go/types, cmd/compile/internal/types2: use regular type printing for unsafe.Pointer

Type string printing special-cased printing of unsafe.Pointer because
it's a built-in type; yet it's declared in a package like any other
imported or used-defined type (unlike built-in types such as int).

Use the same mechanism for printing unsafe.Pointer like any other
(non-basic) type. This will make it possible to use the package
Qualifier if so desired.

Fixes #44515.

Change-Id: I0dd1026f850737ecfc4bb99135cfb8e3c18be9e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/295271
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/issues_test.go

@@ -546,3 +546,25 @@ func TestIssue43088(t *testing.T) {
 	Comparable(T1)
 	Comparable(T2)
 }
+
+func TestIssue44515(t *testing.T) {
+	typ := Unsafe.Scope().Lookup("Pointer").Type()
+
+	got := TypeString(typ, nil)
+	want := "unsafe.Pointer"
+	if got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+
+	qf := func(pkg *Package) string {
+		if pkg == Unsafe {
+			return "foo"
+		}
+		return ""
+	}
+	got = TypeString(typ, qf)
+	want = "foo.Pointer"
+	if got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}

src/cmd/compile/internal/types2/typestring.go

@@ -98,9 +98,15 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 		buf.WriteString("<nil>")
 
 	case *Basic:
-		if t.kind == UnsafePointer {
-			buf.WriteString("unsafe.")
+		// exported basic types go into package unsafe
+		// (currently this is just unsafe.Pointer)
+		if isExported(t.name) {
+			if obj, _ := Unsafe.scope.Lookup(t.name).(*TypeName); obj != nil {
+				writeTypeName(buf, obj, qf)
+				break
+			}
 		}
+
 		if gcCompatibilityMode {
 			// forget the alias names
 			switch t.kind {

src/go/types/issues_test.go

@@ -549,3 +549,25 @@ func TestIssue43088(t *testing.T) {
 	Comparable(T1)
 	Comparable(T2)
 }
+
+func TestIssue44515(t *testing.T) {
+	typ := Unsafe.Scope().Lookup("Pointer").Type()
+
+	got := TypeString(typ, nil)
+	want := "unsafe.Pointer"
+	if got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+
+	qf := func(pkg *Package) string {
+		if pkg == Unsafe {
+			return "foo"
+		}
+		return ""
+	}
+	got = TypeString(typ, qf)
+	want = "foo.Pointer"
+	if got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}

src/go/types/typestring.go

@@ -9,6 +9,7 @@ package types
 import (
 	"bytes"
 	"fmt"
+	"go/token"
 	"unicode/utf8"
 )
 
@@ -98,9 +99,15 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 		buf.WriteString("<nil>")
 
 	case *Basic:
-		if t.kind == UnsafePointer {
-			buf.WriteString("unsafe.")
+		// exported basic types go into package unsafe
+		// (currently this is just unsafe.Pointer)
+		if token.IsExported(t.name) {
+			if obj, _ := Unsafe.scope.Lookup(t.name).(*TypeName); obj != nil {
+				writeTypeName(buf, obj, qf)
+				break
+			}
 		}
+
 		if gcCompatibilityMode {
 			// forget the alias names
 			switch t.kind {