gofix: add mapdelete
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5286043
diff --git a/src/cmd/gofix/Makefile b/src/cmd/gofix/Makefile
index fc12979..72d690f 100644
--- a/src/cmd/gofix/Makefile
+++ b/src/cmd/gofix/Makefile
@@ -16,6 +16,7 @@
imagenew.go\
iocopyn.go\
main.go\
+ mapdelete.go\
math.go\
netdial.go\
netudpgroup.go\
diff --git a/src/cmd/gofix/fix.go b/src/cmd/gofix/fix.go
index 6d15cc8..9e4fd56 100644
--- a/src/cmd/gofix/fix.go
+++ b/src/cmd/gofix/fix.go
@@ -53,6 +53,7 @@
mathFix,
ioCopyNFix,
imagecolorFix,
+ mapdeleteFix,
}
// walk traverses the AST x, calling visit(y) for each node y in the tree but
diff --git a/src/cmd/gofix/mapdelete.go b/src/cmd/gofix/mapdelete.go
new file mode 100644
index 0000000..b99602d
--- /dev/null
+++ b/src/cmd/gofix/mapdelete.go
@@ -0,0 +1,84 @@
+// Copyright 2011 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.
+
+package main
+
+import "go/ast"
+
+var mapdeleteFix = fix{
+ "mapdelete",
+ mapdelete,
+ `Use delete(m, k) instead of m[k] = 0, false.
+
+http://codereview.appspot.com/5272045
+`,
+}
+
+func mapdelete(f *ast.File) bool {
+ fixed := false
+ walk(f, func(n interface{}) {
+ stmt, ok := n.(*ast.Stmt)
+ if !ok {
+ return
+ }
+ as, ok := (*stmt).(*ast.AssignStmt)
+ if !ok || len(as.Lhs) != 1 || len(as.Rhs) != 2 {
+ return
+ }
+ ix, ok := as.Lhs[0].(*ast.IndexExpr)
+ if !ok {
+ return
+ }
+ if !isTopName(as.Rhs[1], "false") {
+ warn(as.Pos(), "two-element map assignment with non-false second value")
+ return
+ }
+ if !canDrop(as.Rhs[0]) {
+ warn(as.Pos(), "two-element map assignment with non-trivial first value")
+ return
+ }
+ *stmt = &ast.ExprStmt{
+ X: &ast.CallExpr{
+ Fun: &ast.Ident{
+ NamePos: as.Pos(),
+ Name: "delete",
+ },
+ Args: []ast.Expr{ix.X, ix.Index},
+ },
+ }
+ fixed = true
+ })
+ return fixed
+}
+
+// canDrop reports whether it is safe to drop the
+// evaluation of n from the program.
+// It is very conservative.
+func canDrop(n ast.Expr) bool {
+ switch n := n.(type) {
+ case *ast.Ident, *ast.BasicLit:
+ return true
+ case *ast.ParenExpr:
+ return canDrop(n.X)
+ case *ast.SelectorExpr:
+ return canDrop(n.X)
+ case *ast.CompositeLit:
+ if !canDrop(n.Type) {
+ return false
+ }
+ for _, e := range n.Elts {
+ if !canDrop(e) {
+ return false
+ }
+ }
+ return true
+ case *ast.StarExpr:
+ // Dropping *x is questionable,
+ // but we have to be able to drop (*T)(nil).
+ return canDrop(n.X)
+ case *ast.ArrayType, *ast.ChanType, *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.StructType:
+ return true
+ }
+ return false
+}
diff --git a/src/cmd/gofix/mapdelete_test.go b/src/cmd/gofix/mapdelete_test.go
new file mode 100644
index 0000000..8ed5032
--- /dev/null
+++ b/src/cmd/gofix/mapdelete_test.go
@@ -0,0 +1,43 @@
+// Copyright 2011 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.
+
+package main
+
+func init() {
+ addTestCases(mapdeleteTests, mapdelete)
+}
+
+var mapdeleteTests = []testCase{
+ {
+ Name: "mapdelete.0",
+ In: `package main
+
+func f() {
+ m[x] = 0, false
+ m[x] = g(), false
+ m[x] = 1
+ delete(m, x)
+ m[x] = 0, b
+}
+
+func g(false bool) {
+ m[x] = 0, false
+}
+`,
+ Out: `package main
+
+func f() {
+ delete(m, x)
+ m[x] = g(), false
+ m[x] = 1
+ delete(m, x)
+ m[x] = 0, b
+}
+
+func g(false bool) {
+ m[x] = 0, false
+}
+`,
+ },
+}
