ClangCodeModel: Enable clangd's new "dirty headers" flag, if possible

This feature will be availabe with LLVM 14,
see https://reviews.llvm.org/D95046.

Task-number: QTCREATORBUG-26810
Change-Id: I0a6797a836c56f5b72cca34be8f2d3edf8ac7359
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangcodemodel/clangdclient.cpp

@@ -613,6 +613,8 @@ static BaseClientInterface *clientInterface(Project *project, const Utils::FileP
         cmd.addArg("--compile-commands-dir=" + jsonDbDir.toString());
     if (clangdLogServer().isDebugEnabled())
         cmd.addArgs({"--log=verbose", "--pretty"});
+    if (settings.clangdVersion() >= QVersionNumber(14))
+        cmd.addArg("--use-dirty-headers");
     const auto interface = new StdIOClientInterface;
     interface->setCommandLine(cmd);
     return interface;

src/plugins/cppeditor/cppcodemodelsettings.cpp

@@ -335,7 +335,7 @@ ClangdSettings::ClangdSettings()
 
 bool ClangdSettings::useClangd() const
 {
-    return m_data.useClangd && clangdVersion(clangdFilePath()) >= QVersionNumber(13);
+    return m_data.useClangd && clangdVersion() >= QVersionNumber(13);
 }
 
 void ClangdSettings::setDefaultClangdPath(const FilePath &filePath)

src/plugins/cppeditor/cppcodemodelsettings.h

@@ -147,6 +147,7 @@ public:
     Data data() const { return m_data; }
 
     static QVersionNumber clangdVersion(const Utils::FilePath &clangdFilePath);
+    QVersionNumber clangdVersion() const { return clangdVersion(clangdFilePath()); }
 
 #ifdef WITH_TESTS
     static void setUseClangd(bool use);