Add jj debug snapshot command and use it in trigger

The command only takes a snapshot and avoids other overhead, so it can
be used as a target for the watchman trigger that gets installed.

cli/src/commands/debug/mod.rs

@@ -17,6 +17,7 @@ pub mod index;
 pub mod operation;
 pub mod reindex;
 pub mod revset;
+pub mod snapshot;
 pub mod template;
 pub mod tree;
 pub mod watchman;
@@ -33,6 +34,7 @@ use self::index::{cmd_debug_index, IndexArgs};
 use self::operation::{cmd_debug_operation, OperationArgs};
 use self::reindex::{cmd_debug_reindex, ReindexArgs};
 use self::revset::{cmd_debug_revset, RevsetArgs};
+use self::snapshot::{cmd_debug_snapshot, SnapshotArgs};
 use self::template::{cmd_debug_template, TemplateArgs};
 use self::tree::{cmd_debug_tree, TreeArgs};
 use self::watchman::{cmd_debug_watchman, WatchmanCommand};
@@ -57,6 +59,7 @@ pub enum DebugCommand {
     Tree(TreeArgs),
     #[command(subcommand)]
     Watchman(WatchmanCommand),
+    Snapshot(SnapshotArgs),
 }
 
 pub fn cmd_debug(
@@ -74,6 +77,7 @@ pub fn cmd_debug(
         DebugCommand::Operation(args) => cmd_debug_operation(ui, command, args),
         DebugCommand::Tree(args) => cmd_debug_tree(ui, command, args),
         DebugCommand::Watchman(args) => cmd_debug_watchman(ui, command, args),
+        DebugCommand::Snapshot(args) => cmd_debug_snapshot(ui, command, args),
     }
 }
 

cli/src/commands/debug/snapshot.rs

@@ -0,0 +1,33 @@
+// Copyright 2024 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::fmt::Debug;
+
+use crate::cli_util::CommandHelper;
+use crate::command_error::CommandError;
+use crate::ui::Ui;
+
+/// Trigger a snapshot in the op log
+#[derive(clap::Args, Clone, Debug)]
+pub struct SnapshotArgs {}
+
+pub fn cmd_debug_snapshot(
+    ui: &mut Ui,
+    command: &CommandHelper,
+    _args: &SnapshotArgs,
+) -> Result<(), CommandError> {
+    // workspace helper will snapshot as needed
+    command.workspace_helper(ui)?;
+    Ok(())
+}

cli/tests/test_workspaces.rs

@@ -782,6 +782,42 @@ fn test_workspaces_root() {
     "###);
 }
 
+#[test]
+fn test_debug_snapshot() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    std::fs::write(repo_path.join("file"), "contents").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["debug", "snapshot"]);
+    let stdout = test_env.jj_cmd_success(&repo_path, &["op", "log"]);
+    insta::assert_snapshot!(stdout, @r###"
+    @  2d01fc903f0f test-username@host.example.com 2001-02-03 04:05:08.000 +07:00 - 2001-02-03 04:05:08.000 +07:00
+    │  snapshot working copy
+    │  args: jj debug snapshot
+    ◉  b51416386f26 test-username@host.example.com 2001-02-03 04:05:07.000 +07:00 - 2001-02-03 04:05:07.000 +07:00
+    │  add workspace 'default'
+    ◉  9a7d829846af test-username@host.example.com 2001-02-03 04:05:07.000 +07:00 - 2001-02-03 04:05:07.000 +07:00
+    │  initialize repo
+    ◉  000000000000 root()
+    "###);
+    test_env.jj_cmd_ok(&repo_path, &["describe", "-m", "initial"]);
+    let stdout = test_env.jj_cmd_success(&repo_path, &["op", "log"]);
+    insta::assert_snapshot!(stdout, @r###"
+    @  53a64275e379 test-username@host.example.com 2001-02-03 04:05:10.000 +07:00 - 2001-02-03 04:05:10.000 +07:00
+    │  describe commit 123ed18e4c4c0d77428df41112bc02ffc83fb935
+    │  args: jj describe -m initial
+    ◉  2d01fc903f0f test-username@host.example.com 2001-02-03 04:05:08.000 +07:00 - 2001-02-03 04:05:08.000 +07:00
+    │  snapshot working copy
+    │  args: jj debug snapshot
+    ◉  b51416386f26 test-username@host.example.com 2001-02-03 04:05:07.000 +07:00 - 2001-02-03 04:05:07.000 +07:00
+    │  add workspace 'default'
+    ◉  9a7d829846af test-username@host.example.com 2001-02-03 04:05:07.000 +07:00 - 2001-02-03 04:05:07.000 +07:00
+    │  initialize repo
+    ◉  000000000000 root()
+    "###);
+}
+
 fn get_log_output(test_env: &TestEnvironment, cwd: &Path) -> String {
     let template = r#"
     separate(" ",

lib/src/fsmonitor.rs

@@ -283,9 +283,8 @@ pub mod watchman {
                         name: "jj-background-monitor".to_string(),
                         command: vec![
                             "jj".to_string(),
-                            "files".to_string(),
-                            "-r".to_string(),
-                            "root()".to_string(),
+                            "debug".to_string(),
+                            "snapshot".to_string(),
                         ],
                         expression: Some(self.build_exclude_expr()),
                         ..Default::default()