Add back X11 legacy WM_NAME encodings

Closes #4924.

Based on patches of the past, such as this work by James Cloos in July
2010:
https://github.com/exg/rxvt-unicode/commit/d7d98751b7385416ad1694b5f1fde6c312ba20d5,
as well as code comments in the Perl module X11::Protocol::WM
(https://metacpan.org/pod/X11::Protocol::WM) and even the code to Xlib
itself, which taught me that we should never have been using
`XStoreName`, all it does is call `XChangeProperty`, hardcoded to
`XA_STRING`!

What can I say, when the task is old school, the sources are too 😂

src/video/x11/SDL_x11messagebox.c

@@ -404,11 +404,10 @@ X11_MessageBoxCreateWindow( SDL_MessageBoxDataX11 *data )
     int x, y;
     XSizeHints *sizehints;
     XSetWindowAttributes wnd_attr;
-    Atom _NET_WM_WINDOW_TYPE, _NET_WM_WINDOW_TYPE_DIALOG, _NET_WM_NAME;
+    Atom _NET_WM_WINDOW_TYPE, _NET_WM_WINDOW_TYPE_DIALOG;
     Display *display = data->display;
     SDL_WindowData *windowdata = NULL;
     const SDL_MessageBoxData *messageboxdata = data->messageboxdata;
-    char *title_locale = NULL;
 
     if ( messageboxdata->window ) {
         SDL_DisplayData *displaydata =
@@ -452,32 +451,7 @@ X11_MessageBoxCreateWindow( SDL_MessageBoxDataX11 *data )
         X11_XSetTransientForHint( display, data->window, windowdata->xwindow );
     }
 
-    X11_XStoreName( display, data->window, messageboxdata->title );
-    _NET_WM_NAME = X11_XInternAtom(display, "_NET_WM_NAME", False);
-
-    title_locale = SDL_iconv_utf8_locale(messageboxdata->title);
-    if (title_locale) {
-        XTextProperty titleprop;
-        Status status = X11_XStringListToTextProperty(&title_locale, 1, &titleprop);
-        SDL_free(title_locale);
-        if (status) {
-            X11_XSetTextProperty(display, data->window, &titleprop, XA_WM_NAME);
-            X11_XFree(titleprop.value);
-        }
-    }
-
-#ifdef X_HAVE_UTF8_STRING
-    if (SDL_X11_HAVE_UTF8) {
-        XTextProperty titleprop;
-        Status status = X11_Xutf8TextListToTextProperty(display, (char **) &messageboxdata->title, 1,
-                                            XUTF8StringStyle, &titleprop);
-        if (status == Success) {
-            X11_XSetTextProperty(display, data->window, &titleprop,
-                                 _NET_WM_NAME);
-            X11_XFree(titleprop.value);
-        }
-    }
-#endif
+    SDL_X11_SetWindowTitle(display, data->window, (char*)messageboxdata->title);
 
     /* Let the window manager know this is a dialog box */
     _NET_WM_WINDOW_TYPE = X11_XInternAtom(display, "_NET_WM_WINDOW_TYPE", False);

src/video/x11/SDL_x11sym.h

@@ -156,6 +156,9 @@ SDL_X11_SYM(SDL_X11_XESetWireToEventRetType,XESetWireToEvent,(Display* a,int b,S
 SDL_X11_SYM(SDL_X11_XESetEventToWireRetType,XESetEventToWire,(Display* a,int b,SDL_X11_XESetEventToWireRetType c),(a,b,c),return)
 SDL_X11_SYM(void,XRefreshKeyboardMapping,(XMappingEvent *a),(a),)
 SDL_X11_SYM(int,XQueryTree,(Display* a,Window b,Window* c,Window* d,Window** e,unsigned int* f),(a,b,c,d,e,f),return)
+SDL_X11_SYM(Bool,XSupportsLocale,(void),(),return)
+SDL_X11_SYM(void,XSetWMName,(Display* a,Window b,XTextProperty* c),(a,b,c),return)
+SDL_X11_SYM(Status,XmbTextListToTextProperty,(Display* a,char** b,int c,XICCEncodingStyle d,XTextProperty* e),(a,b,c,d,e),return)
 
 #if SDL_VIDEO_DRIVER_X11_XFIXES
 SDL_X11_MODULE(XFIXES)

src/video/x11/SDL_x11video.c

@@ -460,6 +460,14 @@ X11_VideoInit(_THIS)
     X11_InitXfixes(_this);
 #endif /* SDL_VIDEO_DRIVER_X11_XFIXES */
 
+#ifndef X_HAVE_UTF8_STRING
+    SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "X server doesn't support UTF8_STRING, a feature introduced in 2000! This is likely to become a hard error in a future libSDL2.");
+#endif
+
+    if (X11_XSupportsLocale() != True) {
+        return SDL_SetError("Current locale not supported by X server, cannot continue.");
+    }
+
     if (X11_InitKeyboard(_this) != 0) {
         return -1;
     }

src/video/x11/SDL_x11window.c

@@ -716,9 +716,11 @@ X11_GetWindowTitle(_THIS, Window xwindow)
                     0L, 8192L, False, XA_STRING, &real_type, &real_format,
                     &items_read, &items_left, &propdata);
         if (status == Success && propdata) {
+            SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Failed to convert _WM_NAME title expecting UTF8! Title: %s", title);
             title = SDL_iconv_string("UTF-8", "", SDL_static_cast(char*, propdata), items_read+1);
             X11_XFree(propdata);
         } else {
+            SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Could not get any window title response from Xorg, returning empty string!");
             title = SDL_strdup("");
         }
     }
@@ -729,30 +731,11 @@ void
 X11_SetWindowTitle(_THIS, SDL_Window * window)
 {
     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
+    Window xwindow = data->xwindow;
     Display *display = data->videodata->display;
-    Status status;
-    const char *title = window->title ? window->title : "";
-
-    Atom UTF8_STRING = data->videodata->UTF8_STRING;
-    Atom _NET_WM_NAME = data->videodata->_NET_WM_NAME;
-    Atom WM_NAME = data->videodata->WM_NAME;
-
-    X11_XChangeProperty(display, data->xwindow, WM_NAME, UTF8_STRING, 8, 0, (const unsigned char *) title, SDL_strlen(title));
+    char *title = window->title ? window->title : "";
 
-    status = X11_XChangeProperty(display, data->xwindow, _NET_WM_NAME, UTF8_STRING, 8, 0, (const unsigned char *) title, SDL_strlen(title));
-
-    if (status != 1) {
-        char *x11_error = NULL;
-        char x11_error_locale[256];
-        if (X11_XGetErrorText(display, status, x11_error_locale, sizeof(x11_error_locale)) == Success)
-        {
-            x11_error = SDL_iconv_string("UTF-8", "", x11_error_locale, SDL_strlen(x11_error_locale)+1);
-            SDL_LogDebug(SDL_LOG_CATEGORY_VIDEO, "Error when setting X11 window title to %s: %s\n", title, x11_error);
-            SDL_free(x11_error);
-        }
-    }
-
-    X11_XFlush(display);
+    SDL_X11_SetWindowTitle(display, xwindow, title);
 }
 
 void
@@ -1888,6 +1871,39 @@ X11_FlashWindow(_THIS, SDL_Window * window, SDL_FlashOperation operation)
     return 0;
 }
 
+bool SDL_X11_SetWindowTitle(Display* display, Window xwindow, char* title) {
+    Atom _NET_WM_NAME = X11_XInternAtom(display, "_NET_WM_NAME", False);
+    XTextProperty titleprop;
+    int conv = X11_XmbTextListToTextProperty(display, (char**) &title, 1, XStdICCTextStyle, &titleprop);
+    Status status;
+
+    if (conv == 0) {
+        X11_XSetTextProperty(display, xwindow, &titleprop, XA_WM_NAME);
+        X11_XFree(titleprop.value);
+    // we know this can't be a locale error as we checked X locale validity in X11_VideoInit
+    } else if (conv <= 0) {
+        SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "X11 reporting it's out of memory");
+        return EXIT_FAILURE;
+    } else { // conv >= 0
+        SDL_LogWarn(SDL_LOG_CATEGORY_VIDEO, "%d characters were not convertable to the current locale!", conv);
+        return EXIT_FAILURE;
+    }
+
+#ifdef X_HAVE_UTF8_STRING
+    status = X11_Xutf8TextListToTextProperty(display, (char **) &title, 1, XUTF8StringStyle, &titleprop);
+    if (status == Success) {
+        X11_XSetTextProperty(display, xwindow, &titleprop, _NET_WM_NAME);
+        X11_XFree(titleprop.value);
+    } else {
+        SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Failed to convert title to UTF8! Bad encoding, or bad Xorg encoding? Window title: «%s»", title);
+        return EXIT_FAILURE;
+    }
+#endif
+
+    X11_XFlush(display);
+    return EXIT_SUCCESS;
+}
+
 #endif /* SDL_VIDEO_DRIVER_X11 */
 
 /* vi: set ts=4 sw=4 expandtab: */

src/video/x11/SDL_x11window.h

@@ -117,6 +117,8 @@ extern int X11_SetWindowHitTest(SDL_Window *window, SDL_bool enabled);
 extern void X11_AcceptDragAndDrop(SDL_Window * window, SDL_bool accept);
 extern int X11_FlashWindow(_THIS, SDL_Window * window, SDL_FlashOperation operation);
 
+bool SDL_X11_SetWindowTitle(Display* display, Window xwindow, char* string);
+
 #endif /* SDL_x11window_h_ */
 
 /* vi: set ts=4 sw=4 expandtab: */