go/types, types2: add a test case to ConvertibleTo

string(int) conversions are somewhat special and deserve an entry.

Change-Id: Ia68d047cfdb2f98e837bf663659f7f46404b16ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/355989
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

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

@@ -1655,15 +1655,15 @@ func TestConvertibleTo(t *testing.T) {
 	}{
 		{Typ[Int], Typ[Int], true},
 		{Typ[Int], Typ[Float32], true},
+		{Typ[Int], Typ[String], true},
 		{newDefined(Typ[Int]), Typ[Int], true},
 		{newDefined(new(Struct)), new(Struct), true},
 		{newDefined(Typ[Int]), new(Struct), false},
 		{Typ[UntypedInt], Typ[Int], true},
 		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Int], 10)), true},
 		{NewSlice(Typ[Int]), NewArray(Typ[Int], 10), false},
 		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Uint], 10)), false},
-		// Untyped string values are not permitted by the spec, so the below
-		// behavior is undefined.
+		// Untyped string values are not permitted by the spec, so the behavior below is undefined.
 		{Typ[UntypedString], Typ[String], true},
 	} {
 		if got := ConvertibleTo(test.v, test.t); got != test.want {

src/go/types/api_test.go

@@ -1631,15 +1631,15 @@ func TestConvertibleTo(t *testing.T) {
 	}{
 		{Typ[Int], Typ[Int], true},
 		{Typ[Int], Typ[Float32], true},
+		{Typ[Int], Typ[String], true},
 		{newDefined(Typ[Int]), Typ[Int], true},
 		{newDefined(new(Struct)), new(Struct), true},
 		{newDefined(Typ[Int]), new(Struct), false},
 		{Typ[UntypedInt], Typ[Int], true},
 		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Int], 10)), true},
 		{NewSlice(Typ[Int]), NewArray(Typ[Int], 10), false},
 		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Uint], 10)), false},
-		// Untyped string values are not permitted by the spec, so the below
-		// behavior is undefined.
+		// Untyped string values are not permitted by the spec, so the behavior below is undefined.
 		{Typ[UntypedString], Typ[String], true},
 	} {
 		if got := ConvertibleTo(test.v, test.t); got != test.want {