gccgo: problems appending string to string subtype

[thanm]

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

Go, gccgo tip

$ go version
go version devel +06e4097f52 Tue Apr 9 12:08:48 2019 -0400 linux/amd64
$ gccgo --version
...
gccgo (GCC) 9.0.1 20190408 (experimental)

Does this issue reproduce with the latest release?

Yes

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

linux/amd64

go env Output

$ go env

What did you do?

Compile this program:

https://play.golang.org/p/1g5oPWL7tQ3

What did you expect to see?

Clean compile

What did you see instead?

Compiles and runs ok with the main Go compiler, but when compiled with gccgo I get:

GO111MODULE=off go build -compiler gccgo meas_a.go
./meas_a.go:19:14: error: argument 2 has incompatible type (cannot use type string as type Name)
   19 |  Register(f, n, d)
      |              ^
./meas_a.go:19:17: error: argument 3 has incompatible type (cannot use type string as type Name)
   19 |  Register(f, n, d)
      |                 ^

I am guessing there is a discrepancy in the way the string "+" operator is handled? Haven't yet looked into it in detail.

[thanm]

Related: for this fragment

package main
type N string
type M string
const B N = "B"
const C M = "C"
func main() {
	q := B + C
	println(q)
}

Main go compiler issues an error, gccgo does not.

[gopherbot]

Change https://golang.org/cl/171761 mentions this issue: test: add testcases for gccgo bug

[gopherbot]

Change https://golang.org/cl/171797 mentions this issue: compiler: improve type handling for string concat ops on constants