patch 8.2.0959: using 'quickfixtextfunc' is a bit slow

Problem:    Using 'quickfixtextfunc' is a bit slow.
Solution:   Process a list of entries. (Yegappan Lakshmanan, closes #6234)

runtime/doc/quickfix.txt

@@ -1947,9 +1947,9 @@ under the current directory tree. The file path may need to be simplified to a
 common parent directory.
 
 The displayed text can be customized by setting the 'quickfixtextfunc' option
-to a Vim function.  This function will be called with a dict argument for
+to a Vim function.  This function will be called with a dict argument and
-every entry in a quickfix or a location list. The dict argument will have the
+should return a List of strings to be displayed in the quickfix or location
-following fields:
+list window. The dict argument will have the following fields:
 
     quickfix	set to 1 when called for a quickfix list and 0 when called for
 		a location list.
@@ -1957,12 +1957,14 @@ following fields:
 		location list. For a quickfix list, set to 0. Can be used in
 		getloclist() to get the location list entry.
     id		quickfix or location list identifier
-    idx		index of the entry in the quickfix or location list
+    start_idx	index of the first entry for which text should be returned
+    end_idx	index of the last entry for which text should be returned
 
 The function should return a single line of text to display in the quickfix
-window for the entry identified by idx. The function can obtain information
+window for each entry from start_idx to end_idx. The function can obtain
-about the current entry using the |getqflist()| function and specifying the
+information about the entries using the |getqflist()| function and specifying
-quickfix list identifier "id" and the entry index "idx".
+the quickfix list identifier "id". For a location list, getloclist() function
+can be used with the 'winid' argument.
 
 If a quickfix or location list specific customization is needed, then the
 'quickfixtextfunc' attribute of the list can be set using the |setqflist()| or
@@ -1977,11 +1979,14 @@ Example: >
     call setqflist([], ' ', {'lines' : v:oldfiles, 'efm' : '%f',
 					\ 'quickfixtextfunc' : 'QfOldFiles'})
     func QfOldFiles(info)
-	" get information about the specific quickfix entry
+	" get information about a range of quickfix entries
-	let e = getqflist({'id' : a:info.id, 'idx' : a:info.idx,
+	let items = getqflist({'id' : a:info.id, 'items' : 1}).items
-						\ 'items' : 1}).items[0]
+	let l = []
-	" return the simplified file name
+	for idx in range(a:info.start_idx - 1, a:info.end_idx - 1)
-	return fnamemodify(bufname(e.bufnr), ':p:.')
+	    " use the simplified file name
+	  call add(l, fnamemodify(bufname(items[idx].bufnr), ':p:.'))
+	endfor
+	return l
     endfunc
 <
 

src/quickfix.c

@@ -4415,49 +4415,17 @@ qf_update_buffer(qf_info_T *qi, qfline_T *old_last)
  */
     static int
 qf_buf_add_line(
-	qf_list_T	*qfl,		// quickfix list
 	buf_T		*buf,		// quickfix window buffer
 	linenr_T	lnum,
 	qfline_T	*qfp,
 	char_u		*dirname,
-	int		qf_winid)
+	char_u		*qftf_str)
 {
     int		len;
     buf_T	*errbuf;
-    char_u	*qftf;
 
-    // If 'quickfixtextfunc' is set, then use the user-supplied function to get
+    if (qftf_str != NULL)
-    // the text to display
+	vim_strncpy(IObuff, qftf_str, IOSIZE - 1);
-    qftf = p_qftf;
-    // Use the local value of 'quickfixtextfunc' if it is set.
-    if (qfl->qf_qftf != NULL)
-	qftf = qfl->qf_qftf;
-    if (qftf != NULL && *qftf != NUL)
-    {
-	char_u		*qfbuf_text;
-	typval_T	args[1];
-	dict_T		*d;
-
-	// create the dict argument
-	if ((d = dict_alloc_lock(VAR_FIXED)) == NULL)
-	    return FAIL;
-	dict_add_number(d, "quickfix", (long)IS_QF_LIST(qfl));
-	dict_add_number(d, "winid", (long)qf_winid);
-	dict_add_number(d, "id", (long)qfl->qf_id);
-	dict_add_number(d, "idx", (long)(lnum + 1));
-	++d->dv_refcount;
-	args[0].v_type = VAR_DICT;
-	args[0].vval.v_dict = d;
-
-	qfbuf_text = call_func_retstr(qftf, 1, args);
-	--d->dv_refcount;
-
-	if (qfbuf_text == NULL)
-	    return FAIL;
-
-	vim_strncpy(IObuff, qfbuf_text, IOSIZE - 1);
-	vim_free(qfbuf_text);
-    }
     else
     {
 	if (qfp->qf_module != NULL)
@@ -4533,6 +4501,41 @@ qf_buf_add_line(
     return OK;
 }
 
+    static list_T *
+call_qftf_func(qf_list_T *qfl, int qf_winid, long start_idx, long end_idx)
+{
+    char_u	*qftf = p_qftf;
+    list_T	*qftf_list = NULL;
+
+    // If 'quickfixtextfunc' is set, then use the user-supplied function to get
+    // the text to display. Use the local value of 'quickfixtextfunc' if it is
+    // set.
+    if (qfl->qf_qftf != NULL)
+	qftf = qfl->qf_qftf;
+    if (qftf != NULL && *qftf != NUL)
+    {
+	typval_T	args[1];
+	dict_T		*d;
+
+	// create the dict argument
+	if ((d = dict_alloc_lock(VAR_FIXED)) == NULL)
+	    return NULL;
+	dict_add_number(d, "quickfix", (long)IS_QF_LIST(qfl));
+	dict_add_number(d, "winid", (long)qf_winid);
+	dict_add_number(d, "id", (long)qfl->qf_id);
+	dict_add_number(d, "start_idx", start_idx);
+	dict_add_number(d, "end_idx", end_idx);
+	++d->dv_refcount;
+	args[0].v_type = VAR_DICT;
+	args[0].vval.v_dict = d;
+
+	qftf_list = call_func_retlist(qftf, 1, args);
+	--d->dv_refcount;
+    }
+
+    return qftf_list;
+}
+
 /*
  * Fill current buffer with quickfix errors, replacing any previous contents.
  * curbuf must be the quickfix buffer!
@@ -4546,6 +4549,8 @@ qf_fill_buffer(qf_list_T *qfl, buf_T *buf, qfline_T *old_last, int qf_winid)
     linenr_T	lnum;
     qfline_T	*qfp;
     int		old_KeyTyped = KeyTyped;
+    list_T	*qftf_list = NULL;
+    listitem_T	*qftf_li = NULL;
 
     if (old_last == NULL)
     {
@@ -4578,15 +4583,30 @@ qf_fill_buffer(qf_list_T *qfl, buf_T *buf, qfline_T *old_last, int qf_winid)
 	    qfp = old_last->qf_next;
 	    lnum = buf->b_ml.ml_line_count;
 	}
+
+	qftf_list = call_qftf_func(qfl, qf_winid, (long)(lnum + 1),
+							(long)qfl->qf_count);
+	if (qftf_list != NULL)
+	    qftf_li = qftf_list->lv_first;
+
 	while (lnum < qfl->qf_count)
 	{
-	    if (qf_buf_add_line(qfl, buf, lnum, qfp, dirname, qf_winid) == FAIL)
+	    char_u	*qftf_str = NULL;
+
+	    if (qftf_li != NULL)
+		// Use the text supplied by the user defined function
+		qftf_str = tv_get_string_chk(&qftf_li->li_tv);
+
+	    if (qf_buf_add_line(buf, lnum, qfp, dirname, qftf_str) == FAIL)
 		break;
 
 	    ++lnum;
 	    qfp = qfp->qf_next;
 	    if (qfp == NULL)
 		break;
+
+	    if (qftf_li != NULL)
+		qftf_li = qftf_li->li_next;
 	}
 
 	if (old_last == NULL)

src/testdir/test_quickfix.vim

@@ -4818,24 +4818,26 @@ endfunc
 " Test for the 'quickfixtextfunc' setting
 func Tqfexpr(info)
   if a:info.quickfix
-    let qfl = getqflist({'id' : a:info.id, 'idx' : a:info.idx,
+    let qfl = getqflist({'id' : a:info.id, 'items' : 1}).items
-          \ 'items' : 1}).items
   else
-    let qfl = getloclist(a:info.winid, {'id' : a:info.id, 'idx' : a:info.idx,
+    let qfl = getloclist(a:info.winid, {'id' : a:info.id, 'items' : 1}).items
-          \ 'items' : 1}).items
   endif
 
-  let e = qfl[0]
+  let l = []
-  let s = ''
+  for idx in range(a:info.start_idx - 1, a:info.end_idx - 1)
-  if e.bufnr != 0
+    let e = qfl[idx]
-    let bname = bufname(e.bufnr)
+    let s = ''
-    let s ..= fnamemodify(bname, ':.')
+    if e.bufnr != 0
-  endif
+      let bname = bufname(e.bufnr)
-  let s ..= '-'
+      let s ..= fnamemodify(bname, ':.')
-  let s ..= 'L' .. string(e.lnum) .. 'C' .. string(e.col) .. '-'
+    endif
-  let s ..= e.text
+    let s ..= '-'
+    let s ..= 'L' .. string(e.lnum) .. 'C' .. string(e.col) .. '-'
+    let s ..= e.text
+    call add(l, s)
+  endfor
 
-  return s
+  return l
 endfunc
 
 func Xtest_qftextfunc(cchar)
@@ -4859,16 +4861,18 @@ func Xtest_qftextfunc(cchar)
   " Test for per list 'quickfixtextfunc' setting
   func PerQfText(info)
     if a:info.quickfix
-      let qfl = getqflist({'id' : a:info.id, 'idx' : a:info.idx,
+      let qfl = getqflist({'id' : a:info.id, 'items' : 1}).items
-            \ 'items' : 1}).items
     else
-      let qfl = getloclist(a:info.winid, {'id' : a:info.id, 'idx' : a:info.idx,
+      let qfl = getloclist(a:info.winid, {'id' : a:info.id, 'items' : 1}).items
-            \ 'items' : 1}).items
     endif
     if empty(qfl)
-      return ''
+      return []
     endif
-    return 'Line ' .. qfl[0].lnum .. ', Col ' .. qfl[0].col
+    let l = []
+    for idx in range(a:info.start_idx - 1, a:info.end_idx - 1)
+      call add(l, 'Line ' .. qfl[idx].lnum .. ', Col ' .. qfl[idx].col)
+    endfor
+    return l
   endfunc
   set quickfixtextfunc=Tqfexpr
   call g:Xsetlist([], ' ', {'quickfixtextfunc' : "PerQfText"})
@@ -4908,8 +4912,21 @@ func Xtest_qftextfunc(cchar)
   call assert_fails("Xexpr ['F1:10:2:green', 'F1:20:4:blue']", 'E119:')
   call assert_fails("Xwindow", 'E119:')
   Xclose
+
+  " set option to a function that returns a list with non-strings
+  func Xqftext2(d)
+    return ['one', [], 'two']
+  endfunc
+  set quickfixtextfunc=Xqftext2
+  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', 'two'], getline(1, '$'))
+  Xclose
+
   set quickfixtextfunc&
   delfunc Xqftext
+  delfunc Xqftext2
 endfunc
 
 func Test_qftextfunc()

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    959,
 /**/
     958,
 /**/