cli: add builder type that handles CLI initialization and teardown

parse_args() will probably become more involved to deal with --config-toml,
-R, and repository configs. This builder will hopefully allow us to move
things around without changing the high-level interface.

examples/custom-backend/main.rs

@@ -17,7 +17,7 @@ use std::path::Path;
 
 use clap::{FromArgMatches, Subcommand};
 use git2::Repository;
-use jujutsu::cli_util::{handle_command_result, parse_args, CommandError, TracingSubscription};
+use jujutsu::cli_util::{parse_args, CliRunner, CommandError, TracingSubscription};
 use jujutsu::commands::{default_app, run_command};
 use jujutsu::config::read_config;
 use jujutsu::ui::Ui;
@@ -64,13 +64,7 @@ fn run(ui: &mut Ui, tracing_subscription: &TracingSubscription) -> Result<(), Co
 }
 
 fn main() {
-    let tracing_subscription = TracingSubscription::init();
+    CliRunner::init().set_dispatch_fn(run).run_and_exit();
-    jujutsu::cleanup_guard::init();
-    let mut ui = Ui::new();
-    let result = run(&mut ui, &tracing_subscription);
-    let exit_code = handle_command_result(&mut ui, result);
-    ui.finalize_writes();
-    std::process::exit(exit_code);
 }
 
 /// A commit backend that's extremely similar to the Git backend

examples/custom-command/main.rs

@@ -14,7 +14,7 @@
 
 use clap::{FromArgMatches, Subcommand};
 use jujutsu::cli_util::{
-    handle_command_result, parse_args, short_commit_description, CommandError, TracingSubscription,
+    parse_args, short_commit_description, CliRunner, CommandError, TracingSubscription,
 };
 use jujutsu::commands::{default_app, run_command};
 use jujutsu::config::read_config;
@@ -62,11 +62,5 @@ fn run(ui: &mut Ui, tracing_subscription: &TracingSubscription) -> Result<(), Co
 }
 
 fn main() {
-    let tracing_subscription = TracingSubscription::init();
+    CliRunner::init().set_dispatch_fn(run).run_and_exit();
-    jujutsu::cleanup_guard::init();
-    let mut ui = Ui::new();
-    let result = run(&mut ui, &tracing_subscription);
-    let exit_code = handle_command_result(&mut ui, result);
-    ui.finalize_writes();
-    std::process::exit(exit_code);
 }

src/cli_util.rs

@@ -1682,3 +1682,51 @@ pub fn handle_command_result(ui: &mut Ui, result: Result<(), CommandError>) -> i
         }
     }
 }
+
+/// CLI command builder and runner.
+#[must_use]
+pub struct CliRunner<F> {
+    tracing_subscription: TracingSubscription,
+    dispatch_fn: F,
+}
+
+impl CliRunner<()> {
+    /// Initializes CLI environment and returns a builder. This should be called
+    /// as early as possible.
+    pub fn init() -> Self {
+        let tracing_subscription = TracingSubscription::init();
+        crate::cleanup_guard::init();
+        CliRunner {
+            tracing_subscription,
+            dispatch_fn: (),
+        }
+    }
+
+    // TODO: use crate::commands::run_command() by default
+    pub fn set_dispatch_fn<F>(self, dispatch_fn: F) -> CliRunner<F>
+    where
+        F: FnOnce(&mut Ui, &TracingSubscription) -> Result<(), CommandError>,
+    {
+        CliRunner {
+            tracing_subscription: self.tracing_subscription,
+            dispatch_fn,
+        }
+    }
+}
+
+impl<F> CliRunner<F>
+where
+    F: FnOnce(&mut Ui, &TracingSubscription) -> Result<(), CommandError>,
+{
+    pub fn run(self, ui: &mut Ui) -> Result<(), CommandError> {
+        (self.dispatch_fn)(ui, &self.tracing_subscription)
+    }
+
+    pub fn run_and_exit(self) -> ! {
+        let mut ui = Ui::new();
+        let result = self.run(&mut ui);
+        let exit_code = handle_command_result(&mut ui, result);
+        ui.finalize_writes();
+        std::process::exit(exit_code);
+    }
+}

src/main.rs

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use jujutsu::cli_util::{handle_command_result, parse_args, CommandError, TracingSubscription};
+use jujutsu::cli_util::{parse_args, CliRunner, CommandError, TracingSubscription};
 use jujutsu::commands::{default_app, run_command};
 use jujutsu::config::read_config;
 use jujutsu::ui::Ui;
@@ -25,11 +25,5 @@ fn run(ui: &mut Ui, tracing_subscription: &TracingSubscription) -> Result<(), Co
 }
 
 fn main() {
-    let tracing_subscription = TracingSubscription::init();
+    CliRunner::init().set_dispatch_fn(run).run_and_exit();
-    jujutsu::cleanup_guard::init();
-    let mut ui = Ui::new();
-    let result = run(&mut ui, &tracing_subscription);
-    let exit_code = handle_command_result(&mut ui, result);
-    ui.finalize_writes();
-    std::process::exit(exit_code);
 }