go/analysis/passes/nilfunc: split out of vet

Change-Id: Ibbe8dfddfcabd2bb71753c969eef14f92603c17d
Reviewed-on: https://go-review.googlesource.com/c/140762
Reviewed-by: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>

go/analysis/passes/nilfunc/nilfunc.go

@@ -0,0 +1,70 @@
+// 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
+
+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"
+)
+
+var Analyzer = &analysis.Analyzer{
+	Name: "nilfunc",
+	Doc: `check for useless comparisons between functions and nil
+
+A useless comparison is one like f == nil as opposed to f() == nil.`,
+	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
+}

go/analysis/passes/nilfunc/nilfunc_test.go

@@ -0,0 +1,13 @@
+package nilfunc_test
+
+import (
+	"testing"
+
+	"golang.org/x/tools/go/analysis/analysistest"
+	"golang.org/x/tools/go/analysis/passes/nilfunc"
+)
+
+func Test(t *testing.T) {
+	testdata := analysistest.TestData()
+	analysistest.Run(t, testdata, nilfunc.Analyzer, "a")
+}

go/analysis/passes/nilfunc/testdata/src/a/a.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package testdata
+package a
 
 func F() {}
 
@@ -20,14 +20,14 @@ func Comparison() {
 	if fn == nil || Fv == nil || t.F == nil {
 		// no error; these func vars or fields may be nil
 	}
-	if F == nil { // ERROR "comparison of function F == nil is always false"
+	if F == nil { // want "comparison of function F == nil is always false"
 		panic("can't happen")
 	}
-	if t.M == nil { // ERROR "comparison of function M == nil is always false"
+	if t.M == nil { // want "comparison of function M == nil is always false"
 		panic("can't happen")
 	}
-	if F != nil { // ERROR "comparison of function F != nil is always true"
-		if t.M != nil { // ERROR "comparison of function M != nil is always true"
+	if F != nil { // want "comparison of function F != nil is always true"
+		if t.M != nil { // want "comparison of function M != nil is always true"
 			return
 		}
 	}

go/analysis/passes/vet/nilfunc.go

@@ -1,69 +0,0 @@
-// +build ignore
-
-// 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]
-}