Tk Source Code

wm iconbitmap does not correctly set hints.icon_pixmap and hints.flags on macOS unless the argument is an empty string. After wm iconbitmap . hourglass, wm iconbitmap . returns "hourglass" on Linux and Windows, but an empty string on macOS.

It looks that the else block is placed after wrong if. Other bug is that the function always returns TCL_OK even if WmSetAttribute() fails. Comparing with the code on Linux and Windows, I believe that the following patch should fix the issue:

Index: macosx/tkMacOSXWm.c
==================================================================
--- macosx/tkMacOSXWm.c
+++ macosx/tkMacOSXWm.c
@@ -2975,18 +2975,19 @@
     }
     if (!TkMacOSXHostToplevelExists(winPtr)) {
        TkMacOSXMakeRealWindowExist(winPtr);
     }
     if (WmSetAttribute(winPtr, TkMacOSXGetNSWindowForDrawable(winPtr->window), interp,
-           WMATT_TITLEPATH, objv[3]) == TCL_OK) {
-       if (!len) {
-           if (wmPtr->hints.icon_pixmap != None) {
-               Tk_FreeBitmap(winPtr->display, wmPtr->hints.icon_pixmap);
-               wmPtr->hints.icon_pixmap = None;
-           }
-           wmPtr->hints.flags &= ~IconPixmapHint;
-       }
+           WMATT_TITLEPATH, objv[3]) != TCL_OK) {
+       return TCL_ERROR;
+    }
+    if (!len) {
+       if (wmPtr->hints.icon_pixmap != None) {
+           Tk_FreeBitmap(winPtr->display, wmPtr->hints.icon_pixmap);
+           wmPtr->hints.icon_pixmap = None;
+       }
+       wmPtr->hints.flags &= ~IconPixmapHint;
     } else {
        pixmap = Tk_GetBitmap(interp, (Tk_Window)winPtr, str);
        if (pixmap == None) {
            return TCL_ERROR;
        }

I encountered this bug after adding tests for Tkinter (https://github.com/python/cpython/pull/128015).

This bug was already known (ticket [119bb094afd86d959039]), but it was closed without proper fix. So you need also to restore the skipped tests on macOS.