Fix incorrect checkbox placement in Markdown preview (#19383)

- Closes #12515

Before fix:
<img width="1506" alt="Screenshot 2024-10-17 at 09 50 19"
src="https://github.com/user-attachments/assets/250f50cb-0119-4b96-bc9b-7258aa83247c">

After fix:
<img width="1027" alt="Screenshot 2024-10-17 at 09 52 36"
src="https://github.com/user-attachments/assets/c2eb7e4a-3c03-466c-b215-7fcc22eed024">

Testing:
- Manual testing 
- Added unit test

Test results, these tests fail on the main branch for my setup as well,
I have docker running but still had some failures:
```
failures:
    tests::integration_tests::test_context_collaboration_with_reconnect
    tests::integration_tests::test_formatting_buffer
    tests::integration_tests::test_fs_operations
    tests::integration_tests::test_git_branch_name
    tests::integration_tests::test_git_diff_base_change
    tests::integration_tests::test_git_status_sync
    tests::integration_tests::test_join_after_restart
    tests::integration_tests::test_join_call_after_screen_was_shared
    tests::integration_tests::test_joining_channels_and_calling_multiple_users_simultaneously
    tests::integration_tests::test_leaving_project
    tests::integration_tests::test_leaving_worktree_while_opening_buffer
    tests::integration_tests::test_local_settings
    tests::integration_tests::test_lsp_hover
    tests::integration_tests::test_mute_deafen
    tests::integration_tests::test_open_buffer_while_getting_definition_pointing_to_it
    tests::integration_tests::test_pane_split_left
    tests::integration_tests::test_prettier_formatting_buffer
    tests::integration_tests::test_preview_tabs
    tests::integration_tests::test_project_reconnect
    tests::integration_tests::test_project_search
    tests::integration_tests::test_project_symbols
    tests::integration_tests::test_propagate_saves_and_fs_changes
    tests::integration_tests::test_references
    tests::integration_tests::test_reloading_buffer_manually
    tests::integration_tests::test_right_click_menu_behind_collab_panel
    tests::integration_tests::test_room_location
    tests::integration_tests::test_room_uniqueness
    tests::integration_tests::test_server_restarts
    tests::integration_tests::test_unshare_project
    tests::notification_tests::test_notifications
    tests::random_project_collaboration_tests::test_random_project_collaboration
    tests::remote_editing_collaboration_tests::test_sharing_an_ssh_remote_project

test result: FAILED. 156 passed; 32 failed; 0 ignored; 0 measured; 0 filtered out; finished in 100.98s
```
Comments:
I do not have a ton of rust knowledge, so very open to feedback. TYSM

Release Notes:

- Fix Incorrect checkbox placement in Markdown preview

---------

Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>

crates/markdown_preview/src/markdown_parser.rs

@@ -36,6 +36,20 @@ struct MarkdownParser<'a> {
     language_registry: Option<Arc<LanguageRegistry>>,
 }
 
+struct MarkdownListItem {
+    content: Vec<ParsedMarkdownElement>,
+    item_type: ParsedMarkdownListItemType,
+}
+
+impl Default for MarkdownListItem {
+    fn default() -> Self {
+        Self {
+            content: Vec::new(),
+            item_type: ParsedMarkdownListItemType::Unordered,
+        }
+    }
+}
+
 impl<'a> MarkdownParser<'a> {
     fn new(
         tokens: Vec<(Event<'a>, Range<usize>)>,
@@ -475,9 +489,8 @@ impl<'a> MarkdownParser<'a> {
         let (_, list_source_range) = self.previous().unwrap();
 
         let mut items = Vec::new();
-        let mut items_stack = vec![Vec::new()];
+        let mut items_stack = vec![MarkdownListItem::default()];
         let mut depth = 1;
-        let mut task_item = None;
         let mut order = order;
         let mut order_stack = Vec::new();
 
@@ -517,8 +530,9 @@ impl<'a> MarkdownParser<'a> {
                     start_item_range = source_range.clone();
 
                     self.cursor += 1;
-                    items_stack.push(Vec::new());
+                    items_stack.push(MarkdownListItem::default());
 
+                    let mut task_list = None;
                     // Check for task list marker (`- [ ]` or `- [x]`)
                     if let Some(event) = self.current_event() {
                         // If there is a linebreak in between two list items the task list marker will actually be the first element of the paragraph
@@ -527,7 +541,7 @@ impl<'a> MarkdownParser<'a> {
                         }
 
                         if let Some((Event::TaskListMarker(checked), range)) = self.current() {
-                            task_item = Some((*checked, range.clone()));
+                            task_list = Some((*checked, range.clone()));
                             self.cursor += 1;
                         }
                     }
@@ -539,13 +553,21 @@ impl<'a> MarkdownParser<'a> {
                             let text = self.parse_text(false, Some(range.clone()));
                             let block = ParsedMarkdownElement::Paragraph(text);
                             if let Some(content) = items_stack.last_mut() {
-                                content.push(block);
+                                let item_type = if let Some((checked, range)) = task_list {
+                                    ParsedMarkdownListItemType::Task(checked, range)
+                                } else if let Some(order) = order {
+                                    ParsedMarkdownListItemType::Ordered(order)
+                                } else {
+                                    ParsedMarkdownListItemType::Unordered
+                                };
+                                content.item_type = item_type;
+                                content.content.push(block);
                             }
                         } else {
                             let block = self.parse_block().await;
                             if let Some(block) = block {
-                                if let Some(content) = items_stack.last_mut() {
-                                    content.extend(block);
+                                if let Some(list_item) = items_stack.last_mut() {
+                                    list_item.content.extend(block);
                                 }
                             }
                         }
@@ -559,19 +581,11 @@ impl<'a> MarkdownParser<'a> {
                 Event::End(TagEnd::Item) => {
                     self.cursor += 1;
 
-                    let item_type = if let Some((checked, range)) = task_item {
-                        ParsedMarkdownListItemType::Task(checked, range)
-                    } else if let Some(order) = order {
-                        ParsedMarkdownListItemType::Ordered(order)
-                    } else {
-                        ParsedMarkdownListItemType::Unordered
-                    };
-
                     if let Some(current) = order {
                         order = Some(current + 1);
                     }
 
-                    if let Some(content) = items_stack.pop() {
+                    if let Some(list_item) = items_stack.pop() {
                         let source_range = source_ranges
                             .remove(&depth)
                             .unwrap_or(start_item_range.clone());
@@ -580,9 +594,9 @@ impl<'a> MarkdownParser<'a> {
                         let source_range = source_range.start..source_range.end - 1;
                         let item = ParsedMarkdownElement::ListItem(ParsedMarkdownListItem {
                             source_range,
-                            content,
+                            content: list_item.content,
                             depth,
-                            item_type,
+                            item_type: list_item.item_type,
                         });
 
                         if let Some(index) = insertion_indices.get(&depth) {
@@ -592,8 +606,6 @@ impl<'a> MarkdownParser<'a> {
                             items.push(item);
                         }
                     }
-
-                    task_item = None;
                 }
                 _ => {
                     if depth == 0 {
@@ -603,10 +615,10 @@ impl<'a> MarkdownParser<'a> {
                     // or the list item contains blocks that should be rendered after the nested list items
                     let block = self.parse_block().await;
                     if let Some(block) = block {
-                        if let Some(items_stack) = items_stack.last_mut() {
+                        if let Some(list_item) = items_stack.last_mut() {
                             // If we did not insert any nested items yet (in this case insertion index is set), we can append the block to the current list item
                             if !insertion_indices.contains_key(&depth) {
-                                items_stack.extend(block);
+                                list_item.content.extend(block);
                                 continue;
                             }
                         }
@@ -722,7 +734,6 @@ mod tests {
     use gpui::BackgroundExecutor;
     use language::{tree_sitter_rust, HighlightId, Language, LanguageConfig, LanguageMatcher};
     use pretty_assertions::assert_eq;
-
     use ParsedMarkdownListItemType::*;
 
     async fn parse(input: &str) -> ParsedMarkdown {
@@ -956,6 +967,33 @@ Some other content
         );
     }
 
+    #[gpui::test]
+    async fn test_list_with_indented_task() {
+        let parsed = parse(
+            "\
+- [ ] TODO
+  - [x] Checked
+  - Unordered
+  1. Number 1
+  1. Number 2
+1. Number A
+",
+        )
+        .await;
+
+        assert_eq!(
+            parsed.children,
+            vec![
+                list_item(0..12, 1, Task(false, 2..5), vec![p("TODO", 6..10)]),
+                list_item(13..26, 2, Task(true, 15..18), vec![p("Checked", 19..26)]),
+                list_item(29..40, 2, Unordered, vec![p("Unordered", 31..40)]),
+                list_item(43..54, 2, Ordered(1), vec![p("Number 1", 46..54)]),
+                list_item(57..68, 2, Ordered(2), vec![p("Number 2", 60..68)]),
+                list_item(69..80, 1, Ordered(1), vec![p("Number A", 72..80)]),
+            ],
+        );
+    }
+
     #[gpui::test]
     async fn test_list_with_linebreak_is_handled_correctly() {
         let parsed = parse(