go/printer: fix printing of variadic function calls

Fixes #3130.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5697062

src/pkg/go/printer/nodes.go

@@ -804,9 +804,14 @@ func (p *printer) expr1(expr ast.Expr, prec1, depth int, multiLine *bool) {
 		}
 		p.expr1(x.Fun, token.HighestPrec, depth, multiLine)
 		p.print(x.Lparen, token.LPAREN)
-		p.exprList(x.Lparen, x.Args, depth, commaSep|commaTerm, multiLine, x.Rparen)
 		if x.Ellipsis.IsValid() {
+			p.exprList(x.Lparen, x.Args, depth, commaSep, multiLine, x.Ellipsis)
 			p.print(x.Ellipsis, token.ELLIPSIS)
+			if x.Rparen.IsValid() && p.lineFor(x.Ellipsis) < p.lineFor(x.Rparen) {
+				p.print(token.COMMA, formfeed)
+			}
+		} else {
+			p.exprList(x.Lparen, x.Args, depth, commaSep|commaTerm, multiLine, x.Rparen)
 		}
 		p.print(x.Rparen, token.RPAREN)
 

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

@@ -625,3 +625,25 @@ func f() {
 		log.Fatal(err)
 	}
 }
+
+// Handle multi-line argument lists ending in ... correctly.
+// Was issue 3130.
+func _() {
+	_ = append(s, a...)
+	_ = append(
+		s, a...)
+	_ = append(s,
+		a...)
+	_ = append(
+		s,
+		a...)
+	_ = append(s, a...,
+	)
+	_ = append(s,
+		a...,
+	)
+	_ = append(
+		s,
+		a...,
+	)
+}

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

@@ -654,3 +654,25 @@ func f() {
 	    log.Fatal(err)
 	}
 }
+
+// Handle multi-line argument lists ending in ... correctly.
+// Was issue 3130.
+func _() {
+	_ = append(s, a...)
+	_ = append(
+		s, a...)
+	_ = append(s,
+		a...)
+	_ = append(
+		s,
+		a...)
+	_ = append(s, a...,
+	)
+	_ = append(s,
+		a...,
+	)
+	_ = append(
+		s,
+		a...,
+	)
+}

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

@@ -625,3 +625,25 @@ func f() {
 		log.Fatal(err)
 	}
 }
+
+// Handle multi-line argument lists ending in ... correctly.
+// Was issue 3130.
+func _() {
+	_ = append(s, a...)
+	_ = append(
+		s, a...)
+	_ = append(s,
+		a...)
+	_ = append(
+		s,
+		a...)
+	_ = append(s, a...,
+	)
+	_ = append(s,
+		a...,
+	)
+	_ = append(
+		s,
+		a...,
+	)
+}