cmd/compile/internal/types2: use TypeList in the Inferred struct

This is a port of CL 343934 from go/types with the necessary
adjustments to the compiler.

Change-Id: I810144e6e2eb2bc8fa0d34dc206403c993cbbe7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/344616
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dan Scales <danscales@google.com>

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

@@ -116,12 +116,12 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 		// The key for the Inferred map is the CallExpr (if inferring
 		// types required the function arguments) or the IndexExpr below
 		// (if types could be inferred without the function arguments).
-		if inferred, ok := g.info.Inferred[expr]; ok && len(inferred.TArgs) > 0 {
+		if inferred, ok := g.info.Inferred[expr]; ok && inferred.TArgs.Len() > 0 {
 			// This is the case where inferring types required the
 			// types of the function arguments.
-			targs := make([]ir.Node, len(inferred.TArgs))
+			targs := make([]ir.Node, inferred.TArgs.Len())
-			for i, targ := range inferred.TArgs {
+			for i := range targs {
-				targs[i] = ir.TypeNode(g.typ(targ))
+				targs[i] = ir.TypeNode(g.typ(inferred.TArgs.At(i)))
 			}
 			if fun.Op() == ir.OFUNCINST {
 				// Replace explicit type args with the full list that
@@ -149,13 +149,13 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 	case *syntax.IndexExpr:
 		var targs []ir.Node
 
-		if inferred, ok := g.info.Inferred[expr]; ok && len(inferred.TArgs) > 0 {
+		if inferred, ok := g.info.Inferred[expr]; ok && inferred.TArgs.Len() > 0 {
 			// This is the partial type inference case where the types
 			// can be inferred from other type arguments without using
 			// the types of the function arguments.
-			targs = make([]ir.Node, len(inferred.TArgs))
+			targs = make([]ir.Node, inferred.TArgs.Len())
-			for i, targ := range inferred.TArgs {
+			for i := range targs {
-				targs[i] = ir.TypeNode(g.typ(targ))
+				targs[i] = ir.TypeNode(g.typ(inferred.TArgs.At(i)))
 			}
 		} else if _, ok := expr.Index.(*syntax.ListExpr); ok {
 			targs = g.exprList(expr.Index)

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

@@ -1212,12 +1212,12 @@ func (w *writer) expr(expr syntax.Expr) {
 	if obj != nil {
 		if isGlobal(obj) {
 			w.code(exprName)
-			w.obj(obj, types2.NewTypeList(targs))
+			w.obj(obj, targs)
 			return
 		}
 
 		obj := obj.(*types2.Var)
-		assert(len(targs) == 0)
+		assert(targs.Len() == 0)
 
 		w.code(exprLocal)
 		w.useLocal(expr.Pos(), obj)
@@ -1321,7 +1321,7 @@ func (w *writer) expr(expr syntax.Expr) {
 
 				// As if w.expr(expr.Fun), but using inf.TArgs instead.
 				w.code(exprName)
-				w.obj(obj, types2.NewTypeList(inf.TArgs))
+				w.obj(obj, inf.TArgs)
 			} else {
 				w.expr(expr.Fun)
 			}
@@ -1770,7 +1770,7 @@ func isGlobal(obj types2.Object) bool {
 // lookupObj returns the object that expr refers to, if any. If expr
 // is an explicit instantiation of a generic object, then the type
 // arguments are returned as well.
-func lookupObj(info *types2.Info, expr syntax.Expr) (obj types2.Object, targs []types2.Type) {
+func lookupObj(info *types2.Info, expr syntax.Expr) (obj types2.Object, targs *types2.TypeList) {
 	if index, ok := expr.(*syntax.IndexExpr); ok {
 		if inf, ok := info.Inferred[index]; ok {
 			targs = inf.TArgs
@@ -1785,13 +1785,14 @@ func lookupObj(info *types2.Info, expr syntax.Expr) (obj types2.Object, targs []
 				}
 			}
 
-			targs = make([]types2.Type, len(args))
+			list := make([]types2.Type, len(args))
 			for i, arg := range args {
 				tv, ok := info.Types[arg]
 				assert(ok)
 				assert(tv.IsType())
-				targs[i] = tv.Type
+				list[i] = tv.Type
 			}
+			targs = types2.NewTypeList(list)
 		}
 
 		expr = index.X

src/cmd/compile/internal/types2/api.go

@@ -373,7 +373,7 @@ func (tv TypeAndValue) HasOk() bool {
 // Inferred reports the inferred type arguments and signature
 // for a parameterized function call that uses type inference.
 type Inferred struct {
-	TArgs []Type
+	TArgs *TypeList
 	Sig   *Signature
 }
 

src/cmd/compile/internal/types2/api_test.go

@@ -500,7 +500,7 @@ func TestInferredInfo(t *testing.T) {
 		}
 
 		// look for inferred type arguments and signature
-		var targs []Type
+		var targs *TypeList
 		var sig *Signature
 		for call, inf := range info.Inferred {
 			var fun syntax.Expr
@@ -524,11 +524,12 @@ func TestInferredInfo(t *testing.T) {
 		}
 
 		// check that type arguments are correct
-		if len(targs) != len(test.targs) {
+		if targs.Len() != len(test.targs) {
-			t.Errorf("package %s: got %d type arguments; want %d", name, len(targs), len(test.targs))
+			t.Errorf("package %s: got %d type arguments; want %d", name, targs.Len(), len(test.targs))
 			continue
 		}
-		for i, targ := range targs {
+		for i := 0; i < targs.Len(); i++ {
+			targ := targs.At(i)
 			if got := targ.String(); got != test.targs[i] {
 				t.Errorf("package %s, %d. type argument: got %s; want %s", name, i, got, test.targs[i])
 				continue

src/cmd/compile/internal/types2/check.go

@@ -416,7 +416,7 @@ func (check *Checker) recordInferred(call syntax.Expr, targs []Type, sig *Signat
 	assert(call != nil)
 	assert(sig != nil)
 	if m := check.Inferred; m != nil {
-		m[call] = Inferred{targs, sig}
+		m[call] = Inferred{NewTypeList(targs), sig}
 	}
 }