(Fw32_set_clipboard_data): Save a copy of what is put on the clipboard.

(Fw32_get_clipboard_data): Compare data on clipboard with saved copy
of what Emacs last put there. If they are the same, do not use the
clipboard copy to avoid losing data due to coding conversions.

1 files changed, 44 insertions, 10 deletions

diff --git a/src/w32select.c b/src/w32select.c
index 560fad01a20..520610ee961 100644
--- a/src/w32select.c
+++ b/src/w32select.c
@@ -37,9 +37,18 @@ Lisp_Object QCLIPBOARD;
    clipboard.  */
 static Lisp_Object Vselection_coding_system;
 
-/* Coding system for the next communicating with other X clients.  */
+/* Coding system for the next communicating with other Windows programs.  */
 static Lisp_Object Vnext_selection_coding_system;
 
+/* The last text we put into the clipboard.  This is used to prevent
+   passing back our own text from the clipboard, instead of using the
+   kill ring.  The former is undesirable because the clipboard data
+   could be MULEtilated by inappropriately chosen
+   (next-)selection-coding-system.  For this reason, we must store the
+   text *after* it was encoded/Unix-to-DOS-converted.  */
+static unsigned char *last_clipboard_text = NULL;
+static size_t clipboard_storage_size = 0;
+
 #if 0
 DEFUN ("w32-open-clipboard", Fw32_open_clipboard, Sw32_open_clipboard, 0, 1, 0,
        "This opens the clipboard with the given frame pointer.")
@@ -174,10 +183,8 @@ DEFUN ("w32-set-clipboard-data", Fw32_set_clipboard_data, Sw32_set_clipboard_dat
       }
     else
       {
-        /* We must encode contents of OBJ to compound text format.
-           The format is compatible with what the target `STRING'
-           expects if OBJ contains only ASCII and Latin-1
-           characters.  */
+        /* We must encode contents of OBJ to the selection coding
+           system. */
         int bufsize;
         struct coding_system coding;
         HANDLE htext2;
@@ -197,16 +204,31 @@ DEFUN ("w32-set-clipboard-data", Fw32_set_clipboard_data, Sw32_set_clipboard_dat
           goto error;
         encode_coding (&coding, src, dst, nbytes, bufsize);
         Vlast_coding_system_used = coding.symbol;
+
+        /* Stash away the data we are about to put into the clipboard, so we
+           could later check inside Fw32_get_clipboard_data whether
+           the clipboard still holds our data.  */
+        if (clipboard_storage_size < coding.produced)
+          {
+            clipboard_storage_size = coding.produced + 100;
+            last_clipboard_text = (char *) xrealloc (last_clipboard_text,
+                                                     clipboard_storage_size);
+          }
+        if (last_clipboard_text)
+          memcpy (last_clipboard_text, dst, coding.produced);
+
         GlobalUnlock (htext);
+
         /* Shrink data block to actual size.  */
-        htext2 = GlobalReAlloc (htext, coding.produced, GMEM_MOVEABLE | GMEM_DDESHARE);
+        htext2 = GlobalReAlloc (htext, coding.produced,
+                                GMEM_MOVEABLE | GMEM_DDESHARE);
         if (htext2 != NULL) htext = htext2;
       }
   }
   
   if (!OpenClipboard ((!NILP (frame) && FRAME_W32_P (XFRAME (frame))) ? FRAME_W32_WINDOW (XFRAME (frame)) : NULL))
     goto error;
-  
+
   ok = EmptyClipboard () && SetClipboardData (CF_TEXT, htext);
   
   CloseClipboard ();
@@ -217,7 +239,9 @@ DEFUN ("w32-set-clipboard-data", Fw32_set_clipboard_data, Sw32_set_clipboard_dat
   
   ok = FALSE;
   if (htext) GlobalFree (htext);
-  
+  if (last_clipboard_text)
+    *last_clipboard_text = '\0';
+
  done:
   UNBLOCK_INPUT;
   
@@ -255,6 +279,16 @@ DEFUN ("w32-get-clipboard-data", Fw32_get_clipboard_data, Sw32_get_clipboard_dat
     
     nbytes = strlen (src);
 
+    /* If the text in clipboard is identical to what we put there
+       last time w32_set_clipboard_data was called, pretend there's no
+       data in the clipboard.  This is so we don't pass our own text
+       from the clipboard (which might be troublesome if the killed
+       text includes null characters).  */
+    if (last_clipboard_text
+        && clipboard_storage_size >= nbytes
+        && memcmp(last_clipboard_text, src, nbytes) == 0)
+      goto closeclip;
+
     if (
 #if 1
         1
@@ -295,8 +329,8 @@ DEFUN ("w32-get-clipboard-data", Fw32_get_clipboard_data, Sw32_get_clipboard_dat
         buf = (unsigned char *) xmalloc (bufsize);
         decode_coding (&coding, src, buf, nbytes, bufsize);
         Vlast_coding_system_used = coding.symbol;
-        ret = make_string_from_bytes ((char *) buf,
-                                      coding.produced_char, coding.produced);
+        ret = make_string_from_bytes ((char *) buf,
+                                      coding.produced_char, coding.produced);
         xfree (buf);
       }
     else