[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>

1 files changed, 3 insertions, 1 deletions

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
 }