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Viewing changes to src/cmd/fix/mapdelete.go

  • Committer: Package Import Robot
  • Author(s): James Page
  • Date: 2013-08-20 14:06:23 UTC
  • mfrom: (14.1.23 saucy-proposed)
  • Revision ID: package-import@ubuntu.com-20130820140623-b414jfxi3m0qkmrq
Tags: 2:1.1.2-2ubuntu1
https://launchpad.net/bugs/1211749
https://launchpad.net/bugs/1202027
* Merge from Debian unstable (LP: #1211749, #1202027). Remaining changes:
  - 016-armhf-elf-header.patch: Use correct ELF header for armhf binaries.
  - d/control,control.cross: Update Breaks/Replaces for Ubuntu
    versions to ensure smooth upgrades, regenerate control file.

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src/cmd/fix/mapdelete.go
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// Copyright 2011 The Go Authors.  All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "go/ast"
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func init() {
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        register(mapdeleteFix)
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}
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var mapdeleteFix = fix{
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        "mapdelete",
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        "2011-10-18",
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        mapdelete,
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        `Use delete(m, k) instead of m[k] = 0, false.
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http://codereview.appspot.com/5272045
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`,
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}
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func mapdelete(f *ast.File) bool {
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        fixed := false
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        walk(f, func(n interface{}) {
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                stmt, ok := n.(*ast.Stmt)
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                if !ok {
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                        return
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                }
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                as, ok := (*stmt).(*ast.AssignStmt)
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                if !ok || len(as.Lhs) != 1 || len(as.Rhs) != 2 {
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                        return
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                }
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                ix, ok := as.Lhs[0].(*ast.IndexExpr)
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                if !ok {
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                        return
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                }
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                if !isTopName(as.Rhs[1], "false") {
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                        warn(as.Pos(), "two-element map assignment with non-false second value")
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                        return
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                }
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                if !canDrop(as.Rhs[0]) {
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                        warn(as.Pos(), "two-element map assignment with non-trivial first value")
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                        return
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                }
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                *stmt = &ast.ExprStmt{
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                        X: &ast.CallExpr{
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                                Fun: &ast.Ident{
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                                        NamePos: as.Pos(),
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                                        Name:    "delete",
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                                },
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                                Args: []ast.Expr{ix.X, ix.Index},
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                        },
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                }
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                fixed = true
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        })
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        return fixed
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}
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// canDrop reports whether it is safe to drop the
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// evaluation of n from the program.
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// It is very conservative.
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func canDrop(n ast.Expr) bool {
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        switch n := n.(type) {
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        case *ast.Ident, *ast.BasicLit:
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                return true
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        case *ast.ParenExpr:
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                return canDrop(n.X)
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        case *ast.SelectorExpr:
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                return canDrop(n.X)
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        case *ast.CompositeLit:
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                if !canDrop(n.Type) {
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                        return false
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                }
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                for _, e := range n.Elts {
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                        if !canDrop(e) {
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                                return false
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                        }
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                }
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                return true
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        case *ast.StarExpr:
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                // Dropping *x is questionable,
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                // but we have to be able to drop (*T)(nil).
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                return canDrop(n.X)
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        case *ast.ArrayType, *ast.ChanType, *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.StructType:
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                return true
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        }
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        return false
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}