Fix logic error in QString::replace(ch, after, cs)

Coverage analysis showed that an if-branch marked "Q_LIKELY" was never
taken. It turns out the code was incorrect, but behaved correctly.
This patch fixes the logic and adds a unit test.

Pick-to: 5.15
Change-Id: I9b4ba76392b52f07b8e21188496e23f98dba95a9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 12 insertions, 1 deletions

diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 091f44736e..dd00456fb2 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -3382,7 +3382,7 @@ QString& QString::replace(QChar ch, const QString &after, Qt::CaseSensitivity cs
 
         replace_helper(indices, pos, 1, after.constData(), after.size());
 
-        if (Q_LIKELY(index == -1)) // Nothing left to replace
+        if (Q_LIKELY(index == size())) // Nothing left to replace
             break;
         // The call to replace_helper just moved what index points at:
         index += pos*(after.size() - 1);
diff --git a/tests/auto/corelib/text/qstring/tst_qstring.cpp b/tests/auto/corelib/text/qstring/tst_qstring.cpp
index 47470abd6f..e6d73c6ef1 100644
--- a/tests/auto/corelib/text/qstring/tst_qstring.cpp
+++ b/tests/auto/corelib/text/qstring/tst_qstring.cpp
@@ -2876,6 +2876,17 @@ void tst_QString::replace_string_extra()
         s.replace( QString("BBB"), smallReplacement );
         QCOMPARE( s, smallReplacement );
     }
+
+    {
+        QString s(QLatin1String("BBB"));
+        QString expected(QLatin1String("BBB"));
+        for (int i = 0; i < 1028; ++i) {
+            s.append("X");
+            expected.append("GXU");
+        }
+        s.replace(QChar('X'), "GXU");
+        QCOMPARE(s, expected);
+    }
 }
 
 void tst_QString::replace_regexp()