Wayland: Fix erratic fallback decoration behavior

The handler for xdg_toplevel::configure treated the provided size as the
content area size when instead it is the size of the bounding rectangle
of the wl_surface and all its subsurfaces.

This caused the fallback decorations to try positioning themselves
outside themselves, causing feedback loops during interactive resizing.

Fixes #1991
Fixes #2115
Closes #2127
Related to #1914

CONTRIBUTORS.md

@@ -24,6 +24,7 @@ video tutorials.
  - Waris Boonyasiriwat
  - Kyle Brenneman
  - Rok Breulj
+ - TheBrokenRail
  - Kai Burjack
  - Martin Capitanio
  - Nicolas Caramelli
@@ -145,6 +146,7 @@ video tutorials.
  - Pierre Moulon
  - Martins Mozeiko
  - Pascal Muetschard
+ - James Murphy
  - Julian Møller
  - ndogxj
  - n3rdopolis

README.md

@@ -343,6 +343,8 @@ information on what to include when reporting a bug.
  - [Wayland] Bugfix: A window content scale event would be emitted every time
    the window resized
  - [Wayland] Bugfix: If `glfwInit` failed it would close stdin
+ - [Wayland] Bugfix: Manual resizing with fallback decorations behaved erratically
+   (#1991,#2115,#2127)
  - [POSIX] Removed use of deprecated function `gettimeofday`
  - [POSIX] Bugfix: `CLOCK_MONOTONIC` was not correctly tested for or enabled
  - [WGL] Disabled the DWM swap interval hack for Windows 8 and later (#1072)

src/wl_window.c

@@ -495,8 +495,17 @@ static void xdgToplevelHandleConfigure(void* userData,
 
     if (width && height)
     {
-        window->wl.pending.width  = width;
-        window->wl.pending.height = height;
+        if (window->wl.decorations.top.surface)
+        {
+            window->wl.pending.width  = _glfw_max(0, width - GLFW_BORDER_SIZE * 2);
+            window->wl.pending.height =
+                _glfw_max(0, height - GLFW_BORDER_SIZE - GLFW_CAPTION_HEIGHT);
+        }
+        else
+        {
+            window->wl.pending.width  = width;
+            window->wl.pending.height = height;
+        }
     }
     else
     {