70 lines
1.4 KiB
Go
70 lines
1.4 KiB
Go
// +build ignore
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// Copyright 2013 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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/*
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This file contains the code to check for useless function comparisons.
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A useless comparison is one like f == nil as opposed to f() == nil.
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*/
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package main
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import (
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"go/ast"
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"go/token"
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"go/types"
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)
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func init() {
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register("nilfunc",
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"check for comparisons between functions and nil",
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checkNilFuncComparison,
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binaryExpr)
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}
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func checkNilFuncComparison(f *File, node ast.Node) {
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e := node.(*ast.BinaryExpr)
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// Only want == or != comparisons.
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if e.Op != token.EQL && e.Op != token.NEQ {
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return
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}
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// Only want comparisons with a nil identifier on one side.
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var e2 ast.Expr
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switch {
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case f.isNil(e.X):
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e2 = e.Y
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case f.isNil(e.Y):
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e2 = e.X
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default:
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return
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}
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// Only want identifiers or selector expressions.
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var obj types.Object
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switch v := e2.(type) {
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case *ast.Ident:
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obj = f.pkg.uses[v]
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case *ast.SelectorExpr:
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obj = f.pkg.uses[v.Sel]
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default:
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return
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}
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// Only want functions.
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if _, ok := obj.(*types.Func); !ok {
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return
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}
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f.Badf(e.Pos(), "comparison of function %v %v nil is always %v", obj.Name(), e.Op, e.Op == token.NEQ)
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}
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// isNil reports whether the provided expression is the built-in nil
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// identifier.
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func (f *File) isNil(e ast.Expr) bool {
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return f.pkg.types[e].Type == types.Typ[types.UntypedNil]
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}
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