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 fc129790a5622f1296c748d40055b73870420a69..72d690f58d87cf7071b43a0d364c99b62231e41c 100644 (file)
--- a/src/cmd/gofix/Makefile
+++ b/src/cmd/gofix/Makefile
@@ -16,6 +16,7 @@ GOFILES=\
        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 6d15cc8dc7fb22cdba5596af08561359d341a818..9e4fd56a6ef8826db521bcc0a0eb501194f8da41 100644 (file)
--- a/src/cmd/gofix/fix.go
+++ b/src/cmd/gofix/fix.go
@@ -53,6 +53,7 @@ var fixes = fixlist{
        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 (file)
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 (file)
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
+}
+`,
+       },
+}