fix: keep the marker and numbers a list was authored with

[Azganoth]

Summary

A list is now written with the marker it was authored with, -, +, or * for a bullet list and . or ) for an ordered one, with the numbers its items were written with, the spaces between each marker and its content, and the blank line an item opening on a later line was written with. mdast-util-to-markdown picks one bullet for the whole document from options.bullet and moves each list off whatever the list before it used, so a file written with - came back as a mixture of * and - that followed the order the lists appeared in, 3. followed by 8. was renumbered to 3. and 4., and 4) became 4..

leafdownListForm stamps the authored form onto the mdast nodes the way leafdownTableForm stamps a table's outer pipes. It reads the head of each item's own slice, which opens at the marker whatever the container indented it by. CommonMark reads a change of marker as the start of another list, so the first item that carries a position answers for the whole list, while the number and the spacing are each item's own. The three list schemas carry the form as attributes, and list and listItem stringify handlers of Leafdown's own write it.

The list handler holds the authored marker in the options the upstream handler reads, for the length of that list, rather than replacing it. Two adjacent lists sharing a marker are read back as one list, and that guard is upstream's; keeping it means the marker gives way exactly where the file would not reload as the document that wrote it. No file holds two adjacent lists with one marker, because a repeated marker opens one list to begin with, so only an edit that deletes what stood between two lists reaches the collision: a bullet list then moves to *, or to - where * is what collided, and an ordered list to the other delimiter.

The listItem handler is written out rather than delegated. The upstream handler sizes every item by one space after its marker, or by the tab stop a document-wide option names, and neither can answer for the spaces a single item was written with; an item's own number would have to be forged through its list's start. Owning the handler is also what keeps a task marker GFM's own handler drops, since it inserts the checkbox by matching a . delimiter followed by at most three spaces: an ordered item written 1) [x], or any item written with four spaces of padding, lost its checkbox before this.

Two positions give way rather than write a list the next open reads differently:

• The marker collision above.
• An item opening on a blank line cannot interrupt the paragraph above its list, so where the list follows a paragraph directly, which only a tight list item does, the content is written on the marker's line. An item is written where its own list's parent is out of reach, so the list resolves that question and hands the item down without the form.

A bullet no longer gives way to a thematic break opening its item. mdast-util-to-markdown moves the bullet off the rule character it was configured with, which cannot answer for a run the node carries, while serializeThematicBreak already answers it from the break itself. The option is now held to _, a character no bullet can be, so only the run gives way: * --- was written - ***, giving way at both ends, and is now written as authored. The run still moves where an edit puts it on its bullet's character.

The first item of an ordered list is written with the list's own start rather than the number recorded on the item, because that is the number the file is read back with and the list is what holds it. A list the editor makes carries no authored marker and writes *, or . when ordered, with one space after it; that default is recorded in docs/specification.md, since it was not defined before.

joinsWithoutBlankLine moves out of thematicBreakMarkdown.ts into markdownJoins.ts, because both fallbacks ask the serializer the same question about what it will write between two blocks. withBooleanSpread and withoutFilledLeadingParagraph move out of createMilkdownEditor.ts into the list module, alongside the runners that now apply them.

Related Issue

Closes #317

Verification

markdownCompatibility.test.ts gains List marker form, which pins the written bytes across a save. Twelve sources keep their markers, covering each bullet, each ordered delimiter, adjacent lists of both kinds, a list nested under either kind, and task items under - and 1). Five keep their numbers, covering a consecutive run, a run that skips, a repeated 1., a 0. start, and the nine-digit marker beside a short one. Eight keep their marker padding, covering one to four spaces, a wider ordered marker, a task marker after the padding, and the two places the padding sets a column: a second paragraph in the item, and a nested list. Five keep an item opening on the line after its marker, including a task marker and a block other than a paragraph.

One row per fallback covers what no source can author. Two adjacent lists are built by deleting the <!----> between two lists that share a marker, for a bullet pair and an ordered pair; each asserts the written bytes and that reopening the save gives two lists rather than one. The blank first line is built by tightening the item that holds the list, which is the only way a list comes to follow a paragraph with no blank line between them.

blocks.test.ts already asserted the marker an inserted list writes, and List marker form asserts the same default through the command, since a list read from a file now writes its own.

Measured by diffing corpus/commonmark/lists-and-blockquotes.md against its first save: every difference under Bullet-marker forms, Ordered-marker forms, Tight lists, Marker-padding boundaries, and A list item can begin with a blank line is gone. What still differs in that file is the lazy continuation gaining its marker, the blank lines written between blocks, the setext heading rewritten as ATX, and the indented code rewritten as fenced, each of which belongs to a class #251 tracks separately.

Existing expectations that recorded the old rewriting were updated rather than kept. The fixture in markdownCompatibility.test.ts is now derived from its source, since the save differs from it only by the final newline; four rows there that asserted * for a - source now assert -, as do the task-checkbox, command-keymap, and keyboard tests that open a - list. The thematic-break test that asserted - *** for * --- now asserts the authored bytes, and the collision it covered moved to two rows that edit a run onto its bullet's character.

pnpm check:frontend passes. The backend is untouched, so pnpm check:backend was not run.

Not verified: the manual pass over corpus/ in the running application, which covers rendering, interaction, and navigator behavior beyond the automated round trip. The desktop E2E suite was not run locally; its fixtures hold no lists.

Notes

A list that reaches the document without a parse, a pasted one, carries the default rather than the form of the document it came from. The rendered list would have to carry the marker the way a thematic break carries its run in data-marker, which is clipboard scope. A table's outer pipes are held the same way.

A nested list made with Tab carries the default marker rather than the marker of the list around it, because the command builds the list from the schema's own attributes. It is a list the editor made, so the recorded default applies, but a marker inherited from the enclosing list would read better in the file and is worth its own issue.

A fallback rewrites the recorded form as well as the bytes, so a list whose marker was withdrawn reopens holding the marker it was written with rather than the one it was authored with. The content is identical; only the recorded attribute differs. A thematic break and a table behave the same way.

An item written with five or more spaces after its marker keeps one, because CommonMark reads the rest as the indented code inside it. That item is rewritten as a fenced block, which is the indented-code class rather than this one.