feat(dispatch): walk subcommands and detect revset flag from help

Two real failures motivated this:

- `jjf bm main` (where `bm` is a user alias for `bookmark move`) ran
  `jj bm main -r <id>` — but bookmark move uses `--to`, not `-r`.
- `jjf tag set v0.2.0` errored with "doesn't take revisions" because
  jjf only inspected `jj tag --help` (parent) instead of walking
  into the `set` leaf, which does take `-r`.

Replace the boolean `supports_revisions()` (a substring match on
"REVSET") with `RevsetTarget { leaf, passthrough, flag }`:

- Walks multi-level subcommands by parsing each parent's `Commands:`
  block — including `[aliases: …]` annotations, so `jjf tag s` walks
  to `tag set`. Aliases like `bm` work transparently because `jj bm
  --help` already emits the resolved leaf's help.
- Parses the leaf's `Options:` block and picks the revset flag in
  priority order: `-r`/`--revision[s]` first, then `-t, --to`.
  `--from` is intentionally not a fallback (different semantics from
  "the revision the picker chose").
- Bypasses the picker entirely when the user already passed a revset
  flag in their args, so `jjf describe -r @-` runs verbatim instead
  of double-injecting `-r`.

`exec` and `command_line` now take `&RevsetTarget` and emit the
resolved flag; signatures thread through `tui.rs` and `main.rs`.

New unit tests cover the help parsers and command-line construction
against captured fixtures of `jj tag set --help`, `jj bookmark move
--help`, and `jj tag --help`.

src/jj.rs

@@ -265,42 +265,294 @@ fn parse_show_summary(bytes: &[u8]) -> PreviewParts {
     PreviewParts { description, files }
 }
 
-pub fn supports_revisions(subcommand: &str) -> Result<bool> {
+/// Which flag a leaf jj subcommand uses to accept a revset, picked in
+/// priority order: `-r`/`--revision[s]` first, then `-t, --to`. `--from` is
+/// intentionally not a fallback — its semantics ("filter source revisions")
+/// differ enough from "the revision the picker chose" that silently injecting
+/// it would surprise users.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RevsetFlag {
+    Revision,
+    To,
+}
+
+impl RevsetFlag {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            RevsetFlag::Revision => "-r",
+            RevsetFlag::To => "--to",
+        }
+    }
+}
+
+/// A jj invocation jjf has analyzed and is ready to dispatch on. `leaf` is
+/// the resolved subcommand path (preserving the user's tokens, including
+/// aliases like `bm` — jj resolves them again at exec time). `passthrough`
+/// is everything after the leaf. `flag` is `None` when the leaf accepts no
+/// revset; in that case jjf refuses to run the picker.
+#[derive(Debug, Clone)]
+pub struct RevsetTarget {
+    pub leaf: Vec<String>,
+    pub passthrough: Vec<String>,
+    pub flag: Option<RevsetFlag>,
+}
+
+pub fn resolve_target(args: &[String]) -> Result<RevsetTarget> {
+    debug_assert!(!args.is_empty(), "resolve_target requires at least one arg");
+
+    let first_help = match run_help(std::slice::from_ref(&args[0]))? {
+        Some(h) => h,
+        None => {
+            // Unknown subcommand or jj help failed for some reason. Fall
+            // through optimistically so jj surfaces its own error message at
+            // exec time.
+            return Ok(RevsetTarget {
+                leaf: vec![args[0].clone()],
+                passthrough: args[1..].to_vec(),
+                flag: Some(RevsetFlag::Revision),
+            });
+        }
+    };
+
+    let (leaf, leaf_help) = resolve_leaf(args, first_help)?;
+    let passthrough = args[leaf.len()..].to_vec();
+    let flag = parse_revset_flag(&leaf_help);
+
+    Ok(RevsetTarget {
+        leaf,
+        passthrough,
+        flag,
+    })
+}
+
+fn resolve_leaf(args: &[String], first_help: String) -> Result<(Vec<String>, String)> {
+    let mut leaf = vec![args[0].clone()];
+    let mut help = first_help;
+    for arg in &args[1..] {
+        if arg.starts_with('-') {
+            break;
+        }
+        let children = parse_commands_section(&help);
+        if !children.contains(arg.as_str()) {
+            break;
+        }
+        let mut candidate = leaf.clone();
+        candidate.push(arg.clone());
+        match run_help(&candidate)? {
+            Some(next_help) => {
+                leaf = candidate;
+                help = next_help;
+            }
+            None => break,
+        }
+    }
+    Ok((leaf, help))
+}
+
+fn run_help(path: &[String]) -> Result<Option<String>> {
     let output = Command::new("jj")
-        .arg(subcommand)
+        .args(path)
         .arg("--help")
+        .stderr(Stdio::null())
         .output()
         .context("failed to spawn jj for preflight")?;
     if !output.status.success() {
-        // unknown subcommand or other error — let the main flow surface jj's error
-        return Ok(true);
+        return Ok(None);
     }
-    let help = String::from_utf8_lossy(&output.stdout);
-    Ok(help.contains("REVSET"))
+    Ok(Some(String::from_utf8_lossy(&output.stdout).into_owned()))
 }
 
-pub fn exec(subcommand: &str, passthrough: &[String], ids: &[String]) -> Result<ExitStatus> {
-    let revset = ids.join("|");
-    let status = Command::new("jj")
-        .arg(subcommand)
-        .args(passthrough)
-        .arg("-r")
-        .arg(&revset)
-        .status()
-        .context("failed to spawn jj")?;
+/// Parse the `Commands:` block of a jj help output. Returns the set of
+/// subcommand names AND their `[aliases: …]` annotations, so a user typing
+/// `jjf tag s` (where `s` is the alias for `set`) walks correctly.
+fn parse_commands_section(help: &str) -> std::collections::HashSet<String> {
+    let mut set = std::collections::HashSet::new();
+    let mut in_commands = false;
+    for line in help.lines() {
+        if line == "Commands:" {
+            in_commands = true;
+            continue;
+        }
+        if !in_commands {
+            continue;
+        }
+        if line.is_empty() {
+            break;
+        }
+        if !line.starts_with(' ') {
+            break;
+        }
+        let trimmed = line.trim_start();
+        let indent = line.len() - trimmed.len();
+        // Primary entries have exactly 2-space indent. Anything deeper is
+        // a description continuation we don't care about.
+        if indent != 2 {
+            continue;
+        }
+        if let Some(name) = trimmed.split_whitespace().next() {
+            set.insert(name.to_string());
+        }
+        scan_aliases(line, &mut set);
+    }
+    set
+}
+
+fn scan_aliases(line: &str, names: &mut std::collections::HashSet<String>) {
+    let Some(start) = line.find("[aliases:") else {
+        return;
+    };
+    let after = &line[start + "[aliases:".len()..];
+    let Some(end) = after.find(']') else {
+        return;
+    };
+    for a in after[..end].split(',') {
+        let n = a.trim();
+        if !n.is_empty() {
+            names.insert(n.to_string());
+        }
+    }
+}
+
+/// Pick the right revset-accepting flag from a leaf's help, preferring
+/// `-r`/`--revision[s]` over `-t, --to`. Returns `None` if the leaf has
+/// neither.
+pub fn parse_revset_flag(help: &str) -> Option<RevsetFlag> {
+    let opts = parse_options(help);
+    for opt in &opts {
+        if opt.is_revset
+            && opt
+                .longs
+                .iter()
+                .any(|n| n == "--revision" || n == "--revisions")
+        {
+            return Some(RevsetFlag::Revision);
+        }
+    }
+    for opt in &opts {
+        if opt.is_revset && opt.longs.iter().any(|n| n == "--to") {
+            return Some(RevsetFlag::To);
+        }
+    }
+    None
+}
+
+#[derive(Debug)]
+struct OptionEntry {
+    longs: Vec<String>,
+    /// True when the placeholder is `<REVSET>` or `<REVSETS>`.
+    is_revset: bool,
+}
+
+fn parse_options(help: &str) -> Vec<OptionEntry> {
+    let mut opts = Vec::new();
+    let mut in_options = false;
+    let mut current: Option<OptionEntry> = None;
+
+    for line in help.lines() {
+        if line == "Options:" {
+            in_options = true;
+            continue;
+        }
+        if !in_options {
+            continue;
+        }
+        // A non-indented non-empty line ends `Options:` (e.g. `Global Options:`).
+        if !line.is_empty() && !line.starts_with(' ') {
+            if let Some(o) = current.take() {
+                opts.push(o);
+            }
+            break;
+        }
+        if line.is_empty() {
+            // Blank lines separate options inside the section; don't end it.
+            continue;
+        }
+
+        let trimmed = line.trim_start();
+        let indent = line.len() - trimmed.len();
+
+        // New entry: 2-space indent with `-X,` (short + long) OR 6-space
+        // indent with `--` (long-only flag, e.g. `--allow-move`).
+        let is_new_entry = (indent == 2 && trimmed.starts_with('-'))
+            || (indent == 6 && trimmed.starts_with("--"));
+
+        if is_new_entry {
+            if let Some(o) = current.take() {
+                opts.push(o);
+            }
+            current = Some(parse_option_header(trimmed));
+        } else if let Some(ref mut o) = current {
+            // Continuation line. Pull any `[aliases: --foo, --bar]` into the
+            // current option's long-name set so the priority match sees them.
+            let mut alias_set = std::collections::HashSet::new();
+            scan_aliases(line, &mut alias_set);
+            for n in alias_set {
+                if n.starts_with("--") {
+                    o.longs.push(n);
+                }
+            }
+        }
+    }
+    if let Some(o) = current {
+        opts.push(o);
+    }
+    opts
+}
+
+fn parse_option_header(s: &str) -> OptionEntry {
+    let mut longs = Vec::new();
+    let mut placeholder: Option<String> = None;
+    for token in s.split(|c: char| c == ',' || c.is_whitespace()) {
+        let t = token.trim();
+        if t.is_empty() {
+            continue;
+        }
+        if let Some(rest) = t.strip_prefix("--") {
+            // Strip a trailing `=...` if clap ever emits one (it doesn't
+            // today, but cheap insurance).
+            let name = rest.split('=').next().unwrap_or(rest);
+            longs.push(format!("--{name}"));
+        } else if let Some(stripped) = t.strip_prefix('<') {
+            // Placeholder: `<REVSET>`, `<REVSETS>`, `<NAMES>...`, etc.
+            let inner = stripped.trim_end_matches("...");
+            if let Some(end) = inner.find('>') {
+                placeholder = Some(inner[..end].to_string());
+            }
+        }
+    }
+    let is_revset = matches!(placeholder.as_deref(), Some("REVSET") | Some("REVSETS"));
+    OptionEntry { longs, is_revset }
+}
+
+pub fn exec(target: &RevsetTarget, ids: &[String]) -> Result<ExitStatus> {
+    let mut cmd = Command::new("jj");
+    cmd.args(&target.leaf);
+    cmd.args(&target.passthrough);
+    if !ids.is_empty() {
+        if let Some(flag) = target.flag {
+            cmd.arg(flag.as_str());
+            cmd.arg(ids.join("|"));
+        }
+    }
+    let status = cmd.status().context("failed to spawn jj")?;
     Ok(status)
 }
 
-pub fn command_line(subcommand: &str, passthrough: &[String], ids: &[String]) -> String {
-    let mut parts: Vec<String> = Vec::with_capacity(4 + passthrough.len());
+pub fn command_line(target: &RevsetTarget, ids: &[String]) -> String {
+    let mut parts: Vec<String> =
+        Vec::with_capacity(2 + target.leaf.len() + target.passthrough.len() + 2);
     parts.push("jj".into());
-    parts.push(subcommand.into());
-    for a in passthrough {
+    for w in &target.leaf {
+        parts.push(w.clone());
+    }
+    for a in &target.passthrough {
         parts.push(shell_quote(a));
     }
     if !ids.is_empty() {
-        parts.push("-r".into());
-        parts.push(shell_quote(&ids.join("|")));
+        if let Some(flag) = target.flag {
+            parts.push(flag.as_str().into());
+            parts.push(shell_quote(&ids.join("|")));
+        }
     }
     parts.join(" ")
 }
@@ -326,3 +578,147 @@ pub fn shell_quote(s: &str) -> String {
     out.push('\'');
     out
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TAG_SET_HELP: &str = "Create or update tags
+
+Usage: jj tag set [OPTIONS] <NAMES>...
+
+Arguments:
+  <NAMES>...
+          Tag names to create or update
+
+Options:
+  -r, --revision <REVSET>
+          Target revision to point to
+
+          [default: @]
+          [aliases: --to]
+
+      --allow-move
+          Allow moving existing tags
+
+  -h, --help
+          Print help (see a summary with '-h')
+
+Global Options:
+  -R, --repository <REPOSITORY>
+          Path to repository
+";
+
+    const BOOKMARK_MOVE_HELP: &str = "Move existing bookmarks to target revision
+
+Usage: jj bookmark move [OPTIONS] <NAMES|--from <REVSETS>>
+
+Arguments:
+  [NAMES]...
+          Move bookmarks matching the given name patterns
+
+Options:
+  -f, --from <REVSETS>
+          Move bookmarks from the given revisions
+
+  -t, --to <REVSET>
+          Move bookmarks to this revision
+
+          [default: @]
+
+  -B, --allow-backwards
+          Allow moving bookmarks backwards or sideways
+
+  -h, --help
+          Print help (see a summary with '-h')
+
+Global Options:
+  -R, --repository <REPOSITORY>
+          Path to repository
+";
+
+    const TAG_PARENT_HELP: &str = "Manage tags
+
+Usage: jj tag [OPTIONS] <COMMAND>
+
+Commands:
+  delete  Delete existing tags [aliases: d]
+  list    List tags and their targets [aliases: l]
+  set     Create or update tags [aliases: s]
+
+Options:
+  -h, --help
+          Print help (see a summary with '-h')
+
+Global Options:
+  -R, --repository <REPOSITORY>
+          Path to repository
+";
+
+    #[test]
+    fn revset_flag_prefers_revision_over_to_alias() {
+        // tag set has `-r, --revision <REVSET>` with `[aliases: --to]`.
+        // The Revision-class match must win over the To-class match.
+        assert_eq!(parse_revset_flag(TAG_SET_HELP), Some(RevsetFlag::Revision));
+    }
+
+    #[test]
+    fn revset_flag_falls_back_to_to_when_no_revision() {
+        // bookmark move has only `-f, --from <REVSETS>` and `-t, --to <REVSET>`.
+        assert_eq!(parse_revset_flag(BOOKMARK_MOVE_HELP), Some(RevsetFlag::To));
+    }
+
+    #[test]
+    fn revset_flag_none_for_parent_without_options() {
+        assert_eq!(parse_revset_flag(TAG_PARENT_HELP), None);
+    }
+
+    #[test]
+    fn commands_section_includes_names_and_aliases() {
+        let cmds = parse_commands_section(TAG_PARENT_HELP);
+        for name in ["delete", "list", "set", "d", "l", "s"] {
+            assert!(cmds.contains(name), "missing {name} in {cmds:?}");
+        }
+    }
+
+    #[test]
+    fn commands_section_empty_for_leaf() {
+        let cmds = parse_commands_section(BOOKMARK_MOVE_HELP);
+        assert!(cmds.is_empty(), "expected no commands, got {cmds:?}");
+    }
+
+    #[test]
+    fn command_line_emits_revision_flag() {
+        let target = RevsetTarget {
+            leaf: vec!["tag".into(), "set".into()],
+            passthrough: vec!["v0.2.0".into()],
+            flag: Some(RevsetFlag::Revision),
+        };
+        let s = command_line(&target, &["abcd1234".into()]);
+        assert_eq!(s, "jj tag set v0.2.0 -r abcd1234");
+    }
+
+    #[test]
+    fn command_line_emits_to_flag() {
+        let target = RevsetTarget {
+            leaf: vec!["bm".into()],
+            passthrough: vec!["main".into()],
+            flag: Some(RevsetFlag::To),
+        };
+        let s = command_line(&target, &["abcd1234".into()]);
+        assert_eq!(s, "jj bm main --to abcd1234");
+    }
+
+    #[test]
+    fn command_line_omits_flag_when_no_ids() {
+        let target = RevsetTarget {
+            leaf: vec!["describe".into()],
+            passthrough: vec!["-r".into(), "@".into()],
+            flag: Some(RevsetFlag::Revision),
+        };
+        // When the user already supplied -r, jjf calls command_line with empty
+        // ids — no extra flag should be appended.
+        let s = command_line(&target, &[]);
+        assert_eq!(s, "jj describe -r @");
+    }
+}

src/main.rs

@@ -25,19 +25,19 @@ fn real_main() -> Result<u8> {
 
     match first.as_str() {
         "init" => run_init(args),
-        "--emit" => match args.next() {
-            Some(sub) => {
-                let passthrough: Vec<String> = args.collect();
-                run_pick(&sub, &passthrough, /* emit = */ true)
-            }
-            None => {
+        "--emit" => {
+            let rest: Vec<String> = args.collect();
+            if rest.is_empty() {
                 eprintln!("usage: jjf --emit <jj-subcommand> [args...]");
-                Ok(2)
+                return Ok(2);
             }
-        },
-        sub => {
-            let passthrough: Vec<String> = args.collect();
-            run_pick(sub, &passthrough, /* emit = */ false)
+            run_pick(&rest, /* emit = */ true)
+        }
+        _ => {
+            let mut all = Vec::with_capacity(1 + args.size_hint().0);
+            all.push(first);
+            all.extend(args);
+            run_pick(&all, /* emit = */ false)
         }
     }
 }
@@ -65,10 +65,29 @@ fn run_init(mut args: impl Iterator<Item = String>) -> Result<u8> {
     }
 }
 
-fn run_pick(subcommand: &str, passthrough: &[String], emit: bool) -> Result<u8> {
-    if !jj::supports_revisions(subcommand)? {
+fn run_pick(args: &[String], emit: bool) -> Result<u8> {
+    let target = jj::resolve_target(args)?;
+
+    // Case 1: user already supplied a revset flag — bypass the picker entirely
+    // and run their command verbatim. Avoids double-`-r` and respects what
+    // they explicitly asked for.
+    if has_user_revset_flag(&target.passthrough) {
+        if emit {
+            let cmd = jj::command_line(&target, &[]);
+            println!("{cmd}");
+            return Ok(0);
+        }
+        echo_command(&target, &[]);
+        let status = jj::exec(&target, &[])?;
+        return Ok(status.code().unwrap_or(1) as u8);
+    }
+
+    // Case 2: leaf accepts no revset flag at all (e.g. `jj operation`,
+    // `jj workspace list`). Refuse to run the picker.
+    if target.flag.is_none() {
+        let leaf = target.leaf.join(" ");
         eprintln!(
-            "jjf: 'jj {subcommand}' doesn't take revisions — run 'jj {subcommand}' directly."
+            "jjf: 'jj {leaf}' takes no revset flag (-r/--to) — run 'jj {leaf}' directly."
         );
         return Ok(2);
     }
@@ -89,7 +108,7 @@ fn run_pick(subcommand: &str, passthrough: &[String], emit: bool) -> Result<u8>
         None
     };
 
-    let tui_result = tui::run(rows, subcommand, passthrough);
+    let tui_result = tui::run(rows, &target);
 
     if let Some(saved) = saved_stdout {
         restore_stdout(saved)?;
@@ -103,16 +122,25 @@ fn run_pick(subcommand: &str, passthrough: &[String], emit: bool) -> Result<u8>
     }
 
     if emit {
-        let cmd = jj::command_line(subcommand, passthrough, &ids);
+        let cmd = jj::command_line(&target, &ids);
         println!("{cmd}");
         Ok(0)
     } else {
-        echo_command(subcommand, passthrough, &ids);
-        let status = jj::exec(subcommand, passthrough, &ids)?;
+        echo_command(&target, &ids);
+        let status = jj::exec(&target, &ids)?;
         Ok(status.code().unwrap_or(1) as u8)
     }
 }
 
+fn has_user_revset_flag(passthrough: &[String]) -> bool {
+    passthrough.iter().any(|a| {
+        matches!(
+            a.as_str(),
+            "-r" | "--revision" | "--revisions" | "-t" | "--to"
+        )
+    })
+}
+
 #[cfg(unix)]
 fn redirect_stdout_to_tty() -> Result<libc::c_int> {
     use std::os::fd::AsRawFd;
@@ -142,9 +170,9 @@ fn restore_stdout(saved: libc::c_int) -> Result<()> {
     Ok(())
 }
 
-fn echo_command(subcommand: &str, passthrough: &[String], ids: &[String]) {
+fn echo_command(target: &jj::RevsetTarget, ids: &[String]) {
     use std::io::IsTerminal;
-    let cmd = jj::command_line(subcommand, passthrough, ids);
+    let cmd = jj::command_line(target, ids);
     if std::io::stdout().is_terminal() {
         println!("\x1b[2m$\x1b[0m {cmd}");
     } else {

src/tui.rs

@@ -278,8 +278,7 @@ fn score_row(
 
 pub fn run(
     rows: Vec<Row>,
-    subcommand: &str,
-    passthrough: &[String],
+    target: &jj::RevsetTarget,
 ) -> Result<Option<Vec<String>>> {
     install_panic_hook();
     let mut tty = OpenOptions::new()
@@ -295,7 +294,7 @@ pub fn run(
     tty.write_all(HIDE_CURSOR).context("hide cursor")?;
     tty.flush().ok();
 
-    let result = run_loop(&mut tty, rows, subcommand, passthrough);
+    let result = run_loop(&mut tty, rows, target);
 
     let _ = tty.write_all(SHOW_CURSOR);
     let _ = tty.write_all(b"\x1b[?1049l");
@@ -320,15 +319,14 @@ fn install_panic_hook() {
 fn run_loop(
     tty: &mut File,
     rows: Vec<Row>,
-    subcommand: &str,
-    passthrough: &[String],
+    target: &jj::RevsetTarget,
 ) -> Result<Option<Vec<String>>> {
     let mut app = App::new(rows);
     let (mut term_cols, mut term_rows) = crossterm::terminal::size().unwrap_or((80, 24));
     // Chrome rows: input(1) + cmd_preview(1) + hint(1) = 3.
     app.last_height = (term_rows as usize).saturating_sub(3);
     loop {
-        render(tty, &mut app, term_rows, term_cols, subcommand, passthrough)?;
+        render(tty, &mut app, term_rows, term_cols, target)?;
         if !event::poll(Duration::from_millis(250)).context("event poll failed")? {
             continue;
         }
@@ -454,8 +452,7 @@ fn render(
     app: &mut App,
     term_rows: u16,
     term_cols: u16,
-    subcommand: &str,
-    passthrough: &[String],
+    target: &jj::RevsetTarget,
 ) -> Result<()> {
     let viewport_y: u16 = 0;
     let viewport_height = term_rows;
@@ -601,7 +598,7 @@ fn render(
     let cmd_y = viewport_y + 1 + log_height as u16 + 1;
     write!(buf, "\x1b[{};1H", cmd_y)?;
     buf.extend_from_slice(ERASE_TO_EOL);
-    let cmd = jj::command_line(subcommand, passthrough, &app.pending_ids());
+    let cmd = jj::command_line(target, &app.pending_ids());
     let cmd_max = (term_cols as usize).saturating_sub(2); // for "▶ "
     let cmd_visible: String = if cmd.chars().count() <= cmd_max {
         cmd