line-arguments
./bug.go:11:6: internal compiler error: cannot handle alias type declaration (issue #25838): FT

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

[cuonglm]

There's an issue for tracking this bug #25838

[mdavis-ciena]

This is not contrived, but a problem that is distilled WAAAAAAY down from a logging library that I am writing. A struct type holds references to functions that reconfigure child objects by taking and returning the struct type (along with other parameters), etc.

[mdavis-ciena]

@cuonglm - Thanks. That was referenced in the compile output, but since it mentioned reporting the bug here, I did.

[mdavis-ciena]

Confirmed the compile error also goes away if interface I is defined last.

[cuonglm]

@cuonglm - Thanks. That was referenced in the compile output, but since it mentioned reporting the bug here, I did.

The error message points you to #25838, so you should not fire new issue, they're just duplicated.

[mdavis-ciena]

All right. Should I file a new bug report about the error message that literally says:

... (issue #25838)...Please file a bug report including a short program that triggers the error.

then?