Text: AutoFormat starts bulleted and numbered lists as you type

A paragraph that starts with *, -, --, >, <>, 1., 1), I., i., A., a.
or a) followed by a space or tab now becomes a bulleted or numbered
list in that style through format.bullets or format.numbering, and the
typed lead and space are removed. The keystroke is one undo step.
Backspace right after the change puts the typed text and the
paragraph's formatting back.

Tools ▸ AutoCorrect has "Automatic bulleted and numbered lists" to turn
it off, and text.autocorrect takes and reports it as lists.

crates/engine/src/cmd/text.rs

@@ -31,7 +31,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "AutoCorrect Options",
             ["Tools"],
             None,
-            "{on?, twoInitials?, sentenceCaps?, days?, capsLock?, fractions?, ordinals?: bool, add?: [from, to], remove?: from} → the options and the replacement list",
+            "{on?, twoInitials?, sentenceCaps?, days?, capsLock?, fractions?, ordinals?, lists?: bool, add?: [from, to], remove?: from} → the options and the replacement list",
             always,
             autocorrect_options
         ),
@@ -631,6 +631,13 @@ fn autocorrect(s: &mut Session, typing: bool) -> Result<()> {
     if end == 0 || !line.get(end - 1).is_some_and(|c| c.is_whitespace() || ".,;:!?".contains(*c)) {
         return Ok(());
     }
+    if typing && s.prefs.ac_lists {
+        // A lead such as `i.` or `a.` is kept as typed, so the space after it starts its list.
+        let lead: String = line.get(..end).map(|l| l.iter().collect()).unwrap_or_default();
+        if auto_list_style(&lead).is_some() || start_auto_list(s, &t, &line, end)? {
+            return Ok(());
+        }
+    }
     let mut word_end = end - 1;
     let mut start = word_end;
     while start > 0 && line.get(start - 1).is_some_and(|c| !c.is_whitespace()) {
@@ -679,6 +686,83 @@ fn autocorrect(s: &mut Session, typing: bool) -> Result<()> {
     Ok(())
 }
 
+/// A list AutoFormat started: the text being edited right after it, the typed lead with its
+/// space, the paragraph's own formatting before, and the revision the change left.
+#[derive(Clone, Debug)]
+pub struct AutoList {
+    sel: TextSel,
+    typed: String,
+    props: deckcraft_model::text::ParaProps,
+    revision: u64,
+}
+
+/// The list a paragraph that starts with `lead` and a space or tab becomes, as the command and
+/// parameters that make it: `*` •, `-` or `–` –, `--` or `—` ■, `>` ➢, `<>` ◆, and the numbering
+/// styles `1.`, `1)`, `I.`, `i.`, `A.`, `a.` and `a)`.
+fn auto_list_style(lead: &str) -> Option<(&'static str, Value)> {
+    let bullet = |c: &str| Some(("format.bullets", json!({"on": true, "char": c})));
+    let number = |scheme: &str| Some(("format.numbering", json!({"on": true, "scheme": scheme})));
+    match lead {
+        "*" => bullet("•"),
+        "-" | "–" => bullet("–"),
+        "--" | "—" => bullet("■"),
+        ">" => bullet("➢"),
+        "<>" => bullet("◆"),
+        "1." => number("arabicPeriod"),
+        "1)" => number("arabicParenR"),
+        "I." => number("romanUcPeriod"),
+        "i." => number("romanLcPeriod"),
+        "A." => number("alphaUcPeriod"),
+        "a." => number("alphaLcPeriod"),
+        "a)" => number("alphaLcParenR"),
+        _ => None,
+    }
+}
+
+/// AutoFormat's automatic bulleted and numbered lists: when the caret's paragraph holds only a
+/// list lead (`*`, `1.`…) before the space or tab just typed, the lead and the space are removed
+/// and the paragraph becomes a list paragraph in that style. `false` when nothing changed.
+fn start_auto_list(s: &mut Session, t: &TextSel, line: &[char], end: usize) -> Result<bool> {
+    if t.is_range() || !line.get(end - 1).is_some_and(|c| *c == ' ' || *c == '\t') {
+        return Ok(false);
+    }
+    let lead: String = line.get(..end - 1).map(|l| l.iter().collect()).unwrap_or_default();
+    let Some((id, params)) = auto_list_style(&lead) else { return Ok(false) };
+    let typed: String = line.get(..end).map(|l| l.iter().collect()).unwrap_or_default();
+    let para = t.caret.0;
+    let props = body_of(s.doc()?, t).and_then(|b| b.paragraphs.get(para)).map(|p| p.props.clone()).unwrap_or_default();
+    edit_text(s, |body, tt| {
+        ed::delete(body, (para, 0), (para, end));
+        tt.anchor = (para, 0);
+        tt.caret = (para, 0);
+    })?;
+    s.execute(id, &params)?;
+    let st = s.doc_mut()?;
+    if let Some(sel) = st.selection.text.clone() {
+        st.auto_list = Some(AutoList { sel, typed, props, revision: st.revision });
+    }
+    Ok(true)
+}
+
+/// Backspace right after AutoFormat started a list: the paragraph gets back the typed lead and
+/// space and the formatting it had. `false` when the last change was anything else.
+fn undo_auto_list(s: &mut Session) -> Result<bool> {
+    let st = s.doc_mut()?;
+    let Some(a) = st.auto_list.take() else { return Ok(false) };
+    if a.revision != st.revision || st.selection.text.as_ref() != Some(&a.sel) {
+        return Ok(false);
+    }
+    edit_text(s, |body, t| {
+        if let Some(p) = body.paragraphs.get_mut(a.sel.caret.0) {
+            p.props = a.props.clone();
+        }
+        let c = ed::insert(body, a.sel.caret, &a.typed, None);
+        t.anchor = c;
+        t.caret = c;
+    })?;
+    Ok(true)
+}
+
 /// `word` is a number with the ordinal suffix it takes (1st, 22nd, 103rd, 11th), as AutoFormat
 /// superscripts it.
 fn is_ordinal(word: &str) -> bool {
@@ -726,6 +810,7 @@ fn autocorrect_options(s: &mut Session, p: &Value) -> Result<Value> {
         ("capsLock", &mut pr.ac_caps_lock),
         ("fractions", &mut pr.ac_fractions),
         ("ordinals", &mut pr.ac_ordinals),
+        ("lists", &mut pr.ac_lists),
     ] {
         if let Some(v) = p.get(key).and_then(Value::as_bool) {
             *slot = v;
@@ -772,7 +857,7 @@ fn autocorrect_options(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(json!({
         "on": pr.autocorrect, "twoInitials": pr.ac_two_initials, "sentenceCaps": pr.ac_sentence_caps,
         "days": pr.ac_days, "capsLock": pr.ac_caps_lock, "fractions": pr.ac_fractions,
-        "ordinals": pr.ac_ordinals, "entries": list,
+        "ordinals": pr.ac_ordinals, "lists": pr.ac_lists, "entries": list,
     }))
 }
 
@@ -1026,6 +1111,9 @@ fn insert(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 pub(crate) fn delete_dir(s: &mut Session, dir: &str) -> Result<Value> {
+    if dir == "backward" && undo_auto_list(s)? {
+        return ok();
+    }
     let dir = dir.to_string();
     edit_text(s, move |body, t| {
         let (a, b) = t.ordered();