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 "go/types" 16 ) 17 18 func init() { 19 register("nilfunc", 20 "check for comparisons between functions and nil", 21 checkNilFuncComparison, 22 binaryExpr) 23 } 24 25 func checkNilFuncComparison(f *File, node ast.Node) { 26 e := node.(*ast.BinaryExpr) 27 28 // Only want == or != comparisons. 29 if e.Op != token.EQL && e.Op != token.NEQ { 30 return 31 } 32 33 // Only want comparisons with a nil identifier on one side. 34 var e2 ast.Expr 35 switch { 36 case f.isNil(e.X): 37 e2 = e.Y 38 case f.isNil(e.Y): 39 e2 = e.X 40 default: 41 return 42 } 43 44 // Only want identifiers or selector expressions. 45 var obj types.Object 46 switch v := e2.(type) { 47 case *ast.Ident: 48 obj = f.pkg.uses[v] 49 case *ast.SelectorExpr: 50 obj = f.pkg.uses[v.Sel] 51 default: 52 return 53 } 54 55 // Only want functions. 56 if _, ok := obj.(*types.Func); !ok { 57 return 58 } 59 60 f.Badf(e.Pos(), "comparison of function %v %v nil is always %v", obj.Name(), e.Op, e.Op == token.NEQ) 61 } 62 63 // isNil reports whether the provided expression is the built-in nil 64 // identifier. 65 func (f *File) isNil(e ast.Expr) bool { 66 return f.pkg.types[e].Type == types.Typ[types.UntypedNil] 67 } 68
