Clang: Add file cache

The database is using file path integer ids to handle file paths because
otherwise we would save many redundant data. This patch is improving it
further with the introduction of a database based file path cache. The
entries are now divided in a directory path and file name. This is quite
handy for directory based file watching.

Change-Id: I03f2e388e43f3d521d6bf8e39dfb95eb2309dc73
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/smallstring.h

@@ -145,25 +145,7 @@ public:
     BasicSmallString(std::initializer_list<Utils::SmallStringView> list)
         : m_data(Internal::StringDataLayout<Size>())
     {
-        std::size_t size = std::accumulate(list.begin(),
-                                           list.end(),
-                                           std::size_t(0),
-                                           [] (std::size_t size, Utils::SmallStringView string) {
-                return size + string.size();
-         });
-
-        reserve(size);
-        setSize(size);
-
-        char *currentData = data();
-
-        for (Utils::SmallStringView string : list) {
-            std::memcpy(currentData, string.data(), string.size());
-
-            currentData += string.size();
-        }
-
-        at(size) = 0;
+        appendInitializerList(list, 0);
     }
 
     ~BasicSmallString() noexcept
@@ -478,6 +460,13 @@ public:
         return *this;
     }
 
+    BasicSmallString &operator+=(std::initializer_list<SmallStringView> list)
+    {
+        appendInitializerList(list, size());
+
+        return *this;
+    }
+
     void replace(SmallStringView fromText, SmallStringView toText)
     {
         if (toText.size() == fromText.size())
@@ -690,6 +679,27 @@ private:
     {
     }
 
+    void appendInitializerList(std::initializer_list<SmallStringView> list, std::size_t initialSize)
+    {
+        auto addSize =  [] (std::size_t size, Utils::SmallStringView string) {
+            return size + string.size();
+        };
+
+        std::size_t size = std::accumulate(list.begin(), list.end(), initialSize, addSize);
+
+        reserve(size);
+        setSize(size);
+
+        char *currentData = data() + initialSize;
+
+        for (Utils::SmallStringView string : list) {
+            std::memcpy(currentData, string.data(), string.size());
+            currentData += string.size();
+        }
+
+        at(size) = 0;
+    }
+
     void initializeLongString(size_type size, size_type capacity)
     {
         m_data.allocated.data.pointer[size] = 0;