CMakeProjectManager: Add File System virtual folder

If a CMake project cannot be parsed by CMake, it is practically unusable in
Qt Creator. According to discussion in QTCREATORBUG-24677, a virtual
folder with the project's file system view is added to the project
manager as a convenience feature.

Fixes: QTCREATORBUG-24677
Change-Id: I48775bb89c704d3f7e5bb21ec6481bd5cc0f4b6c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/fileapidataextractor.cpp

@@ -692,5 +692,29 @@ FileApiQtcData extractData(FileApiData &input,
     return result;
 }
 
+FileApiQtcData generateFallbackData(const FilePath &topCmakeFile,
+                                    const FilePath &sourceDirectory,
+                                    const FilePath &buildDirectory,
+                                    QString errorMessage)
+{
+    FileApiQtcData result;
+
+    result.rootProjectNode.reset(new CMakeProjectNode{sourceDirectory});
+    result.rootProjectNode->setDisplayName(sourceDirectory.fileName());
+    result.errorMessage = errorMessage;
+
+    if (!topCmakeFile.isEmpty()) {
+        auto node = std::make_unique<FileNode>(topCmakeFile, FileType::Project);
+        node->setIsGenerated(false);
+
+        std::vector<std::unique_ptr<FileNode>> fileNodes;
+        fileNodes.emplace_back(std::move(node));
+
+        addCMakeLists(result.rootProjectNode.get(), std::move(fileNodes));
+    }
+
+    return result;
+}
+
 } // namespace Internal
 } // namespace CMakeProjectManager