[dev.typeparams] go/types: use scope numbers to identify local types

This is a port of CL 333192 to go/types.

Change-Id: I12fd6b682d40c4d30b9ac0e87c463843cf5030d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/335114
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/instance.go

@@ -16,7 +16,7 @@ type instance struct {
 	base    *Named      // parameterized type to be instantiated
 	targs   []Type      // type arguments
 	poslist []token.Pos // position of each targ; for error reporting only
-	value   Type        // base(targs...) after instantiation or Typ[Invalid]; nil if not yet set
+	value   Type        // base[targs...] after instantiation or Typ[Invalid]; nil if not yet set
 }
 
 // expand returns the instantiated (= expanded) type of t.

src/go/types/scope.go

@@ -23,6 +23,7 @@ import (
 type Scope struct {
 	parent   *Scope
 	children []*Scope
+	number   int               // parent.children[number-1] is this scope; 0 if there is no parent
 	elems    map[string]Object // lazily allocated
 	pos, end token.Pos         // scope extent; may be invalid
 	comment  string            // for debugging only
@@ -32,10 +33,11 @@ type Scope struct {
 // NewScope returns a new, empty scope contained in the given parent
 // scope, if any. The comment is for debugging only.
 func NewScope(parent *Scope, pos, end token.Pos, comment string) *Scope {
-	s := &Scope{parent, nil, nil, pos, end, comment, false}
+	s := &Scope{parent, nil, 0, nil, pos, end, comment, false}
 	// don't add children to Universe scope!
 	if parent != nil && parent != Universe {
 		parent.children = append(parent.children, s)
+		s.number = len(parent.children)
 	}
 	return s
 }

src/go/types/sizeof_test.go

@@ -46,7 +46,7 @@ func TestSizeof(t *testing.T) {
 		{Nil{}, 40, 72},
 
 		// Misc
-		{Scope{}, 40, 80},
+		{Scope{}, 44, 88},
 		{Package{}, 40, 80},
 		{TypeSet{}, 20, 40},
 	}

src/go/types/subst.go

@@ -430,8 +430,6 @@ func (subst *subster) typ(typ Type) Type {
 
 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++

src/go/types/typestring.go

@@ -358,22 +358,27 @@ func writeTypeName(buf *bytes.Buffer, obj *TypeName, qf Qualifier) {
 	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.
+		// For local defined types, use the (original!) TypeName's scope
+		// numbers to disambiguate.
 		typ := obj.typ.(*Named)
+		// TODO(gri) Figure out why typ.orig != typ.orig.orig sometimes
+		//           and whether the loop can iterate more than twice.
+		//           (It seems somehow connected to instance types.)
 		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)
+		writeScopeNumbers(buf, typ.obj.parent)
 	}
+}
+
+// writeScopeNumbers writes the number sequence for this scope to buf
+// in the form ".i.j.k" where i, j, k, etc. stand for scope numbers.
+// If a scope is nil or has no parent (such as a package scope), nothing
+// is written.
+func writeScopeNumbers(buf *bytes.Buffer, s *Scope) {
+	if s != nil && s.number > 0 {
+		writeScopeNumbers(buf, s.parent)
+		fmt.Fprintf(buf, ".%d", s.number)
 	}
 }
 

src/go/types/universe.go

@@ -87,21 +87,25 @@ func defPredeclaredTypes() {
 
 	// type error interface{ Error() string }
 	{
+		obj := NewTypeName(token.NoPos, nil, "error", nil)
+		obj.setColor(black)
 		res := NewVar(token.NoPos, nil, "", Typ[String])
 		sig := NewSignature(nil, nil, NewTuple(res), false)
 		err := NewFunc(token.NoPos, nil, "Error", sig)
-		typ := &Named{underlying: NewInterfaceType([]*Func{err}, nil)}
+		typ := NewNamed(obj, NewInterfaceType([]*Func{err}, nil), nil)
 		sig.recv = NewVar(token.NoPos, nil, "", typ)
-		def(NewTypeName(token.NoPos, nil, "error", typ))
+		def(obj)
 	}
 
 	// type comparable interface{ ==() }
 	{
+		obj := NewTypeName(token.NoPos, nil, "comparable", nil)
+		obj.setColor(black)
 		sig := NewSignature(nil, nil, nil, false)
 		eql := NewFunc(token.NoPos, nil, "==", sig)
-		typ := &Named{underlying: NewInterfaceType([]*Func{eql}, nil)}
+		typ := NewNamed(obj, NewInterfaceType([]*Func{eql}, nil), nil)
 		sig.recv = NewVar(token.NoPos, nil, "", typ)
-		def(NewTypeName(token.NoPos, nil, "comparable", typ))
+		def(obj)
 	}
 }