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// Copyright 2010 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 printf-checker.
package main
import (
"bytes"
"flag"
"go/ast"
"go/constant"
"go/token"
"go/types"
"strconv"
"strings"
"unicode/utf8"
)
var printfuncs = flag.String("printfuncs", "", "comma-separated list of print function names to check")
func init() {
register("printf",
"check printf-like invocations",
checkFmtPrintfCall,
funcDecl, callExpr)
}
func initPrintFlags() {
if *printfuncs == "" {
return
}
for _, name := range strings.Split(*printfuncs, ",") {
if len(name) == 0 {
flag.Usage()
}
// Backwards compatibility: skip optional first argument
// index after the colon.
if colon := strings.LastIndex(name, ":"); colon > 0 {
name = name[:colon]
}
name = strings.ToLower(name)
if name[len(name)-1] == 'f' {
isFormattedPrint[name] = true
} else {
isPrint[name] = true
}
}
}
// isFormattedPrint records the formatted-print functions. Names are
// lower-cased so the lookup is case insensitive.
var isFormattedPrint = map[string]bool{
"errorf": true,
"fatalf": true,
"fprintf": true,
"logf": true,
"panicf": true,
"printf": true,
"sprintf": true,
}
// isPrint records the unformatted-print functions. Names are lower-cased
// so the lookup is case insensitive.
var isPrint = map[string]bool{
"error": true,
"fatal": true,
"fprint": true,
"fprintln": true,
"log": true,
"panic": true,
"panicln": true,
"print": true,
"println": true,
"sprint": true,
"sprintln": true,
}
// formatString returns the format string argument and its index within
// the given printf-like call expression.
//
// The last parameter before variadic arguments is assumed to be
// a format string.
//
// The first string literal or string constant is assumed to be a format string
// if the call's signature cannot be determined.
//
// If it cannot find any format string parameter, it returns ("", -1).
func formatString(f *File, call *ast.CallExpr) (string, int) {
typ := f.pkg.types[call.Fun].Type
if typ != nil {
if sig, ok := typ.(*types.Signature); ok {
if !sig.Variadic() {
// Skip checking non-variadic functions
return "", -1
}
idx := sig.Params().Len() - 2
if idx < 0 {
// Skip checking variadic functions without
// fixed arguments.
return "", -1
}
s, ok := stringLiteralArg(f, call, idx)
if !ok {
// The last argument before variadic args isn't a string
return "", -1
}
return s, idx
}
}
// Cannot determine call's signature. Fallback to scanning for the first
// string argument in the call
for idx := range call.Args {
if s, ok := stringLiteralArg(f, call, idx); ok {
return s, idx
}
}
return "", -1
}
// stringLiteralArg returns call's string constant argument at the index idx.
//
// ("", false) is returned if call's argument at the index idx isn't a string
// literal.
func stringLiteralArg(f *File, call *ast.CallExpr, idx int) (string, bool) {
if idx >= len(call.Args) {
return "", false
}
arg := call.Args[idx]
lit := f.pkg.types[arg].Value
if lit != nil && lit.Kind() == constant.String {
return constant.StringVal(lit), true
}
return "", false
}
// checkCall triggers the print-specific checks if the call invokes a print function.
func checkFmtPrintfCall(f *File, node ast.Node) {
if d, ok := node.(*ast.FuncDecl); ok && isStringer(f, d) {
// Remember we saw this.
if f.stringers == nil {
f.stringers = make(map[*ast.Object]bool)
}
if l := d.Recv.List; len(l) == 1 {
if n := l[0].Names; len(n) == 1 {
f.stringers[n[0].Obj] = true
}
}
return
}
call, ok := node.(*ast.CallExpr)
if !ok {
return
}
var Name string
switch x := call.Fun.(type) {
case *ast.Ident:
Name = x.Name
case *ast.SelectorExpr:
Name = x.Sel.Name
default:
return
}
name := strings.ToLower(Name)
if _, ok := isFormattedPrint[name]; ok {
f.checkPrintf(call, Name)
return
}
if _, ok := isPrint[name]; ok {
f.checkPrint(call, Name)
return
}
}
// isStringer returns true if the provided declaration is a "String() string"
// method, an implementation of fmt.Stringer.
func isStringer(f *File, d *ast.FuncDecl) bool {
return d.Recv != nil && d.Name.Name == "String" && d.Type.Results != nil &&
len(d.Type.Params.List) == 0 && len(d.Type.Results.List) == 1 &&
f.pkg.types[d.Type.Results.List[0].Type].Type == types.Typ[types.String]
}
// formatState holds the parsed representation of a printf directive such as "%3.*[4]d".
// It is constructed by parsePrintfVerb.
type formatState struct {
verb rune // the format verb: 'd' for "%d"
format string // the full format directive from % through verb, "%.3d".
name string // Printf, Sprintf etc.
flags []byte // the list of # + etc.
argNums []int // the successive argument numbers that are consumed, adjusted to refer to actual arg in call
indexed bool // whether an indexing expression appears: %[1]d.
firstArg int // Index of first argument after the format in the Printf call.
// Used only during parse.
file *File
call *ast.CallExpr
argNum int // Which argument we're expecting to format now.
indexPending bool // Whether we have an indexed argument that has not resolved.
nbytes int // number of bytes of the format string consumed.
}
// checkPrintf checks a call to a formatted print routine such as Printf.
func (f *File) checkPrintf(call *ast.CallExpr, name string) {
format, idx := formatString(f, call)
if idx < 0 {
if *verbose {
f.Warn(call.Pos(), "can't check non-constant format in call to", name)
}
return
}
firstArg := idx + 1 // Arguments are immediately after format string.
if !strings.Contains(format, "%") {
if len(call.Args) > firstArg {
f.Badf(call.Pos(), "no formatting directive in %s call", name)
}
return
}
// Hard part: check formats against args.
argNum := firstArg
indexed := false
for i, w := 0, 0; i < len(format); i += w {
w = 1
if format[i] == '%' {
state := f.parsePrintfVerb(call, name, format[i:], firstArg, argNum)
if state == nil {
return
}
w = len(state.format)
if state.indexed {
indexed = true
}
if !f.okPrintfArg(call, state) { // One error per format is enough.
return
}
if len(state.argNums) > 0 {
// Continue with the next sequential argument.
argNum = state.argNums[len(state.argNums)-1] + 1
}
}
}
// Dotdotdot is hard.
if call.Ellipsis.IsValid() && argNum >= len(call.Args)-1 {
return
}
// If the arguments were direct indexed, we assume the programmer knows what's up.
// Otherwise, there should be no leftover arguments.
if !indexed && argNum != len(call.Args) {
expect := argNum - firstArg
numArgs := len(call.Args) - firstArg
f.Badf(call.Pos(), "wrong number of args for format in %s call: %d needed but %d args", name, expect, numArgs)
}
}
// parseFlags accepts any printf flags.
func (s *formatState) parseFlags() {
for s.nbytes < len(s.format) {
switch c := s.format[s.nbytes]; c {
case '#', '0', '+', '-', ' ':
s.flags = append(s.flags, c)
s.nbytes++
default:
return
}
}
}
// scanNum advances through a decimal number if present.
func (s *formatState) scanNum() {
for ; s.nbytes < len(s.format); s.nbytes++ {
c := s.format[s.nbytes]
if c < '0' || '9' < c {
return
}
}
}
// parseIndex scans an index expression. It returns false if there is a syntax error.
func (s *formatState) parseIndex() bool {
if s.nbytes == len(s.format) || s.format[s.nbytes] != '[' {
return true
}
// Argument index present.
s.indexed = true
s.nbytes++ // skip '['
start := s.nbytes
s.scanNum()
if s.nbytes == len(s.format) || s.nbytes == start || s.format[s.nbytes] != ']' {
s.file.Badf(s.call.Pos(), "illegal syntax for printf argument index")
return false
}
arg32, err := strconv.ParseInt(s.format[start:s.nbytes], 10, 32)
if err != nil {
s.file.Badf(s.call.Pos(), "illegal syntax for printf argument index: %s", err)
return false
}
s.nbytes++ // skip ']'
arg := int(arg32)
arg += s.firstArg - 1 // We want to zero-index the actual arguments.
s.argNum = arg
s.indexPending = true
return true
}
// parseNum scans a width or precision (or *). It returns false if there's a bad index expression.
func (s *formatState) parseNum() bool {
if s.nbytes < len(s.format) && s.format[s.nbytes] == '*' {
if s.indexPending { // Absorb it.
s.indexPending = false
}
s.nbytes++
s.argNums = append(s.argNums, s.argNum)
s.argNum++
} else {
s.scanNum()
}
return true
}
// parsePrecision scans for a precision. It returns false if there's a bad index expression.
func (s *formatState) parsePrecision() bool {
// If there's a period, there may be a precision.
if s.nbytes < len(s.format) && s.format[s.nbytes] == '.' {
s.flags = append(s.flags, '.') // Treat precision as a flag.
s.nbytes++
if !s.parseIndex() {
return false
}
if !s.parseNum() {
return false
}
}
return true
}
// parsePrintfVerb looks the formatting directive that begins the format string
// and returns a formatState that encodes what the directive wants, without looking
// at the actual arguments present in the call. The result is nil if there is an error.
func (f *File) parsePrintfVerb(call *ast.CallExpr, name, format string, firstArg, argNum int) *formatState {
state := &formatState{
format: format,
name: name,
flags: make([]byte, 0, 5),
argNum: argNum,
argNums: make([]int, 0, 1),
nbytes: 1, // There's guaranteed to be a percent sign.
indexed: false,
firstArg: firstArg,
file: f,
call: call,
}
// There may be flags.
state.parseFlags()
indexPending := false
// There may be an index.
if !state.parseIndex() {
return nil
}
// There may be a width.
if !state.parseNum() {
return nil
}
// There may be a precision.
if !state.parsePrecision() {
return nil
}
// Now a verb, possibly prefixed by an index (which we may already have).
if !indexPending && !state.parseIndex() {
return nil
}
if state.nbytes == len(state.format) {
f.Badf(call.Pos(), "missing verb at end of format string in %s call", name)
return nil
}
verb, w := utf8.DecodeRuneInString(state.format[state.nbytes:])
state.verb = verb
state.nbytes += w
if verb != '%' {
state.argNums = append(state.argNums, state.argNum)
}
state.format = state.format[:state.nbytes]
return state
}
// printfArgType encodes the types of expressions a printf verb accepts. It is a bitmask.
type printfArgType int
const (
argBool printfArgType = 1 << iota
argInt
argRune
argString
argFloat
argComplex
argPointer
anyType printfArgType = ^0
)
type printVerb struct {
verb rune // User may provide verb through Formatter; could be a rune.
flags string // known flags are all ASCII
typ printfArgType
}
// Common flag sets for printf verbs.
const (
noFlag = ""
numFlag = " -+.0"
sharpNumFlag = " -+.0#"
allFlags = " -+.0#"
)
// printVerbs identifies which flags are known to printf for each verb.
// TODO: A type that implements Formatter may do what it wants, and vet
// will complain incorrectly.
var printVerbs = []printVerb{
// '-' is a width modifier, always valid.
// '.' is a precision for float, max width for strings.
// '+' is required sign for numbers, Go format for %v.
// '#' is alternate format for several verbs.
// ' ' is spacer for numbers
{'%', noFlag, 0},
{'b', numFlag, argInt | argFloat | argComplex},
{'c', "-", argRune | argInt},
{'d', numFlag, argInt},
{'e', numFlag, argFloat | argComplex},
{'E', numFlag, argFloat | argComplex},
{'f', numFlag, argFloat | argComplex},
{'F', numFlag, argFloat | argComplex},
{'g', numFlag, argFloat | argComplex},
{'G', numFlag, argFloat | argComplex},
{'o', sharpNumFlag, argInt},
{'p', "-#", argPointer},
{'q', " -+.0#", argRune | argInt | argString},
{'s', " -+.0", argString},
{'t', "-", argBool},
{'T', "-", anyType},
{'U', "-#", argRune | argInt},
{'v', allFlags, anyType},
{'x', sharpNumFlag, argRune | argInt | argString},
{'X', sharpNumFlag, argRune | argInt | argString},
}
// okPrintfArg compares the formatState to the arguments actually present,
// reporting any discrepancies it can discern. If the final argument is ellipsissed,
// there's little it can do for that.
func (f *File) okPrintfArg(call *ast.CallExpr, state *formatState) (ok bool) {
var v printVerb
found := false
// Linear scan is fast enough for a small list.
for _, v = range printVerbs {
if v.verb == state.verb {
found = true
break
}
}
if !found {
f.Badf(call.Pos(), "unrecognized printf verb %q", state.verb)
return false
}
for _, flag := range state.flags {
if !strings.ContainsRune(v.flags, rune(flag)) {
f.Badf(call.Pos(), "unrecognized printf flag for verb %q: %q", state.verb, flag)
return false
}
}
// Verb is good. If len(state.argNums)>trueArgs, we have something like %.*s and all
// but the final arg must be an integer.
trueArgs := 1
if state.verb == '%' {
trueArgs = 0
}
nargs := len(state.argNums)
for i := 0; i < nargs-trueArgs; i++ {
argNum := state.argNums[i]
if !f.argCanBeChecked(call, i, true, state) {
return
}
arg := call.Args[argNum]
if !f.matchArgType(argInt, nil, arg) {
f.Badf(call.Pos(), "arg %s for * in printf format not of type int", f.gofmt(arg))
return false
}
}
if state.verb == '%' {
return true
}
argNum := state.argNums[len(state.argNums)-1]
if !f.argCanBeChecked(call, len(state.argNums)-1, false, state) {
return false
}
arg := call.Args[argNum]
if f.isFunctionValue(arg) && state.verb != 'p' && state.verb != 'T' {
f.Badf(call.Pos(), "arg %s in printf call is a function value, not a function call", f.gofmt(arg))
return false
}
if !f.matchArgType(v.typ, nil, arg) {
typeString := ""
if typ := f.pkg.types[arg].Type; typ != nil {
typeString = typ.String()
}
f.Badf(call.Pos(), "arg %s for printf verb %%%c of wrong type: %s", f.gofmt(arg), state.verb, typeString)
return false
}
if v.typ&argString != 0 && v.verb != 'T' && !bytes.Contains(state.flags, []byte{'#'}) && f.recursiveStringer(arg) {
f.Badf(call.Pos(), "arg %s for printf causes recursive call to String method", f.gofmt(arg))
return false
}
return true
}
// recursiveStringer reports whether the provided argument is r or &r for the
// fmt.Stringer receiver identifier r.
func (f *File) recursiveStringer(e ast.Expr) bool {
if len(f.stringers) == 0 {
return false
}
var obj *ast.Object
switch e := e.(type) {
case *ast.Ident:
obj = e.Obj
case *ast.UnaryExpr:
if id, ok := e.X.(*ast.Ident); ok && e.Op == token.AND {
obj = id.Obj
}
}
// It's unlikely to be a recursive stringer if it has a Format method.
if typ := f.pkg.types[e].Type; typ != nil {
// Not a perfect match; see issue 6259.
if f.hasMethod(typ, "Format") {
return false
}
}
// We compare the underlying Object, which checks that the identifier
// is the one we declared as the receiver for the String method in
// which this printf appears.
return f.stringers[obj]
}
// isFunctionValue reports whether the expression is a function as opposed to a function call.
// It is almost always a mistake to print a function value.
func (f *File) isFunctionValue(e ast.Expr) bool {
if typ := f.pkg.types[e].Type; typ != nil {
_, ok := typ.(*types.Signature)
return ok
}
return false
}
// argCanBeChecked reports whether the specified argument is statically present;
// it may be beyond the list of arguments or in a terminal slice... argument, which
// means we can't see it.
func (f *File) argCanBeChecked(call *ast.CallExpr, formatArg int, isStar bool, state *formatState) bool {
argNum := state.argNums[formatArg]
if argNum < 0 {
// Shouldn't happen, so catch it with prejudice.
panic("negative arg num")
}
if argNum == 0 {
f.Badf(call.Pos(), `index value [0] for %s("%s"); indexes start at 1`, state.name, state.format)
return false
}
if argNum < len(call.Args)-1 {
return true // Always OK.
}
if call.Ellipsis.IsValid() {
return false // We just can't tell; there could be many more arguments.
}
if argNum < len(call.Args) {
return true
}
// There are bad indexes in the format or there are fewer arguments than the format needs.
// This is the argument number relative to the format: Printf("%s", "hi") will give 1 for the "hi".
arg := argNum - state.firstArg + 1 // People think of arguments as 1-indexed.
f.Badf(call.Pos(), `missing argument for %s("%s"): format reads arg %d, have only %d args`, state.name, state.format, arg, len(call.Args)-state.firstArg)
return false
}
// checkPrint checks a call to an unformatted print routine such as Println.
func (f *File) checkPrint(call *ast.CallExpr, name string) {
firstArg := 0
typ := f.pkg.types[call.Fun].Type
if typ == nil {
// Skip checking functions with unknown type.
return
}
if sig, ok := typ.(*types.Signature); ok {
if !sig.Variadic() {
// Skip checking non-variadic functions.
return
}
params := sig.Params()
firstArg = params.Len() - 1
typ := params.At(firstArg).Type()
typ = typ.(*types.Slice).Elem()
it, ok := typ.(*types.Interface)
if !ok || !it.Empty() {
// Skip variadic functions accepting non-interface{} args.
return
}
}
args := call.Args
if len(args) <= firstArg {
// Skip calls without variadic args.
return
}
args = args[firstArg:]
// check for Println(os.Stderr, ...)
if firstArg == 0 {
if sel, ok := args[0].(*ast.SelectorExpr); ok {
if x, ok := sel.X.(*ast.Ident); ok {
if x.Name == "os" && strings.HasPrefix(sel.Sel.Name, "Std") {
f.Badf(call.Pos(), "first argument to %s is %s.%s", name, x.Name, sel.Sel.Name)
}
}
}
}
arg := args[0]
if lit, ok := arg.(*ast.BasicLit); ok && lit.Kind == token.STRING {
if strings.Contains(lit.Value, "%") {
f.Badf(call.Pos(), "possible formatting directive in %s call", name)
}
}
if strings.HasSuffix(name, "ln") {
// The last item, if a string, should not have a newline.
arg = args[len(args)-1]
if lit, ok := arg.(*ast.BasicLit); ok && lit.Kind == token.STRING {
if strings.HasSuffix(lit.Value, `\n"`) {
f.Badf(call.Pos(), "%s call ends with newline", name)
}
}
}
for _, arg := range args {
if f.isFunctionValue(arg) {
f.Badf(call.Pos(), "arg %s in %s call is a function value, not a function call", f.gofmt(arg), name)
}
if f.recursiveStringer(arg) {
f.Badf(call.Pos(), "arg %s in %s call causes recursive call to String method", f.gofmt(arg), name)
}
}
}