patch 8.2.3727: in a gnome terminal keys are recognized as mouse events

Problem:    In a gnome terminal keys are recognized as mouse events.
Solution:   Only recognize DEC mouse events when four numbers are following.
            (closes #9256)

src/term.c

@@ -5412,6 +5412,8 @@ check_termcode(
 		if (STRNCMP(termcodes[idx].code, tp,
 				     (size_t)(slen > len ? len : slen)) == 0)
 		{
+		    int	    looks_like_mouse_start = FALSE;
+
 		    if (len < slen)		// got a partial sequence
 			return -1;		// need to get more chars
 
@@ -5434,15 +5436,48 @@ check_termcode(
 			    }
 		    }
 
-		    // The mouse termcode "ESC [" is also the prefix of
-		    // "ESC [ I" (focus gained).  Only use it when there is
-		    // no other match.  Do use it when a digit is following to
-		    // avoid waiting for more bytes.
 		    if (slen == 2 && len > 2
 			    && termcodes[idx].code[0] == ESC
-			    && termcodes[idx].code[1] == '['
-			    && !isdigit(tp[2]))
+			    && termcodes[idx].code[1] == '[')
 		    {
+			// The mouse termcode "ESC [" is also the prefix of
+			// "ESC [ I" (focus gained) and other keys.  Check some
+			// more bytes to find out.
+			if (!isdigit(tp[2]))
+			{
+			    // ESC [ without number following: Only use it when
+			    // there is no other match.
+			    looks_like_mouse_start = TRUE;
+			}
+			else if (termcodes[idx].name[0] == KS_DEC_MOUSE)
+			{
+			    char_u  *nr = tp + 2;
+			    int	    count = 0;
+
+			    // If a digit is following it could be a key with
+			    // modifier, e.g., ESC [ 1;2P.  Can be confused
+			    // with DEC_MOUSE, which requires four numbers
+			    // following.  If not then it can't be a DEC_MOUSE
+			    // code.
+			    for (;;)
+			    {
+				++count;
+				(void)getdigits(&nr);
+				if (nr >= tp + len)
+				    return -1;	// partial sequence
+				if (*nr != ';')
+				    break;
+				++nr;
+				if (nr >= tp + len)
+				    return -1;	// partial sequence
+			    }
+			    if (count < 4)
+				continue;	// no match
+			}
+		    }
+		    if (looks_like_mouse_start)
+		    {
+			// Only use it when there is no other match.
 			if (mouse_index_found < 0)
 			    mouse_index_found = idx;
 		    }

src/testdir/test_termcodes.vim

@@ -2039,6 +2039,28 @@ func Test_modifyOtherKeys_no_mapping()
   set timeoutlen&
 endfunc
 
+" Check that when DEC mouse codes are recognized a special key is handled.
+func Test_ignore_dec_mouse()
+
+  new
+  let save_mouse = &mouse
+  let save_term = &term
+  let save_ttymouse = &ttymouse
+  call test_override('no_query_mouse', 1)
+  set mouse=a term=gnome ttymouse=
+
+  execute "set <xF1>=\<Esc>[1;*P"
+  nnoremap <S-F1> agot it<Esc>
+  call feedkeys("\<Esc>[1;2P", 'Lx!')
+  call assert_equal('got it', getline(1))
+
+  let &mouse = save_mouse
+  let &term = save_term
+  let &ttymouse = save_ttymouse
+  call test_override('no_query_mouse', 0)
+  bwipe!
+endfunc
+
 func RunTest_mapping_shift(key, func)
   call setline(1, '')
   if a:key == '|'

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3727,
 /**/
     3726,
 /**/