fix(marks): issues with invalid marks and marks beyond eob (#32862)

Problem:  Marks that go beyond the end of the buffer, and paired marks
          whose end is in front of its start mark are added to and
          removed from the decor. This results in incorrect tracking
          of the signcolumn.
Solution: Ensure such marks are not added to and removed from the decor.

src/nvim/decoration.c

@@ -182,8 +182,9 @@ DecorSignHighlight decor_sh_from_inline(DecorHighlightInline item)
 
 void buf_put_decor(buf_T *buf, DecorInline decor, int row, int row2)
 {
-  if (decor.ext) {
+  if (decor.ext && row < buf->b_ml.ml_line_count) {
     uint32_t idx = decor.data.ext.sh_idx;
+    row2 = MIN(buf->b_ml.ml_line_count - 1, row2);
     while (idx != DECOR_ID_INVALID) {
       DecorSignHighlight *sh = &kv_A(decor_items, idx);
       buf_put_decor_sh(buf, sh, row, row2);
@@ -222,16 +223,17 @@ void buf_put_decor_sh(buf_T *buf, DecorSignHighlight *sh, int row1, int row2)
 void buf_decor_remove(buf_T *buf, int row1, int row2, int col1, DecorInline decor, bool free)
 {
   decor_redraw(buf, row1, row2, col1, decor);
-  if (decor.ext) {
+  if (decor.ext && row1 < buf->b_ml.ml_line_count) {
     uint32_t idx = decor.data.ext.sh_idx;
+    row2 = MIN(buf->b_ml.ml_line_count - 1, row2);
     while (idx != DECOR_ID_INVALID) {
       DecorSignHighlight *sh = &kv_A(decor_items, idx);
       buf_remove_decor_sh(buf, row1, row2, sh);
       idx = sh->next;
     }
-    if (free) {
-      decor_free(decor);
-    }
+  }
+  if (free) {
+    decor_free(decor);
   }
 }
 

src/nvim/drawscreen.c

@@ -1238,7 +1238,7 @@ static bool win_redraw_signcols(win_T *wp)
   if (!buf->b_signcols.autom
       && (*wp->w_p_stc != NUL || (wp->w_maxscwidth > 1 && wp->w_minscwidth != wp->w_maxscwidth))) {
     buf->b_signcols.autom = true;
-    buf_signcols_count_range(buf, 0, buf->b_ml.ml_line_count, MAXLNUM, kFalse);
+    buf_signcols_count_range(buf, 0, buf->b_ml.ml_line_count - 1, MAXLNUM, kFalse);
   }
 
   while (buf->b_signcols.max > 0 && buf->b_signcols.count[buf->b_signcols.max - 1] == 0) {

src/nvim/extmark.c

@@ -135,7 +135,7 @@ static void extmark_setraw(buf_T *buf, uint64_t mark, int row, colnr_T col, bool
   } else if (!mt_invalid(key) && key.flags & MT_FLAG_DECOR_SIGNTEXT && buf->b_signcols.autom) {
     row1 = MIN(alt.pos.row, MIN(key.pos.row, row));
     row2 = MAX(alt.pos.row, MAX(key.pos.row, row));
-    buf_signcols_count_range(buf, row1, row2, 0, kTrue);
+    buf_signcols_count_range(buf, row1, MIN(curbuf->b_ml.ml_line_count - 1, row2), 0, kTrue);
   }
 
   if (move) {
@@ -145,7 +145,7 @@ static void extmark_setraw(buf_T *buf, uint64_t mark, int row, colnr_T col, bool
   if (invalid) {
     buf_put_decor(buf, mt_decor(key), MIN(row, key.pos.row), MAX(row, key.pos.row));
   } else if (!mt_invalid(key) && key.flags & MT_FLAG_DECOR_SIGNTEXT && buf->b_signcols.autom) {
-    buf_signcols_count_range(buf, row1, row2, 0, kNone);
+    buf_signcols_count_range(buf, row1, MIN(curbuf->b_ml.ml_line_count - 1, row2), 0, kNone);
   }
 }
 
@@ -180,7 +180,9 @@ void extmark_del(buf_T *buf, MarkTreeIter *itr, MTKey key, bool restore)
   }
 
   if (mt_decor_any(key)) {
-    if (mt_invalid(key)) {
+    // If key is an end mark it has been found first while iterating the marktree,
+    // indicating the decor is already invalid.
+    if (mt_invalid(key) || mt_end(key)) {
       decor_free(mt_decor(key));
     } else {
       buf_decor_remove(buf, key.pos.row, key2.pos.row, key.pos.col, mt_decor(key), true);
@@ -575,7 +577,8 @@ void extmark_splice_impl(buf_T *buf, int start_row, colnr_T start_col, bcount_t
 
   // Remove signs inside edited region from "b_signcols.count", add after splicing.
   if (old_row > 0 || new_row > 0) {
-    buf_signcols_count_range(buf, start_row, start_row + old_row, 0, kTrue);
+    int row2 = MIN(buf->b_ml.ml_line_count - (new_row - old_row) - 1, start_row + old_row);
+    buf_signcols_count_range(buf, start_row, row2, 0, kTrue);
   }
 
   marktree_splice(buf->b_marktree, (int32_t)start_row, start_col,
@@ -583,7 +586,8 @@ void extmark_splice_impl(buf_T *buf, int start_row, colnr_T start_col, bcount_t
                   new_row, new_col);
 
   if (old_row > 0 || new_row > 0) {
-    buf_signcols_count_range(buf, start_row, start_row + new_row, 0, kNone);
+    int row2 = MIN(buf->b_ml.ml_line_count - 1, start_row + new_row);
+    buf_signcols_count_range(buf, start_row, row2, 0, kNone);
   }
 
   if (undo == kExtmarkUndo) {

test/functional/ui/decorations_spec.lua

@@ -6366,6 +6366,30 @@ l5
       ]]
     })
   end)
+
+  it('signcolumn correctly tracked with signs beyond eob and pair end before start', function()
+    api.nvim_set_option_value('signcolumn', 'auto:2', {})
+    api.nvim_set_option_value('filetype', 'lua', {})
+    api.nvim_buf_set_lines(0, 0, -1, false, {'foo', 'bar'})
+    api.nvim_buf_set_extmark(0, ns, 2, 0, {sign_text='S1'})
+    api.nvim_set_hl(0, 'SignColumn', { link = 'Error' })
+    screen:expect([[
+      ^foo                                               |
+      bar                                               |
+      {1:~                                                 }|*7
+                                                        |
+    ]])
+    api.nvim_buf_set_extmark(0, ns, 0, 0, {sign_text='S2', end_row = 1})
+    api.nvim_buf_set_lines(0, 0, -1, false, {'-- foo', '-- bar'})
+    api.nvim_buf_clear_namespace(0, ns, 0, -1)
+    screen:expect([[
+      ^-- foo                                            |
+      -- bar                                            |
+      {1:~                                                 }|*7
+                                                        |
+    ]])
+    assert_alive()
+  end)
 end)
 
 describe('decorations: virt_text', function()