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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.
// Package nilfunc defines an Analyzer that checks for useless
// comparisons against nil.
package nilfunc
import (
"go/ast"
"go/token"
"go/types"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/ast/inspector"
)
const Doc = `check for useless comparisons between functions and nil
A useless comparison is one like f == nil as opposed to f() == nil.`
var Analyzer = &analysis.Analyzer{
Name: "nilfunc",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
}
func run(pass *analysis.Pass) (interface{}, error) {
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{
(*ast.BinaryExpr)(nil),
}
inspect.Preorder(nodeFilter, func(n ast.Node) {
e := n.(*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 pass.TypesInfo.Types[e.X].IsNil():
e2 = e.Y
case pass.TypesInfo.Types[e.Y].IsNil():
e2 = e.X
default:
return
}
// Only want identifiers or selector expressions.
var obj types.Object
switch v := e2.(type) {
case *ast.Ident:
obj = pass.TypesInfo.Uses[v]
case *ast.SelectorExpr:
obj = pass.TypesInfo.Uses[v.Sel]
default:
return
}
// Only want functions.
if _, ok := obj.(*types.Func); !ok {
return
}
pass.Reportf(e.Pos(), "comparison of function %v %v nil is always %v", obj.Name(), e.Op, e.Op == token.NEQ)
})
return nil, nil
}