Stop walking window tree if we get zero

[brndnmtthws]

It looks like some of the child windows are zero, which causes the next call to XQueryTree to blow up.

cc @Caellian

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[Caellian]

I'm going to test this locally because no parent should return 0 (root window) as child from XQueryTree. I'd like to install your WM and debug last_descendant() a bit because 0 being returned as child is weird.

It might be better to check whether conky is drawing on root (if that's your config) from code that's calling last_descendant() before calling last_descendant in order to skip to bound checking - query_result being default initialized would work the same for that case without the extra X11 calls.

The reason that function was needed is because plasma created 2/3 nested nodes for conky with the following settings:

own_window = true,
own_window_type = 'normal',
own_window_hints = 'undecorated,below,sticky,skip_taskbar,skip_pager',

so there was no simpler way to check whether the cursor was over conky, because the window stored in globals points to the deepest descendant, and one of container windows is returned by XQueryPointer.

I think it's also redundant to check for all three of root, window, desktop from conky_x11_window in the if statement below, so I'd like to clean up/simplify that check.

EDIT: Checking it out now on plasma. XFCE worked fine (1 crash with weird setup; hard to reproduce).

[brndnmtthws]

I'm going to test this locally because no parent should return 0 (root window) as child from XQueryTree. I'd like to install your WM and debug last_descendant() a bit because 0 being returned as child is weird.

From the stack trace, it's calling XQueryTree with current=0, like this:

#13 0x00007ffff7dfac3c in XQueryTree (dpy=0x5555557b4c10, w=0, root=0x7fffffffdac0, parent=0x7fffffffdac0, children=0x7fffffffdad0, nchildren=0x7fffffffdaac) at /usr/src/debug/libx11/libX11-1.8.7/src/QuTree.c:47

So if current is 0, that implies it's either 1) calling with 0 on the first pass, or 2) eventually getting 0 as a child.

[Caellian]

Calling XQueryTree with w=0 causes BadWindow and then children array is empty (which exits the loop). That's caught by x11_error_handler, X11 errors don't terminate conky though (or apps in general).

The cause of the crash from the issues is in x11_error_handler and it crashes because I incorrectly calculated size for error_name when calling snprintf. Fixed it in: #1748.

Calling XQueryTree on root (0) happens when the cursor is on desktop (i.e. 0 on the first pass case). query_x11_window_at_pos should check if last == 0 and return 0 instead of calling last_descendant. I added this check in the linker PR.

[brndnmtthws]

Closing this in favour of #1748