QRegularExpression: fix matching over QStringRefs

Playing with the offset argument of pcre_exec is not equivalent to
adjusting the pointer to the subject string. In particular, PCRE
can go behind the offset to check for lookbehinds or "transition"
metacharacters (\b, \B, etc.).

This made the code that deals with QStringRefs not matching in behavior
with the corresponding code dealing with QStrings. For instance,

   QString subject("Miss");
   QRegularExpression re("(?<=M)iss");
   re.match(subject.mid(1));           // doesn't match
   re.match(subject.midRef(1));        // matches!!!

Instead, actually adjust the pointer to the subject string so that
the behavior is identical. A broken test that relied on the
equivalence is also removed.

Change-Id: If96333241ef59621d7f5a6a170ebd0a186844874
Reviewed-by: Volker Krause <volker.krause@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 21 insertions, 24 deletions

diff --git a/src/corelib/tools/qregularexpression.cpp b/src/corelib/tools/qregularexpression.cpp
index 2e3c2ca79f..070e68154f 100644
--- a/src/corelib/tools/qregularexpression.cpp
+++ b/src/corelib/tools/qregularexpression.cpp
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
-** Copyright (C) 2012 Giuseppe D'Angelo <dangelog@gmail.com>.
-** Copyright (C) 2012 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
+** Copyright (C) 2015 Giuseppe D'Angelo <dangelog@gmail.com>.
+** Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
 ** Copyright (C) 2015 The Qt Company Ltd.
 ** Contact: http://www.qt.io/licensing/
 **
@@ -1325,48 +1325,45 @@ QRegularExpressionMatchPrivate *QRegularExpressionPrivate::doMatch(const QString
     int * const captureOffsets = priv->capturedOffsets.data();
     const int captureOffsetsCount = priv->capturedOffsets.size();
 
-    int realOffset = offset + subjectStart;
-    const int realSubjectLength = subjectLength + subjectStart;
-
-    const unsigned short * const subjectUtf16 = subject.utf16();
+    const unsigned short * const subjectUtf16 = subject.utf16() + subjectStart;
 
     int result;
 
     if (!previousMatchWasEmpty) {
         result = pcre16SafeExec(compiledPattern, currentStudyData,
-                                subjectUtf16, realSubjectLength,
-                                realOffset, pcreOptions,
+                                subjectUtf16, subjectLength,
+                                offset, pcreOptions,
                                 captureOffsets, captureOffsetsCount);
     } else {
         result = pcre16SafeExec(compiledPattern, currentStudyData,
-                                subjectUtf16, realSubjectLength,
-                                realOffset, pcreOptions | PCRE_NOTEMPTY_ATSTART | PCRE_ANCHORED,
+                                subjectUtf16, subjectLength,
+                                offset, pcreOptions | PCRE_NOTEMPTY_ATSTART | PCRE_ANCHORED,
                                 captureOffsets, captureOffsetsCount);
 
         if (result == PCRE_ERROR_NOMATCH) {
-            ++realOffset;
+            ++offset;
 
             if (usingCrLfNewlines
-                    && realOffset < realSubjectLength
-                    && subjectUtf16[realOffset - 1] == QLatin1Char('\r')
-                    && subjectUtf16[realOffset] == QLatin1Char('\n')) {
-                ++realOffset;
-            } else if (realOffset < realSubjectLength
-                       && QChar::isLowSurrogate(subjectUtf16[realOffset])) {
-                ++realOffset;
+                    && offset < subjectLength
+                    && subjectUtf16[offset - 1] == QLatin1Char('\r')
+                    && subjectUtf16[offset] == QLatin1Char('\n')) {
+                ++offset;
+            } else if (offset < subjectLength
+                       && QChar::isLowSurrogate(subjectUtf16[offset])) {
+                ++offset;
             }
 
             result = pcre16SafeExec(compiledPattern, currentStudyData,
-                                    subjectUtf16, realSubjectLength,
-                                    realOffset, pcreOptions,
+                                    subjectUtf16, subjectLength,
+                                    offset, pcreOptions,
                                     captureOffsets, captureOffsetsCount);
         }
     }
 
 #ifdef QREGULAREXPRESSION_DEBUG
     qDebug() << "Matching" <<  pattern << "against" << subject
-             << "starting at" << subjectStart << "len" << subjectLength << "real len" << realSubjectLength
-             << "offset" << offset << "real offset" << realOffset
+             << "starting at" << subjectStart << "len" << subjectLength
+             << "offset" << offset
              << matchType << matchOptions << previousMatchWasEmpty
              << "result" << result;
 #endif
@@ -2041,7 +2038,7 @@ QString QRegularExpressionMatch::captured(int nth) const
     if (start == -1) // didn't capture
         return QString();
 
-    return d->subject.mid(start, capturedLength(nth));
+    return d->subject.mid(start + d->subjectStart, capturedLength(nth));
 }
 
 /*!
@@ -2062,7 +2059,7 @@ QStringRef QRegularExpressionMatch::capturedRef(int nth) const
     if (start == -1) // didn't capture
         return QStringRef();
 
-    return d->subject.midRef(start, capturedLength(nth));
+    return d->subject.midRef(start + d->subjectStart, capturedLength(nth));
 }
 
 /*!