go/types: improved type strings for instantiated generic types

Better output for now, but the printing code is a hack and needs
a rethink and cleanup.

Change-Id: Ieb1f13a21645b48f9494ceda50f58017b31bbd82

src/go/types/decl.go

@@ -772,6 +772,11 @@ func (check *Checker) declareTypeParams(tparams []*TypeName, names []*ast.Ident)
 		check.declare(check.scope, name, tpar, check.scope.pos) // TODO(gri) check scope position
 		tparams = append(tparams, tpar)
 	}
+
+	if check.conf.Trace && len(names) > 0 {
+		check.trace(names[0].Pos(), "type params = %v", tparams[len(tparams)-len(names):])
+	}
+
 	return tparams
 }
 

src/go/types/subst.go

@@ -250,7 +250,7 @@ func (subst *subster) typ(typ Type) Type {
 
 			// already instantiated
 			dump(">>> %s already instantiated", t)
-			assert(len(t.targs) == len(t.targs))
+			assert(len(t.targs) == len(t.tparams))
 			// For each (existing) type argument targ, determine if it needs
 			// to be substituted; i.e., if it is or contains a type parameter
 			// that has a type argument for it.
@@ -282,7 +282,9 @@ func (subst *subster) typ(typ Type) Type {
 
 		// TODO(gri) revisit name creation (function local types, etc.) and factor out
 		//           (also, stripArgNames call is an awful hack)
-		name := stripArgNames(TypeString(t, nil)) + "<" + typeListString(new_targs) + ">"
+		var buf bytes.Buffer
+		writeTypeName(&buf, t.obj, nil)
+		name := stripArgNames(buf.String()) + "<" + typeListString(new_targs) + ">"
 		dump(">>> new type name: %s", name)
 		if tname, found := subst.check.typMap[name]; found {
 			dump(">>> instantiated %s found", tname)

src/go/types/typestring.go

@@ -259,7 +259,10 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 
 	case *Named:
 		writeTypeName(buf, t.obj, qf)
-		if t.tparams != nil {
+		// Don't write type parameter list again if we have an instantiated type,
+		// recognized by a closing '>'.
+		// TODO(gri) clean up - this is too subtle a hack and too dependent on subst.
+		if buf.Bytes()[buf.Len()-1] != '>' && t.tparams != nil {
 			writeTParamList(buf, t.tparams, qf, visited)
 		}