fix(marks): skip right_gravity marks when deleting text

Problem:  Marks that are properly restored by the splice associated with
          an undo edit, are unnecessarily pushed to the undo header. This
          results in incorrect mark tracking in the "copy_only"
          save/restore completion path.
Solution: Avoid pushing left gravity marks at the beginning of the range,
          and right gravity marks at the end of the range to the undo
          header.
(cherry picked from commit c4f76299f0)

src/nvim/extmark.c

@@ -367,12 +367,23 @@ void extmark_splice_delete(buf_T *buf, int l_row, colnr_T l_col, int u_row, coln
   marktree_itr_get(buf->b_marktree, (int32_t)l_row, l_col, itr);
   while (true) {
     MTKey mark = marktree_itr_current(itr);
-    if (mark.pos.row < 0
+    if (mark.pos.row < 0 || mark.pos.row > u_row) {
-        || mark.pos.row > u_row
-        || (mark.pos.row == u_row && mark.pos.col > u_col)) {
       break;
     }
 
+    bool copy = true;
+    // No need to copy left gravity marks at the beginning of the range,
+    // and right gravity marks at the end of the range, unless invalidated.
+    if (mark.pos.row == l_row && mark.pos.col - !mt_right(mark) < l_col) {
+      copy = false;
+    } else if (mark.pos.row == u_row) {
+      if (mark.pos.col > u_col + 1) {
+        break;
+      } else if (mark.pos.col + mt_right(mark) > u_col) {
+        copy = false;
+      }
+    }
+
     bool invalidated = false;
     // Invalidate/delete mark
     if (!only_copy && !mt_invalid(mark) && mt_invalidate(mark) && !mt_end(mark)) {
@@ -388,6 +399,7 @@ void extmark_splice_delete(buf_T *buf, int l_row, colnr_T l_col, int u_row, coln
           extmark_del(buf, itr, mark, true);
           continue;
         } else {
+          copy = true;
           invalidated = true;
           mt_itr_rawkey(itr).flags |= MT_FLAG_INVALID;
           marktree_revise_meta(buf->b_marktree, itr, mark);
@@ -397,7 +409,7 @@ void extmark_splice_delete(buf_T *buf, int l_row, colnr_T l_col, int u_row, coln
     }
 
     // Push mark to undo header
-    if (only_copy || (uvp != NULL && op == kExtmarkUndo && !mt_no_undo(mark))) {
+    if (copy && (only_copy || (uvp != NULL && op == kExtmarkUndo && !mt_no_undo(mark)))) {
       ExtmarkSavePos pos = {
         .mark = mt_lookup_key(mark),
         .invalidated = invalidated,
@@ -541,10 +553,8 @@ void extmark_splice_impl(buf_T *buf, int start_row, colnr_T start_col, bcount_t
 
   if (old_row > 0 || old_col > 0) {
     // Copy and invalidate marks that would be effected by delete
-    // TODO(bfredl): Be "smart" about gravity here, left-gravity at the
+    // TODO(bfredl): Be smart about marks that already have been
-    // beginning and right-gravity at the end need not be preserved.
+    // saved (important for merge!)
-    // Also be smart about marks that already have been saved (important for
-    // merge!)
     int end_row = start_row + old_row;
     int end_col = (old_row ? 0 : start_col) + old_col;
     u_header_T *uhp = u_force_get_undo_header(buf);

test/functional/api/extmark_spec.lua

@@ -249,7 +249,7 @@ describe('API/extmarks', function()
     set_extmark(ns, 2, 1, 0, { right_gravity = false })
     eq({ { 1, 0, 0 }, { 2, 1, 0 } }, get_extmarks(ns, { 0, 0 }, { -1, -1 }))
     feed('u')
-    eq({ { 1, 0, 0 }, { 2, 1, 0 } }, get_extmarks(ns, { 0, 0 }, { -1, -1 }))
+    eq({ { 1, 0, 0 }, { 2, 0, 0 } }, get_extmarks(ns, { 0, 0 }, { -1, -1 }))
     api.nvim_buf_clear_namespace(0, ns, 0, -1)
   end)