extmarks: better linewise/charwise handling

lua/u/range.lua

@@ -93,6 +93,8 @@ end
 --- @param bufnr number
 --- @param id number
 function Range.from_extmark(bufnr, id)
+  local mode = 'v'
+
   ---@type integer, integer, vim.api.keyset.extmark_details | nil
   local start_row0, start_col0, details =
     unpack(vim.api.nvim_buf_get_extmark_by_id(bufnr, NS, id, { details = true }))
@@ -100,15 +102,16 @@ function Range.from_extmark(bufnr, id)
   local start = Pos.new(bufnr, start_row0 + 1, start_col0 + 1)
   local stop = details and Pos.new(bufnr, details.end_row + 1, details.end_col)
 
-  local max_line_num = vim.api.nvim_buf_line_count(bufnr)
-  if stop and stop.lnum > max_line_num then
-    stop.lnum = max_line_num
-    stop.col = Pos.MAX_COL
-    stop = stop:as_real()
-  end
-  if stop and stop.col == 0 then stop = stop:must_next(-1) end
+  -- Check for invalid extmark range:
+  if stop and stop < start then return Range.new(stop) end
 
-  return Range.new(start, stop, 'v')
+  if stop and stop.col == 0 then
+    mode = 'V'
+    stop = stop:must_next(-1)
+    stop.col = Pos.MAX_COL
+  end
+
+  return Range.new(start, stop, mode)
 end
 
 --- @param bufnr? number
@@ -371,9 +374,15 @@ end
 
 function Range:save_to_extmark()
   local r = self:to_charwise()
+  local end_row = r.stop.lnum - 1
+  local end_col = r.stop.col
+  if self.mode == 'V' then
+    end_row = end_row + 1
+    end_col = 0
+  end
   local id = vim.api.nvim_buf_set_extmark(r.start.bufnr, NS, r.start.lnum - 1, r.start.col - 1, {
-    end_row = r.stop.lnum - 1,
-    end_col = r.stop.col,
+    end_row = end_row,
+    end_col = end_col,
   })
   return ExtmarkRange.new(r.start.bufnr, id)
 end