QRegularExpression: coalesce consecutive * tokens in wildcards

When converting a wildcard into a regexp, convert a series of
consecutive '*' tokens in just one '.*' (instead of a series of '.*').
The pattern matched is the same, but we reduce the effects of a
possible catastrophic backtracking. I'm not actually sure whether
PCRE optimizes this case out of its own or it doesn't; Perl appears
not to.

Change-Id: Ia83336391593d56cf6d8332c96649a034a83a15b
Pick-to: 6.8
Fixes: QTBUG-127672
Reviewed-by: Thiago Macieira <[email protected]>

src/corelib/text/qregularexpression.cpp

@@ -1964,6 +1964,9 @@ QString QRegularExpression::wildcardToRegularExpression(QStringView pattern, Wil
         switch (c.unicode()) {
         case '*':
             rx += settings.starEscape;
+            // Coalesce sequences of *
+            while (i < wclen && wc[i] == u'*')
+                ++i;
             break;
         case '?':
             rx += settings.questionMarkEscape;

tests/auto/corelib/text/qregularexpression/tst_qregularexpression.cpp

@@ -2486,6 +2486,30 @@ void tst_QRegularExpression::wildcard_data()
     addRow("foo*bar", "foo\nbar", true, true);
     addRow("foo*bar", "foo\r\nbar", true, true);
 
+    addRow("foo**********bar", "foo/fie/baz/bar", false, true);
+    addRow("foo**********bar", "foo bar bar test bar bar bar", true, true);
+    addRow("foo**********bar", "foo\tbar", true, true);
+    addRow("foo**********bar", "foo\nbar", true, true);
+    addRow("foo**********bar", "foo\r\nbar", true, true);
+
+    addRow("foo**********bar", "foo/fie/baz/baz", false, false);
+    addRow("foo**********bar", "foo bar bar test bar bar baz", false, false);
+    addRow("foo**********bar", "foo\tbaz", false, false);
+    addRow("foo**********bar", "foo\nbaz", false, false);
+    addRow("foo**********bar", "foo\r\nbaz", false, false);
+
+    addRow("foo*****x*****bar", "foo/fie/bax/bar", false, true);
+    addRow("foo*****x*****bar", "foo bar bax test bar bar bar", true, true);
+    addRow("foo*****x*****bar", "foo\tbar foo\tbax foo\tbar foo\tbar", true, true);
+    addRow("foo*****x*****bar", "foo\nx\nbar", true, true);
+    addRow("foo*****x*****bar", "foo\r\nxbar", true, true);
+
+    addRow("foo*****x*****bar", "foo/fie/baz/bar", false, false);
+    addRow("foo*****x*****bar", "foo bar baz test bar bar bar", false, false);
+    addRow("foo*****x*****bar", "foo\tbar foo\tbar foo\tbar foo\tbar", false, false);
+    addRow("foo*****x*****bar", "foo\nbar", false, false);
+    addRow("foo*****x*****bar", "foo\r\nbar", false, false);
+
     // different anchor modes
     addRow("foo", "afoob", false, false, true);
     addRow("foo", "afoob", true, true, false);