vim-patch:8.0.1361: some users don't want to diff with hidden buffers

Problem:    Some users don't want to diff with hidden buffers.
Solution:   Add the "hiddenoff" item to 'diffopt'. (Alisue, closes vim/vim#2394)
97ce419201

runtime/doc/options.txt

@@ -1960,6 +1960,9 @@ A jump table for the options with a short description can be found at |Q_op|.
 		vertical	Start diff mode with vertical splits (unless
 				explicitly specified otherwise).
 
+		hiddenoff	Do not use diff mode for a buffer when it
+				becomes hidden.
+
 		foldcolumn:{n}	Set the 'foldcolumn' option to {n} when
 				starting diff mode.  Without this 2 is used.
 

src/nvim/buffer.c

@@ -509,6 +509,10 @@ void close_buffer(win_T *win, buf_T *buf, int action, int abort_if_last)
   if (buf->b_nwindows > 0)
     --buf->b_nwindows;
 
+  if (diffopt_hiddenoff() && !unload_buf && buf->b_nwindows == 0) {
+    diff_buf_delete(buf);   // Clear 'diff' for hidden buffer.
+  }
+
   /* Return when a window is displaying the buffer or when it's not
    * unloaded. */
   if (buf->b_nwindows > 0 || !unload_buf)

src/nvim/diff.c

@@ -44,6 +44,7 @@ static int diff_busy = FALSE;    // ex_diffgetput() is busy
 #define DIFF_IWHITE     4        // ignore change in white space
 #define DIFF_HORIZONTAL 8        // horizontal splits
 #define DIFF_VERTICAL   16       // vertical splits
+#define DIFF_HIDDEN_OFF 32       // diffoff when hidden
 static int diff_flags = DIFF_FILLER;
 
 #define LBUFLEN 50               // length of line in diff file
@@ -1838,6 +1839,9 @@ int diffopt_changed(void)
     } else if ((STRNCMP(p, "foldcolumn:", 11) == 0) && ascii_isdigit(p[11])) {
       p += 11;
       diff_foldcolumn_new = getdigits_int(&p);
+    } else if (STRNCMP(p, "hiddenoff", 9) == 0) {
+      p += 9;
+      diff_flags_new |= DIFF_HIDDEN_OFF;
     }
 
     if ((*p != ',') && (*p != NUL)) {
@@ -1880,6 +1884,12 @@ bool diffopt_horizontal(void)
   return (diff_flags & DIFF_HORIZONTAL) != 0;
 }
 
+// Return true if 'diffopt' contains "hiddenoff".
+bool diffopt_hiddenoff(void)
+{
+  return (diff_flags & DIFF_HIDDEN_OFF) != 0;
+}
+
 /// Find the difference within a changed line.
 ///
 /// @param  wp      window whose current buffer to check

src/nvim/testdir/test_diffmode.vim

@@ -375,6 +375,29 @@ func Test_diffopt_vertical()
   %bwipe
 endfunc
 
+func Test_diffopt_hiddenoff()
+  set diffopt=filler,foldcolumn:0,hiddenoff
+  e! one
+  call setline(1, ['Two', 'Three'])
+  redraw
+  let normattr = screenattr(1, 1)
+  diffthis
+  botright vert new two
+  call setline(1, ['One', 'Four'])
+  diffthis
+  redraw
+  call assert_notequal(normattr, screenattr(1, 1))
+  set hidden
+  close
+  redraw
+  " should not diffing with hidden buffer two while 'hiddenoff' is enabled
+  call assert_equal(normattr, screenattr(1, 1))
+
+  bwipe!
+  bwipe!
+  set hidden& diffopt&
+endfunc
+
 func Test_diffoff_hidden()
   set diffopt=filler,foldcolumn:0
   e! one