logic: fixes for handling pch flags for cdb source groups

* use flags of first source file that specifies an "-include-pch" flag for generating the .pch file
* allow to save project settings without specifying input header file if cdb contains -include-pch args

src/lib_cxx/project/SourceGroupCxxCdb.cpp

@@ -164,7 +164,7 @@ std::shared_ptr<Task> SourceGroupCxxCdb::getPreIndexTask(
 		std::shared_ptr<clang::tooling::JSONCompilationDatabase> cdb = IndexerCommandCxx::loadCDB(cdbPath);
 		if (cdb)
 		{
-			const std::set<FilePath>& sourceFilePaths = getAllSourceFilePaths(cdb);
+			const std::set<FilePath> sourceFilePaths = getAllSourceFilePaths(cdb);
 			for (const clang::tooling::CompileCommand& command: cdb->getAllCompileCommands())
 			{
 				FilePath sourcePath = FilePath(utility::decodeFromUtf8(command.Filename)).makeCanonical();
@@ -177,11 +177,11 @@ std::shared_ptr<Task> SourceGroupCxxCdb::getPreIndexTask(
 					}
 				}
 
-				if (sourceFilePaths.find(sourcePath) != sourceFilePaths.end())
+				if (sourceFilePaths.find(sourcePath) != sourceFilePaths.end() && utility::containsIncludePchFlag(command.CommandLine))
 				{
 					for (const std::string& arg : command.CommandLine)
 					{
-						if ((compilerFlags.size() || utility::isPrefix<std::string>("-", arg)) &&
+						if ((!compilerFlags.empty() || utility::isPrefix<std::string>("-", arg)) &&
 							FilePath(arg).fileName() != sourcePath.fileName())
 						{
 							compilerFlags.emplace_back(utility::decodeFromUtf8(arg));

src/lib_cxx/project/utilitySourceGroupCxx.cpp

@@ -109,10 +109,21 @@ namespace utility
 	{
 		for (const clang::tooling::CompileCommand& command : cdb->getAllCompileCommands())
 		{
-			if (command.CommandLine.size() != getWithRemoveIncludePchFlag(utility::convert<std::string, std::wstring>(
-				command.CommandLine,
-				[](const std::string& s) {return utility::decodeFromUtf8(s); }
-				)).size())
+			if (containsIncludePchFlag(command.CommandLine))
+			{
+				return true;
+			}
+		}
+		return false;
+	}
+
+	bool containsIncludePchFlag(const std::vector<std::string>& args)
+	{
+		const std::string includePchPrefix = "-include-pch";
+		for (size_t i = 0; i < args.size(); i++)
+		{
+			const std::string arg = utility::trim(args[i]);
+			if (utility::isPrefix(includePchPrefix, arg))
 			{
 				return true;
 			}

src/lib_cxx/project/utilitySourceGroupCxx.h

@@ -22,6 +22,7 @@ namespace utility
 		const SourceGroupSettingsCxx* settings, std::vector<std::wstring> compilerFlags,
 		std::shared_ptr<StorageProvider> storageProvider, std::shared_ptr<DialogView> dialogView);
 	bool containsIncludePchFlags(std::shared_ptr<clang::tooling::JSONCompilationDatabase> cdb);
+	bool containsIncludePchFlag(const std::vector<std::string>& args);
 	std::vector<std::wstring> getWithRemoveIncludePchFlag(const std::vector<std::wstring>& args);
 	void removeIncludePchFlag(std::vector<std::wstring>& args);
 	std::vector<std::wstring> getIncludePchFlags(const SourceGroupSettingsCxx* settings);

src/lib_gui/qt/project_wizard/content/path/QtProjectWizardContentPathCxxPch.cpp

@@ -22,6 +22,9 @@ QtProjectWizardContentPathCxxPch::QtProjectWizardContentPathCxxPch(
 	setHelpString(
 		"Specify the path to the input header file that should be used to generate a precompiled header before indexing.<br />"
 		"If the indexed source code is usually built using precompiled headers, using this option will speed up your indexing performance.<br />"
+		"<br />"
+		"If your source files use precompiled headers via \"#include &lt;pch.h&gt;\", specify \"path/to/pch.h\".<br />"
+		"<br />"
 		"Leave blank to disable the use of precompiled headers. You can make use of environment variables with ${ENV_VAR}."
 	);
 	setAllowEmpty(true);
@@ -64,9 +67,18 @@ bool QtProjectWizardContentPathCxxPch::check()
 			if (m_settingsCxxPch->getPchInputFilePath().empty())
 			{
 				QMessageBox msgBox;
-				msgBox.setText("The provided compilation database file uses precompiled headers. Please specify a Precompiled Header input file.");
+				msgBox.setText(
+					"The provided compilation database file uses precompiled headers. If you want to make use of "
+					"precompiled headers to speed up your indexer, please specify an input at Precompiled Header File."
+				);
+				QPushButton* cancelButton = msgBox.addButton("Cancel", QMessageBox::ButtonRole::RejectRole);
+				QPushButton* continueButton = msgBox.addButton("Continue", QMessageBox::ButtonRole::AcceptRole);
 				msgBox.exec();
-				return false;
+				if (msgBox.clickedButton() == cancelButton)
+				{
+					return false;
+				}
+				return true;
 			}
 		}
 		else
@@ -74,9 +86,12 @@ bool QtProjectWizardContentPathCxxPch::check()
 			if (!m_settingsCxxPch->getPchInputFilePath().empty())
 			{
 				QMessageBox msgBox;
-				msgBox.setText("The provided compilation database file does not use precompiled headers. Please do not specify a Precompiled Header input file.");
+				msgBox.setText(
+					"The provided compilation database file does not use precompiled headers. The specified input file at "
+					"Precompiled Header File will not be used."
+				);
 				msgBox.exec();
-				return false;
+				return true;
 			}
 		}
 	}