Utils: Fix replace function in SmallString

You need to allocate the memory before you replace a smaller text with
a larger one. It has some overhead because you go two times over the text
but it is anyway not designed for a large text.

Change-Id: I2f56f1300a5daf9e26632b5b0667023a09ff4bd2
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/smallstring.h

@@ -761,6 +761,27 @@ unittest_public:
         return cacheLineBlocks * cacheLineSize;
     }
 
+    size_type countOccurrence(SmallStringView text)
+    {
+        auto found = begin();
+
+        size_type count = 0;
+
+        while (true) {
+            found = std::search(found,
+                                end(),
+                                text.begin(),
+                                text.end());
+            if (found == end())
+                break;
+
+            ++count;
+            found += text.size();
+        }
+
+        return count;
+    }
+
 private:
     BasicSmallString(Internal::StringDataLayout<Size> data) noexcept
         : m_data(data)
@@ -883,7 +904,6 @@ private:
             std::memcpy(replacementTextStartPosition.data(), toText.data(), toText.size());
         } else {
             size_type newSize = size() + sizeDifference;
-            reserve(optimalCapacity(newSize));
             setSize(newSize);
             at(newSize) = 0;
         }
@@ -896,8 +916,16 @@ private:
         size_type sizeDifference = 0;
         size_type startIndex = 0;
 
+        size_type replacementTextSizeDifference = toText.size() - fromText.size();
+        size_type occurrences = countOccurrence(fromText);
+        size_type newSize = size() + (replacementTextSizeDifference * occurrences);
+
+        if (occurrences > 0) {
+            reserve(optimalCapacity(newSize));
+
             replaceLargerSizedRecursive(startIndex, fromText, toText, sizeDifference);
         }
+    }
 
     void setSize(size_type size)
     {

tests/unit/unittest/smallstring-test.cpp

@@ -753,6 +753,42 @@ TEST(SmallString, Clear)
     ASSERT_TRUE(text.isEmpty());
 }
 
+TEST(SmallString, NoOccurrencesForEmptyText)
+{
+    SmallString text;
+
+    auto occurrences = text.countOccurrence("text");
+
+    ASSERT_THAT(occurrences, 0);
+}
+
+TEST(SmallString, NoOccurrencesInText)
+{
+    SmallString text("here is some text, here is some text, here is some text");
+
+    auto occurrences = text.countOccurrence("texts");
+
+    ASSERT_THAT(occurrences, 0);
+}
+
+TEST(SmallString, SomeOccurrences)
+{
+    SmallString text("here is some text, here is some text, here is some text");
+
+    auto occurrences = text.countOccurrence("text");
+
+    ASSERT_THAT(occurrences, 3);
+}
+
+TEST(SmallString, SomeMoreOccurrences)
+{
+    SmallString text("texttexttext");
+
+    auto occurrences = text.countOccurrence("text");
+
+    ASSERT_THAT(occurrences, 3);
+}
+
 TEST(SmallString, ReplaceWithCharacter)
 {
     SmallString text("here is some text, here is some text, here is some text");