[dev.unified] cmd/compile/internal/noder: stop handling type expressions as expressions

There are two places currently where we rely on type expressions as
generic expressions: the first argument to "make" and "new", and the
selectable operand within a method expression.

This CL makes that code responsible for handling the type expressions
directly. Longer term, this will be relevant to appropriately handling
derived types, because it will provide additional context about how
the derived type is to be used.

Change-Id: I9d7dcf9d32dada032ff411cd103b9df413c298a5
Reviewed-on: https://go-review.googlesource.com/c/go/+/410101
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

@@ -39,7 +39,6 @@ func (c codeExpr) Value() int                 { return int(c) }
 // TODO(mdempsky): Split expr into addr, for lvalues.
 const (
 	exprConst  codeExpr = iota
-	exprType            // type expression
 	exprLocal           // local variable
 	exprGlobal          // global variable or function
 	exprCompLit
@@ -52,6 +51,8 @@ const (
 	exprBinaryOp
 	exprCall
 	exprConvert
+	exprNew
+	exprMake
 )
 
 type codeAssign int

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

@@ -1567,9 +1567,6 @@ func (r *reader) expr() (res ir.Node) {
 		// TODO(mdempsky): Handle builtins directly in exprCall, like method calls?
 		return typecheck.Callee(r.obj())
 
-	case exprType:
-		return r.exprType(false)
-
 	case exprConst:
 		pos := r.pos()
 		typ := r.typ()
@@ -1585,9 +1582,9 @@ func (r *reader) expr() (res ir.Node) {
 		return r.funcLit()
 
 	case exprSelector:
-		x := r.expr()
+		var x ir.Node
-		pos := r.pos()
+		if r.Bool() { // MethodExpr
-		_, sym := r.selector()
+			x = r.exprType(false)
 
 			// Method expression with derived receiver type.
 			if x.Op() == ir.ODYNAMICTYPE {
@@ -1596,6 +1593,11 @@ func (r *reader) expr() (res ir.Node) {
 				n.SetTypecheck(1)
 				x = n
 			}
+		} else { // FieldVal, MethodVal
+			x = r.expr()
+		}
+		pos := r.pos()
+		_, sym := r.selector()
 
 		n := typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, x, sym)).(*ir.SelectorExpr)
 		if n.Op() == ir.OMETHVALUE {
@@ -1679,6 +1681,17 @@ func (r *reader) expr() (res ir.Node) {
 		dots := r.Bool()
 		return typecheck.Call(pos, fun, args, dots)
 
+	case exprMake:
+		pos := r.pos()
+		typ := r.exprType(false)
+		extra := r.exprs()
+		return typecheck.Expr(ir.NewCallExpr(pos, ir.OMAKE, nil, append([]ir.Node{typ}, extra...)))
+
+	case exprNew:
+		pos := r.pos()
+		typ := r.exprType(false)
+		return typecheck.Expr(ir.NewUnaryExpr(pos, ir.ONEW, typ))
+
 	case exprConvert:
 		typ := r.typ()
 		pos := r.pos()

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

@@ -619,6 +619,8 @@ func (w *writer) doObj(wext *writer, obj types2.Object) pkgbits.CodeObj {
 }
 
 // typExpr writes the type represented by the given expression.
+//
+// TODO(mdempsky): Document how this differs from exprType.
 func (w *writer) typExpr(expr syntax.Expr) {
 	tv, ok := w.p.info.Types[expr]
 	assert(ok)
@@ -1228,9 +1230,7 @@ func (w *writer) expr(expr syntax.Expr) {
 		}
 
 		if tv.IsType() {
-			w.Code(exprType)
+			w.p.fatalf(expr, "unexpected type expression %v", syntax.String(expr))
-			w.exprType(nil, expr, false)
-			return
 		}
 
 		if tv.Value != nil {
@@ -1280,7 +1280,11 @@ func (w *writer) expr(expr syntax.Expr) {
 		assert(ok)
 
 		w.Code(exprSelector)
+		if w.Bool(sel.Kind() == types2.MethodExpr) {
+			w.exprType(nil, expr.X, false)
+		} else {
 			w.expr(expr.X)
+		}
 		w.pos(expr)
 		w.selector(sel.Obj())
 
@@ -1339,6 +1343,29 @@ func (w *writer) expr(expr syntax.Expr) {
 			break
 		}
 
+		if name, ok := unparen(expr.Fun).(*syntax.Name); ok && tv.IsBuiltin() {
+			switch name.Value {
+			case "make":
+				assert(len(expr.ArgList) >= 1)
+				assert(!expr.HasDots)
+
+				w.Code(exprMake)
+				w.pos(expr)
+				w.exprType(nil, expr.ArgList[0], false)
+				w.exprs(expr.ArgList[1:])
+				return
+
+			case "new":
+				assert(len(expr.ArgList) == 1)
+				assert(!expr.HasDots)
+
+				w.Code(exprNew)
+				w.pos(expr)
+				w.exprType(nil, expr.ArgList[0], false)
+				return
+			}
+		}
+
 		writeFunExpr := func() {
 			if selector, ok := unparen(expr.Fun).(*syntax.SelectorExpr); ok {
 				if sel, ok := w.p.info.Selections[selector]; ok && sel.Kind() == types2.MethodVal {
@@ -1438,10 +1465,6 @@ func (w *writer) exprList(expr syntax.Expr) {
 }
 
 func (w *writer) exprs(exprs []syntax.Expr) {
-	if len(exprs) == 0 {
-		assert(exprs == nil)
-	}
-
 	w.Sync(pkgbits.SyncExprs)
 	w.Len(len(exprs))
 	for _, expr := range exprs {