Clang: Watch directories instead of files

Because there a limited resources to watch files we watch now directories.
So we need much less resources.

Change-Id: Iac558832e9521a7a1a67c5ea99b42ad1b0b5129c
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

19 files changed, 905 insertions, 127 deletions

diff --git a/src/libs/clangsupport/clangpathwatcher.h b/src/libs/clangsupport/clangpathwatcher.h
index dab52996c2..7a7d6ccfcf 100644
--- a/src/libs/clangsupport/clangpathwatcher.h
+++ b/src/libs/clangsupport/clangpathwatcher.h
@@ -1,4 +1,4 @@
-/****************************************************************************
+; /****************************************************************************
 **
 ** Copyright (C) 2016 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
@@ -27,71 +27,94 @@
 
 #include "clangpathwatcherinterface.h"
 #include "clangpathwatchernotifier.h"
-#include "changedfilepathcompressor.h"
+#include "directorypathcompressor.h"
 #include "filepathcachinginterface.h"
+#include "filesystem.h"
 #include "stringcache.h"
 
+#include <utils/algorithm.h>
+
 #include <QTimer>
 
 namespace ClangBackEnd {
 
+template<class InputIt1, class InputIt2, class Callable>
+void set_greedy_intersection_call(
+    InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Callable callable)
+{
+    while (first1 != last1 && first2 != last2) {
+        if (*first1 < *first2) {
+            ++first1;
+        } else {
+            if (*first2 < *first1)
+                ++first2;
+            else
+                callable(*first1++);
+        }
+    }
+}
+
 class WatcherEntry
 {
 public:
     ProjectPartId id;
-    FilePathId pathId;
+    DirectoryPathId directoryPathId;
+    FilePathId filePathId;
+    long long lastModified = -1;
 
     friend bool operator==(WatcherEntry first, WatcherEntry second)
     {
-        return first.id == second.id && first.pathId == second.pathId;
+        return first.id == second.id && first.directoryPathId == second.directoryPathId
+               && first.filePathId == second.filePathId;
     }
 
     friend bool operator<(WatcherEntry first, WatcherEntry second)
     {
-        return std::tie(first.pathId, first.id) < std::tie(second.pathId, second.id);
+        return std::tie(first.directoryPathId, first.filePathId, first.id)
+               < std::tie(second.directoryPathId, second.filePathId, second.id);
     }
 
-    friend bool operator<(WatcherEntry entry, FilePathId pathId)
+    friend bool operator<(DirectoryPathId directoryPathId, WatcherEntry entry)
     {
-        return entry.pathId < pathId;
+        return directoryPathId < entry.directoryPathId;
     }
 
-    friend bool operator<(FilePathId pathId, WatcherEntry entry)
+    friend bool operator<(WatcherEntry entry, DirectoryPathId directoryPathId)
     {
-        return pathId < entry.pathId;
+        return entry.directoryPathId < directoryPathId;
     }
 
-    operator FilePathId() const
-    {
-        return pathId;
-    }
+    operator FilePathId() const { return filePathId; }
+
+    operator DirectoryPathId() const { return directoryPathId; }
 };
 
 using WatcherEntries = std::vector<WatcherEntry>;
 
-template <typename FileSystemWatcher,
-          typename Timer>
+template<typename FileSystemWatcher, typename Timer>
 class CLANGSUPPORT_GCCEXPORT ClangPathWatcher : public ClangPathWatcherInterface
 {
 public:
     ClangPathWatcher(FilePathCachingInterface &pathCache,
-                     ClangPathWatcherNotifier *notifier=nullptr)
-        : m_changedFilePathCompressor(pathCache),
-          m_pathCache(pathCache),
-          m_notifier(notifier)
+                     FileSystemInterface &fileSystem,
+                     ClangPathWatcherNotifier *notifier = nullptr)
+        : m_pathCache(pathCache)
+        , m_fileStatusCache(fileSystem)
+        , m_fileSystem(fileSystem)
+        , m_notifier(notifier)
     {
         QObject::connect(&m_fileSystemWatcher,
-                         &FileSystemWatcher::fileChanged,
-                         [&] (const QString &filePath) { compressChangedFilePath(filePath); });
+                         &FileSystemWatcher::directoryChanged,
+                         [&](const QString &path) { compressChangedDirectoryPath(path); });
 
-        m_changedFilePathCompressor.setCallback([&] (ClangBackEnd::FilePathIds &&filePathIds) {
-            addChangedPathForFilePath(std::move(filePathIds));
+        m_directoryPathCompressor.setCallback([&](ClangBackEnd::DirectoryPathIds &&directoryPathIds) {
+            addChangedPathForFilePath(std::move(directoryPathIds));
         });
     }
 
     ~ClangPathWatcher()
     {
-        m_changedFilePathCompressor.setCallback([&] (FilePathIds &&) {});
+        m_directoryPathCompressor.setCallback([&](DirectoryPathIds &&) {});
     }
 
     void updateIdPaths(const std::vector<IdPaths> &idPaths) override
@@ -109,7 +132,7 @@ public:
         auto filteredPaths = filterNotWatchedPaths(removedEntries);
 
         if (!filteredPaths.empty())
-            m_fileSystemWatcher.removePaths(convertWatcherEntriesToQStringList(filteredPaths));
+            m_fileSystemWatcher.removePaths(convertWatcherEntriesToDirectoryPathList(filteredPaths));
     }
 
     void setNotifier(ClangPathWatcherNotifier *notifier) override
@@ -164,7 +187,13 @@ public:
             outputIterator = std::transform(idPath.filePathIds.begin(),
                                             idPath.filePathIds.end(),
                                             outputIterator,
-                                            [&] (FilePathId pathId) { return WatcherEntry{id, pathId}; });
+                                            [&](FilePathId filePathId) {
+                                                return WatcherEntry{
+                                                    id,
+                                                    m_pathCache.directoryPathId(filePathId),
+                                                    filePathId,
+                                                    m_fileStatusCache.lastModifiedTime(filePathId)};
+                                            });
         }
 
         std::sort(entries.begin(), entries.end());
@@ -182,7 +211,7 @@ public:
         mergeToWatchedEntries(newEntries);
 
         if (!filteredPaths.empty())
-            m_fileSystemWatcher.addPaths(convertWatcherEntriesToQStringList(filteredPaths));
+            m_fileSystemWatcher.addPaths(convertWatcherEntriesToDirectoryPathList(filteredPaths));
     }
 
     void removeUnusedEntries(const WatcherEntries &entries, const ProjectPartIds &ids)
@@ -194,33 +223,31 @@ public:
         auto filteredPaths = filterNotWatchedPaths(oldEntries);
 
         if (!filteredPaths.empty())
-            m_fileSystemWatcher.removePaths(convertWatcherEntriesToQStringList(filteredPaths));
+            m_fileSystemWatcher.removePaths(convertWatcherEntriesToDirectoryPathList(filteredPaths));
     }
 
-    FileSystemWatcher &fileSystemWatcher()
+    FileSystemWatcher &fileSystemWatcher() { return m_fileSystemWatcher; }
+
+    QStringList convertWatcherEntriesToDirectoryPathList(const DirectoryPathIds &directoryPathIds) const
     {
-        return m_fileSystemWatcher;
+        return Utils::transform<QStringList>(directoryPathIds, [&](DirectoryPathId id) {
+            return QString(m_pathCache.directoryPath(id));
+        });
     }
 
-    QStringList convertWatcherEntriesToQStringList(
-            const WatcherEntries &watcherEntries)
+    QStringList convertWatcherEntriesToDirectoryPathList(const WatcherEntries &watcherEntries) const
     {
-        QStringList paths;
-        paths.reserve(int(watcherEntries.size()));
+        DirectoryPathIds directoryPathIds = Utils::transform<DirectoryPathIds>(
+            watcherEntries, [&](WatcherEntry entry) { return entry.directoryPathId; });
 
-        std::transform(watcherEntries.begin(),
-                       watcherEntries.end(),
-                       std::back_inserter(paths),
-                       [&] (WatcherEntry entry) {
-            return QString(m_pathCache.filePath(entry.pathId).path());
-        });
+        std::sort(directoryPathIds.begin(), directoryPathIds.end());
+        directoryPathIds.erase(std::unique(directoryPathIds.begin(), directoryPathIds.end()),
+                               directoryPathIds.end());
 
-        return paths;
+        return convertWatcherEntriesToDirectoryPathList(directoryPathIds);
     }
 
-    template <typename Compare>
-    WatcherEntries notWatchedEntries(const WatcherEntries &entries,
-                                     Compare compare) const
+    WatcherEntries notWatchedEntries(const WatcherEntries &entries) const
     {
         WatcherEntries notWatchedEntries;
         notWatchedEntries.reserve(entries.size());
@@ -229,24 +256,23 @@ public:
                             entries.end(),
                             m_watchedEntries.cbegin(),
                             m_watchedEntries.cend(),
-                            std::back_inserter(notWatchedEntries),
-                            compare);
+                            std::back_inserter(notWatchedEntries));
 
         return notWatchedEntries;
     }
 
-    WatcherEntries notWatchedEntries(const WatcherEntries &entries) const
+    DirectoryPathIds notWatchedPaths(const DirectoryPathIds &ids) const
     {
-        return notWatchedEntries(entries, std::less<WatcherEntry>());
-    }
+        DirectoryPathIds notWatchedDirectoryIds;
+        notWatchedDirectoryIds.reserve(ids.size());
 
-    WatcherEntries notWatchedPaths(const WatcherEntries &entries) const
-    {
-        auto compare = [] (WatcherEntry first, WatcherEntry second) {
-            return first.pathId < second.pathId;
-        };
+        std::set_difference(ids.begin(),
+                            ids.end(),
+                            m_watchedEntries.cbegin(),
+                            m_watchedEntries.cend(),
+                            std::back_inserter(notWatchedDirectoryIds));
 
-        return notWatchedEntries(entries, compare);
+        return notWatchedDirectoryIds;
     }
 
     template <typename Compare>
@@ -297,25 +323,24 @@ public:
         m_watchedEntries = std::move(newWatchedEntries);
     }
 
-    static
-    WatcherEntries uniquePaths(const WatcherEntries &pathEntries)
+    static DirectoryPathIds uniquePaths(const WatcherEntries &pathEntries)
     {
-        WatcherEntries uniqueEntries;
-        uniqueEntries.reserve(pathEntries.size());
+        DirectoryPathIds uniqueDirectoryIds;
+        uniqueDirectoryIds.reserve(pathEntries.size());
 
-        auto compare = [] (WatcherEntry first, WatcherEntry second) {
-            return first.pathId == second.pathId;
+        auto compare = [](WatcherEntry first, WatcherEntry second) {
+            return first.directoryPathId == second.directoryPathId;
         };
 
         std::unique_copy(pathEntries.begin(),
                          pathEntries.end(),
-                         std::back_inserter(uniqueEntries),
+                         std::back_inserter(uniqueDirectoryIds),
                          compare);
 
-        return uniqueEntries;
+        return uniqueDirectoryIds;
     }
 
-    WatcherEntries filterNotWatchedPaths(const WatcherEntries &entries)
+    DirectoryPathIds filterNotWatchedPaths(const WatcherEntries &entries) const
     {
         return notWatchedPaths(uniquePaths(entries));
     }
@@ -351,40 +376,48 @@ public:
                             oldEntries.end(),
                             std::back_inserter(newWatchedEntries));
 
-
-        m_watchedEntries = newWatchedEntries;
+        m_watchedEntries = std::move(newWatchedEntries);
     }
 
-    void compressChangedFilePath(const QString &filePath)
+    void compressChangedDirectoryPath(const QString &path)
     {
-        m_changedFilePathCompressor.addFilePath(filePath);
+        m_directoryPathCompressor.addDirectoryPathId(
+            m_pathCache.directoryPathId(Utils::PathString{path}));
     }
 
-    WatcherEntries watchedEntriesForPaths(ClangBackEnd::FilePathIds &&filePathIds)
+    WatcherEntries watchedEntriesForPaths(ClangBackEnd::DirectoryPathIds &&directoryPathIds)
     {
         WatcherEntries foundEntries;
-        foundEntries.reserve(filePathIds.size());
-
-        for (FilePathId pathId : filePathIds) {
-            auto range = std::equal_range(m_watchedEntries.begin(), m_watchedEntries.end(), pathId);
-            foundEntries.insert(foundEntries.end(), range.first, range.second);
-        }
+        foundEntries.reserve(m_watchedEntries.size());
+
+        set_greedy_intersection_call(m_watchedEntries.begin(),
+                                     m_watchedEntries.end(),
+                                     directoryPathIds.begin(),
+                                     directoryPathIds.end(),
+                                     [&](WatcherEntry &entry) {
+                                         m_fileStatusCache.update(entry.filePathId);
+                                         auto currentLastModified = m_fileStatusCache.lastModifiedTime(
+                                             entry.filePathId);
+                                         if (entry.lastModified < currentLastModified) {
+                                             foundEntries.push_back(entry);
+                                             entry.lastModified = currentLastModified;
+                                         }
+                                     });
 
         return foundEntries;
     }
 
-    FilePathIds watchedPaths(const FilePathIds &filePathIds) const
+    FilePathIds watchedPaths(const WatcherEntries &entries) const
     {
-        FilePathIds watchedFilePathIds;
-        watchedFilePathIds.reserve(filePathIds.size());
+        auto filePathIds = Utils::transform<FilePathIds>(entries, [](WatcherEntry entry) {
+            return entry.filePathId;
+        });
+
+        std::sort(filePathIds.begin(), filePathIds.end());
 
-        std::set_intersection(m_watchedEntries.begin(),
-                              m_watchedEntries.end(),
-                              filePathIds.begin(),
-                              filePathIds.end(),
-                              std::back_inserter(watchedFilePathIds));
+        filePathIds.erase(std::unique(filePathIds.begin(), filePathIds.end()), filePathIds.end());
 
-        return watchedFilePathIds;
+        return filePathIds;
     }
 
     ProjectPartIds idsForWatcherEntries(const WatcherEntries &foundEntries)
@@ -403,21 +436,20 @@ public:
     ProjectPartIds uniqueIds(ProjectPartIds &&ids)
     {
         std::sort(ids.begin(), ids.end());
-        auto newEnd = std::unique(ids.begin(), ids.end());
-        ids.erase(newEnd, ids.end());
+        ids.erase(std::unique(ids.begin(), ids.end()), ids.end());
 
         return std::move(ids);
     }
 
-    void addChangedPathForFilePath(FilePathIds &&filePathIds)
+    void addChangedPathForFilePath(DirectoryPathIds &&directoryPathIds)
     {
         if (m_notifier) {
-            WatcherEntries foundEntries = watchedEntriesForPaths(std::move(filePathIds));
+            WatcherEntries foundEntries = watchedEntriesForPaths(std::move(directoryPathIds));
 
             ProjectPartIds changedIds = idsForWatcherEntries(foundEntries);
 
             m_notifier->pathsWithIdsChanged(uniqueIds(std::move(changedIds)));
-            m_notifier->pathsChanged(watchedPaths(filePathIds));
+            m_notifier->pathsChanged(watchedPaths(foundEntries));
         }
     }
 
@@ -428,10 +460,12 @@ public:
 
 private:
     WatcherEntries m_watchedEntries;
-    ChangedFilePathCompressor<Timer> m_changedFilePathCompressor;
     FileSystemWatcher m_fileSystemWatcher;
+    FileStatusCache m_fileStatusCache;
+    FileSystemInterface &m_fileSystem;
     FilePathCachingInterface &m_pathCache;
     ClangPathWatcherNotifier *m_notifier;
+    DirectoryPathCompressor<Timer> m_directoryPathCompressor;
 };
 
 } // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/clangsupport-lib.pri b/src/libs/clangsupport/clangsupport-lib.pri
index df537f5848..9b6bbdf3ee 100644
--- a/src/libs/clangsupport/clangsupport-lib.pri
+++ b/src/libs/clangsupport/clangsupport-lib.pri
@@ -18,6 +18,7 @@ SOURCES += \
     $$PWD/clangcodemodelserverproxy.cpp \
     $$PWD/alivemessage.cpp \
     $$PWD/completionsmessage.cpp \
+    $$PWD/filesystem.cpp \
     $$PWD/requestcompletionsmessage.cpp \
     $$PWD/echomessage.cpp \
     $$PWD/endmessage.cpp \
@@ -87,7 +88,8 @@ SOURCES += \
     $$PWD/removegeneratedfilesmessage.cpp \
     $$PWD/generatedfiles.cpp \
     $$PWD/projectpartartefact.cpp \
-    $$PWD/projectpartcontainer.cpp
+    $$PWD/projectpartcontainer.cpp \
+    $$PWD/filestatuscache.cpp
 
 HEADERS += \
     $$PWD/cancelmessage.h \
@@ -109,7 +111,11 @@ HEADERS += \
     $$PWD/alivemessage.h \
     $$PWD/clangsupportexceptions.h \
     $$PWD/completionsmessage.h \
+    $$PWD/directoryandfilepathid.h \
+    $$PWD/directorypathid.h \
     $$PWD/executeinloop.h \
+    $$PWD/filesystem.h \
+    $$PWD/filesysteminterface.h \
     $$PWD/pchpaths.h \
     $$PWD/projectpartid.h \
     $$PWD/projectpartsstorage.h \
@@ -217,6 +223,8 @@ HEADERS += \
     $$PWD/sourceentry.h \
     $$PWD/modifiedtimecheckerinterface.h \
     $$PWD/environment.h \
+    $$PWD/filestatus.h \
+    $$PWD/filestatuscache.h \
     $$PWD/modifiedtimechecker.h
 
 contains(QT_CONFIG, reduce_exports):CONFIG += hide_symbols
diff --git a/src/libs/clangsupport/directoryandfilepathid.h b/src/libs/clangsupport/directoryandfilepathid.h
new file mode 100644
index 0000000000..8969372919
--- /dev/null
+++ b/src/libs/clangsupport/directoryandfilepathid.h
@@ -0,0 +1,90 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "directorypathid.h"
+#include "filepathid.h"
+
+#include <QDataStream>
+
+#include <vector>
+
+namespace ClangBackEnd {
+class DirectoryAndFilePathId
+{
+public:
+    constexpr DirectoryAndFilePathId() = default;
+
+    DirectoryAndFilePathId(const char *) = delete;
+
+    DirectoryAndFilePathId(int directoryPathId, int filePathId)
+        : directoryPathId(directoryPathId)
+        , filePathId(filePathId)
+    {}
+
+    bool isValid() const { return directoryPathId.isValid() && filePathId.isValid(); }
+
+    friend bool operator==(DirectoryAndFilePathId first, DirectoryAndFilePathId second)
+    {
+        return first.isValid() && first.directoryPathId == second.directoryPathId
+               && first.filePathId == second.filePathId;
+    }
+
+    friend bool operator!=(DirectoryAndFilePathId first, DirectoryAndFilePathId second)
+    {
+        return !(first == second);
+    }
+
+    friend bool operator<(DirectoryAndFilePathId first, DirectoryAndFilePathId second)
+    {
+        return std::tie(first.directoryPathId, first.filePathId)
+               < std::tie(second.directoryPathId, second.filePathId);
+    }
+
+    friend QDataStream &operator<<(QDataStream &out,
+                                   const DirectoryAndFilePathId &directoryAndFilePathId)
+    {
+        out << directoryAndFilePathId.directoryPathId;
+        out << directoryAndFilePathId.filePathId;
+
+        return out;
+    }
+
+    friend QDataStream &operator>>(QDataStream &in, DirectoryAndFilePathId &directoryAndFilePathId)
+    {
+        in >> directoryAndFilePathId.directoryPathId;
+        in >> directoryAndFilePathId.filePathId;
+        return in;
+    }
+
+public:
+    DirectoryPathId directoryPathId;
+    FilePathId filePathId;
+};
+
+using DirectoryAndFilePathIds = std::vector<DirectoryAndFilePathId>;
+
+} // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/changedfilepathcompressor.h b/src/libs/clangsupport/directorypathcompressor.h
index aa8e1ec71a..cd02948e83 100644
--- a/src/libs/clangsupport/changedfilepathcompressor.h
+++ b/src/libs/clangsupport/directorypathcompressor.h
@@ -27,53 +27,44 @@
 
 #include "clangsupport_global.h"
 
-#include <filepathid.h>
-#include <filepathcache.h>
+#include "filepathcachinginterface.h"
 
+#include <QDir>
 #include <QTimer>
 
-#include <filepathcachinginterface.h>
+#include <utils/algorithm.h>
 
 #include <functional>
 
 namespace ClangBackEnd {
 
-template <typename Timer>
-class ChangedFilePathCompressor
+template<typename Timer>
+class DirectoryPathCompressor
 {
 public:
-    ChangedFilePathCompressor(FilePathCachingInterface &filePathCache)
-        : m_filePathCache(filePathCache)
-    {
-        m_timer.setSingleShot(true);
-    }
+    DirectoryPathCompressor() { m_timer.setSingleShot(true); }
 
-    virtual ~ChangedFilePathCompressor()
-    {
-    }
+    virtual ~DirectoryPathCompressor() = default;
 
-    void addFilePath(const QString &filePath)
+    void addDirectoryPathId(DirectoryPathId directoryPathIdId)
     {
-        FilePathId filePathId = m_filePathCache.filePathId(FilePath(filePath));
+        auto found = std::lower_bound(m_directoryPathIds.begin(),
+                                      m_directoryPathIds.end(),
+                                      directoryPathIdId);
 
-        auto found = std::lower_bound(m_filePaths.begin(), m_filePaths.end(), filePathId);
-
-        if (found == m_filePaths.end() || *found != filePathId)
-            m_filePaths.insert(found, filePathId);
+        if (found == m_directoryPathIds.end() || *found != directoryPathIdId)
+            m_directoryPathIds.insert(found, directoryPathIdId);
 
         restartTimer();
     }
 
-    FilePathIds takeFilePathIds()
-    {
-        return std::move(m_filePaths);
-    }
+    DirectoryPathIds takeDirectoryPathIds() { return std::move(m_directoryPathIds); }
 
-    virtual void setCallback(std::function<void(ClangBackEnd::FilePathIds &&)> &&callback)
+    virtual void setCallback(std::function<void(ClangBackEnd::DirectoryPathIds &&)> &&callback)
     {
-        QObject::connect(&m_timer,
-                         &Timer::timeout,
-                         [this, callback=std::move(callback)] { callback(takeFilePathIds()); });
+        QObject::connect(&m_timer, &Timer::timeout, [this, callback = std::move(callback)] {
+            callback(takeDirectoryPathIds());
+        });
     }
 
 unittest_public:
@@ -88,9 +79,8 @@ unittest_public:
     }
 
 private:
-    FilePathIds m_filePaths;
+    DirectoryPathIds m_directoryPathIds;
     Timer m_timer;
-    FilePathCachingInterface &m_filePathCache;
 };
 
 } // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/directorypathid.h b/src/libs/clangsupport/directorypathid.h
new file mode 100644
index 0000000000..2fd0b5847e
--- /dev/null
+++ b/src/libs/clangsupport/directorypathid.h
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <QDataStream>
+
+#include <vector>
+
+namespace ClangBackEnd {
+class DirectoryPathId
+{
+public:
+    constexpr DirectoryPathId() = default;
+
+    DirectoryPathId(const char *) = delete;
+
+    DirectoryPathId(int directoryPathId)
+        : directoryPathId(directoryPathId)
+    {}
+
+    bool isValid() const { return directoryPathId >= 0; }
+
+    friend bool operator==(DirectoryPathId first, DirectoryPathId second)
+    {
+        return first.isValid() && first.directoryPathId == second.directoryPathId;
+    }
+
+    friend bool operator!=(DirectoryPathId first, DirectoryPathId second)
+    {
+        return !(first == second);
+    }
+
+    friend bool operator<(DirectoryPathId first, DirectoryPathId second)
+    {
+        return first.directoryPathId < second.directoryPathId;
+    }
+
+    friend QDataStream &operator<<(QDataStream &out, const DirectoryPathId &directoryPathId)
+    {
+        out << directoryPathId.directoryPathId;
+
+        return out;
+    }
+
+    friend QDataStream &operator>>(QDataStream &in, DirectoryPathId &directoryPathId)
+    {
+        in >> directoryPathId.directoryPathId;
+
+        return in;
+    }
+
+public:
+    int directoryPathId = -1;
+};
+
+using DirectoryPathIds = std::vector<DirectoryPathId>;
+
+} // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/filepathcache.h b/src/libs/clangsupport/filepathcache.h
index bdd925a79c..4845416d22 100644
--- a/src/libs/clangsupport/filepathcache.h
+++ b/src/libs/clangsupport/filepathcache.h
@@ -25,9 +25,10 @@
 
 #pragma once
 
+#include "directorypathid.h"
+#include "filepath.h"
 #include "filepathexceptions.h"
 #include "filepathid.h"
-#include "filepath.h"
 #include "filepathview.h"
 #include "stringcache.h"
 
@@ -121,10 +122,10 @@ public:
     {
         Utils::SmallStringView directoryPath = filePath.directory();
 
-        int directoryId = m_directoryPathCache.stringId(directoryPath,
-                                                      [&] (const Utils::SmallStringView) {
-            return m_filePathStorage.fetchDirectoryId(directoryPath);
-        });
+        int directoryId = m_directoryPathCache.stringId(
+            directoryPath, [&](const Utils::SmallStringView directoryPath) {
+                return m_filePathStorage.fetchDirectoryId(directoryPath);
+            });
 
         Utils::SmallStringView fileName = filePath.name();
 
@@ -136,6 +137,17 @@ public:
         return fileNameId;
     }
 
+    DirectoryPathId directoryPathId(Utils::SmallStringView directoryPath) const
+    {
+        Utils::SmallStringView path = directoryPath.back() == '/'
+                                          ? directoryPath.mid(0, directoryPath.size() - 1)
+                                          : directoryPath;
+
+        return m_directoryPathCache.stringId(path, [&](const Utils::SmallStringView directoryPath) {
+            return m_filePathStorage.fetchDirectoryId(directoryPath);
+        });
+    }
+
     FilePath filePath(FilePathId filePathId) const
     {
         if (Q_UNLIKELY(!filePathId.isValid()))
@@ -157,6 +169,32 @@ public:
         return FilePath{directoryPath, entry.fileName};
     }
 
+    Utils::PathString directoryPath(DirectoryPathId directoryPathId) const
+    {
+        if (Q_UNLIKELY(!directoryPathId.isValid()))
+            throw NoDirectoryPathForInvalidDirectoryPathId();
+
+        auto fetchDirectoryPath = [&](int id) { return m_filePathStorage.fetchDirectoryPath(id); };
+
+        return m_directoryPathCache.string(directoryPathId.directoryPathId, fetchDirectoryPath);
+    }
+
+    DirectoryPathId directoryPathId(FilePathId filePathId) const
+    {
+        if (Q_UNLIKELY(!filePathId.isValid()))
+            throw NoFilePathForInvalidFilePathId();
+
+        auto fetchSoureNameAndDirectoryId = [&](int id) {
+            auto entry = m_filePathStorage.fetchSourceNameAndDirectoryId(id);
+            return FileNameEntry{entry.sourceName, entry.directoryId};
+        };
+
+        FileNameEntry entry = m_fileNameCache.string(filePathId.filePathId,
+                                                     fetchSoureNameAndDirectoryId);
+
+        return m_fileNameCache.string(filePathId.filePathId, fetchSoureNameAndDirectoryId).directoryId;
+    }
+
 private:
     mutable DirectoryPathCache m_directoryPathCache;
     mutable FileNameCache m_fileNameCache;
diff --git a/src/libs/clangsupport/filepathcaching.cpp b/src/libs/clangsupport/filepathcaching.cpp
index 0a3fc6ee41..372ed86bd3 100644
--- a/src/libs/clangsupport/filepathcaching.cpp
+++ b/src/libs/clangsupport/filepathcaching.cpp
@@ -37,4 +37,19 @@ FilePath FilePathCaching::filePath(FilePathId filePathId) const
     return m_cache.filePath(filePathId);
 }
 
+DirectoryPathId FilePathCaching::directoryPathId(Utils::SmallStringView directoryPath) const
+{
+    return m_cache.directoryPathId(directoryPath);
+}
+
+Utils::PathString FilePathCaching::directoryPath(DirectoryPathId directoryPathId) const
+{
+    return m_cache.directoryPath(directoryPathId);
+}
+
+DirectoryPathId FilePathCaching::directoryPathId(FilePathId filePathId) const
+{
+    return m_cache.directoryPathId(filePathId);
+}
+
 } // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/filepathcaching.h b/src/libs/clangsupport/filepathcaching.h
index a3337755fd..f69b940b15 100644
--- a/src/libs/clangsupport/filepathcaching.h
+++ b/src/libs/clangsupport/filepathcaching.h
@@ -50,6 +50,9 @@ public:
 
     FilePathId filePathId(FilePathView filePath) const override;
     FilePath filePath(FilePathId filePathId) const override;
+    DirectoryPathId directoryPathId(Utils::SmallStringView directoryPath) const override;
+    Utils::PathString directoryPath(DirectoryPathId directoryPathId) const override;
+    DirectoryPathId directoryPathId(FilePathId filePathId) const override;
 
 private:
     Factory m_factory;
diff --git a/src/libs/clangsupport/filepathcachinginterface.h b/src/libs/clangsupport/filepathcachinginterface.h
index b9668362f7..098fd39ca9 100644
--- a/src/libs/clangsupport/filepathcachinginterface.h
+++ b/src/libs/clangsupport/filepathcachinginterface.h
@@ -25,6 +25,7 @@
 
 #pragma once
 
+#include "directorypathid.h"
 #include "filepath.h"
 #include "filepathid.h"
 #include "filepathview.h"
@@ -40,8 +41,11 @@ public:
 
     virtual FilePathId filePathId(FilePathView filePath) const = 0;
     virtual FilePath filePath(FilePathId filePathId) const = 0;
+    virtual DirectoryPathId directoryPathId(Utils::SmallStringView directoryPath) const = 0;
+    virtual DirectoryPathId directoryPathId(FilePathId filePathId) const = 0;
+    virtual Utils::PathString directoryPath(DirectoryPathId directoryPathId) const = 0;
 
-    template <typename Container>
+    template<typename Container>
     FilePathIds filePathIds(Container &&filePaths) const
     {
        FilePathIds filePathIds;
diff --git a/src/libs/clangsupport/filepathexceptions.h b/src/libs/clangsupport/filepathexceptions.h
index 80bded0c66..3174d89479 100644
--- a/src/libs/clangsupport/filepathexceptions.h
+++ b/src/libs/clangsupport/filepathexceptions.h
@@ -38,6 +38,15 @@ public:
     }
 };
 
+class NoDirectoryPathForInvalidDirectoryPathId : std::exception
+{
+public:
+    const char *what() const noexcept override
+    {
+        return "You cannot get a directory path for an invalid directory path id!";
+    }
+};
+
 class SourceNameIdDoesNotExists : std::exception
 {
 public:
diff --git a/src/libs/clangsupport/filepathstorage.h b/src/libs/clangsupport/filepathstorage.h
index 5917504dbf..8aba2ef6d2 100644
--- a/src/libs/clangsupport/filepathstorage.h
+++ b/src/libs/clangsupport/filepathstorage.h
@@ -179,12 +179,32 @@ public:
 
             transaction.commit();
 
-            return optionalSourceName.value();
+            return *optionalSourceName;
         } catch (const Sqlite::StatementIsBusy &) {
             return fetchSourceNameAndDirectoryId(sourceId);
         }
     }
 
+    int fetchDirectoryId(int sourceId)
+    {
+        try {
+            Sqlite::DeferredTransaction transaction{m_statementFactory.database};
+
+            ReadStatement &statement = m_statementFactory.selectDirectoryIdFromSourcesBySourceId;
+
+            auto optionalDirectoryId = statement.template value<int>(sourceId);
+
+            if (!optionalDirectoryId)
+                throw SourceNameIdDoesNotExists();
+
+            transaction.commit();
+
+            return *optionalDirectoryId;
+        } catch (const Sqlite::StatementIsBusy &) {
+            return fetchDirectoryId(sourceId);
+        }
+    }
+
     std::vector<Sources::Source> fetchAllSources()
     {
         try {
diff --git a/src/libs/clangsupport/filepathstoragesqlitestatementfactory.h b/src/libs/clangsupport/filepathstoragesqlitestatementfactory.h
index dbf8071775..27296a1df6 100644
--- a/src/libs/clangsupport/filepathstoragesqlitestatementfactory.h
+++ b/src/libs/clangsupport/filepathstoragesqlitestatementfactory.h
@@ -69,6 +69,8 @@ public:
       "SELECT sourceName, directoryId FROM sources WHERE sourceId = ?",
         database
     };
+    ReadStatement selectDirectoryIdFromSourcesBySourceId{
+        "SELECT directoryId FROM sources WHERE sourceId = ?", database};
     WriteStatement insertIntoSources{
       "INSERT INTO sources(directoryId, sourceName) VALUES (?,?)",
         database
diff --git a/src/libs/clangsupport/filestatus.h b/src/libs/clangsupport/filestatus.h
new file mode 100644
index 0000000000..da2be4a304
--- /dev/null
+++ b/src/libs/clangsupport/filestatus.h
@@ -0,0 +1,63 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <filepathid.h>
+
+#include <ctime>
+#include <sys/types.h>
+#include <vector>
+
+namespace ClangBackEnd {
+
+class FileStatus
+{
+public:
+    FileStatus(FilePathId filePathId, off_t size, std::time_t lastModified)
+        : filePathId(filePathId), size(size), lastModified(lastModified) {}
+
+    friend
+    bool operator==(const FileStatus &first, const FileStatus &second)
+    {
+        return first.filePathId == second.filePathId
+            && first.size == second.size
+            && first.lastModified == second.lastModified;
+    }
+
+    friend
+    bool operator<(const FileStatus &first, const FileStatus &second)
+    {
+        return first.filePathId < second.filePathId;
+    }
+
+public:
+    FilePathId filePathId;
+    off_t size;
+    std::time_t lastModified;
+};
+
+using FileStatuses = std::vector<FileStatus>;
+}
diff --git a/src/libs/clangsupport/filestatuscache.cpp b/src/libs/clangsupport/filestatuscache.cpp
new file mode 100644
index 0000000000..480b745525
--- /dev/null
+++ b/src/libs/clangsupport/filestatuscache.cpp
@@ -0,0 +1,169 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "filestatuscache.h"
+#include "filesystem.h"
+
+#include <utils/algorithm.h>
+
+#include <QDateTime>
+#include <QFileInfo>
+
+namespace ClangBackEnd {
+
+long long FileStatusCache::lastModifiedTime(FilePathId filePathId) const
+{
+    return findEntry(filePathId).lastModified;
+}
+
+void FileStatusCache::update(FilePathId filePathId)
+{
+    auto found = std::lower_bound(m_cacheEntries.begin(),
+                                  m_cacheEntries.end(),
+                                  Internal::FileStatusCacheEntry{filePathId},
+                                  [] (const auto &first, const auto &second) {
+        return first.filePathId < second.filePathId;
+    });
+
+    if (found != m_cacheEntries.end() && found->filePathId == filePathId)
+        found->lastModified = m_fileSystem.lastModified(filePathId);
+}
+
+namespace {
+template<class InputIt1, class InputIt2, class Callable>
+void set_intersection_call(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Callable callable)
+{
+    while (first1 != last1 && first2 != last2) {
+        if (*first1 < *first2) {
+            ++first1;
+        } else {
+            if (!(*first2 < *first1))
+                callable(*first1++);
+            ++first2;
+        }
+    }
+}
+
+template<class InputIt1, class InputIt2, class Callable>
+void set_difference_call(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Callable callable)
+{
+    while (first1 != last1) {
+        if (first2 == last2) {
+            std::for_each(first1, last1, callable);
+            return;
+        }
+        if (*first1 < *first2) {
+            callable(*first1++);
+        } else {
+            if (!(*first2 < *first1))
+                ++first1;
+            ++first2;
+        }
+    }
+}
+} // namespace
+
+void FileStatusCache::update(FilePathIds filePathIds)
+{
+    set_intersection_call(m_cacheEntries.begin(),
+                          m_cacheEntries.end(),
+                          filePathIds.begin(),
+                          filePathIds.end(),
+                          [&](auto &entry) {
+                              entry.lastModified = m_fileSystem.lastModified(entry.filePathId);
+                          });
+}
+
+FilePathIds FileStatusCache::modified(FilePathIds filePathIds) const
+{
+    FilePathIds modifiedFilePathIds;
+    modifiedFilePathIds.reserve(filePathIds.size());
+
+    set_intersection_call(m_cacheEntries.begin(),
+                          m_cacheEntries.end(),
+                          filePathIds.begin(),
+                          filePathIds.end(),
+                          [&](auto &entry) {
+                              auto newLastModified = m_fileSystem.lastModified(entry.filePathId);
+                              if (newLastModified > entry.lastModified) {
+                                  modifiedFilePathIds.push_back(entry.filePathId);
+                                  entry.lastModified = newLastModified;
+                              }
+                          });
+
+    Internal::FileStatusCacheEntries newEntries;
+    newEntries.reserve(filePathIds.size());
+
+    set_difference_call(filePathIds.begin(),
+                        filePathIds.end(),
+                        m_cacheEntries.begin(),
+                        m_cacheEntries.end(),
+                        [&](FilePathId newFilePathId) {
+                            newEntries.emplace_back(newFilePathId,
+                                                    m_fileSystem.lastModified(newFilePathId));
+                            modifiedFilePathIds.push_back(newFilePathId);
+                        });
+
+    if (newEntries.size()) {
+        Internal::FileStatusCacheEntries mergedEntries;
+        mergedEntries.reserve(m_cacheEntries.size() + newEntries.size());
+
+        std::set_union(newEntries.begin(),
+                       newEntries.end(),
+                       m_cacheEntries.begin(),
+                       m_cacheEntries.end(),
+                       std::back_inserter(mergedEntries));
+
+        m_cacheEntries = std::move(mergedEntries);
+    }
+
+    std::sort(modifiedFilePathIds.begin(), modifiedFilePathIds.end());
+
+    return modifiedFilePathIds;
+}
+
+FileStatusCache::size_type FileStatusCache::size() const
+{
+    return m_cacheEntries.size();
+}
+
+Internal::FileStatusCacheEntry FileStatusCache::findEntry(FilePathId filePathId) const
+{
+    auto found = std::lower_bound(m_cacheEntries.begin(),
+                                  m_cacheEntries.end(),
+                                  Internal::FileStatusCacheEntry{filePathId},
+                                  [] (const auto &first, const auto &second) {
+        return first.filePathId < second.filePathId;
+    });
+
+    if (found != m_cacheEntries.end() && found->filePathId == filePathId)
+        return *found;
+
+    auto inserted = m_cacheEntries.emplace(found, filePathId, m_fileSystem.lastModified(filePathId));
+
+    return *inserted;
+}
+
+} // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/filestatuscache.h b/src/libs/clangsupport/filestatuscache.h
new file mode 100644
index 0000000000..3f0af56b3a
--- /dev/null
+++ b/src/libs/clangsupport/filestatuscache.h
@@ -0,0 +1,96 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <filepathcachinginterface.h>
+
+QT_FORWARD_DECLARE_CLASS(QFileInfo)
+
+namespace ClangBackEnd {
+
+class FileSystemInterface;
+
+namespace Internal {
+class FileStatusCacheEntry
+{
+public:
+    FileStatusCacheEntry(ClangBackEnd::FilePathId filePathId,
+                         long long lastModified = 0)
+        : filePathId(filePathId),
+          lastModified(lastModified)
+    {}
+
+    friend bool operator<(FileStatusCacheEntry first, FileStatusCacheEntry second)
+    {
+        return first.filePathId < second.filePathId;
+    }
+
+    friend bool operator<(FileStatusCacheEntry first, FilePathId second)
+    {
+        return first.filePathId < second;
+    }
+
+    friend bool operator<(FilePathId first, FileStatusCacheEntry second)
+    {
+        return first < second.filePathId;
+    }
+
+public:
+    FilePathId filePathId;
+    long long lastModified;
+};
+
+using FileStatusCacheEntries = std::vector<FileStatusCacheEntry>;
+
+}
+
+class CLANGSUPPORT_EXPORT FileStatusCache
+{
+public:
+    using size_type = Internal::FileStatusCacheEntries::size_type;
+
+    FileStatusCache(FileSystemInterface &fileSystem)
+        : m_fileSystem(fileSystem)
+    {}
+    FileStatusCache &operator=(const FileStatusCache &) = delete;
+    FileStatusCache(const FileStatusCache &) = delete;
+
+    long long lastModifiedTime(FilePathId filePathId) const;
+    void update(FilePathId filePathId);
+    void update(FilePathIds filePathIds);
+    FilePathIds modified(FilePathIds filePathIds) const;
+
+    size_type size() const;
+
+private:
+    Internal::FileStatusCacheEntry findEntry(FilePathId filePathId) const;
+
+private:
+    mutable Internal::FileStatusCacheEntries m_cacheEntries;
+    FileSystemInterface &m_fileSystem;
+};
+
+} // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/filesystem.cpp b/src/libs/clangsupport/filesystem.cpp
new file mode 100644
index 0000000000..5b8c037f80
--- /dev/null
+++ b/src/libs/clangsupport/filesystem.cpp
@@ -0,0 +1,61 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "filesystem.h"
+#include "filepathcachinginterface.h"
+
+#include <utils/algorithm.h>
+
+#include <QDateTime>
+#include <QDir>
+#include <QFileInfo>
+
+namespace ClangBackEnd {
+
+FilePathIds FileSystem::directoryEntries(const QString &directoryPath) const
+{
+    QDir directory{directoryPath};
+
+    QFileInfoList fileInfos = directory.entryInfoList();
+
+    FilePathIds filePathIds = Utils::transform<FilePathIds>(fileInfos, [&](const QFileInfo &fileInfo) {
+        return m_filePathCache.filePathId(FilePath{fileInfo.path()});
+    });
+
+    std::sort(filePathIds.begin(), filePathIds.end());
+
+    return filePathIds;
+}
+
+long long FileSystem::lastModified(FilePathId filePathId) const
+{
+    QFileInfo fileInfo(QString(m_filePathCache.filePath(filePathId)));
+
+    fileInfo.refresh();
+
+    return fileInfo.lastModified().toMSecsSinceEpoch() / 1000;
+}
+
+} // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/filesystem.h b/src/libs/clangsupport/filesystem.h
new file mode 100644
index 0000000000..ecf332de55
--- /dev/null
+++ b/src/libs/clangsupport/filesystem.h
@@ -0,0 +1,48 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "filestatuscache.h"
+#include "filesysteminterface.h"
+
+namespace ClangBackEnd {
+class FilePathCachingInterface;
+
+class CLANGSUPPORT_EXPORT FileSystem final : public FileSystemInterface
+{
+public:
+    FileSystem(FilePathCachingInterface &filePathCache)
+        : m_filePathCache(filePathCache)
+    {}
+
+    FilePathIds directoryEntries(const QString &directoryPath) const override;
+    long long lastModified(FilePathId filePathId) const override;
+
+private:
+    FilePathCachingInterface &m_filePathCache;
+};
+
+} // namespace ClangBackEnd
diff --git a/src/libs/clangsupport/filesysteminterface.h b/src/libs/clangsupport/filesysteminterface.h
new file mode 100644
index 0000000000..9d64d2a93a
--- /dev/null
+++ b/src/libs/clangsupport/filesysteminterface.h
@@ -0,0 +1,43 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "filepathid.h"
+
+#include <utils/smallstringview.h>
+
+namespace ClangBackEnd {
+
+class FileSystemInterface
+{
+public:
+    virtual FilePathIds directoryEntries(const QString &directoryPath) const = 0;
+    virtual long long lastModified(FilePathId filePathId) const = 0;
+
+protected:
+    ~FileSystemInterface() = default;
+};
+} // namespace ClangBackEnd
diff --git a/src/libs/utils/smallstringview.h b/src/libs/utils/smallstringview.h
index 6052ff8777..911ba2eafd 100644
--- a/src/libs/utils/smallstringview.h
+++ b/src/libs/utils/smallstringview.h
@@ -179,6 +179,10 @@ public:
         return m_pointer[0] == characterToSearch;
     }
 
+    char back() const { return m_pointer[m_size - 1]; }
+
+    char operator[](std::size_t index) { return m_pointer[index]; }
+
 private:
     const char *m_pointer = "";
     size_type m_size = 0;