vim-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 vim/vim#3902)
https://github.com/vim/vim/commit/ee8188fc74a7cf9ee7acb634b2bb7a032d0cb24c

3 files changed, 58 insertions, 42 deletions

diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 2e2459aecf..3fdc111b6f 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -5333,16 +5333,12 @@ bool buf_hide(const buf_T *const buf)
 char_u *buf_spname(buf_T *buf)
 {
   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.
-    if (find_win_for_buf(buf, &win, &tp) && win->w_llist_ref != NULL) {
-      return (char_u *)_(msg_loclist);
-    } else {
+    // Differentiate between the quickfix and location list buffers using
+    // the buffer number stored in the global quickfix stack.
+    if (buf->b_fnum == qf_stack_get_bufnr()) {
       return (char_u *)_(msg_qflist);
     }
+    return (char_u *)_(msg_loclist);
   }
   // There is no _file_ when 'buftype' is "nofile", b_sfname
   // contains the name as specified by the user.
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index edd4d17e67..83a0080703 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -75,6 +75,7 @@ struct qfline_S {
 // There is a stack of error lists.
 #define LISTCOUNT   10
 #define INVALID_QFIDX (-1)
+#define INVALID_QFBUFNR (0)
 
 /// Quickfix list type.
 typedef enum
@@ -126,6 +127,7 @@ 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
@@ -1703,6 +1705,28 @@ static void locstack_queue_delreq(qf_info_T *qi)
   qf_delq_head = q;
 }
 
+/// 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)
+  FUNC_ATTR_NONNULL_ALL
+{
+  if (qi->qf_bufnr != INVALID_QFBUFNR) {
+    buf_T *const 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
 static void ll_free_all(qf_info_T **pqi)
 {
@@ -1723,6 +1747,9 @@ static void ll_free_all(qf_info_T **pqi)
     if (quickfix_busy > 0) {
       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(qf_get_list(qi, i));
       }
@@ -1885,6 +1912,7 @@ static qf_info_T *qf_alloc_stack(qfltype_T qfltype)
   qf_info_T *qi = xcalloc(1, sizeof(qf_info_T));
   qi->qf_refcount++;
   qi->qfl_type = qfltype;
+  qi->qf_bufnr = INVALID_QFBUFNR;
 
   return qi;
 }
@@ -2520,8 +2548,9 @@ static int jump_to_help_window(qf_info_T *qi, bool newwin, int *opened_window)
   return OK;
 }
 
-// Find a non-quickfix window using the given location list.
-// Returns NULL if a matching window is not found.
+/// 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 *qf_find_win_with_loclist(const qf_info_T *ll)
   FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {
@@ -3612,7 +3641,7 @@ static void qf_set_cwindow_options(void)
   // switch off 'swapfile'
   set_option_value("swf", 0L, NULL, OPT_LOCAL);
   set_option_value("bt", 0L, "quickfix", OPT_LOCAL);
-  set_option_value("bh", 0L, "wipe", OPT_LOCAL);
+  set_option_value("bh", 0L, "hide", OPT_LOCAL);
   RESET_BINDING(curwin);
   curwin->w_p_diff = false;
   set_option_value("fdm", 0L, "manual", OPT_LOCAL);
@@ -3669,6 +3698,8 @@ static int qf_open_new_cwindow(qf_info_T *qi, int height)
     if (do_ecmd(0, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE + ECMD_NOWINENTER, oldwin) == FAIL) {
       return FAIL;
     }
+    // save the number of the new buffer
+    qi->qf_bufnr = curbuf->b_fnum;
   }
 
   // Set the options for the quickfix buffer/window (if not already done)
@@ -3866,6 +3897,15 @@ static win_T *qf_find_win(const qf_info_T *qi)
 static buf_T *qf_find_buf(qf_info_T *qi)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
 {
+  if (qi->qf_bufnr != INVALID_QFBUFNR) {
+    buf_T *const 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;
@@ -6661,20 +6701,6 @@ static int qf_set_properties(qf_info_T *qi, const dict_T *what, int action, char
   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(const qf_info_T *qi)
-  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
-{
-  FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-    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.
 static void qf_free_stack(win_T *wp, qf_info_T *qi)
@@ -6689,12 +6715,10 @@ static void qf_free_stack(win_T *wp, qf_info_T *qi)
     qf_update_buffer(qi, NULL);
   }
 
-  win_T *llwin = NULL;
-  win_T *orig_wp = wp;
   if (wp != NULL && IS_LL_WINDOW(wp)) {
     // 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);
+    win_T *const llwin = qf_find_win_with_loclist(qi);
     if (llwin != NULL) {
       wp = llwin;
     }
@@ -6705,16 +6729,17 @@ static void qf_free_stack(win_T *wp, qf_info_T *qi)
     // quickfix list
     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) {
       win_set_loclist(wp, new_ll);
     }
   }
diff --git a/src/nvim/testdir/test_quickfix.vim b/src/nvim/testdir/test_quickfix.vim
index 6852f53ea8..12bf6d524c 100644
--- a/src/nvim/testdir/test_quickfix.vim
+++ b/src/nvim/testdir/test_quickfix.vim
@@ -4515,7 +4515,6 @@ func Xqfbuf_test(cchar)
 endfunc
 
 func Test_qfbuf()
-  throw 'skipped: enable after porting patch 8.1.0877'
   call Xqfbuf_test('c')
   call Xqfbuf_test('l')
 endfunc
@@ -5207,16 +5206,14 @@ func Xtest_qftextfunc(cchar)
 
   " Non-existing function
   set quickfixtextfunc=Tabc
-  " call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E117:')
-  Xexpr ['F1:10:2:green', 'F1:20:4:blue']"
+  call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E117:')
   call assert_fails("Xwindow", 'E117:')
   Xclose
   set quickfixtextfunc&
 
   " set option to a non-function
   set quickfixtextfunc=[10,\ 20]
-  " call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E117:')
-  Xexpr ['F1:10:2:green', 'F1:20:4:blue']"
+  call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E117:')
   call assert_fails("Xwindow", 'E117:')
   Xclose
   set quickfixtextfunc&
@@ -5226,8 +5223,7 @@ func Xtest_qftextfunc(cchar)
     return a:a .. a:b .. a:c
   endfunc
   set quickfixtextfunc=Xqftext
-  " call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E119:')
-  Xexpr ['F1:10:2:green', 'F1:20:4:blue']"
+  call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E119:')
   call assert_fails("Xwindow", 'E119:')
   Xclose
 
@@ -5236,9 +5232,8 @@ func Xtest_qftextfunc(cchar)
     return ['one', [], 'two']
   endfunc
   set quickfixtextfunc=Xqftext2
-  " call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue', 'F1:30:6:red']",
-  "                                                                 \ 'E730:')
-  Xexpr ['F1:10:2:green', 'F1:20:4:blue', 'F1:30:6:red']
+  call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue', 'F1:30:6:red']",
+                                                                  \ 'E730:')
   call assert_fails('Xwindow', 'E730:')
   call assert_equal(['one', 'F1|20 col 4| blue', 'F1|30 col 6| red'],
         \ getline(1, '$'))