Fix inserting to the end of a range

lua/conform/runner.lua

@@ -227,23 +227,24 @@ M.apply_format = function(
     local is_delete = new_line_count == 0
     local is_replace = not is_insert and not is_delete
     local orig_line_end = orig_line_start + orig_line_count
-    local new_line_end = new_line_start + new_line_count
-
-    if is_insert then
-      -- When the diff is an insert, it actually means to insert after the mentioned line
-      orig_line_start = orig_line_start + 1
-      orig_line_end = orig_line_end + 1
-    end
-
-    local replacement = util.tbl_slice(new_lines, new_line_start, new_line_end - 1)
-
     -- For replacement edits, convert the end line to be inclusive
     if is_replace then
       orig_line_end = orig_line_end - 1
     end
+    local new_line_end = new_line_start + new_line_count
+
+    local replacement = util.tbl_slice(new_lines, new_line_start, new_line_end - 1)
+
     local should_apply_diff = not only_apply_range
       or not range
       or indices_in_range(range, orig_line_start, orig_line_end)
+
+    -- When the diff is an insert, it actually means to insert after the mentioned line
+    if is_insert then
+      orig_line_start = orig_line_start + 1
+      orig_line_end = orig_line_end + 1
+    end
+
     if should_apply_diff then
       local text_edit = create_text_edit(
         original_lines,

tests/runner_spec.lua

@@ -385,6 +385,18 @@ print("a")
         )
         assert.are.same({ "a", "d", "c" }, vim.api.nvim_buf_get_lines(0, 0, -1, false))
       end)
+
+      it("applies edits that are inserting at the end of the range", function()
+        run_formatter(
+          "a\nb\nc",
+          "a\nb\nc\nd",
+          { range = {
+            start = { 2, 0 },
+            ["end"] = { 3, 0 },
+          } }
+        )
+        assert.are.same({ "a", "b", "c", "d" }, vim.api.nvim_buf_get_lines(0, 0, -1, false))
+      end)
     end)
 
     it("can run the format command in the shell", function()