patch 9.2.0443: GUI: cancelling save dialog overwrites or discards unnamed buffer

Problem:  When closing gvim with an unsaved unnamed buffer, choosing
          "Yes" in the "Save changes?" dialog and then "Cancel" in the
          file selection dialog either silently writes the buffer to a
          file named "Untitled" (overwriting any existing file with
          that name) or discards the buffer altogether
          (vibs29, after v9.1.0265).
Solution: In dialog_changed(), if browse_save_fname() leaves the buffer
          without a file name, treat it as a cancel and return without
          saving.  Also stop clearing the modified flag in the restore
          path on write failure, so the unsaved changes are kept and
          the caller (e.g. gui_shell_closed()) can also cancel the
          close.  Pre-fill the file dialog with "Untitled" to match
          the preceding "Save changes to ..." prompt.  Add a test for
          the write-failure path (Hirohito Higashi).

fixes:  #20132
closes: #20143

Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/ex_cmds2.c

@@ -141,7 +141,7 @@ browse_save_fname(buf_T *buf)
     char_u *fname;
 
     fname = do_browse(BROWSE_SAVE, (char_u *)_("Save As"),
-	    NULL, NULL, NULL, NULL, buf);
+	    (char_u *)"Untitled", NULL, NULL, NULL, buf);
     if (fname == NULL)
 	return;
 
@@ -182,6 +182,10 @@ dialog_changed(
 # ifdef FEAT_BROWSE
 	// May get file name, when there is none
 	browse_save_fname(buf);
+
+	// User cancelled the file dialog; keep the buffer modified.
+	if (buf->b_fname == NULL)
+	    return;
 # endif
 	empty_bufname = buf->b_fname == NULL ? TRUE : FALSE;
 	if (empty_bufname)
@@ -194,13 +198,12 @@ dialog_changed(
 		return;
 	}
 
-	// restore to empty when write failed
+	// restore to empty when write failed or was cancelled
 	if (empty_bufname)
 	{
 	    buf->b_fname = NULL;
 	    VIM_CLEAR(buf->b_ffname);
 	    VIM_CLEAR(buf->b_sfname);
-	    unchanged(buf, TRUE, FALSE);
 	}
     }
     else if (ret == VIM_NO)

src/testdir/test_buffer.vim

@@ -342,6 +342,28 @@ func Test_goto_buf_with_confirm()
   close!
 endfunc
 
+" Test for issue #20132: when saving an unnamed buffer fails the modified
+" flag must be kept, otherwise the buffer is silently discarded.
+func Test_dialog_changed_keep_modified_on_write_fail()
+  CheckUnix
+  CheckNotGui
+  CheckFeature dialog_con
+  CheckNotFeature dialog_con_gui
+  CheckNotRoot
+
+  call writefile(['existing'], 'Untitled', 'D')
+  call setfperm('Untitled', 'r--r--r--')
+
+  new
+  call setline(1, 'test')
+  call feedkeys('y', 'L')
+  silent! confirm bdel
+  call assert_true(&modified)
+  call assert_equal(['existing'], readfile('Untitled'))
+
+  bw!
+endfunc
+
 " Test for splitting buffer with 'switchbuf'
 func Test_buffer_switchbuf()
   new Xswitchbuf

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    443,
 /**/
     442,
 /**/