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