gofmt: support for ... after actual arguments

Pending acceptance of the proposed language change.

R=rsc
CC=golang-dev
https://golang.org/cl/2193048

src/pkg/go/ast/ast.go

@@ -213,7 +213,8 @@ type (
 		Fun      Expr           // function expression
 		Lparen   token.Position // position of "("
 		Args     []Expr         // function arguments
-		Rparen token.Position // positions of ")"
+		Ellipsis token.Position // position of "...", if any
+		Rparen   token.Position // position of ")"
 	}
 
 	// A StarExpr node represents an expression of the form "*" Expression.

src/pkg/go/parser/parser.go

@@ -942,8 +942,13 @@ func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
 	lparen := p.expect(token.LPAREN)
 	p.exprLev++
 	var list vector.Vector
-	for p.tok != token.RPAREN && p.tok != token.EOF {
+	var ellipsis token.Position
+	for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
 		list.Push(p.parseExpr())
+		if p.tok == token.ELLIPSIS {
+			ellipsis = p.pos
+			p.next()
+		}
 		if p.tok != token.COMMA {
 			break
 		}
@@ -952,7 +957,7 @@ func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
 	p.exprLev--
 	rparen := p.expect(token.RPAREN)
 
-	return &ast.CallExpr{fun, lparen, makeExprList(&list), rparen}
+	return &ast.CallExpr{fun, lparen, makeExprList(&list), ellipsis, rparen}
 }
 
 

src/pkg/go/parser/parser_test.go

@@ -37,6 +37,7 @@ var validPrograms = []interface{}{
 	`package main; func f(func() func() func())` + "\n",
 	`package main; func f(...T)` + "\n",
 	`package main; func f(float, ...int)` + "\n",
+	`package main; func f(x int, a ...int) { f(0, a...); f(1, a...,) }` + "\n",
 	`package main; type T []int; var a []bool; func f() { if a[T{42}[0]] {} }` + "\n",
 	`package main; type T []int; func g(int) bool { return true }; func f() { if g(T{42}[0]) {} }` + "\n",
 	`package main; type T []int; func f() { for _ = range []int{T{42}[0]} {} }` + "\n",

src/pkg/go/printer/nodes.go

@@ -686,7 +686,7 @@ func splitSelector(expr ast.Expr) (body, suffix ast.Expr) {
 	case *ast.CallExpr:
 		body, suffix = splitSelector(x.Fun)
 		if body != nil {
-			suffix = &ast.CallExpr{suffix, x.Lparen, x.Args, x.Rparen}
+			suffix = &ast.CallExpr{suffix, x.Lparen, x.Args, x.Ellipsis, x.Rparen}
 			return
 		}
 	case *ast.IndexExpr:
@@ -847,6 +847,9 @@ func (p *printer) expr1(expr ast.Expr, prec1, depth int, ctxt exprContext, multi
 		p.expr1(x.Fun, token.HighestPrec, depth, 0, multiLine)
 		p.print(x.Lparen, token.LPAREN)
 		p.exprList(x.Lparen, x.Args, depth, commaSep|commaTerm, multiLine, x.Rparen)
+		if x.Ellipsis.IsValid() {
+			p.print(x.Ellipsis, token.ELLIPSIS)
+		}
 		p.print(x.Rparen, token.RPAREN)
 
 	case *ast.CompositeLit:

src/pkg/go/printer/testdata/expressions.golden

@@ -169,6 +169,13 @@ func _() {
 }
 
 
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+}
+
+
 func _() {
 	_ = T{}
 	_ = struct{}{}

src/pkg/go/printer/testdata/expressions.input

@@ -169,6 +169,13 @@ func _() {
 }
 
 
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+}
+
+
 func _() {
 	_ = T{}
 	_ = struct{}{}

src/pkg/go/printer/testdata/expressions.raw

@@ -169,6 +169,13 @@ func _() {
 }
 
 
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+}
+
+
 func _() {
 	_ = T{}
 	_ = struct{}{}