QRegularExpression: fix matching over null/empty QString(View)

An empty QString(View) is allowed to have nullptr as its data pointer
(of course, only if its size is 0). This wasn't properly
checked in QRegularExpression, which passed such nullptr to
PCRE, and that resulted in PCRE raising an error (PCRE_ERROR_NULL).
Detect this case and pass a dummy pointer to keep PCRE happy.

Fixing and testing this in turn exposed a problem with QStringView
support in QRegularExpression when used over a null QString: the
code is supposed to use the QStringView(QString) constructor and NOT
qToStringViewIgnoringNull. That's because QRE distinguishes null
and empty subjects; when using qToStringViewIgnoringNull over
a null QString, one gets a non-null QStringView (!). Again, this in
turn exposed a problem with a QRegularExpression autotest that assumed
that a null match could only mean "no match" (instead, it can happen at
position 0 of a null QString(View)).

Change-Id: Ifb3cf14dec42ce76fcdbcb07ea1d80784d52ef65
Pick-to: 6.1 6.2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 23 insertions, 2 deletions

diff --git a/tests/auto/corelib/text/qregularexpression/tst_qregularexpression.cpp b/tests/auto/corelib/text/qregularexpression/tst_qregularexpression.cpp
index f2fe382521..48d4de0aa4 100644
--- a/tests/auto/corelib/text/qregularexpression/tst_qregularexpression.cpp
+++ b/tests/auto/corelib/text/qregularexpression/tst_qregularexpression.cpp
@@ -252,8 +252,11 @@ void consistencyCheck(const QRegularExpressionMatch &match)
                     QVERIFY((endPos - startPos) == length);
                     QVERIFY(captured == capturedView);
                 } else {
-                    QVERIFY(startPos == -1);
-                    QVERIFY(endPos == -1);
+                    // A null capture can either mean no capture at all,
+                    // or capture of length 0 over a null subject.
+                    QVERIFY(startPos == endPos);
+                    QVERIFY(((startPos == -1) && (endPos == -1)) // no capture
+                            || ((startPos == 0) && (endPos == 0))); // null subject
                     QVERIFY((endPos - startPos) == length);
                     QVERIFY(capturedView.isNull());
                 }
@@ -860,6 +863,24 @@ void tst_QRegularExpression::normalMatch_data()
                              << QRegularExpression::MatchOptions(QRegularExpression::NoMatchOption)
                              << m;
 
+    m.clear();
+    m.isValid = true; m.hasMatch = true;
+    m.captured << QString();
+    QTest::newRow("empty-in-null-string") << QRegularExpression("")
+                             << QString()
+                             << qsizetype(0)
+                             << QRegularExpression::MatchOptions(QRegularExpression::NoMatchOption)
+                             << m;
+
+    m.clear();
+    m.isValid = true; m.hasMatch = true;
+    m.captured << QString("");
+    QTest::newRow("empty-in-empty-string") << QRegularExpression("")
+                             << QString("")
+                             << qsizetype(0)
+                             << QRegularExpression::MatchOptions(QRegularExpression::NoMatchOption)
+                             << m;
+
     // non existing names for capturing groups
     m.clear();
     m.isValid = true; m.hasMatch = true;