[dev.typeparams] cmd/compile: tweaks to match types2

This CL makes a handful of changes to either bring existing compiler
output consistent with what types2 produces or to make it easier to
reproduce with types2:

1. The position for embedded fields is corrected to the position of
the syntax.Field, rather than the syntax.Type.

2. Methods and embedded types are sorted in export data the same way
that types2 sorts them.

3. Don't write out position information for OLITERALs that don't have
their own position (i.e., references to named constants).

Change-Id: Ic3979215ae9ef280cfbba7b44c236e03fc12a2ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/323209
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/noder/noder.go

@@ -986,6 +986,8 @@ func (p *noder) packname(expr syntax.Expr) *types.Sym {
 }
 
 func (p *noder) embedded(typ syntax.Expr) *ir.Field {
+	pos := p.pos(syntax.StartPos(typ))
+
 	op, isStar := typ.(*syntax.Operation)
 	if isStar {
 		if op.Op != syntax.Mul || op.Y != nil {
@@ -995,11 +997,11 @@ func (p *noder) embedded(typ syntax.Expr) *ir.Field {
 	}
 
 	sym := p.packname(typ)
-	n := ir.NewField(p.pos(typ), typecheck.Lookup(sym.Name), importName(sym).(ir.Ntype), nil)
+	n := ir.NewField(pos, typecheck.Lookup(sym.Name), importName(sym).(ir.Ntype), nil)
 	n.Embedded = true
 
 	if isStar {
-		n.Ntype = ir.NewStarExpr(p.pos(op), n.Ntype)
+		n.Ntype = ir.NewStarExpr(pos, n.Ntype)
 	}
 	return n
 }

src/cmd/compile/internal/typecheck/iexport.go

@@ -540,9 +540,12 @@ func (p *iexporter) doDecl(n *ir.Name) {
 			break
 		}
 
-		ms := t.Methods()
-		w.uint64(uint64(ms.Len()))
-		for _, m := range ms.Slice() {
+		// Sort methods, for consistency with types2.
+		methods := append([]*types.Field(nil), t.Methods().Slice()...)
+		sort.Sort(types.MethodsByName(methods))
+
+		w.uint64(uint64(len(methods)))
+		for _, m := range methods {
 			w.pos(m.Pos)
 			w.selector(m.Sym)
 			w.param(m.Type.Recv())
@@ -550,7 +553,7 @@ func (p *iexporter) doDecl(n *ir.Name) {
 		}
 
 		w.typeExt(t)
-		for _, m := range ms.Slice() {
+		for _, m := range methods {
 			w.methExt(m)
 		}
 
@@ -939,6 +942,12 @@ func (w *exportWriter) doTyp(t *types.Type) {
 			}
 		}
 
+		// Sort methods and embedded types, for consistency with types2.
+		// Note: embedded types may be anonymous, and types2 sorts them
+		// with sort.Stable too.
+		sort.Sort(types.MethodsByName(methods))
+		sort.Stable(types.EmbeddedsByName(embeddeds))
+
 		w.startType(interfaceType)
 		w.setPkg(t.Pkg(), true)
 
@@ -1590,7 +1599,11 @@ func (w *exportWriter) expr(n ir.Node) {
 
 	case ir.OLITERAL:
 		w.op(ir.OLITERAL)
+		if ir.HasUniquePos(n) {
 			w.pos(n.Pos())
+		} else {
+			w.pos(src.NoXPos)
+		}
 		w.value(n.Type(), n.Val())
 
 	case ir.ONAME:

src/cmd/compile/internal/types/size.go

@@ -126,10 +126,15 @@ func expandiface(t *Type) {
 		// (including broken ones, if any) and add to t's
 		// method set.
 		for _, t1 := range m.Type.AllMethods().Slice() {
-			// Use m.Pos rather than t1.Pos to preserve embedding position.
 			f := NewField(m.Pos, t1.Sym, t1.Type)
 			addMethod(f, false)
+
+			// Clear position after typechecking, for consistency with types2.
+			f.Pos = src.NoXPos
 		}
+
+		// Clear position after typechecking, for consistency with types2.
+		m.Pos = src.NoXPos
 	}
 
 	sort.Sort(MethodsByName(methods))

src/cmd/compile/internal/types/sort.go

@@ -4,11 +4,16 @@
 
 package types
 
-// MethodsByName sorts methods by symbol.
+// MethodsByName sorts methods by name.
 type MethodsByName []*Field
 
 func (x MethodsByName) Len() int           { return len(x) }
-
 func (x MethodsByName) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
-
 func (x MethodsByName) Less(i, j int) bool { return x[i].Sym.Less(x[j].Sym) }
+
+// EmbeddedsByName sorts embedded types by name.
+type EmbeddedsByName []*Field
+
+func (x EmbeddedsByName) Len() int           { return len(x) }
+func (x EmbeddedsByName) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
+func (x EmbeddedsByName) Less(i, j int) bool { return x[i].Type.Sym().Less(x[j].Type.Sym()) }