cmd/compile/internal/types2, go/types: don't panic when calling under/underlying

[paulsonkoly]

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

$ go version
go version go1.21.6 darwin/arm64

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='arm64'
GOBIN=''
GOCACHE='/Users/phaul/Library/Caches/go-build'
GOENV='/Users/phaul/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/phaul/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/phaul/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/phaul/.asdf/installs/golang/1.21.6/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/phaul/.asdf/installs/golang/1.21.6/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.6'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/7f/z0kc3pxd6wz4540t2drzzlwm0000gn/T/go-build2303253187=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOROOT/bin/go version: go version go1.21.6 darwin/arm64
GOROOT/bin/go tool compile -V: compile version go1.21.6
uname -v: Darwin Kernel Version 23.3.0: Wed Dec 20 21:33:31 PST 2023; root:xnu-10002.81.5~7/RELEASE_ARM64_T8112
ProductName:		macOS
ProductVersion:		14.3
BuildVersion:		23D56
lldb --version: lldb-1500.0.200.58
Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)

What did you do?

The following code snippet panics the compiler:

package main

type X Int

const (
  Invalid = X(iota)
  Call
  Int
)

func main () {

}

What did you expect to see?

Some errors reported

What did you see instead?

phaul@192 ~ % go build x.go
# command-line-arguments
: internal compiler error: panic: nil underlying

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

[paulsonkoly]

more minimal example:

package main

type X Int

const Int = X(3)

func main () {

}

[mauri870]

cc @golang/compiler

[cuonglm]

This seems to be problem in types2, since go1.17 and go.18 with -G=0 reports an error:

$ cat p.go
package p

type X Int

const Int = X(3)

$ go1.17.13 tool compile p.go                            
p.go:5:14: cannot convert 3 (type int) to type X

cc @griesemer @findleyr

[gopherbot]

Change https://go.dev/cl/559335 mentions this issue: go/types, types2: bail early if we want a type but don't have one

[griesemer]

The specific issue at hand has been fixed with the above CL.
Retitling for broader issue (should not panic when calling under).