cmd/internal/gc: do not show original expression for constants in export data

Fixes #10066.

Change-Id: I43c423793dd094989e921e163a06b12181a35719
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/6750
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Chris Manghane <cmang@golang.org>

src/cmd/internal/gc/fmt.go

@@ -1143,12 +1143,17 @@ func exprfmt(n *Node, prec int) string {
 		return f
 
 	case OLITERAL: // this is a bit of a mess
+		if fmtmode == FErr {
 			if n.Orig != nil && n.Orig != n {
 				return exprfmt(n.Orig, prec)
 			}
-		if fmtmode == FErr && n.Sym != nil {
+			if n.Sym != nil {
 				return fmt.Sprintf("%v", Sconv(n.Sym, 0))
 			}
+		}
+		if n.Val.Ctype == CTNIL && n.Orig != nil && n.Orig != n {
+			return exprfmt(n.Orig, prec)
+		}
 		if n.Type != nil && n.Type != Types[n.Type.Etype] && n.Type != idealbool && n.Type != idealstring {
 			// Need parens when type begins with what might
 			// be misinterpreted as a unary operator: * or <-.

test/fixedbugs/issue10066.dir/a.go

@@ -0,0 +1,11 @@
+package a
+
+import "log"
+
+func Do() {
+	Do2()
+}
+
+func Do2() {
+	println(log.Ldate | log.Ltime | log.Lshortfile)
+}

test/fixedbugs/issue10066.dir/b.go

@@ -0,0 +1,7 @@
+package b
+
+import "./a"
+
+func test() {
+	a.Do()
+}

test/fixedbugs/issue10066.go

@@ -0,0 +1,10 @@
+// compiledir
+
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 10066: constants are printed in the original form
+// in export data. This is the opposite of issue 9076.
+
+package ignored