[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, 8 insertions, 4 deletions

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)
 	}
 }