vim-patch:9.1.0785: cannot preserve error position when setting quickfix list (#30820)

Problem:  cannot preserve error position when setting quickfix lists
Solution: Add the 'u' action for setqflist()/setloclist() and try
          to keep the closes target position (Jeremy Fleischman)

fixes: vim/vim#15839
closes: vim/vim#15841

https://github.com/vim/vim/commit/27fbf6e5e8bee5c6b61819a5e82a0b50b265f0b0

Co-authored-by: Jeremy Fleischman <jeremyfleischman@gmail.com>

5 files changed, 208 insertions, 19 deletions

diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index aa31c59ab2..8916c434e7 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -9039,6 +9039,8 @@ setqflist({list} [, {action} [, {what}]])                          *setqflist()*
 			clear the list: >vim
 				call setqflist([], 'r')
 <
+		'u'	Like 'r', but tries to preserve the current selection
+			in the quickfix list.
 		'f'	All the quickfix lists in the quickfix stack are
 			freed.
 
diff --git a/runtime/lua/vim/_meta/vimfn.lua b/runtime/lua/vim/_meta/vimfn.lua
index 81e7070ac0..f588162112 100644
--- a/runtime/lua/vim/_meta/vimfn.lua
+++ b/runtime/lua/vim/_meta/vimfn.lua
@@ -8229,6 +8229,8 @@ function vim.fn.setpos(expr, list) end
 ---   clear the list: >vim
 ---     call setqflist([], 'r')
 --- <
+--- 'u'  Like 'r', but tries to preserve the current selection
+---   in the quickfix list.
 --- 'f'  All the quickfix lists in the quickfix stack are
 ---   freed.
 ---
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index a440450b9d..f0746e6159 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -9896,6 +9896,8 @@ M.funcs = {
       	clear the list: >vim
       		call setqflist([], 'r')
       <
+      'u'	Like 'r', but tries to preserve the current selection
+      	in the quickfix list.
       'f'	All the quickfix lists in the quickfix stack are
       	freed.
 
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index ddf2a7247f..5bd81ce469 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -6462,6 +6462,64 @@ static int qf_add_entry_from_dict(qf_list_T *qfl, dict_T *d, bool first_entry, b
   return status;
 }
 
+/// Check if `entry` is closer to the target than `other_entry`.
+///
+/// Only returns true if `entry` is definitively closer. If it's further
+/// away, or there's not enough information to tell, return false.
+static bool entry_is_closer_to_target(qfline_T *entry, qfline_T *other_entry, int target_fnum,
+                                      int target_lnum, int target_col)
+{
+  // First, compare entries to target file.
+  if (!target_fnum) {
+    // Without a target file, we can't know which is closer.
+    return false;
+  }
+
+  bool is_target_file = entry->qf_fnum && entry->qf_fnum == target_fnum;
+  bool other_is_target_file = other_entry->qf_fnum && other_entry->qf_fnum == target_fnum;
+  if (!is_target_file && other_is_target_file) {
+    return false;
+  } else if (is_target_file && !other_is_target_file) {
+    return true;
+  }
+
+  // Both entries are pointing at the exact same file. Now compare line numbers.
+  if (!target_lnum) {
+    // Without a target line number, we can't know which is closer.
+    return false;
+  }
+
+  int line_distance = entry->qf_lnum
+                      ? abs(entry->qf_lnum - target_lnum) : INT_MAX;
+  int other_line_distance = other_entry->qf_lnum
+                            ? abs(other_entry->qf_lnum - target_lnum) : INT_MAX;
+  if (line_distance > other_line_distance) {
+    return false;
+  } else if (line_distance < other_line_distance) {
+    return true;
+  }
+
+  // Both entries are pointing at the exact same line number (or no line
+  // number at all). Now compare columns.
+  if (!target_col) {
+    // Without a target column, we can't know which is closer.
+    return false;
+  }
+
+  int column_distance = entry->qf_col
+                        ? abs(entry->qf_col - target_col) : INT_MAX;
+  int other_column_distance = other_entry->qf_col
+                              ? abs(other_entry->qf_col - target_col) : INT_MAX;
+  if (column_distance > other_column_distance) {
+    return false;
+  } else if (column_distance < other_column_distance) {
+    return true;
+  }
+
+  // It's a complete tie! The exact same file, line, and column.
+  return false;
+}
+
 /// Add list of entries to quickfix/location list. Each list entry is
 /// a dictionary with item information.
 static int qf_add_entries(qf_info_T *qi, int qf_idx, list_T *list, char *title, int action)
@@ -6471,19 +6529,48 @@ static int qf_add_entries(qf_info_T *qi, int qf_idx, list_T *list, char *title,
   int retval = OK;
   bool valid_entry = false;
 
+  // If there's an entry selected in the quickfix list, remember its location
+  // (file, line, column), so we can select the nearest entry in the updated
+  // quickfix list.
+  int prev_fnum = 0;
+  int prev_lnum = 0;
+  int prev_col = 0;
+  if (qfl->qf_ptr) {
+    prev_fnum = qfl->qf_ptr->qf_fnum;
+    prev_lnum = qfl->qf_ptr->qf_lnum;
+    prev_col = qfl->qf_ptr->qf_col;
+  }
+
+  bool select_first_entry = false;
+  bool select_nearest_entry = false;
+
   if (action == ' ' || qf_idx == qi->qf_listcount) {
+    select_first_entry = true;
     // make place for a new list
     qf_new_list(qi, title);
     qf_idx = qi->qf_curlist;
     qfl = qf_get_list(qi, qf_idx);
-  } else if (action == 'a' && !qf_list_empty(qfl)) {
-    // Adding to existing list, use last entry.
-    old_last = qfl->qf_last;
+  } else if (action == 'a') {
+    if (qf_list_empty(qfl)) {
+      // Appending to empty list, select first entry.
+      select_first_entry = true;
+    } else {
+      // Adding to existing list, use last entry.
+      old_last = qfl->qf_last;
+    }
   } else if (action == 'r') {
+    select_first_entry = true;
+    qf_free_items(qfl);
+    qf_store_title(qfl, title);
+  } else if (action == 'u') {
+    select_nearest_entry = true;
     qf_free_items(qfl);
     qf_store_title(qfl, title);
   }
 
+  qfline_T *entry_to_select = NULL;
+  int entry_to_select_index = 0;
+
   TV_LIST_ITER_CONST(list, li, {
     if (TV_LIST_ITEM_TV(li)->v_type != VAR_DICT) {
       continue;  // Skip non-dict items.
@@ -6498,6 +6585,16 @@ static int qf_add_entries(qf_info_T *qi, int qf_idx, list_T *list, char *title,
     if (retval == QF_FAIL) {
       break;
     }
+
+    qfline_T *entry = qfl->qf_last;
+    if ((select_first_entry && entry_to_select == NULL)
+        || (select_nearest_entry
+            && (entry_to_select == NULL
+                || entry_is_closer_to_target(entry, entry_to_select, prev_fnum,
+                                             prev_lnum, prev_col)))) {
+      entry_to_select = entry;
+      entry_to_select_index = qfl->qf_count;
+    }
   });
 
   // Check if any valid error entries are added to the list.
@@ -6507,16 +6604,10 @@ static int qf_add_entries(qf_info_T *qi, int qf_idx, list_T *list, char *title,
     qfl->qf_nonevalid = true;
   }
 
-  // If not appending to the list, set the current error to the first entry
-  if (action != 'a') {
-    qfl->qf_ptr = qfl->qf_start;
-  }
-
-  // Update the current error index if not appending to the list or if the
-  // list was empty before and it is not empty now.
-  if ((action != 'a' || qfl->qf_index == 0)
-      && !qf_list_empty(qfl)) {
-    qfl->qf_index = 1;
+  // Set the current error.
+  if (entry_to_select) {
+    qfl->qf_ptr = entry_to_select;
+    qfl->qf_index = entry_to_select_index;
   }
 
   // Don't update the cursor in quickfix window when appending entries
@@ -6632,7 +6723,7 @@ static int qf_setprop_items_from_lines(qf_info_T *qi, int qf_idx, const dict_T *
     return FAIL;
   }
 
-  if (action == 'r') {
+  if (action == 'r' || action == 'u') {
     qf_free_items(&qi->qf_lists[qf_idx]);
   }
   if (qf_init_ext(qi, qf_idx, NULL, NULL, &di->di_tv, errorformat,
@@ -6789,10 +6880,11 @@ static void qf_free_stack(win_T *wp, qf_info_T *qi)
   }
 }
 
-// Populate the quickfix list with the items supplied in the list
-// of dictionaries. "title" will be copied to w:quickfix_title
-// "action" is 'a' for add, 'r' for replace.  Otherwise create a new list.
-// When "what" is not NULL then only set some properties.
+/// Populate the quickfix list with the items supplied in the list
+/// of dictionaries. "title" will be copied to w:quickfix_title
+/// "action" is 'a' for add, 'r' for replace, 'u' for update.  Otherwise
+/// create a new list.
+/// When "what" is not NULL then only set some properties.
 int set_errorlist(win_T *wp, list_T *list, int action, char *title, dict_T *what)
 {
   qf_info_T *qi = &ql_info;
@@ -7433,7 +7525,7 @@ static void set_qf_ll_list(win_T *wp, typval_T *args, typval_T *rettv)
     return;
   }
   const char *const act = tv_get_string_chk(action_arg);
-  if ((*act == 'a' || *act == 'r' || *act == ' ' || *act == 'f')
+  if ((*act == 'a' || *act == 'r' || *act == 'u' || *act == ' ' || *act == 'f')
       && act[1] == NUL) {
     action = *act;
   } else {
diff --git a/test/old/testdir/test_quickfix.vim b/test/old/testdir/test_quickfix.vim
index b4f8b2626a..c50fef1e46 100644
--- a/test/old/testdir/test_quickfix.vim
+++ b/test/old/testdir/test_quickfix.vim
@@ -6340,6 +6340,97 @@ func Test_quickfix_buffer_contents()
   call setqflist([], 'f')
 endfunc
 
+func Test_quickfix_update()
+  " Setup: populate a couple buffers
+  new
+  call setline(1, range(1, 5))
+  let b1 = bufnr()
+  new
+  call setline(1, range(1, 3))
+  let b2 = bufnr()
+  " Setup: set a quickfix list.
+  let items = [{'bufnr': b1, 'lnum': 1}, {'bufnr': b1, 'lnum': 2}, {'bufnr': b2, 'lnum': 1}, {'bufnr': b2, 'lnum': 2}]
+  call setqflist(items)
+
+  " Open the quickfix list, select the third entry.
+  copen
+  exe "normal jj\<CR>"
+  call assert_equal(3, getqflist({'idx' : 0}).idx)
+
+  " Update the quickfix list. Make sure the third entry is still selected.
+  call setqflist([], 'u', { 'items': items })
+  call assert_equal(3, getqflist({'idx' : 0}).idx)
+
+  " Update the quickfix list again, but this time with missing line number
+  " information. Confirm that we keep the current buffer selected.
+  call setqflist([{'bufnr': b1}, {'bufnr': b2}], 'u')
+  call assert_equal(2, getqflist({'idx' : 0}).idx)
+
+  " Cleanup the buffers we allocated during this test.
+  %bwipe!
+  %bwipe!
+endfunc
+
+func Test_quickfix_update_with_missing_coordinate_info()
+  new
+  call setline(1, range(1, 5))
+  let b1 = bufnr()
+
+  new
+  call setline(1, range(1, 3))
+  let b2 = bufnr()
+
+  new
+  call setline(1, range(1, 2))
+  let b3 = bufnr()
+
+  " Setup: set a quickfix list with no coordinate information at all.
+  call setqflist([{}, {}])
+
+  " Open the quickfix list, select the second entry.
+  copen
+  exe "normal j\<CR>"
+  call assert_equal(2, getqflist({'idx' : 0}).idx)
+
+  " Update the quickfix list. As the previously selected entry has no
+  " coordinate information, we expect the first entry to now be selected.
+  call setqflist([{'bufnr': b1}, {'bufnr': b2}, {'bufnr': b3}], 'u')
+  call assert_equal(1, getqflist({'idx' : 0}).idx)
+
+  " Select the second entry in the quickfix list.
+  copen
+  exe "normal j\<CR>"
+  call assert_equal(2, getqflist({'idx' : 0}).idx)
+
+  " Update the quickfix list again. The currently selected entry does not have
+  " a line number, but we should keep the file selected.
+  call setqflist([{'bufnr': b1}, {'bufnr': b2, 'lnum': 3}, {'bufnr': b3}], 'u')
+  call assert_equal(2, getqflist({'idx' : 0}).idx)
+
+  " Update the quickfix list again. The currently selected entry (bufnr=b2, lnum=3)
+  " is no longer present. We should pick the nearest entry.
+  call setqflist([{'bufnr': b1}, {'bufnr': b2, 'lnum': 1}, {'bufnr': b2, 'lnum': 4}], 'u')
+  call assert_equal(3, getqflist({'idx' : 0}).idx)
+
+  " Set the quickfix list again, with a specific column number. The currently selected entry doesn't have a
+  " column number, but they share a line number.
+  call setqflist([{'bufnr': b1}, {'bufnr': b2, 'lnum': 4, 'col': 5}, {'bufnr': b2, 'lnum': 4, 'col': 6}], 'u')
+  call assert_equal(2, getqflist({'idx' : 0}).idx)
+
+  " Set the quickfix list again. The currently selected column number (6) is
+  " no longer present. We should select the nearest column number.
+  call setqflist([{'bufnr': b1}, {'bufnr': b2, 'lnum': 4, 'col': 2}, {'bufnr': b2, 'lnum': 4, 'col': 4}], 'u')
+  call assert_equal(3, getqflist({'idx' : 0}).idx)
+
+  " Now set the quickfix list, but without columns. We should still pick the
+  " same line.
+  call setqflist([{'bufnr': b2, 'lnum': 3}, {'bufnr': b2, 'lnum': 4}, {'bufnr': b2, 'lnum': 4}], 'u')
+  call assert_equal(2, getqflist({'idx' : 0}).idx)
+
+  " Cleanup the buffers we allocated during this test.
+  %bwipe!
+endfunc
+
 " Test for "%b" in "errorformat"
 func Test_efm_format_b()
   call setqflist([], 'f')