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// 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"
func init() {
register(mapdeleteFix)
}
var mapdeleteFix = fix{
"mapdelete",
"2011-10-18",
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
}
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