patch 8.1.0877: new buffer used every time the quickfix window is opened

Problem:    New buffer used every time the quickfix window is opened.
Solution:   Reuse the buffer. (Yegappan Lakshmanan, closes #3902)

src/buffer.c

@@ -5753,17 +5753,14 @@ buf_spname(buf_T *buf)
 #if defined(FEAT_QUICKFIX)
     if (bt_quickfix(buf))
     {
-	win_T	    *win;
-	tabpage_T   *tp;
-
 	/*
-	 * For location list window, w_llist_ref points to the location list.
-	 * For quickfix window, w_llist_ref is NULL.
+	 * Differentiate between the quickfix and location list buffers using
+	 * the buffer number stored in the global quickfix stack.
 	 */
-	if (find_win_for_buf(buf, &win, &tp) == OK && win->w_llist_ref != NULL)
-	    return (char_u *)_(msg_loclist);
-	else
+	if (buf->b_fnum == qf_stack_get_bufnr())
 	    return (char_u *)_(msg_qflist);
+	else
+	    return (char_u *)_(msg_loclist);
     }
 #endif
 

src/proto/quickfix.pro

@@ -1,5 +1,6 @@
 /* quickfix.c */
 int qf_init(win_T *wp, char_u *efile, char_u *errorformat, int newlist, char_u *qf_title, char_u *enc);
+int qf_stack_get_bufnr(void);
 void qf_free_all(win_T *wp);
 void check_quickfix_busy(void);
 void copy_loclist_stack(win_T *from, win_T *to);

src/quickfix.c

@@ -48,6 +48,7 @@ struct qfline_S
  */
 #define LISTCOUNT   10
 #define INVALID_QFIDX (-1)
+#define INVALID_QFBUFNR (0)
 
 /*
  * Quickfix list type.
@@ -107,6 +108,7 @@ struct qf_info_S
     int		qf_curlist;	    // current error list
     qf_list_T	qf_lists[LISTCOUNT];
     qfltype_T	qfl_type;	    // type of list
+    int		qf_bufnr;	    // quickfix window buffer number
 };
 
 static qf_info_T ql_info;	// global quickfix list
@@ -1852,6 +1854,37 @@ locstack_queue_delreq(qf_info_T *qi)
     }
 }
 
+/*
+ * Return the global quickfix stack window buffer number.
+ */
+    int
+qf_stack_get_bufnr(void)
+{
+    return ql_info.qf_bufnr;
+}
+
+/*
+ * Wipe the quickfix window buffer (if present) for the specified
+ * quickfix/location list.
+ */
+    static void
+wipe_qf_buffer(qf_info_T *qi)
+{
+    buf_T	*qfbuf;
+
+    if (qi->qf_bufnr != INVALID_QFBUFNR)
+    {
+	qfbuf = buflist_findnr(qi->qf_bufnr);
+	if (qfbuf != NULL && qfbuf->b_nwindows == 0)
+	{
+	    // If the quickfix buffer is not loaded in any window, then
+	    // wipe the buffer.
+	    close_buffer(NULL, qfbuf, DOBUF_WIPE, FALSE);
+	    qi->qf_bufnr = INVALID_QFBUFNR;
+	}
+    }
+}
+
 /*
  * Free a location list stack
  */
@@ -1876,6 +1909,9 @@ ll_free_all(qf_info_T **pqi)
 	    locstack_queue_delreq(qi);
 	else
 	{
+	    // If the quickfix window buffer is loaded, then wipe it
+	    wipe_qf_buffer(qi);
+
 	    for (i = 0; i < qi->qf_listcount; ++i)
 		qf_free(&qi->qf_lists[i]);
 	    vim_free(qi);
@@ -2066,6 +2102,7 @@ qf_alloc_stack(qfltype_T qfltype)
     {
 	qi->qf_refcount++;
 	qi->qfl_type = qfltype;
+	qi->qf_bufnr = INVALID_QFBUFNR;
     }
     return qi;
 }
@@ -2741,7 +2778,8 @@ jump_to_help_window(qf_info_T *qi, int newwin, int *opened_window)
 }
 
 /*
- * Find a non-quickfix window using the given location list.
+ * Find a non-quickfix window in the current tabpage using the given location
+ * list stack.
  * Returns NULL if a matching window is not found.
  */
     static win_T *
@@ -3988,7 +4026,7 @@ qf_open_new_cwindow(qf_info_T *qi, int height)
 	set_option_value((char_u *)"swf", 0L, NULL, OPT_LOCAL);
 	set_option_value((char_u *)"bt", 0L, (char_u *)"quickfix",
 		OPT_LOCAL);
-	set_option_value((char_u *)"bh", 0L, (char_u *)"wipe", OPT_LOCAL);
+	set_option_value((char_u *)"bh", 0L, (char_u *)"hide", OPT_LOCAL);
 	RESET_BINDING(curwin);
 #ifdef FEAT_DIFF
 	curwin->w_p_diff = FALSE;
@@ -3997,6 +4035,8 @@ qf_open_new_cwindow(qf_info_T *qi, int height)
 	set_option_value((char_u *)"fdm", 0L, (char_u *)"manual",
 		OPT_LOCAL);
 #endif
+	// save the number of the new buffer
+	qi->qf_bufnr = curbuf->b_fnum;
     }
 
     // Only set the height when still in the same tab page and there is no
@@ -4212,6 +4252,16 @@ qf_find_buf(qf_info_T *qi)
     tabpage_T	*tp;
     win_T	*win;
 
+    if (qi->qf_bufnr != INVALID_QFBUFNR)
+    {
+	buf_T	*qfbuf;
+	qfbuf = buflist_findnr(qi->qf_bufnr);
+	if (qfbuf != NULL)
+	    return qfbuf;
+	// buffer is no longer present
+	qi->qf_bufnr = INVALID_QFBUFNR;
+    }
+
     FOR_ALL_TAB_WINDOWS(tp, win)
 	if (is_qf_win(win, qi))
 	    return win->w_buffer;
@@ -6580,22 +6630,6 @@ qf_set_properties(qf_info_T *qi, dict_T *what, int action, char_u *title)
     return retval;
 }
 
-/*
- * Find the non-location list window with the specified location list stack in
- * the current tabpage.
- */
-    static win_T *
-find_win_with_ll(qf_info_T *qi)
-{
-    win_T	*wp = NULL;
-
-    FOR_ALL_WINDOWS(wp)
-	if ((wp->w_llist == qi) && !bt_quickfix(wp->w_buffer))
-	    return wp;
-
-    return NULL;
-}
-
 /*
  * Free the entire quickfix/location list stack.
  * If the quickfix/location list window is open, then clear it.
@@ -6605,7 +6639,6 @@ qf_free_stack(win_T *wp, qf_info_T *qi)
 {
     win_T	*qfwin = qf_find_win(qi);
     win_T	*llwin = NULL;
-    win_T	*orig_wp = wp;
 
     if (qfwin != NULL)
     {
@@ -6619,7 +6652,7 @@ qf_free_stack(win_T *wp, qf_info_T *qi)
     {
 	// If in the location list window, then use the non-location list
 	// window with this location list (if present)
-	llwin = find_win_with_ll(qi);
+	llwin = qf_find_win_with_loclist(qi);
 	if (llwin != NULL)
 	    wp = llwin;
     }
@@ -6631,19 +6664,20 @@ qf_free_stack(win_T *wp, qf_info_T *qi)
 	qi->qf_curlist = 0;
 	qi->qf_listcount = 0;
     }
-    else if (IS_LL_WINDOW(orig_wp))
+    else if (qfwin != NULL)
     {
 	// If the location list window is open, then create a new empty
 	// location list
 	qf_info_T *new_ll = qf_alloc_stack(QFLT_LOCATION);
+	new_ll->qf_bufnr = qfwin->w_buffer->b_fnum;
 
 	// first free the list reference in the location list window
-	ll_free_all(&orig_wp->w_llist_ref);
+	ll_free_all(&qfwin->w_llist_ref);
 
-	orig_wp->w_llist_ref = new_ll;
-	if (llwin != NULL)
+	qfwin->w_llist_ref = new_ll;
+	if (wp != qfwin)
 	{
-	    llwin->w_llist = new_ll;
+	    wp->w_llist = new_ll;
 	    new_ll->qf_refcount++;
 	}
     }

src/testdir/test_quickfix.vim

@@ -3899,3 +3899,46 @@ func Test_viscol()
   set efm&
   call delete('Xfile1')
 endfunc
+
+" Test for the quickfix window buffer
+func Xqfbuf_test(cchar)
+  call s:setup_commands(a:cchar)
+
+  " Quickfix buffer should be reused across closing and opening a quickfix
+  " window
+  Xexpr "F1:10:Line10"
+  Xopen
+  let qfbnum = bufnr('')
+  Xclose
+  " Even after the quickfix window is closed, the buffer should be loaded
+  call assert_true(bufloaded(qfbnum))
+  Xopen
+  " Buffer should be reused when opening the window again
+  call assert_equal(qfbnum, bufnr(''))
+  Xclose
+
+  if a:cchar == 'l'
+    %bwipe
+    " For a location list, when both the file window and the location list
+    " window for the list are closed, then the buffer should be freed.
+    new | only
+    lexpr "F1:10:Line10"
+    let wid = win_getid()
+    lopen
+    let qfbnum = bufnr('')
+    call assert_match(qfbnum . ' %a-  "\[Location List]"', execute('ls'))
+    close
+    " When the location list window is closed, the buffer name should not
+    " change to 'Quickfix List'
+    call assert_match(qfbnum . '  h-  "\[Location List]"', execute('ls'))
+    call assert_true(bufloaded(qfbnum))
+
+    new | only
+    call assert_false(bufloaded(qfbnum))
+  endif
+endfunc
+
+func Test_qfbuf()
+  call Xqfbuf_test('c')
+  call Xqfbuf_test('l')
+endfunc

src/version.c

@@ -783,6 +783,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    877,
 /**/
     876,
 /**/