From 2fded1aab29242a86fe582c7162c2f1bf7bfec28 Mon Sep 17 00:00:00 2001
From: Peru S <perumaal@mindfulplays.com>
Date: Tue, 29 Jul 2025 12:53:19 -0700
Subject: [PATCH 1/2] Fix windowProc when SetPropW() fails silently

**Issue**

In some cases, on Windows, `SetPropW` returns `FALSE`.
glfw currently silently ignores the result.
This means that the message pump `windowProc` fails to work (does not receive keyboard events for example). Drawing is fine though as it's a different GLFW mechanism.

I had this failure frequently infrequently and it was frustrating to deal with (just have to rerun the program a few times and hope `SetPropW` doesn't return `FALSE`). So sending this fix in case others are facing the issue on Windows.

**Fix**

On Windows+GLFW, `windowProc` will fallback to looking up the GLFW window list (just like `PollEvents` does).
Also added the error code to `_glfwInputError` message to aid debugging in the future.

My suggestion is to get rid of `SetPropW`/`GetPropW` as it is a string-based Windows API (slow/fragile) - we already have the lightweight linked list, might as well just use it always - also it's usually just the one or two windows we deal with.

- [x] Verified on Windows - message pump is stable with this fix (once I was able to repro this issue).
---
 src/win32_init.c   |  5 +++--
 src/win32_window.c | 25 +++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/win32_init.c b/src/win32_init.c
index 6b6e9d08..5e06c4de 100644
--- a/src/win32_init.c
+++ b/src/win32_init.c
@@ -493,18 +493,19 @@ void _glfwInputErrorWin32(int error, const char* description)
     WCHAR buffer[_GLFW_MESSAGE_SIZE] = L"";
     char message[_GLFW_MESSAGE_SIZE] = "";
 
+    DWORD lastError = GetLastError();
     FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM |
                        FORMAT_MESSAGE_IGNORE_INSERTS |
                        FORMAT_MESSAGE_MAX_WIDTH_MASK,
                    NULL,
-                   GetLastError() & 0xffff,
+                   lastError & 0xffff,
                    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                    buffer,
                    sizeof(buffer) / sizeof(WCHAR),
                    NULL);
     WideCharToMultiByte(CP_UTF8, 0, buffer, -1, message, sizeof(message), NULL, NULL);
 
-    _glfwInputError(error, "%s: %s", description, message);
+    _glfwInputError(error, "%s (0x%lx / %lu): %s", description, lastError, lastError, message);
 }
 
 // Updates key names according to the current keyboard layout
diff --git a/src/win32_window.c b/src/win32_window.c
index 26f9684b..e9da0821 100644
--- a/src/win32_window.c
+++ b/src/win32_window.c
@@ -548,8 +548,23 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM l
                     EnableNonClientDpiScaling(hWnd);
             }
         }
+        else
+        {
+            // HACK: SetPropW returns FALSE in some instances (GetLastError() = 0x8 Insufficient resources).
+            //       We already have the global list of windows, check against it. It's not many, and we are already
+            //       doing this in the (one of the callers) PollEvents below.
+            window = _glfw.windowListHead;
+            while (window)
+            {
+                if (window->win32.handle == hWnd) { break; }
+                window = window->next;
+            }
+        }
 
-        return DefWindowProcW(hWnd, uMsg, wParam, lParam);
+        if (!window)
+        {
+            return DefWindowProcW(hWnd, uMsg, wParam, lParam);
+        }
     }
 
     switch (uMsg)
@@ -1401,7 +1416,13 @@ static int createNativeWindow(_GLFWwindow* window,
         return GLFW_FALSE;
     }
 
-    SetPropW(window->win32.handle, L"GLFW", window);
+    if (!SetPropW(window->win32.handle, L"GLFW", window))
+    {
+        // In some cases, SetPropW returns FALSE: GetLastError() returns 0x8 (Insufficient resources).
+        // The message pump fails to work because windowProc cannot look up the GLFW property.
+        // Instead of failing the program completely by raising an error instead, windowProc looks up
+        // the global window list to find the hWnd under consideration.
+    }
 
     ChangeWindowMessageFilterEx(window->win32.handle, WM_DROPFILES, MSGFLT_ALLOW, NULL);
     ChangeWindowMessageFilterEx(window->win32.handle, WM_COPYDATA, MSGFLT_ALLOW, NULL);

From 959f13c1bd686821044bc3fae9008167fef22987 Mon Sep 17 00:00:00 2001
From: Peru S <perumaal@mindfulplays.com>
Date: Tue, 29 Jul 2025 12:59:07 -0700
Subject: [PATCH 2/2] Add to CONTRIBUTORS.md and README.md

---
 CONTRIBUTORS.md | 1 +
 README.md       | 1 +
 2 files changed, 2 insertions(+)

diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index 8fa1cb72..ea85f001 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -232,6 +232,7 @@ video tutorials.
  - Jan Schürkamp
  - Christian Sdunek
  - Matt Sealey
+ - Perumaal Shanmugam
  - Steve Sexton
  - Arkady Shapkin
  - Mingjie Shen
diff --git a/README.md b/README.md
index c453739d..4fbfb565 100644
--- a/README.md
+++ b/README.md
@@ -139,6 +139,7 @@ information on what to include when reporting a bug.
  - [Null] Added EGL context creation on Mesa via `EGL_MESA_platform_surfaceless`
  - [EGL] Allowed native access on Wayland with `GLFW_CONTEXT_CREATION_API` set to
    `GLFW_NATIVE_CONTEXT_API` (#2518)
+ - [Win32] Bugfix: Fix `windowProc` to work when `SetPropW` fails silently
 
 
 ## Contact