emacs-27 a4e4510: Fix handling MS-Windows keyboard input above the BMP

[Eli Zaretskii]

branch: emacs-27
commit a4e4510ccd92da8ca17743c7dab9b32fc9d850e7
Author: Eli Zaretskii <address@hidden>
Commit: Eli Zaretskii <address@hidden>

    Fix handling MS-Windows keyboard input above the BMP
    
    * src/w32term.c (w32_read_socket): If we get a WM_UNICHAR message
    with a surrogate codepoint, assemble the corresponding character
    code above the BMP from its UTF-16 encoding, communicated in two
    consecutive WM_UNICHAR messages.
---
 src/w32term.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/w32term.c b/src/w32term.c
index 4eb5045..f515f56 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -4701,6 +4701,10 @@ static short temp_buffer[100];
 /* Temporarily store lead byte of DBCS input sequences.  */
 static char dbcs_lead = 0;
 
+/* Temporarily store pending UTF-16 high surrogate unit and the modifiers.  */
+static unsigned short utf16_high;
+static DWORD utf16_high_modifiers;
+
 /**
   mouse_or_wdesc_frame: When not dropping and the mouse was grabbed
   for DPYINFO, return the frame where the mouse was seen last.  If
@@ -4912,9 +4916,45 @@ w32_read_socket (struct terminal *terminal,
              XSETFRAME (inev.frame_or_window, f);
              inev.timestamp = msg.msg.time;
 
+             if (utf16_high
+                 && (msg.msg.message != WM_UNICHAR
+                     || UTF_16_HIGH_SURROGATE_P (msg.msg.wParam)))
+               {
+                 /* Flush the pending high surrogate if the low one
+                    isn't coming.  (This should never happen, but I
+                    have paranoia about this stuff.)  */
+                 struct input_event inev1;
+                 inev1.modifiers = utf16_high_modifiers;
+                 inev1.code = utf16_high;
+                 inev1.timestamp = inev.timestamp;
+                 inev1.arg = Qnil;
+                 kbd_buffer_store_event_hold (&inev1, hold_quit);
+                 utf16_high = 0;
+                 utf16_high_modifiers = 0;
+               }
+
               if (msg.msg.message == WM_UNICHAR)
                 {
-                  inev.code = msg.msg.wParam;
+                 /* Handle UTF-16 encoded codepoint above the BMP.
+                    This is needed to support Emoji input from input
+                    panel popped up by "Win+." shortcut.  */
+                 if (UTF_16_HIGH_SURROGATE_P (msg.msg.wParam))
+                   {
+                     utf16_high = msg.msg.wParam;
+                     utf16_high_modifiers = inev.modifiers;
+                     inev.kind = NO_EVENT;
+                     break;
+                   }
+                 else if (UTF_16_LOW_SURROGATE_P (msg.msg.wParam)
+                          && utf16_high)
+                   {
+                     inev.code = surrogates_to_codepoint (msg.msg.wParam,
+                                                          utf16_high);
+                     utf16_high = 0;
+                     utf16_high_modifiers = 0;
+                   }
+                 else
+                   inev.code = msg.msg.wParam;
                 }
               else if (msg.msg.wParam < 256)
                 {