go/types: Alias.String should not mention the aliased type

[adonovan]

The current behavior of the new go/types.Alias.String method is to print the aliased type in a comment, but I'm not convinced it should. We don't do this for named types, and it undermines one of the main benefits of aliases, which is brevity. The alias name alone seems clear enough, as it's what appears in the source.

@gri @findleyr

$ go build -o alias ./alias.go
$ ./alias
func([]int)
$ GODEBUG=gotypesalias=1  ./alias 
func([]command-line-arguments.A /* = int */)

package main

import (
	"fmt"
	"log"
	"os"

	"golang.org/x/tools/go/packages"
)

type A = int

var x func([]A)

func main() {
	cfg := &packages.Config{Mode: packages.LoadAllSyntax}
	pkgs, err := packages.Load(cfg, "./alias.go")
	if err != nil {
		log.Fatal(err)
	}
	if packages.PrintErrors(pkgs) > 0 {
		os.Exit(1)
	}
	fmt.Println(pkgs[0].Types.Scope().Lookup("x").Type())
}

[adonovan]

Also: an alias of an alias doesn't nest correctly:

type C = int
type B = []C
type A = B
var x func([]A)

=>

func([]command-line-arguments.A /* = []command-line-arguments.C /* = int */ */)    !!

[gopherbot]

Change https://go.dev/cl/548135 mentions this issue: go/types, types2: don't print aliased type (in comments) for Alias types