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QString: fix lifetime issues with QRegularExpression APIs 

QString has several functions taking a QRegularExpression: indexOf(),
contains(), and so on. Some of those have an out-argument of type
QRegularExpressionMatch, to report the details of the match (if any).
For instance:

  QRegularExpression re(...);
  QRegularExpressionMatch match;

  if (string.contains(re, &match))
    use(match);

The code used to route the implementation of these functions through
QStringView (which has the very same functions). This however opens
up a lifetime problem with temporary strings:

  if (getString().contains(re, &match))
    use(match); // match is dangling

Here `match` is dangling because it is referencing data into the
destroyed temporary -- nothing is keeping the string alive. This is
against the rules we've decided for Qt, and it's also asymmetric with
the corresponding code that uses QRegularExpression directly instead:

  match = re.match(getString());
  if (match.hasMatch())
    use(match); // not dangling

... although we've documented not to do this. (In light of the decision
we've made w.r.t. temporaries, the documentation is wrong anyways.)
Here QRE takes a copy of the string and stores it in the match object,
thus keeping it alive.

Hence, extend the implementation of the QString functions to keep a
(shallow) copy of the string. To keep the code shared as much as
possible with QStringView, in theory one could have a function taking a
std::variant<QString, QStringView> and that uses the currently active
member. However I've found that std::variant here creates some abysmal
codegen, so instead I went for a simpler approach -- pass a QStringView
and an optional pointer to a QString. Use the latter if it's loaded.

QStringView has some inline code that calls into exported functions, so
I can't change the signature of them without breaking BC; I'm instead
adding new unexported functions and a Qt 7 note to unify them.

Change-Id: I7c65885a84069d0fbb902dcc96ddff543ca84562
Fixes: QTBUG-103940
Pick-to: 6.2 6.3 6.4
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
bb10
Giuseppe D'Angelo 2022-07-06 02:20:38 +02:00
parent 54b276be0b
commit 6f852935e0
3 changed files with 87 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
src/corelib/text/qstring.cpp
View File

@ -4560,7 +4560,7 @@ qsizetype QString::count(QStringView str, Qt::CaseSensitivity cs) const
*/
qsizetype QString::indexOf(const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch) const
{
return QtPrivate::indexOf(QStringView(*this), re, from, rmatch);
return QtPrivate::indexOf(QStringView(*this), this, re, from, rmatch);
}
/*!
@ -4594,7 +4594,7 @@ qsizetype QString::indexOf(const QRegularExpression &re, qsizetype from, QRegula
*/
qsizetype QString::lastIndexOf(const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch) const
{
return QtPrivate::lastIndexOf(QStringView(*this), re, from, rmatch);
return QtPrivate::lastIndexOf(QStringView(*this), this, re, from, rmatch);
}
/*!
@ -4633,7 +4633,7 @@ qsizetype QString::lastIndexOf(const QRegularExpression &re, qsizetype from, QRe
bool QString::contains(const QRegularExpression &re, QRegularExpressionMatch *rmatch) const
{
return QtPrivate::contains(QStringView(*this), re, rmatch);
return QtPrivate::contains(QStringView(*this), this, re, rmatch);
}
/*!
@ -10798,14 +10798,16 @@ qsizetype QtPrivate::lastIndexOf(QLatin1StringView haystack, qsizetype from, QLa
}
#if QT_CONFIG(regularexpression)
qsizetype QtPrivate::indexOf(QStringView haystack, const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch)
qsizetype QtPrivate::indexOf(QStringView viewHaystack, const QString *stringHaystack, const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch)
{
if (!re.isValid()) {
qtWarnAboutInvalidRegularExpression(re.pattern(), "QString(View)::indexOf");
return -1;
}
QRegularExpressionMatch match = re.match(haystack, from);
QRegularExpressionMatch match = stringHaystack
? re.match(*stringHaystack, from)
: re.match(viewHaystack, from);
if (match.hasMatch()) {
const qsizetype ret = match.capturedStart();
if (rmatch)
@ -10816,15 +10818,22 @@ qsizetype QtPrivate::indexOf(QStringView haystack, const QRegularExpression &re,
return -1;
}
qsizetype QtPrivate::lastIndexOf(QStringView haystack, const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch)
qsizetype QtPrivate::indexOf(QStringView haystack, const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch)
{
return indexOf(haystack, nullptr, re, from, rmatch);
}
qsizetype QtPrivate::lastIndexOf(QStringView viewHaystack, const QString *stringHaystack, const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch)
{
if (!re.isValid()) {
qtWarnAboutInvalidRegularExpression(re.pattern(), "QString(View)::lastIndexOf");
return -1;
}
qsizetype endpos = (from < 0) ? (haystack.size() + from + 1) : (from + 1);
QRegularExpressionMatchIterator iterator = re.globalMatch(haystack);
qsizetype endpos = (from < 0) ? (viewHaystack.size() + from + 1) : (from + 1);
QRegularExpressionMatchIterator iterator = stringHaystack
? re.globalMatch(*stringHaystack)
: re.globalMatch(viewHaystack);
qsizetype lastIndex = -1;
while (iterator.hasNext()) {
QRegularExpressionMatch match = iterator.next();
@ -10841,19 +10850,31 @@ qsizetype QtPrivate::lastIndexOf(QStringView haystack, const QRegularExpression
return lastIndex;
}
bool QtPrivate::contains(QStringView haystack, const QRegularExpression &re, QRegularExpressionMatch *rmatch)
qsizetype QtPrivate::lastIndexOf(QStringView haystack, const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch)
{
return lastIndexOf(haystack, nullptr, re, from, rmatch);
}
bool QtPrivate::contains(QStringView viewHaystack, const QString *stringHaystack, const QRegularExpression &re, QRegularExpressionMatch *rmatch)
{
if (!re.isValid()) {
qtWarnAboutInvalidRegularExpression(re.pattern(), "QString(View)::contains");
return false;
}
QRegularExpressionMatch m = re.match(haystack);
QRegularExpressionMatch m = stringHaystack
? re.match(*stringHaystack)
: re.match(viewHaystack);
bool hasMatch = m.hasMatch();
if (hasMatch && rmatch)
*rmatch = std::move(m);
return hasMatch;
}
bool QtPrivate::contains(QStringView haystack, const QRegularExpression &re, QRegularExpressionMatch *rmatch)
{
return contains(haystack, nullptr, re, rmatch);
}
qsizetype QtPrivate::count(QStringView haystack, const QRegularExpression &re)
{
if (!re.isValid()) {

16
src/corelib/text/qstringalgorithms.h
View File

@ -69,14 +69,30 @@ namespace QtPrivate {
[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION qsizetype count(QLatin1StringView haystack, QChar needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
#if QT_CONFIG(regularexpression)
// ### Qt 7: unify these overloads;
// remove the ones taking only a QStringView, export the others, adjust callers
[[nodiscard]] qsizetype indexOf(QStringView viewHaystack,
const QString *stringHaystack,
const QRegularExpression &re,
qsizetype from = 0,
QRegularExpressionMatch *rmatch = nullptr);
[[nodiscard]] Q_CORE_EXPORT qsizetype indexOf(QStringView haystack,
const QRegularExpression &re,
qsizetype from = 0,
QRegularExpressionMatch *rmatch = nullptr);
[[nodiscard]] qsizetype lastIndexOf(QStringView viewHaystack,
const QString *stringHaystack,
const QRegularExpression &re,
qsizetype from = -1,
QRegularExpressionMatch *rmatch = nullptr);
[[nodiscard]] Q_CORE_EXPORT qsizetype lastIndexOf(QStringView haystack,
const QRegularExpression &re,
qsizetype from = -1,
QRegularExpressionMatch *rmatch = nullptr);
[[nodiscard]] bool contains(QStringView viewHaystack,
const QString *stringHaystack,
const QRegularExpression &re,
QRegularExpressionMatch *rmatch = nullptr);
[[nodiscard]] Q_CORE_EXPORT bool contains(QStringView haystack,
const QRegularExpression &re,
QRegularExpressionMatch *rmatch = nullptr);

40
tests/auto/corelib/text/qstring/tst_qstring.cpp
View File

@ -537,6 +537,7 @@ private slots:
#if QT_CONFIG(regularexpression)
void split_regularexpression_data();
void split_regularexpression();
void regularexpression_lifetime();
#endif
void fromUtf16_data();
void fromUtf16();
@ -6244,6 +6245,45 @@ void tst_QString::split_regularexpression()
split_regexp<QStringList, QRegularExpression>(string, pattern, result);
split_regexp<QList<QStringView>, QRegularExpression>(string, pattern, result);
}
// Test that rvalue strings (e.g. temporaries) are kept alive in
// QRegularExpression-related APIs
void tst_QString::regularexpression_lifetime()
{
const auto getString = [] {
// deliberately heap-allocated
return QString(QLatin1String("the quick brown fox jumps over the lazy dog"));
};
QRegularExpression re("\\w{5}");
{
QString s = getString();
QRegularExpressionMatch match;
const bool contains = std::move(s).contains(re, &match);
s.fill('X'); // NOLINT(bugprone-use-after-move)
QVERIFY(contains);
QCOMPARE(match.capturedView(), u"quick");
}
{
QString s = getString();
QRegularExpressionMatch match;
const auto index = std::move(s).indexOf(re, 0, &match);
s.fill('X'); // NOLINT(bugprone-use-after-move)
QCOMPARE(index, 4);
QCOMPARE(match.capturedView(), u"quick");
}
{
QString s = getString();
QRegularExpressionMatch match;
const auto lastIndex = std::move(s).lastIndexOf(re, &match);
s.fill('X'); // NOLINT(bugprone-use-after-move)
QCOMPARE(lastIndex, 20);
QCOMPARE(match.capturedView(), u"jumps");
}
}
#endif
void tst_QString::fromUtf16_data()