debug-tree: allow looking up tree by path and id, not just revision

Sometimes only a tree has been created, so we shouldn't require a
commit for `jj debug tree`.

cli/src/commands/debug.rs

@@ -17,9 +17,13 @@ use std::fmt::Debug;
 use std::io::Write as _;
 
 use clap::Subcommand;
+use jj_lib::backend::TreeId;
 use jj_lib::default_index::{AsCompositeIndex as _, DefaultIndexStore, DefaultReadonlyIndex};
 use jj_lib::local_working_copy::LocalWorkingCopy;
+use jj_lib::merged_tree::MergedTree;
 use jj_lib::object_id::ObjectId;
+use jj_lib::repo::Repo;
+use jj_lib::repo_path::RepoPathBuf;
 use jj_lib::working_copy::WorkingCopy;
 use jj_lib::{op_walk, revset};
 
@@ -94,8 +98,12 @@ pub enum DebugOperationDisplay {
 /// List the recursive entries of a tree.
 #[derive(clap::Args, Clone, Debug)]
 pub struct DebugTreeArgs {
-    #[arg(long, short = 'r', default_value = "@")]
-    revision: RevisionArg,
+    #[arg(long, short = 'r')]
+    revision: Option<RevisionArg>,
+    #[arg(long, conflicts_with = "revision")]
+    id: Option<String>,
+    #[arg(long, requires = "id")]
+    dir: Option<String>,
     paths: Vec<String>,
     // TODO: Add an option to include trees that are ancestors of the matched paths
 }
@@ -293,8 +301,22 @@ fn cmd_debug_tree(
     args: &DebugTreeArgs,
 ) -> Result<(), CommandError> {
     let workspace_command = command.workspace_helper(ui)?;
-    let commit = workspace_command.resolve_single_rev(&args.revision)?;
-    let tree = commit.tree()?;
+    let tree = if let Some(tree_id_hex) = &args.id {
+        let tree_id =
+            TreeId::try_from_hex(tree_id_hex).map_err(|_| user_error("Invalid tree id"))?;
+        let dir = if let Some(dir_str) = &args.dir {
+            workspace_command.parse_file_path(dir_str)?
+        } else {
+            RepoPathBuf::root()
+        };
+        let store = workspace_command.repo().store();
+        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("@"))?;
+        commit.tree()?
+    };
     let matcher = workspace_command.matcher_from_values(&args.paths)?;
     for (path, value) in tree.entries_matching(matcher.as_ref()) {
         let ui_path = workspace_command.format_file_path(&path);

cli/tests/test_debug_command.rs

@@ -117,6 +117,87 @@ fn test_debug_reindex() {
     );
 }
 
+#[test]
+fn test_debug_tree() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["init", "repo", "--git"]);
+    let workspace_path = test_env.env_root().join("repo");
+    let subdir = workspace_path.join("dir").join("subdir");
+    std::fs::create_dir_all(&subdir).unwrap();
+    std::fs::write(subdir.join("file1"), "contents 1").unwrap();
+    test_env.jj_cmd_ok(&workspace_path, &["new"]);
+    std::fs::write(subdir.join("file2"), "contents 2").unwrap();
+
+    // Defaults to showing the tree at the current commit
+    let stdout = test_env.jj_cmd_success(&workspace_path, &["debug", "tree"]);
+    assert_snapshot!(stdout.replace('\\',"/"), @r###"
+    dir/subdir/file1: Resolved(Some(File { id: FileId("498e9b01d79cb8d31cdf0df1a663cc1fcefd9de3"), executable: false }))
+    dir/subdir/file2: Resolved(Some(File { id: FileId("b2496eaffe394cd50a9db4de5787f45f09fd9722"), executable: false }))
+    "###
+    );
+
+    // Can show the tree at another commit
+    let stdout = test_env.jj_cmd_success(&workspace_path, &["debug", "tree", "-r@-"]);
+    assert_snapshot!(stdout.replace('\\',"/"), @r###"
+    dir/subdir/file1: Resolved(Some(File { id: FileId("498e9b01d79cb8d31cdf0df1a663cc1fcefd9de3"), executable: false }))
+    "###
+    );
+
+    // Can filter by paths
+    let stdout = test_env.jj_cmd_success(&workspace_path, &["debug", "tree", "dir/subdir/file2"]);
+    assert_snapshot!(stdout.replace('\\',"/"), @r###"
+    dir/subdir/file2: Resolved(Some(File { id: FileId("b2496eaffe394cd50a9db4de5787f45f09fd9722"), executable: false }))
+    "###
+    );
+
+    // Can a show the root tree by id
+    let stdout = test_env.jj_cmd_success(
+        &workspace_path,
+        &[
+            "debug",
+            "tree",
+            "--id=0958358e3f80e794f032b25ed2be96cf5825da6c",
+        ],
+    );
+    assert_snapshot!(stdout.replace('\\',"/"), @r###"
+    dir/subdir/file1: Resolved(Some(File { id: FileId("498e9b01d79cb8d31cdf0df1a663cc1fcefd9de3"), executable: false }))
+    dir/subdir/file2: Resolved(Some(File { id: FileId("b2496eaffe394cd50a9db4de5787f45f09fd9722"), executable: false }))
+    "###
+    );
+
+    // Can a show non-root tree by id
+    let stdout = test_env.jj_cmd_success(
+        &workspace_path,
+        &[
+            "debug",
+            "tree",
+            "--dir=dir",
+            "--id=6ac232efa713535ae518a1a898b77e76c0478184",
+        ],
+    );
+    assert_snapshot!(stdout.replace('\\',"/"), @r###"
+    dir/subdir/file1: Resolved(Some(File { id: FileId("498e9b01d79cb8d31cdf0df1a663cc1fcefd9de3"), executable: false }))
+    dir/subdir/file2: Resolved(Some(File { id: FileId("b2496eaffe394cd50a9db4de5787f45f09fd9722"), executable: false }))
+    "###
+    );
+
+    // Can filter by paths when showing non-root tree (matcher applies from root)
+    let stdout = test_env.jj_cmd_success(
+        &workspace_path,
+        &[
+            "debug",
+            "tree",
+            "--dir=dir",
+            "--id=6ac232efa713535ae518a1a898b77e76c0478184",
+            "dir/subdir/file2",
+        ],
+    );
+    assert_snapshot!(stdout.replace('\\',"/"), @r###"
+    dir/subdir/file2: Resolved(Some(File { id: FileId("b2496eaffe394cd50a9db4de5787f45f09fd9722"), executable: false }))
+    "###
+    );
+}
+
 #[test]
 fn test_debug_operation_id() {
     let test_env = TestEnvironment::default();