go/printer: don't lose relevant parentheses when rewriting selector expressions

Also: Simplified handling of selector expressions. As a result, complicated
multi-line expressions containing selectors and calls/indices with arguments
broken accross lines don't get indented the same way as before, but the change
is minimal (see tests) and there's no such code in the std library. It seems
a worthwhile compromise given the much simpler code.

Applied gofmt -w $GOROOT/src $GOROOT/misc .

Fixes issue 1847.

R=rsc
CC=golang-dev
http://codereview.appspot.com/5675062

3 files changed, 149 insertions, 0 deletions

diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index 303c4f1e1..4b2805009 100644
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -77,6 +77,7 @@ var tests = []struct {
 	{"testdata/rewrite1.input", "-r=Foo->Bar"},
 	{"testdata/rewrite2.input", "-r=int->bool"},
 	{"testdata/rewrite3.input", "-r=x->x"},
+	{"testdata/rewrite4.input", "-r=(x)->x"},
 	{"testdata/stdin*.input", "-stdin"},
 	{"testdata/comments.input", ""},
 	{"testdata/import.input", ""},
diff --git a/src/cmd/gofmt/testdata/rewrite4.golden b/src/cmd/gofmt/testdata/rewrite4.golden
new file mode 100644
index 000000000..8dfc81a07
--- /dev/null
+++ b/src/cmd/gofmt/testdata/rewrite4.golden
@@ -0,0 +1,74 @@
+// Copyright 2012 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.
+
+// Rewriting of parenthesized expressions (x) -> x
+// must not drop parentheses if that would lead to
+// wrong association of the operands.
+// Was issue 1847.
+
+package main
+
+// From example 1 of issue 1847.
+func _() {
+	var t = (&T{1000}).Id()
+}
+
+// From example 2 of issue 1847.
+func _() {
+	fmt.Println((*xpp).a)
+}
+
+// Some more test cases.
+func _() {
+	_ = (-x).f
+	_ = (*x).f
+	_ = (&x).f
+	_ = (!x).f
+	_ = -x.f
+	_ = *x.f
+	_ = &x.f
+	_ = !x.f
+	(-x).f()
+	(*x).f()
+	(&x).f()
+	(!x).f()
+	_ = -x.f()
+	_ = *x.f()
+	_ = &x.f()
+	_ = !x.f()
+
+	_ = (-x).f
+	_ = (*x).f
+	_ = (&x).f
+	_ = (!x).f
+	_ = -x.f
+	_ = *x.f
+	_ = &x.f
+	_ = !x.f
+	(-x).f()
+	(*x).f()
+	(&x).f()
+	(!x).f()
+	_ = -x.f()
+	_ = *x.f()
+	_ = &x.f()
+	_ = !x.f()
+
+	_ = -x.f
+	_ = *x.f
+	_ = &x.f
+	_ = !x.f
+	_ = -x.f
+	_ = *x.f
+	_ = &x.f
+	_ = !x.f
+	_ = -x.f()
+	_ = *x.f()
+	_ = &x.f()
+	_ = !x.f()
+	_ = -x.f()
+	_ = *x.f()
+	_ = &x.f()
+	_ = !x.f()
+}
diff --git a/src/cmd/gofmt/testdata/rewrite4.input b/src/cmd/gofmt/testdata/rewrite4.input
new file mode 100644
index 000000000..164cc0451
--- /dev/null
+++ b/src/cmd/gofmt/testdata/rewrite4.input
@@ -0,0 +1,74 @@
+// Copyright 2012 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.
+
+// Rewriting of parenthesized expressions (x) -> x
+// must not drop parentheses if that would lead to
+// wrong association of the operands.
+// Was issue 1847.
+
+package main
+
+// From example 1 of issue 1847.
+func _() {
+	var t = (&T{1000}).Id()
+}
+
+// From example 2 of issue 1847.
+func _() {
+       fmt.Println((*xpp).a)
+}
+
+// Some more test cases.
+func _() {
+	_ = (-x).f
+	_ = (*x).f
+	_ = (&x).f
+	_ = (!x).f
+	_ = (-x.f)
+	_ = (*x.f)
+	_ = (&x.f)
+	_ = (!x.f)
+	(-x).f()
+	(*x).f()
+	(&x).f()
+	(!x).f()
+	_ = (-x.f())
+	_ = (*x.f())
+	_ = (&x.f())
+	_ = (!x.f())
+
+	_ = ((-x)).f
+	_ = ((*x)).f
+	_ = ((&x)).f
+	_ = ((!x)).f
+	_ = ((-x.f))
+	_ = ((*x.f))
+	_ = ((&x.f))
+	_ = ((!x.f))
+	((-x)).f()
+	((*x)).f()
+	((&x)).f()
+	((!x)).f()
+	_ = ((-x.f()))
+	_ = ((*x.f()))
+	_ = ((&x.f()))
+	_ = ((!x.f()))
+
+	_ = -(x).f
+	_ = *(x).f
+	_ = &(x).f
+	_ = !(x).f
+	_ = -x.f
+	_ = *x.f
+	_ = &x.f
+	_ = !x.f
+	_ = -(x).f()
+	_ = *(x).f()
+	_ = &(x).f()
+	_ = !(x).f()
+	_ = -x.f()
+	_ = *x.f()
+	_ = &x.f()
+	_ = !x.f()
+}