[dev.typeparams] cmd/compile/internal/types2: use scope numbers to identify local types

Rather than using a local types' position information, use the type
name's scope numbers to uniquely identify the type from others with
the same name.

We use scope numbers rather than indices (with number-1 == index)
to preserve the invariant that the zero value for a scope is a ready
to use empty scope.

Using scope numbers turned out to be fairly simple after all and
provides a reasonably stable identification which will make debugging
simpler. A scope number series may be a bit longer than a unique ID for
each type name but local types should be reasonably rare.

Also did a minor cleanup in universe.go to ensure Named.orig is set up
correctly (there's still an open TODO but with a work-around).

Change-Id: I73935fa9bd960809fd5c95fe8b8a535c313cfc8f
Reviewed-on: https://go-review.googlesource.com/c/go/+/333192
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

6 files changed, 30 insertions, 21 deletions

diff --git a/src/cmd/compile/internal/types2/instance.go b/src/cmd/compile/internal/types2/instance.go
index 9d6097e874..b133fd1e65 100644
--- a/src/cmd/compile/internal/types2/instance.go
+++ b/src/cmd/compile/internal/types2/instance.go
@@ -16,7 +16,7 @@ type instance struct {
 	base    *Named       // parameterized type to be instantiated
 	targs   []Type       // type arguments
 	poslist []syntax.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.
diff --git a/src/cmd/compile/internal/types2/scope.go b/src/cmd/compile/internal/types2/scope.go
index 2f1814a631..095875d94b 100644
--- a/src/cmd/compile/internal/types2/scope.go
+++ b/src/cmd/compile/internal/types2/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 syntax.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 syntax.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
 }
diff --git a/src/cmd/compile/internal/types2/sizeof_test.go b/src/cmd/compile/internal/types2/sizeof_test.go
index 0b1f7dacad..a51d0c43d5 100644
--- a/src/cmd/compile/internal/types2/sizeof_test.go
+++ b/src/cmd/compile/internal/types2/sizeof_test.go
@@ -47,7 +47,7 @@ func TestSizeof(t *testing.T) {
 		{Nil{}, 56, 88},
 
 		// Misc
-		{Scope{}, 56, 96},
+		{Scope{}, 60, 104},
 		{Package{}, 40, 80},
 		{TypeSet{}, 20, 40},
 	}
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 7b4796fa2e..59efe8a045 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -422,8 +422,6 @@ 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++
diff --git a/src/cmd/compile/internal/types2/typestring.go b/src/cmd/compile/internal/types2/typestring.go
index f63a23c98c..44099133a0 100644
--- a/src/cmd/compile/internal/types2/typestring.go
+++ b/src/cmd/compile/internal/types2/typestring.go
@@ -363,22 +363,27 @@ 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)
 	}
 }
 
diff --git a/src/cmd/compile/internal/types2/universe.go b/src/cmd/compile/internal/types2/universe.go
index c9b53bac92..d328b13a8e 100644
--- a/src/cmd/compile/internal/types2/universe.go
+++ b/src/cmd/compile/internal/types2/universe.go
@@ -86,21 +86,25 @@ func defPredeclaredTypes() {
 
 	// type error interface{ Error() string }
 	{
+		obj := NewTypeName(nopos, nil, "error", nil)
+		obj.setColor(black)
 		res := NewVar(nopos, nil, "", Typ[String])
 		sig := NewSignature(nil, nil, NewTuple(res), false)
 		err := NewFunc(nopos, nil, "Error", sig)
-		typ := &Named{underlying: NewInterfaceType([]*Func{err}, nil)}
+		typ := NewNamed(obj, NewInterfaceType([]*Func{err}, nil), nil)
 		sig.recv = NewVar(nopos, nil, "", typ)
-		def(NewTypeName(nopos, nil, "error", typ))
+		def(obj)
 	}
 
 	// type comparable interface{ ==() }
 	{
+		obj := NewTypeName(nopos, nil, "comparable", nil)
+		obj.setColor(black)
 		sig := NewSignature(nil, nil, nil, false)
 		eql := NewFunc(nopos, nil, "==", sig)
-		typ := &Named{underlying: NewInterfaceType([]*Func{eql}, nil)}
+		typ := NewNamed(obj, NewInterfaceType([]*Func{eql}, nil), nil)
 		sig.recv = NewVar(nopos, nil, "", typ)
-		def(NewTypeName(nopos, nil, "comparable", typ))
+		def(obj)
 	}
 }