Raise the window in single-instance mode

Other than issuing a warning on the console, now the LyX window is
raised when in single-instance mode and no files to load are specified.
In this way, the user is aware that something happened after double
clicking the program icon. To support this functionality the new lfun
window-raise has been introduced.

src/FuncCode.h

@@ -489,6 +489,7 @@ enum FuncCode
 	// 380
 	LFUN_MASTER_BUFFER_FORALL,      // spitz 20191231
 	LFUN_IF_RELATIVES,              // spitz 20200102
+	LFUN_WINDOW_RAISE,              // forenr, 20202104
 	LFUN_LASTACTION                 // end of the table
 };
 

src/LyXAction.cpp

@@ -4220,6 +4220,18 @@ void LyXAction::init()
  */
 		{ LFUN_WINDOW_NEW, "window-new", NoBuffer, Buffer },
 
+/*!
+ * \var lyx::FuncCode lyx::LFUN_WINDOW_RAISE
+ * \li Action: Raises the LyX window.
+ * \li Notion: Brings the LyX window to the front. Such behavior is allowed
+               on Windows only when no other application has focus.
+               This action is used when LyX is in single instance mode.
+ * \li Syntax: window-raise
+ * \li Origin: forenr, 21 Apr 2020
+ * \endvar
+ */
+		{ LFUN_WINDOW_RAISE, "window-raise", ReadOnly | NoBuffer, Hidden },
+
 /*!
  * \var lyx::FuncCode lyx::LFUN_WORD_BACKWARD
  * \li Action: Moves the cursor to the logically previous beginning of a word.

src/Server.cpp

@@ -1002,14 +1002,25 @@ struct Sleep : QThread
 
 bool LyXComm::loadFilesInOtherInstance()
 {
+	int pipefd;
+	FileName const pipe(inPipeName());
+
 	if (theFilesToLoad().empty()) {
 		LYXERR0("LyX is already running in another instance\n"
 			"and 'use single instance' is active.");
+		// Wait a while for the other instance to reset the connection
+		Sleep::millisec(200);
+		pipefd = ::open(pipe.toFilesystemEncoding().c_str(), O_WRONLY);
+		if (pipefd >= 0) {
+			string const cmd = "LYXCMD:pipe:window-raise\n";
+			if (::write(pipefd, cmd.c_str(), cmd.length()) < 0)
+				LYXERR0("Cannot communicate with running instance!");
+			::close(pipefd);
+		}
 		return true;
 	}
-	int pipefd;
+
 	int loaded_files = 0;
-	FileName const pipe(inPipeName());
 	vector<string>::iterator it = theFilesToLoad().begin();
 	while (it != theFilesToLoad().end()) {
 		FileName fname = fileSearch(string(), os::internal_path(*it),

src/frontends/qt/GuiView.cpp

@@ -2312,6 +2312,7 @@ bool GuiView::getStatus(FuncRequest const & cmd, FuncStatus & flag)
 
 	case LFUN_SERVER_GOTO_FILE_ROW:
 	case LFUN_LYX_ACTIVATE:
+	case LFUN_WINDOW_RAISE:
 		break;
 	case LFUN_FORWARD_SEARCH:
 		enable = !(lyxrc.forward_search_dvi.empty() && lyxrc.forward_search_pdf.empty());
@@ -4502,6 +4503,12 @@ void GuiView::dispatch(FuncRequest const & cmd, DispatchResult & dr)
 			activateWindow();
 			break;
 
+		case LFUN_WINDOW_RAISE:
+			raise();
+			activateWindow();
+			showNormal();
+			break;
+
 		case LFUN_FORWARD_SEARCH: {
 			// it seems safe to assume we have a document buffer, since
 			// getStatus wants one.