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go.tools/cmd/vet: detect stupid boolean conditions
This CL introduces two vet checks. Statistics and code below are from a recent 50mb corpus of public code.
1. Check for redundant conjunctions and disjunctions. This check caught 26 instances, of which 20 were clearly copy/paste bugs and 6 appeared to be mere duplication. A typical example:
if xResolution < 0 || xResolution < 0 {
panic("SetSize(): width < 0 || height < 0")
}
2. Check for expressions of the form 'x != c1 || x != c2' or 'x == c1 && x == c2', with c1 and c2 constant expressions. This check caught 16 instances, of which all were bugs. A typical example:
if rf.uri.Scheme != "http" || rf.uri.Scheme != "ftp" {
rf.uri.Scheme = "file"
}
Fixes golang/go#7622.
LGTM=rsc, r
R=golang-codereviews, jscrockett01, r, gri, rsc
CC=golang-codereviews
https://golang.org/cl/98120043
This commit is contained in:
Josh Bleecher Snyder
parent
ccb18ed35d
commit
7da5f193b7
185
cmd/vet/bool.go
Normal file
185
cmd/vet/bool.go
Normal file
@ -0,0 +1,185 @@
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file contains boolean condition tests.
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package main
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import (
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"go/ast"
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"go/token"
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)
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func init() {
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register("bool",
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"check for mistakes involving boolean operators",
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checkBool,
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binaryExpr)
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}
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func checkBool(f *File, n ast.Node) {
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e := n.(*ast.BinaryExpr)
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var op boolOp
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switch e.Op {
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case token.LOR:
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op = or
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case token.LAND:
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op = and
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default:
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return
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}
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comm := op.commutativeSets(e)
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for _, exprs := range comm {
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op.checkRedundant(f, exprs)
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op.checkSuspect(f, exprs)
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}
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}
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type boolOp struct {
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name string
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tok token.Token // token corresponding to this operator
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badEq token.Token // token corresponding to the equality test that should not be used with this operator
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}
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var (
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or = boolOp{"or", token.LOR, token.NEQ}
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and = boolOp{"and", token.LAND, token.EQL}
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)
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// commutativeSets returns all side effect free sets of
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// expressions in e that are connected by op.
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// For example, given 'a || b || f() || c || d' with the or op,
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// commutativeSets returns {{b, a}, {d, c}}.
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func (op boolOp) commutativeSets(e *ast.BinaryExpr) [][]ast.Expr {
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exprs := op.split(e)
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// Partition the slice of expressions into commutative sets.
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i := 0
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var sets [][]ast.Expr
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for j := 0; j <= len(exprs); j++ {
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if j == len(exprs) || hasSideEffects(exprs[j]) {
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if i < j {
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sets = append(sets, exprs[i:j])
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}
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i = j + 1
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}
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}
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return sets
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}
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// checkRedundant checks for expressions of the form
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// e && e
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// e || e
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// Exprs must contain only side effect free expressions.
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func (op boolOp) checkRedundant(f *File, exprs []ast.Expr) {
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seen := make(map[string]bool)
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for _, e := range exprs {
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efmt := f.gofmt(e)
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if seen[efmt] {
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f.Badf(e.Pos(), "redundant %s: %s %s %s", op.name, efmt, op.tok, efmt)
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} else {
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seen[efmt] = true
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}
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}
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}
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// checkSuspect checks for expressions of the form
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// x != c1 || x != c2
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// x == c1 && x == c2
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// where c1 and c2 are constant expressions.
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// If c1 and c2 are the same then it's redundant;
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// if c1 and c2 are different then it's always true or always false.
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// Exprs must contain only side effect free expressions.
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func (op boolOp) checkSuspect(f *File, exprs []ast.Expr) {
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// seen maps from expressions 'x' to equality expressions 'x != c'.
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seen := make(map[string]string)
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for _, e := range exprs {
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bin, ok := e.(*ast.BinaryExpr)
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if !ok || bin.Op != op.badEq {
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continue
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}
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// In order to avoid false positives, restrict to cases
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// in which one of the operands is constant. We're then
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// interested in the other operand.
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// In the rare case in which both operands are constant
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// (e.g. runtime.GOOS and "windows"), we'll only catch
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// mistakes if the LHS is repeated, which is how most
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// code is written.
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var x ast.Expr
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switch {
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case f.pkg.types[bin.Y].Value != nil:
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x = bin.X
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case f.pkg.types[bin.X].Value != nil:
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x = bin.Y
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default:
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continue
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}
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// e is of the form 'x != c' or 'x == c'.
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xfmt := f.gofmt(x)
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efmt := f.gofmt(e)
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if prev, found := seen[xfmt]; found {
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// checkRedundant handles the case in which efmt == prev.
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if efmt != prev {
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f.Badf(e.Pos(), "suspect %s: %s %s %s", op.name, efmt, op.tok, prev)
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}
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} else {
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seen[xfmt] = efmt
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}
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}
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}
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// hasSideEffects reports whether evaluation of e has side effects.
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func hasSideEffects(e ast.Expr) bool {
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safe := true
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ast.Inspect(e, func(node ast.Node) bool {
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switch n := node.(type) {
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// Using CallExpr here will catch conversions
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// as well as function and method invocations.
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// We'll live with the false negatives for now.
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case *ast.CallExpr:
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safe = false
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return false
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case *ast.UnaryExpr:
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if n.Op == token.ARROW {
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safe = false
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return false
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}
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}
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return true
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})
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return !safe
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}
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// split returns a slice of all subexpressions in e that are connected by op.
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// For example, given 'a || (b || c) || d' with the or op,
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// split returns []{d, c, b, a}.
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func (op boolOp) split(e ast.Expr) (exprs []ast.Expr) {
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for {
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e = unparen(e)
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if b, ok := e.(*ast.BinaryExpr); ok && b.Op == op.tok {
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exprs = append(exprs, op.split(b.Y)...)
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e = b.X
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} else {
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exprs = append(exprs, e)
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break
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}
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}
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return
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}
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func unparen(e ast.Expr) ast.Expr {
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for {
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p, ok := e.(*ast.ParenExpr)
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if !ok {
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return e
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}
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e = p.X
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}
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}
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@ -98,6 +98,12 @@ Flag: -atomic
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Common mistaken usages of the sync/atomic package.
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Boolean conditions
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Flag: -bool
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Mistakes involving boolean operators.
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Build tags
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Flag: -buildtags
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113
cmd/vet/testdata/bool.go
vendored
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113
cmd/vet/testdata/bool.go
vendored
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@ -0,0 +1,113 @@
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file contains tests for the bool checker.
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package testdata
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import "io"
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func RatherStupidConditions() {
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var f, g func() int
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if f() == 0 || f() == 0 { // OK f might have side effects
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}
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if v, w := f(), g(); v == w || v == w { // ERROR "redundant or: v == w || v == w"
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}
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_ = f == nil || f == nil // ERROR "redundant or: f == nil || f == nil"
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_ = i == byte(1) || i == byte(1) // TODO conversions are treated as if they may have side effects
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var c chan int
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_ = 0 == <-c || 0 == <-c // OK subsequent receives may yield different values
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for i, j := <-c, <-c; i == j || i == j; i, j = <-c, <-c { // ERROR "redundant or: i == j || i == j"
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}
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var i, j, k int
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_ = i+1 == 1 || i+1 == 1 // ERROR "redundant or: i\+1 == 1 || i\+1 == 1"
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_ = i == 1 || j+1 == i || i == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || i == 1 || f() == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || f() == 1 || i == 1 // OK f may alter i as a side effect
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_ = f() == 1 || i == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
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// Test partition edge cases
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_ = f() == 1 || i == 1 || i == 1 || j == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = f() == 1 || j == 1 || i == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || f() == 1 || i == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || i == 1 || f() == 1 || i == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || i == 1 || j == 1 || f() == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = j == 1 || i == 1 || i == 1 || f() == 1 // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || f() == 1 || f() == 1 || i == 1
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_ = i == 1 || (i == 1 || i == 2) // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || (f() == 1 || i == 1) // OK f may alter i as a side effect
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_ = i == 1 || (i == 1 || f() == 1) // ERROR "redundant or: i == 1 || i == 1"
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_ = i == 1 || (i == 2 || (i == 1 || i == 3)) // ERROR "redundant or: i == 1 || i == 1"
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var a, b bool
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_ = i == 1 || (a || (i == 1 || b)) // ERROR "redundant or: i == 1 || i == 1"
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// Check that all redundant ors are flagged
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_ = j == 0 ||
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i == 1 ||
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f() == 1 ||
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j == 0 || // ERROR "redundant or: j == 0 || j == 0"
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i == 1 || // ERROR "redundant or: i == 1 || i == 1"
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i == 1 || // ERROR "redundant or: i == 1 || i == 1"
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i == 1 ||
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j == 0 ||
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k == 0
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_ = i == 1*2*3 || i == 1*2*3 // ERROR "redundant or: i == 1\*2\*3 || i == 1\*2\*3"
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// These test that redundant, suspect expressions do not trigger multiple errors.
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_ = i != 0 || i != 0 // ERROR "redundant or: i != 0 || i != 0"
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_ = i == 0 && i == 0 // ERROR "redundant and: i == 0 && i == 0"
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// and is dual to or; check the basics and
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// let the or tests pull the rest of the weight.
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_ = 0 != <-c && 0 != <-c // OK subsequent receives may yield different values
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_ = f() != 0 && f() != 0 // OK f might have side effects
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_ = f != nil && f != nil // ERROR "redundant and: f != nil && f != nil"
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_ = i != 1 && i != 1 && f() != 1 // ERROR "redundant and: i != 1 && i != 1"
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_ = i != 1 && f() != 1 && i != 1 // OK f may alter i as a side effect
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_ = f() != 1 && i != 1 && i != 1 // ERROR "redundant and: i != 1 && i != 1"
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}
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func RoyallySuspectConditions() {
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var i, j int
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_ = i == 0 || i == 1 // OK
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_ = i != 0 || i != 1 // ERROR "suspect or: i != 0 || i != 1"
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_ = i != 0 || 1 != i // ERROR "suspect or: i != 0 || 1 != i"
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_ = 0 != i || 1 != i // ERROR "suspect or: 0 != i || 1 != i"
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_ = 0 != i || i != 1 // ERROR "suspect or: 0 != i || i != 1"
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_ = (0 != i) || i != 1 // ERROR "suspect or: 0 != i || i != 1"
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_ = i+3 != 7 || j+5 == 0 || i+3 != 9 // ERROR "suspect or: i\+3 != 7 || i\+3 != 9"
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_ = i != 0 || j == 0 || i != 1 // ERROR "suspect or: i != 0 || i != 1"
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_ = i != 0 || i != 1<<4 // ERROR "suspect or: i != 0 || i != 1<<4"
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_ = i != 0 || j != 0
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_ = 0 != i || 0 != j
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var s string
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_ = s != "one" || s != "the other" // ERROR "suspect or: s != .one. || s != .the other."
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_ = "et" != "alii" || "et" != "cetera" // ERROR "suspect or: .et. != .alii. || .et. != .cetera."
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_ = "me gustas" != "tu" || "le gustas" != "tu" // OK we could catch this case, but it's not worth the code
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var err error
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_ = err != nil || err != io.EOF // TODO catch this case?
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// Sanity check and.
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_ = i != 0 && i != 1 // OK
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_ = i == 0 && i == 1 // ERROR "suspect and: i == 0 && i == 1"
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_ = i == 0 && 1 == i // ERROR "suspect and: i == 0 && 1 == i"
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_ = 0 == i && 1 == i // ERROR "suspect and: 0 == i && 1 == i"
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_ = 0 == i && i == 1 // ERROR "suspect and: 0 == i && i == 1"
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}
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