patch 8.1.0720: cannot easily change the current quickfx list index

Problem:    Cannot easily change the current quickfx list index.
Solution:   Add the "idx" argument to setqflist(). (Yegappan Lakshmanan,
            closes #3701)

src/quickfix.c

@@ -3266,13 +3266,7 @@ qf_jump_to_buffer(
 }
 
 /*
- * Jump to a quickfix line.
- * If dir == FORWARD go "errornr" valid entries forward.
- * If dir == BACKWARD go "errornr" valid entries backward.
- * If dir == FORWARD_FILE go "errornr" valid entries files backward.
- * If dir == BACKWARD_FILE go "errornr" valid entries files backward
- * else if "errornr" is zero, redisplay the same line
- * else go to entry "errornr".
+ * Jump to a quickfix line and try to use an existing window.
  */
     void
 qf_jump(qf_info_T	*qi,
@@ -3284,7 +3278,14 @@ qf_jump(qf_info_T	*qi,
 }
 
 /*
- * As qf_info().
+ * Jump to a quickfix line.
+ * If dir == 0 go to entry "errornr".
+ * If dir == FORWARD go "errornr" valid entries forward.
+ * If dir == BACKWARD go "errornr" valid entries backward.
+ * If dir == FORWARD_FILE go "errornr" valid entries files backward.
+ * If dir == BACKWARD_FILE go "errornr" valid entries files backward
+ * else if "errornr" is zero, redisplay the same line
+ * If 'forceit' is TRUE, then can discard changes to the current buffer.
  * If 'newwin' is TRUE, then open the file in a new window.
  */
     void
@@ -3687,7 +3688,7 @@ qf_history(exarg_T *eap)
 
     if (is_loclist_cmd(eap->cmdidx))
 	qi = GET_LOC_LIST(curwin);
-    if (qf_stack_empty(qi) || qf_list_empty(qi, qi->qf_curlist))
+    if (qf_stack_empty(qi))
 	MSG(_("No entries"));
     else
 	for (i = 0; i < qi->qf_listcount; ++i)
@@ -6548,6 +6549,50 @@ qf_setprop_context(qf_list_T *qfl, dictitem_T *di)
     return OK;
 }
 
+/*
+ * Set the current index in the specified quickfix list
+ */
+    static int
+qf_setprop_curidx(qf_info_T *qi, qf_list_T *qfl, dictitem_T *di)
+{
+    int		denote = FALSE;
+    int		newidx;
+    int		old_qfidx;
+    qfline_T	*qf_ptr;
+
+    // If the specified index is '$', then use the last entry
+    if (di->di_tv.v_type == VAR_STRING
+	    && di->di_tv.vval.v_string != NULL
+	    && STRCMP(di->di_tv.vval.v_string, "$") == 0)
+	newidx = qfl->qf_count;
+    else
+    {
+	// Otherwise use the specified index
+	newidx = tv_get_number_chk(&di->di_tv, &denote);
+	if (denote)
+	    return FAIL;
+    }
+
+    if (newidx < 1)		// sanity check
+	return FAIL;
+    if (newidx > qfl->qf_count)
+	newidx = qfl->qf_count;
+
+    old_qfidx = qfl->qf_index;
+    qf_ptr = get_nth_entry(qfl, newidx, &newidx);
+    if (qf_ptr == NULL)
+	return FAIL;
+    qfl->qf_ptr = qf_ptr;
+    qfl->qf_index = newidx;
+
+    // If the current list is modified and it is displayed in the quickfix
+    // window, then Update it.
+    if (qi->qf_lists[qi->qf_curlist].qf_id == qfl->qf_id)
+	qf_win_pos_update(qi, old_qfidx);
+
+    return OK;
+}
+
 /*
  * Set quickfix/location list properties (title, items, context).
  * Also used to add items from parsing a list of lines.
@@ -6585,6 +6630,8 @@ qf_set_properties(qf_info_T *qi, dict_T *what, int action, char_u *title)
 	retval = qf_setprop_items_from_lines(qi, qf_idx, what, di, action);
     if ((di = dict_find(what, (char_u *)"context", -1)) != NULL)
 	retval = qf_setprop_context(qfl, di);
+    if ((di = dict_find(what, (char_u *)"idx", -1)) != NULL)
+	retval = qf_setprop_curidx(qi, qfl, di);
 
     if (retval == OK)
 	qf_list_changed(qfl);

src/testdir/test_quickfix.vim

@@ -1811,6 +1811,13 @@ func HistoryTest(cchar)
   call g:Xsetlist([], 'f')
   let l = split(execute(a:cchar . 'hist'), "\n")
   call assert_equal('No entries', l[0])
+
+  " An empty list should still show the stack history
+  call g:Xsetlist([])
+  let res = split(execute(a:cchar . 'hist'), "\n")
+  call assert_equal('> error list 1 of 1; 0 ' . common, res[0])
+
+  call g:Xsetlist([], 'f')
 endfunc
 
 func Test_history()
@@ -2068,6 +2075,56 @@ func Test_qf_property()
     call Xproperty_tests('l')
 endfunc
 
+" Test for setting the current index in the location/quickfix list
+func Xtest_setqfidx(cchar)
+  call s:setup_commands(a:cchar)
+
+  Xgetexpr "F1:10:1:Line1\nF2:20:2:Line2\nF3:30:3:Line3"
+  Xgetexpr "F4:10:1:Line1\nF5:20:2:Line2\nF6:30:3:Line3"
+  Xgetexpr "F7:10:1:Line1\nF8:20:2:Line2\nF9:30:3:Line3"
+
+  call g:Xsetlist([], 'a', {'nr' : 3, 'idx' : 2})
+  call g:Xsetlist([], 'a', {'nr' : 2, 'idx' : 2})
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : 3})
+  Xolder 2
+  Xopen
+  call assert_equal(3, line('.'))
+  Xnewer
+  call assert_equal(2, line('.'))
+  Xnewer
+  call assert_equal(2, line('.'))
+  " Update the current index with the quickfix window open
+  wincmd w
+  call g:Xsetlist([], 'a', {'nr' : 3, 'idx' : 3})
+  Xopen
+  call assert_equal(3, line('.'))
+  Xclose
+
+  " Set the current index to the last entry
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : '$'})
+  call assert_equal(3, g:Xgetlist({'nr' : 1, 'idx' : 0}).idx)
+  " A large value should set the index to the last index
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : 1})
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : 999})
+  call assert_equal(3, g:Xgetlist({'nr' : 1, 'idx' : 0}).idx)
+  " Invalid index values
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : -1})
+  call assert_equal(3, g:Xgetlist({'nr' : 1, 'idx' : 0}).idx)
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : 0})
+  call assert_equal(3, g:Xgetlist({'nr' : 1, 'idx' : 0}).idx)
+  call g:Xsetlist([], 'a', {'nr' : 1, 'idx' : 'xx'})
+  call assert_equal(3, g:Xgetlist({'nr' : 1, 'idx' : 0}).idx)
+  call assert_fails("call g:Xsetlist([], 'a', {'nr':1, 'idx':[]})", 'E745:')
+
+  call g:Xsetlist([], 'f')
+  new | only
+endfunc
+
+func Test_setqfidx()
+  call Xtest_setqfidx('c')
+  call Xtest_setqfidx('l')
+endfunc
+
 " Tests for the QuickFixCmdPre/QuickFixCmdPost autocommands
 func QfAutoCmdHandler(loc, cmd)
   call add(g:acmds, a:loc . a:cmd)

src/version.c

@@ -795,6 +795,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    720,
 /**/
     719,
 /**/