cli: preserve RevisionArg type as much as possible

Just for a bit of type safety.

cli/src/commands/branch.rs

@@ -240,7 +240,7 @@ fn cmd_branch_create(
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
     let target_commit =
-        workspace_command.resolve_single_rev(args.revision.as_deref().unwrap_or("@"))?;
+        workspace_command.resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
     let view = workspace_command.repo().view();
     let branch_names = &args.names;
     if let Some(branch_name) = branch_names
@@ -341,7 +341,7 @@ fn cmd_branch_set(
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
     let target_commit =
-        workspace_command.resolve_single_rev(args.revision.as_deref().unwrap_or("@"))?;
+        workspace_command.resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
     let repo = workspace_command.repo().as_ref();
     let is_fast_forward = |old_target: &RefTarget| {
         // Strictly speaking, "all" old targets should be ancestors, but we allow

cli/src/commands/debug.rs

@@ -313,8 +313,8 @@ fn cmd_debug_tree(
         let tree = store.get_tree(&dir, &tree_id)?;
         MergedTree::resolved(tree)
     } else {
-        let commit =
-            workspace_command.resolve_single_rev(args.revision.as_deref().unwrap_or("@"))?;
+        let commit = workspace_command
+            .resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
         commit.tree()?
     };
     let matcher = workspace_command.matcher_from_values(&args.paths)?;

cli/src/commands/diff.rs

@@ -63,13 +63,15 @@ pub(crate) fn cmd_diff(
     let from_tree;
     let to_tree;
     if args.from.is_some() || args.to.is_some() {
-        let from = workspace_command.resolve_single_rev(args.from.as_deref().unwrap_or("@"))?;
+        let from =
+            workspace_command.resolve_single_rev(args.from.as_ref().unwrap_or(&RevisionArg::AT))?;
         from_tree = from.tree()?;
-        let to = workspace_command.resolve_single_rev(args.to.as_deref().unwrap_or("@"))?;
+        let to =
+            workspace_command.resolve_single_rev(args.to.as_ref().unwrap_or(&RevisionArg::AT))?;
         to_tree = to.tree()?;
     } else {
-        let commit =
-            workspace_command.resolve_single_rev(args.revision.as_deref().unwrap_or("@"))?;
+        let commit = workspace_command
+            .resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
         let parents = commit.parents();
         from_tree = merge_commit_trees(workspace_command.repo().as_ref(), &parents)?;
         to_tree = commit.tree()?

cli/src/commands/diffedit.rs

@@ -66,16 +66,18 @@ pub(crate) fn cmd_diffedit(
 
     let (target_commit, base_commits, diff_description);
     if args.from.is_some() || args.to.is_some() {
-        target_commit = workspace_command.resolve_single_rev(args.to.as_deref().unwrap_or("@"))?;
+        target_commit =
+            workspace_command.resolve_single_rev(args.to.as_ref().unwrap_or(&RevisionArg::AT))?;
         base_commits =
-            vec![workspace_command.resolve_single_rev(args.from.as_deref().unwrap_or("@"))?];
+            vec![workspace_command
+                .resolve_single_rev(args.from.as_ref().unwrap_or(&RevisionArg::AT))?];
         diff_description = format!(
             "The diff initially shows the commit's changes relative to:\n{}",
             workspace_command.format_commit_summary(&base_commits[0])
         );
     } else {
-        target_commit =
-            workspace_command.resolve_single_rev(args.revision.as_deref().unwrap_or("@"))?;
+        target_commit = workspace_command
+            .resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
         base_commits = target_commit.parents();
         diff_description = "The diff initially shows the commit's changes.".to_string();
     };

cli/src/commands/interdiff.rs

@@ -49,8 +49,9 @@ pub(crate) fn cmd_interdiff(
     args: &InterdiffArgs,
 ) -> Result<(), CommandError> {
     let workspace_command = command.workspace_helper(ui)?;
-    let from = workspace_command.resolve_single_rev(args.from.as_deref().unwrap_or("@"))?;
-    let to = workspace_command.resolve_single_rev(args.to.as_deref().unwrap_or("@"))?;
+    let from =
+        workspace_command.resolve_single_rev(args.from.as_ref().unwrap_or(&RevisionArg::AT))?;
+    let to = workspace_command.resolve_single_rev(args.to.as_ref().unwrap_or(&RevisionArg::AT))?;
 
     let from_tree = rebase_to_dest_parent(workspace_command.repo().as_ref(), &from, &to)?;
     let to_tree = to.tree()?;

cli/src/commands/move.rs

@@ -71,8 +71,10 @@ pub(crate) fn cmd_move(
         "`jj move` will be removed in a future version, and this will be a hard error"
     )?;
     let mut workspace_command = command.workspace_helper(ui)?;
-    let source = workspace_command.resolve_single_rev(args.from.as_deref().unwrap_or("@"))?;
-    let destination = workspace_command.resolve_single_rev(args.to.as_deref().unwrap_or("@"))?;
+    let source =
+        workspace_command.resolve_single_rev(args.from.as_ref().unwrap_or(&RevisionArg::AT))?;
+    let destination =
+        workspace_command.resolve_single_rev(args.to.as_ref().unwrap_or(&RevisionArg::AT))?;
     if source.id() == destination.id() {
         return Err(user_error("Source and destination cannot be the same."));
     }

cli/src/commands/rebase.rs

@@ -197,7 +197,7 @@ Please use `jj rebase -d 'all:x|y'` instead of `jj rebase --allow-large-revsets
         .resolve_some_revsets_default_single(&args.destination)?
         .into_iter()
         .collect_vec();
-    if let Some(rev_str) = &args.revision {
+    if let Some(rev_arg) = &args.revision {
         assert_eq!(
             // In principle, `-r --skip-empty` could mean to abandon the `-r`
             // commit if it becomes empty. This seems internally consistent with
@@ -218,7 +218,7 @@ Please use `jj rebase -d 'all:x|y'` instead of `jj rebase --allow-large-revsets
             command.settings(),
             &mut workspace_command,
             &new_parents,
-            rev_str,
+            rev_arg,
         )?;
     } else if !args.source.is_empty() {
         let source_commits = workspace_command.resolve_some_revsets_default_single(&args.source)?;
@@ -232,7 +232,7 @@ Please use `jj rebase -d 'all:x|y'` instead of `jj rebase --allow-large-revsets
         )?;
     } else {
         let branch_commits = if args.branch.is_empty() {
-            IndexSet::from([workspace_command.resolve_single_rev("@")?])
+            IndexSet::from([workspace_command.resolve_single_rev(&RevisionArg::AT)?])
         } else {
             workspace_command.resolve_some_revsets_default_single(&args.branch)?
         };
@@ -350,9 +350,9 @@ fn rebase_revision(
     settings: &UserSettings,
     workspace_command: &mut WorkspaceCommandHelper,
     new_parents: &[Commit],
-    rev_str: &str,
+    rev_arg: &RevisionArg,
 ) -> Result<(), CommandError> {
-    let old_commit = workspace_command.resolve_single_rev(rev_str)?;
+    let old_commit = workspace_command.resolve_single_rev(rev_arg)?;
     workspace_command.check_rewritable([&old_commit])?;
     if new_parents.contains(&old_commit) {
         return Err(user_error(format!(

cli/src/commands/restore.rs

@@ -86,13 +86,14 @@ pub(crate) fn cmd_restore(
         ));
     }
     if args.from.is_some() || args.to.is_some() {
-        to_commit = workspace_command.resolve_single_rev(args.to.as_deref().unwrap_or("@"))?;
+        to_commit =
+            workspace_command.resolve_single_rev(args.to.as_ref().unwrap_or(&RevisionArg::AT))?;
         from_tree = workspace_command
-            .resolve_single_rev(args.from.as_deref().unwrap_or("@"))?
+            .resolve_single_rev(args.from.as_ref().unwrap_or(&RevisionArg::AT))?
             .tree()?;
     } else {
-        to_commit =
-            workspace_command.resolve_single_rev(args.changes_in.as_deref().unwrap_or("@"))?;
+        to_commit = workspace_command
+            .resolve_single_rev(args.changes_in.as_ref().unwrap_or(&RevisionArg::AT))?;
         from_tree = merge_commit_trees(workspace_command.repo().as_ref(), &to_commit.parents())?;
     }
     workspace_command.check_rewritable([&to_commit])?;

cli/src/commands/squash.rs

@@ -85,10 +85,11 @@ pub(crate) fn cmd_squash(
     let destination;
     if args.from.is_some() || args.into.is_some() {
         sources = workspace_command
-            .parse_revset(args.from.as_deref().unwrap_or("@"))?
+            .parse_revset(args.from.as_ref().unwrap_or(&RevisionArg::AT))?
             .evaluate_to_commits()?
             .try_collect()?;
-        destination = workspace_command.resolve_single_rev(args.into.as_deref().unwrap_or("@"))?;
+        destination =
+            workspace_command.resolve_single_rev(args.into.as_ref().unwrap_or(&RevisionArg::AT))?;
         if sources.iter().any(|source| source.id() == destination.id()) {
             return Err(user_error("Source and destination cannot be the same"));
         }
@@ -97,8 +98,8 @@ pub(crate) fn cmd_squash(
         // a little faster.
         sources.reverse();
     } else {
-        let source =
-            workspace_command.resolve_single_rev(args.revision.as_deref().unwrap_or("@"))?;
+        let source = workspace_command
+            .resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
         let mut parents = source.parents();
         if parents.len() != 1 {
             return Err(user_error("Cannot squash merge commits"));