[dev.typeparams] cmd/compile/internal/types2: support local defined types

This CL changes types2's instance hashing logic to include position
information for function-scope defined types as disambiguation. This
isn't ideal, but it worked for getting nested.go passing.

Updates #46592.

Change-Id: Id83ba0001f44af69b81260306cc8b05e44fc4f09
Reviewed-on: https://go-review.googlesource.com/c/go/+/327170
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

2 files changed, 30 insertions, 9 deletions

diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index dd8dd74161..3ef65c2e92 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -425,14 +425,19 @@ func (subst *subster) typ(typ Type) Type {
 	return typ
 }
 
+var instanceHashing = 0
+
 // TODO(gri) Eventually, this should be more sophisticated.
 //           It won't work correctly for locally declared types.
 func instantiatedHash(typ *Named, targs []Type) string {
+	assert(instanceHashing == 0)
+	instanceHashing++
 	var buf bytes.Buffer
 	writeTypeName(&buf, typ.obj, nil)
 	buf.WriteByte('[')
 	writeTypeList(&buf, targs, nil, nil)
 	buf.WriteByte(']')
+	instanceHashing--
 
 	// With respect to the represented type, whether a
 	// type is fully expanded or stored as instance
diff --git a/src/cmd/compile/internal/types2/typestring.go b/src/cmd/compile/internal/types2/typestring.go
index 07ed510d11..f08c41c2a3 100644
--- a/src/cmd/compile/internal/types2/typestring.go
+++ b/src/cmd/compile/internal/types2/typestring.go
@@ -350,17 +350,33 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 }
 
 func writeTypeName(buf *bytes.Buffer, obj *TypeName, qf Qualifier) {
-	s := "<Named w/o object>"
-	if obj != nil {
-		if obj.pkg != nil {
-			writePackage(buf, obj.pkg, qf)
+	if obj == nil {
+		buf.WriteString("<Named w/o object>")
+		return
+	}
+	if obj.pkg != nil {
+		writePackage(buf, obj.pkg, qf)
+	}
+	buf.WriteString(obj.name)
+
+	if instanceHashing != 0 {
+		// For local defined types, use the (original!) TypeName's position
+		// to disambiguate. This is overkill, and could probably instead
+		// just be the pointer value (if we assume a non-moving GC) or
+		// a unique ID (like cmd/compile uses). But this works for now,
+		// and is convenient for debugging.
+
+		// TODO(mdempsky): I still don't fully understand why typ.orig.orig
+		// can differ from typ.orig, or whether looping more than twice is
+		// ever necessary.
+		typ := obj.typ.(*Named)
+		for typ.orig != typ {
+			typ = typ.orig
+		}
+		if orig := typ.obj; orig.pkg != nil && orig.parent != orig.pkg.scope {
+			fmt.Fprintf(buf, "@%q", orig.pos)
 		}
-		// TODO(gri): function-local named types should be displayed
-		// differently from named types at package level to avoid
-		// ambiguity.
-		s = obj.name
 	}
-	buf.WriteString(s)
 }
 
 func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {