ClangTools: Add automatic clang tool runner for open documents

Fixes: QTCREATORBUG-23349
Change-Id: I81197180c9d69c7df6184f8fcbf05f2256eaf7f6
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

24 files changed, 781 insertions, 79 deletions

diff --git a/src/plugins/clangtools/CMakeLists.txt b/src/plugins/clangtools/CMakeLists.txt
index 4ac94e7c25..829b77c97a 100644
--- a/src/plugins/clangtools/CMakeLists.txt
+++ b/src/plugins/clangtools/CMakeLists.txt
@@ -32,11 +32,13 @@ add_qtc_plugin(ClangTools
     clazychecks.ui
     diagnosticconfigswidget.cpp diagnosticconfigswidget.h
     diagnosticmark.cpp diagnosticmark.h
+    documentclangtoolrunner.cpp documentclangtoolrunner.h
     executableinfo.cpp executableinfo.h
     filterdialog.cpp filterdialog.h filterdialog.ui
     runsettingswidget.cpp runsettingswidget.h runsettingswidget.ui
     settingswidget.cpp settingswidget.h settingswidget.ui
     tidychecks.ui
+    virtualfilesystemoverlay.cpp virtualfilesystemoverlay.h
 )
 
 extend_qtc_plugin(ClangTools
diff --git a/src/plugins/clangtools/clangtidyclazyrunner.cpp b/src/plugins/clangtools/clangtidyclazyrunner.cpp
index 8fbc09ff5a..d3e2b34198 100644
--- a/src/plugins/clangtools/clangtidyclazyrunner.cpp
+++ b/src/plugins/clangtools/clangtidyclazyrunner.cpp
@@ -80,6 +80,13 @@ static QStringList mainToolArguments(const QString &mainFilePath, const QString
     };
 }
 
+static QString virtualFileSystemOverlay(const QString &overlayFilePath)
+{
+    if (overlayFilePath.isEmpty())
+        return {};
+    return "--vfsoverlay=" + overlayFilePath;
+}
+
 static QStringList clangArguments(const ClangDiagnosticConfig &diagnosticConfig,
                                   const QStringList &baseOptions)
 {
@@ -102,11 +109,11 @@ ClangTidyRunner::ClangTidyRunner(const ClangDiagnosticConfig &config, QObject *p
     setOutputFileFormat(OutputFileFormat::Yaml);
     setExecutable(clangTidyExecutable());
     setArgsCreator([this, config](const QStringList &baseOptions) {
-        return QStringList()
-            << tidyChecksArguments(config)
-            << mainToolArguments(fileToAnalyze(), outputFilePath())
-            << "--"
-            << clangArguments(config, baseOptions);
+        return QStringList() << tidyChecksArguments(config)
+                             << mainToolArguments(fileToAnalyze(), outputFilePath())
+                             << virtualFileSystemOverlay(m_overlayFilePath)
+                             << "--"
+                             << clangArguments(config, baseOptions);
     });
 }
 
diff --git a/src/plugins/clangtools/clangtool.cpp b/src/plugins/clangtools/clangtool.cpp
index 49f389b4f2..fde54fe130 100644
--- a/src/plugins/clangtools/clangtool.cpp
+++ b/src/plugins/clangtools/clangtool.cpp
@@ -376,13 +376,6 @@ static RunSettings runSettings()
     return ClangToolsSettings::instance()->runSettings();
 }
 
-static ClangDiagnosticConfig diagnosticConfig(const Utils::Id &diagConfigId)
-{
-    const ClangDiagnosticConfigsModel configs = diagnosticConfigsModel();
-    QTC_ASSERT(configs.hasConfigWithId(diagConfigId), return ClangDiagnosticConfig());
-    return configs.configWithId(diagConfigId);
-}
-
 ClangTool *ClangTool::instance()
 {
     return s_instance;
diff --git a/src/plugins/clangtools/clangtoolruncontrol.cpp b/src/plugins/clangtools/clangtoolruncontrol.cpp
index ac054135de..738e98fa6c 100644
--- a/src/plugins/clangtools/clangtoolruncontrol.cpp
+++ b/src/plugins/clangtools/clangtoolruncontrol.cpp
@@ -73,45 +73,6 @@ using namespace Utils;
 
 static Q_LOGGING_CATEGORY(LOG, "qtc.clangtools.runcontrol", QtWarningMsg)
 
-static QStringList splitArgs(QString &argsString)
-{
-    QStringList result;
-    Utils::QtcProcess::ArgIterator it(&argsString);
-    while (it.next())
-        result.append(it.value());
-    return result;
-}
-
-static QStringList extraOptions(const char *environment)
-{
-    if (!qEnvironmentVariableIsSet(environment))
-        return QStringList();
-    QString arguments = QString::fromLocal8Bit(qgetenv(environment));
-    return splitArgs(arguments);
-}
-
-static QStringList extraClangToolsPrependOptions()
-{
-    constexpr char csaPrependOptions[] = "QTC_CLANG_CSA_CMD_PREPEND";
-    constexpr char toolsPrependOptions[] = "QTC_CLANG_TOOLS_CMD_PREPEND";
-    static const QStringList options = extraOptions(csaPrependOptions)
-            + extraOptions(toolsPrependOptions);
-    if (!options.isEmpty())
-        qWarning() << "ClangTools options are prepended with " << options.toVector();
-    return options;
-}
-
-static QStringList extraClangToolsAppendOptions()
-{
-    constexpr char csaAppendOptions[] = "QTC_CLANG_CSA_CMD_APPEND";
-    constexpr char toolsAppendOptions[] = "QTC_CLANG_TOOLS_CMD_APPEND";
-    static const QStringList options = extraOptions(csaAppendOptions)
-            + extraOptions(toolsAppendOptions);
-    if (!options.isEmpty())
-        qWarning() << "ClangTools options are appended with " << options.toVector();
-    return options;
-}
-
 namespace ClangTools {
 namespace Internal {
 
@@ -154,26 +115,21 @@ private:
      bool m_success = false;
 };
 
-static AnalyzeUnits toAnalyzeUnits(const FileInfos &fileInfos, const FilePath &clangIncludeDir,
-                                   const QString &clangVersion)
+AnalyzeUnit::AnalyzeUnit(const FileInfo &fileInfo,
+                         const FilePath &clangIncludeDir,
+                         const QString &clangVersion)
 {
-    AnalyzeUnits unitsToAnalyze;
-    const UsePrecompiledHeaders usePrecompiledHeaders = CppTools::getPchUsage();
-    for (const FileInfo &fileInfo : fileInfos) {
-        CompilerOptionsBuilder optionsBuilder(*fileInfo.projectPart,
-                                              UseSystemHeader::No,
-                                              UseTweakedHeaderPaths::Yes,
-                                              UseLanguageDefines::No,
-                                              UseBuildSystemWarnings::No,
-                                              clangVersion,
-                                              clangIncludeDir.toString());
-        QStringList arguments = extraClangToolsPrependOptions();
-        arguments.append(optionsBuilder.build(fileInfo.kind, usePrecompiledHeaders));
-        arguments.append(extraClangToolsAppendOptions());
-        unitsToAnalyze << AnalyzeUnit(fileInfo.file.toString(), arguments);
-    }
-
-    return unitsToAnalyze;
+    CompilerOptionsBuilder optionsBuilder(*fileInfo.projectPart,
+                                          UseSystemHeader::No,
+                                          UseTweakedHeaderPaths::Yes,
+                                          UseLanguageDefines::No,
+                                          UseBuildSystemWarnings::No,
+                                          clangVersion,
+                                          clangIncludeDir.toString());
+    file = fileInfo.file.toString();
+    arguments = extraClangToolsPrependOptions();
+    arguments.append(optionsBuilder.build(fileInfo.kind, CppTools::getPchUsage()));
+    arguments.append(extraClangToolsAppendOptions());
 }
 
 AnalyzeUnits ClangToolRunWorker::unitsToAnalyze(const FilePath &clangIncludeDir,
@@ -181,7 +137,10 @@ AnalyzeUnits ClangToolRunWorker::unitsToAnalyze(const FilePath &clangIncludeDir,
 {
     QTC_ASSERT(m_projectInfo.isValid(), return AnalyzeUnits());
 
-    return toAnalyzeUnits(m_fileInfos, clangIncludeDir, clangVersion);
+    AnalyzeUnits units;
+    for (const FileInfo &fileInfo : m_fileInfos)
+        units << AnalyzeUnit(fileInfo, clangIncludeDir, clangVersion);
+    return units;
 }
 
 static QDebug operator<<(QDebug debug, const Utils::Environment &environment)
@@ -292,6 +251,8 @@ void ClangToolRunWorker::start()
             getClangIncludeDirAndVersion(runControl()->runnable().executable);
     const AnalyzeUnits unitsToProcess = unitsToAnalyze(clangIncludeDirAndVersion.first,
                                                        clangIncludeDirAndVersion.second);
+    qCDebug(LOG) << Q_FUNC_INFO << runControl()->runnable().executable
+                 << clangIncludeDirAndVersion.first << clangIncludeDirAndVersion.second;
     qCDebug(LOG) << "Files to process:" << unitsToProcess;
 
     m_queue.clear();
diff --git a/src/plugins/clangtools/clangtoolruncontrol.h b/src/plugins/clangtools/clangtoolruncontrol.h
index e72df21c68..9f46d0f2e3 100644
--- a/src/plugins/clangtools/clangtoolruncontrol.h
+++ b/src/plugins/clangtools/clangtoolruncontrol.h
@@ -46,8 +46,9 @@ class ClangToolRunner;
 class ProjectBuilder;
 
 struct AnalyzeUnit {
-    AnalyzeUnit(const QString &file, const QStringList &options)
-        : file(file), arguments(options) {}
+    AnalyzeUnit(const FileInfo &fileInfo,
+                const Utils::FilePath &clangResourceDir,
+                const QString &clangVersion);
 
     QString file;
     QStringList arguments; // without file itself and "-o somePath"
diff --git a/src/plugins/clangtools/clangtoolrunner.cpp b/src/plugins/clangtools/clangtoolrunner.cpp
index 0a63e8731b..b0fc220e04 100644
--- a/src/plugins/clangtools/clangtoolrunner.cpp
+++ b/src/plugins/clangtools/clangtoolrunner.cpp
@@ -75,7 +75,15 @@ void ClangToolRunner::init(const QString &outputDirPath,
 
 ClangToolRunner::~ClangToolRunner()
 {
-    Utils::SynchronousProcess::stopProcess(m_process);
+    if (m_process.state() != QProcess::NotRunning) {
+        // asking politly to terminate costs ~300 ms on windows so skip the courtasy and direct kill the process
+        if (Utils::HostOsInfo::isWindowsHost()) {
+            m_process.kill();
+            m_process.waitForFinished(100);
+        } else {
+            Utils::SynchronousProcess::stopProcess(m_process);
+        }
+    }
 }
 
 static QString createOutputFilePath(const QString &dirPath, const QString &fileToAnalyze)
diff --git a/src/plugins/clangtools/clangtoolrunner.h b/src/plugins/clangtools/clangtoolrunner.h
index 575876ff6c..87ec5d5f06 100644
--- a/src/plugins/clangtools/clangtoolrunner.h
+++ b/src/plugins/clangtools/clangtoolrunner.h
@@ -52,6 +52,7 @@ public:
     void setExecutable(const QString &executable) { m_executable = executable; }
     void setArgsCreator(const ArgsCreator &argsCreator) { m_argsCreator = argsCreator; }
     void setOutputFileFormat(const OutputFileFormat &format) { m_outputFileFormat = format; }
+    void setVFSOverlay(const QString overlayFilePath) { m_overlayFilePath = overlayFilePath; }
 
     QString name() const { return m_name; }
     QString executable() const { return m_executable; }
@@ -68,6 +69,9 @@ signals:
     void finishedWithSuccess(const QString &fileToAnalyze);
     void finishedWithFailure(const QString &errorMessage, const QString &errorDetails);
 
+protected:
+    QString m_overlayFilePath;
+
 private:
     void onProcessOutput();
     void onProcessFinished(int exitCode, QProcess::ExitStatus exitStatus);
diff --git a/src/plugins/clangtools/clangtools.pro b/src/plugins/clangtools/clangtools.pro
index 2d2c3b3c27..f4a85c24e6 100644
--- a/src/plugins/clangtools/clangtools.pro
+++ b/src/plugins/clangtools/clangtools.pro
@@ -30,10 +30,12 @@ SOURCES += \
     clangtoolsutils.cpp \
     diagnosticconfigswidget.cpp \
     diagnosticmark.cpp \
+    documentclangtoolrunner.cpp \
     executableinfo.cpp \
     filterdialog.cpp \
     runsettingswidget.cpp \
     settingswidget.cpp \
+    virtualfilesystemoverlay.cpp \
 
 HEADERS += \
     clangfileinfo.h \
@@ -56,10 +58,12 @@ HEADERS += \
     clangtoolsutils.h \
     diagnosticconfigswidget.h \
     diagnosticmark.h \
+    documentclangtoolrunner.h \
     executableinfo.h \
     filterdialog.h \
     runsettingswidget.h \
     settingswidget.h \
+    virtualfilesystemoverlay.h \
 
 FORMS += \
     clangselectablefilesdialog.ui \
diff --git a/src/plugins/clangtools/clangtools.qbs b/src/plugins/clangtools/clangtools.qbs
index eab5cd240c..6e9d83b14d 100644
--- a/src/plugins/clangtools/clangtools.qbs
+++ b/src/plugins/clangtools/clangtools.qbs
@@ -68,6 +68,8 @@ QtcPlugin {
         "diagnosticconfigswidget.h",
         "diagnosticmark.cpp",
         "diagnosticmark.h",
+        "documentclangtoolrunner.cpp",
+        "documentclangtoolrunner.h",
         "executableinfo.cpp",
         "executableinfo.h",
         "filterdialog.cpp",
@@ -80,6 +82,8 @@ QtcPlugin {
         "settingswidget.h",
         "settingswidget.ui",
         "tidychecks.ui",
+        "virtualfilesystemoverlay.cpp",
+        "virtualfilesystemoverlay.h",
     ]
 
     Group {
diff --git a/src/plugins/clangtools/clangtoolsplugin.cpp b/src/plugins/clangtools/clangtoolsplugin.cpp
index 242575d5fc..63f5df80cc 100644
--- a/src/plugins/clangtools/clangtoolsplugin.cpp
+++ b/src/plugins/clangtools/clangtoolsplugin.cpp
@@ -29,6 +29,7 @@
 #include "clangtoolsconstants.h"
 #include "clangtoolsprojectsettings.h"
 #include "clangtoolsprojectsettingswidget.h"
+#include "documentclangtoolrunner.h"
 #include "settingswidget.h"
 
 #ifdef WITH_TESTS
@@ -84,6 +85,7 @@ class ClangToolsPluginPrivate
 public:
     ClangTool clangTool;
     ClangToolsOptionsPage optionsPage;
+    QMap<Core::IDocument *, DocumentClangToolRunner *> documentRunners;
 };
 
 ClangToolsPlugin::~ClangToolsPlugin()
@@ -111,9 +113,28 @@ bool ClangToolsPlugin::initialize(const QStringList &arguments, QString *errorSt
     panelFactory->setCreateWidgetFunction([](Project *project) { return new ProjectSettingsWidget(project); });
     ProjectPanelFactory::registerFactory(panelFactory);
 
+    connect(Core::EditorManager::instance(),
+            &Core::EditorManager::currentEditorChanged,
+            this,
+            &ClangToolsPlugin::onCurrentEditorChanged);
+
     return true;
 }
 
+void ClangToolsPlugin::onCurrentEditorChanged()
+{
+    for (Core::IEditor *editor : Core::EditorManager::visibleEditors()) {
+        IDocument *document = editor->document();
+        if (d->documentRunners.contains(document))
+            continue;
+        auto runner = new DocumentClangToolRunner(document);
+        connect(runner, &DocumentClangToolRunner::destroyed, this, [this, document]() {
+            d->documentRunners.remove(document);
+        });
+        d->documentRunners[document] = runner;
+    }
+}
+
 void ClangToolsPlugin::registerAnalyzeActions()
 {
     ActionManager::registerAction(d->clangTool.startAction(), Constants::RUN_ON_PROJECT);
diff --git a/src/plugins/clangtools/clangtoolsplugin.h b/src/plugins/clangtools/clangtoolsplugin.h
index aaf1711fd6..fb6d4b279c 100644
--- a/src/plugins/clangtools/clangtoolsplugin.h
+++ b/src/plugins/clangtools/clangtoolsplugin.h
@@ -27,6 +27,7 @@
 
 #include <extensionsystem/iplugin.h>
 
+namespace Core { class IDocument; }
 namespace ProjectExplorer { class ProjectPanelFactory; }
 
 namespace ClangTools {
@@ -46,6 +47,7 @@ public:
 private:
     bool initialize(const QStringList &arguments, QString *errorString) final;
     void registerAnalyzeActions();
+    void onCurrentEditorChanged();
 
     QVector<QObject *> createTestObjects() const final;
 
diff --git a/src/plugins/clangtools/clangtoolsprojectsettings.cpp b/src/plugins/clangtools/clangtoolsprojectsettings.cpp
index e83c3b36f1..e92d87771b 100644
--- a/src/plugins/clangtools/clangtoolsprojectsettings.cpp
+++ b/src/plugins/clangtools/clangtoolsprojectsettings.cpp
@@ -48,6 +48,8 @@ ClangToolsProjectSettings::ClangToolsProjectSettings(ProjectExplorer::Project *p
     : m_project(project)
 {
     load();
+    connect(this, &ClangToolsProjectSettings::suppressedDiagnosticsChanged,
+            this, &ClangToolsProjectSettings::changed);
     connect(project, &ProjectExplorer::Project::settingsLoaded,
             this, &ClangToolsProjectSettings::load);
     connect(project, &ProjectExplorer::Project::aboutToSaveSettings, this,
@@ -59,6 +61,38 @@ ClangToolsProjectSettings::~ClangToolsProjectSettings()
     store();
 }
 
+void ClangToolsProjectSettings::setUseGlobalSettings(bool useGlobalSettings)
+{
+    if (m_useGlobalSettings == useGlobalSettings)
+        return;
+    m_useGlobalSettings = useGlobalSettings;
+    emit changed();
+}
+
+void ClangToolsProjectSettings::setRunSettings(const RunSettings &settings)
+{
+    if (m_runSettings == settings)
+        return;
+    m_runSettings = settings;
+    emit changed();
+}
+
+void ClangToolsProjectSettings::setSelectedDirs(const QSet<Utils::FilePath> &value)
+{
+    if (m_selectedDirs == value)
+        return;
+    m_selectedDirs = value;
+    emit changed();
+}
+
+void ClangToolsProjectSettings::setSelectedFiles(const QSet<Utils::FilePath> &value)
+{
+    if (m_selectedFiles == value)
+        return;
+    m_selectedFiles = value;
+    emit changed();
+}
+
 void ClangToolsProjectSettings::addSuppressedDiagnostic(const SuppressedDiagnostic &diag)
 {
     QTC_ASSERT(!m_suppressedDiagnostics.contains(diag), return);
diff --git a/src/plugins/clangtools/clangtoolsprojectsettings.h b/src/plugins/clangtools/clangtoolsprojectsettings.h
index aa6c035395..ed3c57fd72 100644
--- a/src/plugins/clangtools/clangtoolsprojectsettings.h
+++ b/src/plugins/clangtools/clangtoolsprojectsettings.h
@@ -70,16 +70,16 @@ public:
     ~ClangToolsProjectSettings() override;
 
     bool useGlobalSettings() const { return m_useGlobalSettings; }
-    void setUseGlobalSettings(bool useGlobalSettings) { m_useGlobalSettings = useGlobalSettings; }
+    void setUseGlobalSettings(bool useGlobalSettings);
 
     RunSettings runSettings() const { return m_runSettings; }
-    void setRunSettings(const RunSettings &settings) { m_runSettings = settings; }
+    void setRunSettings(const RunSettings &settings);
 
     QSet<Utils::FilePath> selectedDirs() const { return m_selectedDirs; }
-    void setSelectedDirs(const QSet<Utils::FilePath> &value) { m_selectedDirs = value; }
+    void setSelectedDirs(const QSet<Utils::FilePath> &value);
 
     QSet<Utils::FilePath> selectedFiles() const { return m_selectedFiles; }
-    void setSelectedFiles(const QSet<Utils::FilePath> &value) { m_selectedFiles = value; }
+    void setSelectedFiles(const QSet<Utils::FilePath> &value);
 
     SuppressedDiagnosticsList suppressedDiagnostics() const { return m_suppressedDiagnostics; }
     void addSuppressedDiagnostic(const SuppressedDiagnostic &diag);
@@ -91,6 +91,7 @@ public:
 
 signals:
     void suppressedDiagnosticsChanged();
+    void changed();
 
 private:
     void load();
diff --git a/src/plugins/clangtools/clangtoolssettings.cpp b/src/plugins/clangtools/clangtoolssettings.cpp
index ec76cdd729..2342e12b1d 100644
--- a/src/plugins/clangtools/clangtoolssettings.cpp
+++ b/src/plugins/clangtools/clangtoolssettings.cpp
@@ -42,7 +42,7 @@ static const char clazyStandaloneExecutableKey[] = "ClazyStandaloneExecutable";
 
 static const char parallelJobsKey[] = "ParallelJobs";
 static const char buildBeforeAnalysisKey[] = "BuildBeforeAnalysis";
-
+static const char analyzeOpenFilesKey[] = "AnalyzeOpenFiles";
 static const char oldDiagnosticConfigIdKey[] = "diagnosticConfigId";
 
 using namespace CppTools;
@@ -66,6 +66,7 @@ void RunSettings::fromMap(const QVariantMap &map, const QString &prefix)
     m_diagnosticConfigId = Utils::Id::fromSetting(map.value(prefix + diagnosticConfigIdKey));
     m_parallelJobs = map.value(prefix + parallelJobsKey).toInt();
     m_buildBeforeAnalysis = map.value(prefix + buildBeforeAnalysisKey).toBool();
+    m_analyzeOpenFiles = map.value(prefix + analyzeOpenFilesKey).toBool();
 }
 
 void RunSettings::toMap(QVariantMap &map, const QString &prefix) const
@@ -73,6 +74,7 @@ void RunSettings::toMap(QVariantMap &map, const QString &prefix) const
     map.insert(prefix + diagnosticConfigIdKey, m_diagnosticConfigId.toSetting());
     map.insert(prefix + parallelJobsKey, m_parallelJobs);
     map.insert(prefix + buildBeforeAnalysisKey, m_buildBeforeAnalysis);
+    map.insert(prefix + analyzeOpenFilesKey, m_analyzeOpenFiles);
 }
 
 Utils::Id RunSettings::diagnosticConfigId() const
@@ -82,6 +84,14 @@ Utils::Id RunSettings::diagnosticConfigId() const
     return m_diagnosticConfigId;
 }
 
+bool RunSettings::operator==(const RunSettings &other) const
+{
+    return m_diagnosticConfigId == other.m_diagnosticConfigId
+           && m_parallelJobs == other.m_parallelJobs
+           && m_buildBeforeAnalysis == other.m_buildBeforeAnalysis
+           && m_analyzeOpenFiles == other.m_analyzeOpenFiles;
+}
+
 ClangToolsSettings::ClangToolsSettings()
 {
     readSettings();
@@ -154,6 +164,7 @@ void ClangToolsSettings::readSettings()
         defaults.insert(diagnosticConfigIdKey, defaultDiagnosticId().toSetting());
         defaults.insert(parallelJobsKey, m_runSettings.parallelJobs());
         defaults.insert(buildBeforeAnalysisKey, m_runSettings.buildBeforeAnalysis());
+        defaults.insert(analyzeOpenFilesKey, m_runSettings.analyzeOpenFiles());
         map = defaults;
         for (QVariantMap::ConstIterator it = defaults.constBegin(); it != defaults.constEnd(); ++it)
             map.insert(it.key(), s->value(it.key(), it.value()));
diff --git a/src/plugins/clangtools/clangtoolssettings.h b/src/plugins/clangtools/clangtoolssettings.h
index 21b62e02a4..ac2a6b4185 100644
--- a/src/plugins/clangtools/clangtoolssettings.h
+++ b/src/plugins/clangtools/clangtoolssettings.h
@@ -54,10 +54,16 @@ public:
     int parallelJobs() const { return m_parallelJobs; }
     void setParallelJobs(int jobs) { m_parallelJobs = jobs; }
 
+    bool analyzeOpenFiles() const { return m_analyzeOpenFiles; }
+    void setAnalyzeOpenFiles(bool analyzeOpenFiles) { m_analyzeOpenFiles = analyzeOpenFiles; }
+
+    bool operator==(const RunSettings &other) const;
+
 private:
     Utils::Id m_diagnosticConfigId;
     int m_parallelJobs = -1;
     bool m_buildBeforeAnalysis = true;
+    bool m_analyzeOpenFiles = true;
 };
 
 class ClangToolsSettings : public QObject
diff --git a/src/plugins/clangtools/clangtoolsutils.cpp b/src/plugins/clangtools/clangtoolsutils.cpp
index 6c394aebc0..99cb1c9dd3 100644
--- a/src/plugins/clangtools/clangtoolsutils.cpp
+++ b/src/plugins/clangtools/clangtoolsutils.cpp
@@ -35,6 +35,7 @@
 #include <cpptools/cpptoolsreuse.h>
 #include <projectexplorer/projectexplorerconstants.h>
 
+#include <utils/qtcprocess.h>
 #include <utils/checkablemessagebox.h>
 #include <utils/environment.h>
 #include <utils/hostosinfo.h>
@@ -304,5 +305,51 @@ QString documentationUrl(const QString &checkName)
     return url;
 }
 
+ClangDiagnosticConfig diagnosticConfig(const Utils::Id &diagConfigId)
+{
+    const ClangDiagnosticConfigsModel configs = diagnosticConfigsModel();
+    QTC_ASSERT(configs.hasConfigWithId(diagConfigId), return ClangDiagnosticConfig());
+    return configs.configWithId(diagConfigId);
+}
+
+QStringList splitArgs(QString &argsString)
+{
+    QStringList result;
+    Utils::QtcProcess::ArgIterator it(&argsString);
+    while (it.next())
+        result.append(it.value());
+    return result;
+}
+
+QStringList extraOptions(const char *envVar)
+{
+    if (!qEnvironmentVariableIsSet(envVar))
+        return QStringList();
+    QString arguments = QString::fromLocal8Bit(qgetenv(envVar));
+    return splitArgs(arguments);
+}
+
+QStringList extraClangToolsPrependOptions()
+{
+    constexpr char csaPrependOptions[] = "QTC_CLANG_CSA_CMD_PREPEND";
+    constexpr char toolsPrependOptions[] = "QTC_CLANG_TOOLS_CMD_PREPEND";
+    static const QStringList options = extraOptions(csaPrependOptions)
+                                       + extraOptions(toolsPrependOptions);
+    if (!options.isEmpty())
+        qWarning() << "ClangTools options are prepended with " << options.toVector();
+    return options;
+}
+
+QStringList extraClangToolsAppendOptions()
+{
+    constexpr char csaAppendOptions[] = "QTC_CLANG_CSA_CMD_APPEND";
+    constexpr char toolsAppendOptions[] = "QTC_CLANG_TOOLS_CMD_APPEND";
+    static const QStringList options = extraOptions(csaAppendOptions)
+                                       + extraOptions(toolsAppendOptions);
+    if (!options.isEmpty())
+        qWarning() << "ClangTools options are appended with " << options.toVector();
+    return options;
+}
+
 } // namespace Internal
 } // namespace ClangTools
diff --git a/src/plugins/clangtools/clangtoolsutils.h b/src/plugins/clangtools/clangtoolsutils.h
index 4aa6f7eac9..9b6ddfa4c2 100644
--- a/src/plugins/clangtools/clangtoolsutils.h
+++ b/src/plugins/clangtools/clangtoolsutils.h
@@ -80,5 +80,10 @@ CppTools::ClangDiagnosticConfigsModel diagnosticConfigsModel();
 CppTools::ClangDiagnosticConfigsModel diagnosticConfigsModel(
     const CppTools::ClangDiagnosticConfigs &customConfigs);
 
+CppTools::ClangDiagnosticConfig diagnosticConfig(const Utils::Id &diagConfigId);
+
+QStringList extraClangToolsPrependOptions();
+QStringList extraClangToolsAppendOptions();
+
 } // namespace Internal
 } // namespace ClangTools
diff --git a/src/plugins/clangtools/diagnosticmark.h b/src/plugins/clangtools/diagnosticmark.h
index 040ce16adc..38cbe281a2 100644
--- a/src/plugins/clangtools/diagnosticmark.h
+++ b/src/plugins/clangtools/diagnosticmark.h
@@ -41,6 +41,8 @@ public:
     void disable();
     bool enabled() const;
 
+    QString source;
+
 private:
     const Diagnostic m_diagnostic;
     bool m_enabled = true;
diff --git a/src/plugins/clangtools/documentclangtoolrunner.cpp b/src/plugins/clangtools/documentclangtoolrunner.cpp
new file mode 100644
index 0000000000..b37c39087d
--- /dev/null
+++ b/src/plugins/clangtools/documentclangtoolrunner.cpp
@@ -0,0 +1,314 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 "documentclangtoolrunner.h"
+
+#include "clangfileinfo.h"
+#include "clangtidyclazyrunner.h"
+#include "clangtoolruncontrol.h"
+#include "clangtoolsprojectsettings.h"
+#include "clangtoolsutils.h"
+#include "diagnosticmark.h"
+#include "executableinfo.h"
+#include "virtualfilesystemoverlay.h"
+
+#include <coreplugin/documentmanager.h>
+#include <coreplugin/editormanager/editormanager.h>
+#include <coreplugin/editormanager/ieditor.h>
+#include <cpptools/cppmodelmanager.h>
+#include <projectexplorer/buildtargettype.h>
+#include <projectexplorer/session.h>
+#include <projectexplorer/target.h>
+#include <texteditor/textdocument.h>
+#include <texteditor/textmark.h>
+#include <utils/qtcassert.h>
+#include <utils/utilsicons.h>
+
+#include <QLoggingCategory>
+
+static Q_LOGGING_CATEGORY(LOG, "qtc.clangtools.cftr", QtWarningMsg)
+
+namespace ClangTools {
+namespace Internal {
+
+DocumentClangToolRunner::DocumentClangToolRunner(Core::IDocument *document)
+    : QObject(document)
+    , m_document(document)
+    , m_temporaryDir("clangtools-single-XXXXXX")
+{
+    using namespace CppTools;
+
+    m_runTimer.setInterval(500);
+    m_runTimer.setSingleShot(true);
+
+    connect(m_document,
+            &Core::IDocument::contentsChanged,
+            this,
+            &DocumentClangToolRunner::scheduleRun);
+    connect(CppModelManager::instance(),
+            &CppModelManager::projectPartsUpdated,
+            this,
+            &DocumentClangToolRunner::scheduleRun);
+    connect(ClangToolsSettings::instance(),
+            &ClangToolsSettings::changed,
+            this,
+            &DocumentClangToolRunner::scheduleRun);
+    connect(&m_runTimer, &QTimer::timeout, this, &DocumentClangToolRunner::run);
+    run();
+}
+
+DocumentClangToolRunner::~DocumentClangToolRunner()
+{
+    cancel();
+    qDeleteAll(m_marks);
+}
+
+void DocumentClangToolRunner::scheduleRun()
+{
+    for (DiagnosticMark *mark : m_marks)
+        mark->disable();
+    m_runTimer.start();
+}
+
+static ProjectExplorer::Project *findProject(const Utils::FilePath &file)
+{
+    ProjectExplorer::Project *project = ProjectExplorer::SessionManager::projectForFile(file);
+    return project ? project : ProjectExplorer::SessionManager::startupProject();
+}
+
+static VirtualFileSystemOverlay &vfso()
+{
+    static VirtualFileSystemOverlay overlay("clangtools-vfso-XXXXXX");
+    return overlay;
+}
+
+static FileInfo getFileInfo(const Utils::FilePath &file, ProjectExplorer::Project *project)
+{
+    CppTools::ProjectInfo projectInfo = CppTools::CppModelManager::instance()->projectInfo(project);
+    if (!projectInfo.isValid())
+        return {};
+
+    FileInfo candidate;
+    for (const CppTools::ProjectPart::Ptr &projectPart : projectInfo.projectParts()) {
+        QTC_ASSERT(projectPart, continue);
+
+        for (const CppTools::ProjectFile &projectFile : qAsConst(projectPart->files)) {
+            QTC_ASSERT(projectFile.kind != CppTools::ProjectFile::Unclassified, continue);
+            QTC_ASSERT(projectFile.kind != CppTools::ProjectFile::Unsupported, continue);
+            if (projectFile.path == CppTools::CppModelManager::configurationFileName())
+                continue;
+            if (file.toString() != projectFile.path)
+                continue;
+            if (!projectFile.active)
+                continue;
+            if (projectPart->buildTargetType != ProjectExplorer::BuildTargetType::Unknown) {
+                // found the best candidate, early return
+                return FileInfo(Utils::FilePath::fromString(projectFile.path),
+                                projectFile.kind,
+                                projectPart);
+            }
+            if (candidate.projectPart.isNull()) {
+                // found at least something but keep looking for better candidates
+                candidate = FileInfo(Utils::FilePath::fromString(projectFile.path),
+                                     projectFile.kind,
+                                     projectPart);
+            }
+        }
+    }
+
+    return candidate;
+}
+
+static Utils::Environment projectBuildEnvironment(ProjectExplorer::Project *project)
+{
+    Utils::Environment env;
+    if (ProjectExplorer::Target *target = project->activeTarget()) {
+        if (ProjectExplorer::BuildConfiguration *buildConfig = target->activeBuildConfiguration())
+            env = buildConfig->environment();
+    }
+    if (env.size() == 0)
+        env = Utils::Environment::systemEnvironment();
+    return env;
+}
+
+void DocumentClangToolRunner::run()
+{
+    cancel();
+    auto isEditorForCurrentDocument = [this](const Core::IEditor *editor) {
+        return editor->document() == m_document;
+    };
+    if (Utils::anyOf(Core::EditorManager::visibleEditors(), isEditorForCurrentDocument)) {
+        const Utils::FilePath filePath = m_document->filePath();
+        if (ProjectExplorer::Project *project = findProject(filePath)) {
+            m_fileInfo = getFileInfo(filePath, project);
+            if (m_fileInfo.file.exists()) {
+                const auto projectSettings = ClangToolsProjectSettings::getSettings(project);
+
+                const RunSettings &runSettings = projectSettings->useGlobalSettings()
+                                                     ? ClangToolsSettings::instance()->runSettings()
+                                                     : projectSettings->runSettings();
+                m_projectSettingsUpdate = connect(projectSettings.data(),
+                                                  &ClangToolsProjectSettings::changed,
+                                                  this,
+                                                  &DocumentClangToolRunner::run);
+
+                if (runSettings.analyzeOpenFiles()) {
+                    vfso().update();
+
+                    CppTools::ClangDiagnosticConfig config = diagnosticConfig(
+                        runSettings.diagnosticConfigId());
+
+                    Utils::Environment env = projectBuildEnvironment(project);
+                    if (config.isClangTidyEnabled()) {
+                        m_runnerCreators << [this, env, config]() {
+                            return createRunner<ClangTidyRunner>(config, env);
+                        };
+                    }
+                    if (config.isClazyEnabled() && !m_document->isModified()) {
+                        m_runnerCreators << [this, env, config]() {
+                            return createRunner<ClazyStandaloneRunner>(config, env);
+                        };
+                    }
+                }
+            }
+        }
+    } else {
+        deleteLater();
+    }
+
+    runNext();
+}
+
+QPair<Utils::FilePath, QString> getClangIncludeDirAndVersion(ClangToolRunner *runner)
+{
+    static QMap<Utils::FilePath, QPair<Utils::FilePath, QString>> cache;
+    const Utils::FilePath tool = Utils::FilePath::fromString(runner->executable());
+    auto it = cache.find(tool);
+    if (it == cache.end())
+        it = cache.insert(tool, getClangIncludeDirAndVersion(tool));
+    return it.value();
+}
+
+void DocumentClangToolRunner::runNext()
+{
+    m_currentRunner.reset(m_runnerCreators.isEmpty() ? nullptr : m_runnerCreators.takeFirst()());
+    if (m_currentRunner) {
+        auto [clangIncludeDir, clangVersion] = getClangIncludeDirAndVersion(m_currentRunner.get());
+        qCDebug(LOG) << Q_FUNC_INFO << m_currentRunner->executable() << clangIncludeDir
+                     << clangVersion << m_fileInfo.file;
+        AnalyzeUnit unit(m_fileInfo, clangIncludeDir, clangVersion);
+        QTC_ASSERT(Utils::FilePath::fromString(unit.file).exists(), runNext(); return;);
+        m_currentRunner->setVFSOverlay(vfso().overlayFilePath().toString());
+        if (!m_currentRunner->run(unit.file, unit.arguments))
+            runNext();
+    } else {
+        finalize();
+    }
+}
+
+void DocumentClangToolRunner::onSuccess()
+{
+    QString errorMessage;
+    Utils::FilePath mappedPath = vfso().filePath(m_document);
+    Diagnostics diagnostics = readExportedDiagnostics(
+        Utils::FilePath::fromString(m_currentRunner->outputFilePath()),
+        [&](const Utils::FilePath &path) { return path == mappedPath; },
+        &errorMessage);
+
+    if (mappedPath != m_document->filePath()) {
+        const QString originalPath = m_document->filePath().toString();
+        for (Diagnostic &diag : diagnostics)
+            diag.location.filePath = originalPath;
+    }
+
+    // remove outdated marks of the current runner
+    auto [toDelete, newMarks] = Utils::partition(m_marks, [this](DiagnosticMark *mark) {
+        return mark->source == m_currentRunner->name();
+    });
+    m_marks = newMarks;
+    qDeleteAll(toDelete);
+
+    m_marks << Utils::transform(diagnostics, [this](const Diagnostic &diagnostic) {
+        auto mark = new DiagnosticMark(diagnostic);
+        mark->source = m_currentRunner->name();
+        return mark;
+    });
+    runNext();
+}
+
+void DocumentClangToolRunner::onFailure(const QString &errorMessage, const QString &errorDetails)
+{
+    qCDebug(LOG) << "Failed to analyze " << m_fileInfo.file << ":" << errorMessage << errorDetails;
+    runNext();
+}
+
+void DocumentClangToolRunner::finalize()
+{
+    // remove all disabled textMarks
+    auto [newMarks, toDelete] = Utils::partition(m_marks, &DiagnosticMark::enabled);
+    m_marks = newMarks;
+    qDeleteAll(toDelete);
+}
+
+void DocumentClangToolRunner::cancel()
+{
+    if (m_projectSettingsUpdate)
+        disconnect(m_projectSettingsUpdate);
+    m_runnerCreators.clear();
+    if (m_currentRunner) {
+        m_currentRunner->disconnect(this);
+        m_currentRunner.reset(nullptr);
+    }
+}
+
+const CppTools::ClangDiagnosticConfig DocumentClangToolRunner::getDiagnosticConfig(ProjectExplorer::Project *project)
+{
+    const auto projectSettings = ClangToolsProjectSettings::getSettings(project);
+    m_projectSettingsUpdate = connect(projectSettings.data(),
+                                      &ClangToolsProjectSettings::changed,
+                                      this,
+                                      &DocumentClangToolRunner::run);
+
+    const Utils::Id &id = projectSettings->useGlobalSettings()
+                              ? ClangToolsSettings::instance()->runSettings().diagnosticConfigId()
+                              : projectSettings->runSettings().diagnosticConfigId();
+    return diagnosticConfig(id);
+}
+
+template<class T>
+ClangToolRunner *DocumentClangToolRunner::createRunner(const CppTools::ClangDiagnosticConfig &config,
+                                                       const Utils::Environment &env)
+{
+    auto runner = new T(config, this);
+    runner->init(m_temporaryDir.path(), env);
+    connect(runner, &ClangToolRunner::finishedWithSuccess,
+            this, &DocumentClangToolRunner::onSuccess);
+    connect(runner, &ClangToolRunner::finishedWithFailure,
+            this, &DocumentClangToolRunner::onFailure);
+    return runner;
+}
+
+} // namespace Internal
+} // namespace ClangTools
diff --git a/src/plugins/clangtools/documentclangtoolrunner.h b/src/plugins/clangtools/documentclangtoolrunner.h
new file mode 100644
index 0000000000..4cf263c1aa
--- /dev/null
+++ b/src/plugins/clangtools/documentclangtoolrunner.h
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 "clangfileinfo.h"
+
+#include <utils/fileutils.h>
+#include <utils/temporarydirectory.h>
+
+#include <QObject>
+#include <QTimer>
+
+namespace Core { class IDocument; }
+namespace CppTools { class ClangDiagnosticConfig; }
+
+namespace ClangTools {
+
+namespace Internal {
+
+class ClangToolRunner;
+class DiagnosticMark;
+
+class DocumentClangToolRunner : public QObject
+{
+    Q_OBJECT
+public:
+    DocumentClangToolRunner(Core::IDocument *doc);
+    ~DocumentClangToolRunner();
+
+private:
+    void scheduleRun();
+    void run();
+    void runNext();
+
+    void onSuccess();
+    void onFailure(const QString &errorMessage, const QString &errorDetails);
+
+    void finalize();
+
+    void cancel();
+
+    const CppTools::ClangDiagnosticConfig getDiagnosticConfig(ProjectExplorer::Project *project);
+    template<class T>
+    ClangToolRunner *createRunner(const CppTools::ClangDiagnosticConfig &config,
+                                  const Utils::Environment &env);
+
+    QTimer m_runTimer;
+    Core::IDocument *m_document = nullptr;
+    Utils::TemporaryDirectory m_temporaryDir;
+    std::unique_ptr<ClangToolRunner> m_currentRunner;
+    QList<std::function<ClangToolRunner *()>> m_runnerCreators;
+    QList<DiagnosticMark *> m_marks;
+    FileInfo m_fileInfo;
+    QMetaObject::Connection m_projectSettingsUpdate;
+};
+
+} // namespace Internal
+} // namespace ClangTools
diff --git a/src/plugins/clangtools/runsettingswidget.cpp b/src/plugins/clangtools/runsettingswidget.cpp
index 76fc820373..64fd25836e 100644
--- a/src/plugins/clangtools/runsettingswidget.cpp
+++ b/src/plugins/clangtools/runsettingswidget.cpp
@@ -110,6 +110,9 @@ void RunSettingsWidget::fromSettings(const RunSettings &s)
     connect(m_ui->parallelJobsSpinBox,
             QOverload<int>::of(&QSpinBox::valueChanged),
             [this](int) { emit changed(); });
+    m_ui->analyzeOpenFiles->setChecked(s.analyzeOpenFiles());
+    connect(m_ui->analyzeOpenFiles, &QCheckBox::toggled, this, &RunSettingsWidget::changed);
+
 }
 
 RunSettings RunSettingsWidget::toSettings() const
@@ -118,6 +121,7 @@ RunSettings RunSettingsWidget::toSettings() const
     s.setDiagnosticConfigId(m_ui->diagnosticWidget->currentConfigId());
     s.setBuildBeforeAnalysis(m_ui->buildBeforeAnalysis->checkState() == Qt::CheckState::Checked);
     s.setParallelJobs(m_ui->parallelJobsSpinBox->value());
+    s.setAnalyzeOpenFiles(m_ui->analyzeOpenFiles->checkState() == Qt::CheckState::Checked);
 
     return s;
 }
diff --git a/src/plugins/clangtools/runsettingswidget.ui b/src/plugins/clangtools/runsettingswidget.ui
index e7ad362c84..370932c9a8 100644
--- a/src/plugins/clangtools/runsettingswidget.ui
+++ b/src/plugins/clangtools/runsettingswidget.ui
@@ -43,6 +43,13 @@
        </widget>
       </item>
       <item>
+       <widget class="QCheckBox" name="analyzeOpenFiles">
+        <property name="text">
+         <string>Analyze open files</string>
+        </property>
+       </widget>
+      </item>
+      <item>
        <layout class="QHBoxLayout" name="processesLayout">
         <item>
          <widget class="QLabel" name="label_2">
diff --git a/src/plugins/clangtools/virtualfilesystemoverlay.cpp b/src/plugins/clangtools/virtualfilesystemoverlay.cpp
new file mode 100644
index 0000000000..a0f9f2725c
--- /dev/null
+++ b/src/plugins/clangtools/virtualfilesystemoverlay.cpp
@@ -0,0 +1,124 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 "virtualfilesystemoverlay.h"
+
+#include <coreplugin/documentmanager.h>
+#include <texteditor/textdocument.h>
+
+#include <QJsonArray>
+#include <QJsonDocument>
+#include <QJsonObject>
+#include <QLoggingCategory>
+#include <QTextDocument>
+
+static Q_LOGGING_CATEGORY(LOG, "qtc.clangtools.vfso", QtWarningMsg)
+
+namespace ClangTools {
+namespace Internal {
+
+VirtualFileSystemOverlay::VirtualFileSystemOverlay(const QString &rootPattern)
+    : m_root(rootPattern)
+    , m_overlayFilePath(Utils::FilePath::fromString(m_root.filePath("vfso.yaml")))
+{ }
+
+void VirtualFileSystemOverlay::update()
+{
+    Utils::FileUtils::removeRecursively(overlayFilePath());
+    QFile overlayFile(m_overlayFilePath.toString());
+    if (!overlayFile.open(QFile::ReadWrite))
+        return;
+    std::map<Utils::FilePath, QList<Core::IDocument *>> documentRoots;
+    const QList<Core::IDocument *> &modifiedDocuments = Core::DocumentManager::modifiedDocuments();
+    QMap<Core::IDocument *, AutoSavedPath> newSaved;
+    for (Core::IDocument *doc : modifiedDocuments) {
+        auto document = qobject_cast<TextEditor::TextDocument *>(doc);
+        if (!document)
+            continue;
+        documentRoots[doc->filePath().absolutePath()] << doc;
+        AutoSavedPath saved = m_saved.take(document);
+        if (saved.revision != document->document()->revision()) {
+            saved.revision = document->document()->revision();
+            QString error;
+            saved.path = Utils::FilePath::fromString(m_root.path())
+                    .pathAppended(doc->filePath().fileName() + ".auto");
+            while (saved.path.exists())
+                saved.path = saved.path + ".1";
+            if (!doc->save(&error, saved.path.toString(), true)) {
+                qCDebug(LOG) << error;
+                continue;
+            }
+        }
+        newSaved[doc] = saved;
+    }
+
+    for (const AutoSavedPath &path : qAsConst(m_saved)) {
+        QString error;
+        if (!Utils::FileUtils::removeRecursively(path.path, &error))
+            qCDebug(LOG) << error;
+    }
+    m_saved = newSaved;
+
+    auto toContent = [this](Core::IDocument *document) {
+        QJsonObject content;
+        content["name"] = document->filePath().fileName();
+        content["type"] = "file";
+        content["external-contents"] = m_saved[document].path.toUserOutput();
+        return content;
+    };
+
+    QJsonObject main;
+    main["version"] = 0;
+    QJsonArray jsonRoots;
+    for (auto [root, documents] : documentRoots) {
+        QJsonObject jsonRoot;
+        jsonRoot["type"] = "directory";
+        jsonRoot["name"] = root.toUserOutput();
+        QJsonArray contents;
+        for (auto doc : documents)
+            contents << toContent(doc);
+        jsonRoot["contents"] = contents;
+        jsonRoots << jsonRoot;
+    }
+    main["roots"] = jsonRoots;
+
+    QJsonDocument overlay(main);
+    if (!overlayFile.write(overlay.toJson(QJsonDocument::Compact)))
+        qCDebug(LOG) << "failed to write vfso to " << m_overlayFilePath;
+    overlayFile.close();
+}
+
+Utils::FilePath VirtualFileSystemOverlay::overlayFilePath() { return m_overlayFilePath; }
+
+Utils::FilePath VirtualFileSystemOverlay::filePath(Core::IDocument *doc)
+{
+    auto it = m_saved.find(doc);
+    if (it != m_saved.end())
+        return it.value().path;
+    return doc->filePath();
+}
+
+} // namespace Internal
+} // namespace ClangTools
diff --git a/src/plugins/clangtools/virtualfilesystemoverlay.h b/src/plugins/clangtools/virtualfilesystemoverlay.h
new file mode 100644
index 0000000000..f6077f12a5
--- /dev/null
+++ b/src/plugins/clangtools/virtualfilesystemoverlay.h
@@ -0,0 +1,59 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 <utils/fileutils.h>
+#include <utils/temporarydirectory.h>
+
+namespace Core { class IDocument; }
+
+namespace ClangTools {
+namespace Internal {
+
+class VirtualFileSystemOverlay
+{
+public:
+    VirtualFileSystemOverlay(const QString &rootPattern);
+
+    void update();
+
+    Utils::FilePath overlayFilePath();
+    Utils::FilePath filePath(Core::IDocument *doc);
+
+private:
+    Utils::TemporaryDirectory m_root;
+    Utils::FilePath m_overlayFilePath;
+    struct AutoSavedPath
+    {
+        int revision = -1;
+        Utils::FilePath path;
+    };
+
+    QMap<Core::IDocument *, AutoSavedPath> m_saved;
+};
+
+} // namespace Internal
+} // namespace ClangTools