[PATCH 2/2] user32: Post message when callback pointer is NULL and callback data is 1 in SendMessageCallbackA/W().

[Zhiyi Zhang]

From: Zhiyi Zhang

This is an undocumented behavior needed by React Native apps, based on Nikolay's findings.
---
 dlls/user32/message.c   | 7 +++++++
 dlls/user32/tests/msg.c | 8 ++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/dlls/user32/message.c b/dlls/user32/message.c
index 205d3e01c02..3b541959faf 100644
--- a/dlls/user32/message.c
+++ b/dlls/user32/message.c
@@ -640,6 +640,9 @@ BOOL WINAPI SendMessageCallbackA( HWND hwnd, UINT msg, WPARAM wparam, LPARAM lpa
 {
     struct send_message_callback_params params = { .callback = callback, .data = data };

+    if (!callback && data == 1)
+        return PostMessageA( hwnd, msg, wparam, lparam );
+
     if (!WIN_IsCurrentThread( hwnd ) && !map_wparam_AtoW( msg, &wparam, WMCHAR_MAP_SENDMESSAGE ))
         return FALSE;

@@ -654,6 +657,10 @@ BOOL WINAPI SendMessageCallbackW( HWND hwnd, UINT msg, WPARAM wparam, LPARAM lpa
                                   SENDASYNCPROC callback, ULONG_PTR data )
 {
     struct send_message_callback_params params = { .callback = callback, .data = data };
+
+    if (!callback && data == 1)
+        return PostMessageW( hwnd, msg, wparam, lparam );
+
     return NtUserMessageCall( hwnd, msg, wparam, lparam, &params, NtUserSendMessageCallback, FALSE );
 }

diff --git a/dlls/user32/tests/msg.c b/dlls/user32/tests/msg.c
index 1c2d61c7781..9089e96aa84 100644
--- a/dlls/user32/tests/msg.c
+++ b/dlls/user32/tests/msg.c
@@ -16525,16 +16525,16 @@ static void test_nullCallback(void)
     /* NULL callback and data being 1. The result suggests that the message is posted to the window */
     flush_sequence();
     SendMessageCallbackA(hwnd, WM_USER, 0, 0, NULL, 1);
-    ok_sequence(WmEmptySeq, "WM_USER with NULL callback", TRUE);
+    ok_sequence(WmEmptySeq, "WM_USER with NULL callback", FALSE);
     flush_events();
-    ok_sequence(WmUserSeq, "WM_USER with NULL callback after flushing events", TRUE);
+    ok_sequence(WmUserSeq, "WM_USER with NULL callback after flushing events", FALSE);

/* NULL callback and data being 1. The result suggests that the message is posted to the window */
     flush_sequence();
     SendMessageCallbackW(hwnd, WM_USER, 0, 0, NULL, 1);
-    ok_sequence(WmEmptySeq, "WM_USER with NULL callback", TRUE);
+    ok_sequence(WmEmptySeq, "WM_USER with NULL callback", FALSE);
     flush_events();
-    ok_sequence(WmUserSeq, "WM_USER with NULL callback after flushing events", TRUE);
+    ok_sequence(WmUserSeq, "WM_USER with NULL callback after flushing events", FALSE);

/* NULL callback and data being 2 */
     flush_sequence();