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| 1 // Copyright 2013 The Go Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style |
| 3 // license that can be found in the LICENSE file. |
| 4 |
| 5 /* |
| 6 This file contains the code to check for useless function comparisons. |
| 7 A useless comparison is one like f == nil as opposed to f() == nil. |
| 8 */ |
| 9 |
| 10 package main |
| 11 |
| 12 import ( |
| 13 "go/ast" |
| 14 "go/token" |
| 15 |
| 16 "code.google.com/p/go.tools/go/types" |
| 17 ) |
| 18 |
| 19 func (f *File) checkNilFuncComparison(e *ast.BinaryExpr) { |
| 20 if !vet("nilfunc") { |
| 21 return |
| 22 } |
| 23 |
| 24 // Only want == or != comparisons. |
| 25 if e.Op != token.EQL && e.Op != token.NEQ { |
| 26 return |
| 27 } |
| 28 |
| 29 // Only want comparisons with a nil identifier on one side. |
| 30 var e2 ast.Expr |
| 31 switch { |
| 32 case f.isNil(e.X): |
| 33 e2 = e.Y |
| 34 case f.isNil(e.Y): |
| 35 e2 = e.X |
| 36 default: |
| 37 return |
| 38 } |
| 39 |
| 40 // Only want identifiers or selector expressions. |
| 41 var obj types.Object |
| 42 switch v := e2.(type) { |
| 43 case *ast.Ident: |
| 44 obj = f.pkg.idents[v] |
| 45 case *ast.SelectorExpr: |
| 46 obj = f.pkg.idents[v.Sel] |
| 47 default: |
| 48 return |
| 49 } |
| 50 |
| 51 // Only want functions. |
| 52 if _, ok := obj.(*types.Func); !ok { |
| 53 return |
| 54 } |
| 55 |
| 56 f.Badf(e.Pos(), "comparison of function %v %v nil is always %v", obj.Nam
e(), e.Op, e.Op == token.NEQ) |
| 57 } |
| 58 |
| 59 // isNil reports whether the provided expression is the built-in nil |
| 60 // identifier. |
| 61 func (f *File) isNil(e ast.Expr) bool { |
| 62 return f.pkg.types[e] == types.Typ[types.UntypedNil] |
| 63 } |
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