gofmt: handle &T in composite literal simplify

R=gri
CC=golang-dev
https://golang.org/cl/5448086

3 files changed, 213 insertions, 1 deletions

diff --git a/src/cmd/gofmt/simplify.go b/src/cmd/gofmt/simplify.go
index d9afc0e7b4..9d3cb91439 100644
--- a/src/cmd/gofmt/simplify.go
+++ b/src/cmd/gofmt/simplify.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"go/ast"
+	"go/token"
 	"reflect"
 )
 
@@ -26,10 +27,12 @@ func (s *simplifier) Visit(node ast.Node) ast.Visitor {
 
 		if eltType != nil {
 			typ := reflect.ValueOf(eltType)
-			for _, x := range outer.Elts {
+			for i, x := range outer.Elts {
+				px := &outer.Elts[i]
 				// look at value of indexed/named elements
 				if t, ok := x.(*ast.KeyValueExpr); ok {
 					x = t.Value
+					px = &t.Value
 				}
 				simplify(x)
 				// if the element is a composite literal and its literal type
@@ -40,6 +43,19 @@ func (s *simplifier) Visit(node ast.Node) ast.Visitor {
 						inner.Type = nil
 					}
 				}
+				// if the outer literal's element type is a pointer type *T
+				// and the element is & of a composite literal of type T,
+				// the inner &T may be omitted.
+				if ptr, ok := eltType.(*ast.StarExpr); ok {
+					if addr, ok := x.(*ast.UnaryExpr); ok && addr.Op == token.AND {
+						if inner, ok := addr.X.(*ast.CompositeLit); ok {
+							if match(nil, reflect.ValueOf(ptr.X), reflect.ValueOf(inner.Type)) {
+								inner.Type = nil  // drop T
+								*px = inner // drop &
+							}
+						}
+					}
+				}
 			}
 
 			// node was simplified - stop walk (there are no subnodes to simplify)
diff --git a/src/cmd/gofmt/testdata/composites.golden b/src/cmd/gofmt/testdata/composites.golden
index 1fd5847c11..b2825e732a 100644
--- a/src/cmd/gofmt/testdata/composites.golden
+++ b/src/cmd/gofmt/testdata/composites.golden
@@ -102,3 +102,101 @@ var pieces4 = []Piece{
 	{2, 0, Point{4, 1}, []Point{{0, 0}, {1, 0}, {1, 0}, {1, 0}}, nil, nil},
 	{3, 0, Point{1, 4}, []Point{{0, 0}, {0, 1}, {0, 1}, {0, 1}}, nil, nil},
 }
+
+var _ = [42]*T{
+	{},
+	{1, 2},
+	{3, 4},
+}
+
+var _ = [...]*T{
+	{},
+	{1, 2},
+	{3, 4},
+}
+
+var _ = []*T{
+	{},
+	{1, 2},
+	{3, 4},
+}
+
+var _ = []*T{
+	{},
+	10: {1, 2},
+	20: {3, 4},
+}
+
+var _ = []*struct {
+	x, y int
+}{
+	{},
+	10: {1, 2},
+	20: {3, 4},
+}
+
+var _ = []interface{}{
+	&T{},
+	10: &T{1, 2},
+	20: &T{3, 4},
+}
+
+var _ = []*[]int{
+	{},
+	{1, 2},
+	{3, 4},
+}
+
+var _ = []*[]int{
+	(&[]int{}),
+	(&[]int{1, 2}),
+	{3, 4},
+}
+
+var _ = []*[]*[]int{
+	{},
+	{
+		{},
+		{0, 1, 2, 3},
+		{4, 5},
+	},
+}
+
+var _ = map[string]*T{
+	"foo": {},
+	"bar": {1, 2},
+	"bal": {3, 4},
+}
+
+var _ = map[string]*struct {
+	x, y int
+}{
+	"foo": {},
+	"bar": {1, 2},
+	"bal": {3, 4},
+}
+
+var _ = map[string]interface{}{
+	"foo": &T{},
+	"bar": &T{1, 2},
+	"bal": &T{3, 4},
+}
+
+var _ = map[string]*[]int{
+	"foo": {},
+	"bar": {1, 2},
+	"bal": {3, 4},
+}
+
+var _ = map[string]*[]int{
+	"foo": (&[]int{}),
+	"bar": (&[]int{1, 2}),
+	"bal": {3, 4},
+}
+
+var pieces4 = []*Piece{
+	{0, 0, Point{4, 1}, []Point{{0, 0}, {1, 0}, {1, 0}, {1, 0}}, nil, nil},
+	{1, 0, Point{1, 4}, []Point{{0, 0}, {0, 1}, {0, 1}, {0, 1}}, nil, nil},
+	{2, 0, Point{4, 1}, []Point{{0, 0}, {1, 0}, {1, 0}, {1, 0}}, nil, nil},
+	{3, 0, Point{1, 4}, []Point{{0, 0}, {0, 1}, {0, 1}, {0, 1}}, nil, nil},
+}
diff --git a/src/cmd/gofmt/testdata/composites.input b/src/cmd/gofmt/testdata/composites.input
index 15afd9e5c4..7210dafc96 100644
--- a/src/cmd/gofmt/testdata/composites.input
+++ b/src/cmd/gofmt/testdata/composites.input
@@ -102,3 +102,101 @@ var pieces4 = []Piece{
 	Piece{2, 0, Point{4, 1}, []Point{Point{0, 0}, Point{1, 0}, Point{1, 0}, Point{1, 0}}, nil, nil},
 	Piece{3, 0, Point{1, 4}, []Point{Point{0, 0}, Point{0, 1}, Point{0, 1}, Point{0, 1}}, nil, nil},
 }
+
+var _ = [42]*T{
+	&T{},
+	&T{1, 2},
+	&T{3, 4},
+}
+
+var _ = [...]*T{
+	&T{},
+	&T{1, 2},
+	&T{3, 4},
+}
+
+var _ = []*T{
+	&T{},
+	&T{1, 2},
+	&T{3, 4},
+}
+
+var _ = []*T{
+	&T{},
+	10: &T{1, 2},
+	20: &T{3, 4},
+}
+
+var _ = []*struct {
+	x, y int
+}{
+	&struct{ x, y int }{},
+	10: &struct{ x, y int }{1, 2},
+	20: &struct{ x, y int }{3, 4},
+}
+
+var _ = []interface{}{
+	&T{},
+	10: &T{1, 2},
+	20: &T{3, 4},
+}
+
+var _ = []*[]int{
+	&[]int{},
+	&[]int{1, 2},
+	&[]int{3, 4},
+}
+
+var _ = []*[]int{
+	(&[]int{}),
+	(&[]int{1, 2}),
+	&[]int{3, 4},
+}
+
+var _ = []*[]*[]int{
+	&[]*[]int{},
+	&[]*[]int{
+		&[]int{},
+		&[]int{0, 1, 2, 3},
+		&[]int{4, 5},
+	},
+}
+
+var _ = map[string]*T{
+	"foo": &T{},
+	"bar": &T{1, 2},
+	"bal": &T{3, 4},
+}
+
+var _ = map[string]*struct {
+	x, y int
+}{
+	"foo": &struct{ x, y int }{},
+	"bar": &struct{ x, y int }{1, 2},
+	"bal": &struct{ x, y int }{3, 4},
+}
+
+var _ = map[string]interface{}{
+	"foo": &T{},
+	"bar": &T{1, 2},
+	"bal": &T{3, 4},
+}
+
+var _ = map[string]*[]int{
+	"foo": &[]int{},
+	"bar": &[]int{1, 2},
+	"bal": &[]int{3, 4},
+}
+
+var _ = map[string]*[]int{
+	"foo": (&[]int{}),
+	"bar": (&[]int{1, 2}),
+	"bal": &[]int{3, 4},
+}
+
+var pieces4 = []*Piece{
+	&Piece{0, 0, Point{4, 1}, []Point{Point{0, 0}, Point{1, 0}, Point{1, 0}, Point{1, 0}}, nil, nil},
+	&Piece{1, 0, Point{1, 4}, []Point{Point{0, 0}, Point{0, 1}, Point{0, 1}, Point{0, 1}}, nil, nil},
+	&Piece{2, 0, Point{4, 1}, []Point{Point{0, 0}, Point{1, 0}, Point{1, 0}, Point{1, 0}}, nil, nil},
+	&Piece{3, 0, Point{1, 4}, []Point{Point{0, 0}, Point{0, 1}, Point{0, 1}, Point{0, 1}}, nil, nil},
+}