completion: teach jj about aliases

cli/src/cli_util.rs

@@ -3079,8 +3079,12 @@ fn handle_shell_completion(
         let resolved_aliases = expand_args(ui, app, env::args_os().skip(2), config)?;
         args.extend(resolved_aliases.into_iter().map(OsString::from));
     }
-    let ran_completion = clap_complete::CompleteEnv::with_factory(|| app.clone())
-        .try_complete(args.iter(), Some(cwd))?;
+    let ran_completion = clap_complete::CompleteEnv::with_factory(|| {
+        app.clone()
+            // for completing aliases
+            .allow_external_subcommands(true)
+    })
+    .try_complete(args.iter(), Some(cwd))?;
     assert!(
         ran_completion,
         "This function should not be called without the COMPLETE variable set."

cli/src/commands/mod.rs

@@ -63,17 +63,20 @@ use std::fmt::Debug;
 use clap::CommandFactory;
 use clap::FromArgMatches;
 use clap::Subcommand;
+use clap_complete::engine::SubcommandCandidates;
 use tracing::instrument;
 
 use crate::cli_util::Args;
 use crate::cli_util::CommandHelper;
 use crate::command_error::user_error_with_hint;
 use crate::command_error::CommandError;
+use crate::complete;
 use crate::ui::Ui;
 
 #[derive(clap::Parser, Clone, Debug)]
 #[command(disable_help_subcommand = true)]
 #[command(after_long_help = help::show_keyword_hint_after_help())]
+#[command(add = SubcommandCandidates::new(complete::aliases))]
 enum Command {
     Abandon(abandon::AbandonArgs),
     Backout(backout::BackoutArgs),

cli/src/complete.rs

@@ -44,6 +44,21 @@ pub fn local_bookmarks() -> Vec<CompletionCandidate> {
     })
 }
 
+pub fn aliases() -> Vec<CompletionCandidate> {
+    with_jj(|_, config| {
+        Ok(config
+            .get_table("aliases")?
+            .into_keys()
+            // This is opinionated, but many people probably have several
+            // single- or two-letter aliases they use all the time. These
+            // aliases don't need to be completed and they would only clutter
+            // the output of `jj <TAB>`.
+            .filter(|alias| alias.len() > 2)
+            .map(CompletionCandidate::new)
+            .collect())
+    })
+}
+
 /// Shell out to jj during dynamic completion generation
 ///
 /// In case of errors, print them and early return an empty vector.
@@ -107,6 +122,14 @@ fn get_jj_command() -> Result<(std::process::Command, Config), CommandError> {
         .disable_version_flag(true)
         .disable_help_flag(true)
         .ignore_errors(true)
+        // Here, allow_external_subcommands fixes a weird issue. Without it,
+        // parsing GlobalArgs will fail with the message that a required arg
+        // is missing, where the required arg is a boolean flag. This seems
+        // unexpected, because missing boolean flags are usually treated as
+        // false. It is also not clear to me why allow_external_subcommands
+        // changes this behavior. See the discussion in the clap repo:
+        // https://github.com/clap-rs/clap/discussions/5812
+        .allow_external_subcommands(true)
         .try_get_matches_from(args)?;
     let args: GlobalArgs = GlobalArgs::from_arg_matches(&args)?;
 

cli/tests/test_completion.rs

@@ -115,3 +115,47 @@ fn test_completions_are_generated() {
     let stdout = test_env.jj_cmd_success(test_env.env_root(), &["--"]);
     assert!(stdout.starts_with("complete --keep-order --exclusive --command jj --arguments"));
 }
+
+#[test]
+fn test_aliases_are_completed() {
+    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");
+
+    // user config alias
+    test_env.add_config(r#"aliases.user-alias = ["bookmark"]"#);
+    // repo config alias
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &[
+            "config",
+            "set",
+            "--repo",
+            "aliases.repo-alias",
+            "['bookmark']",
+        ],
+    );
+
+    let mut test_env = test_env;
+    test_env.add_env_var("COMPLETE", "fish");
+    let test_env = test_env;
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["--", "jj", "user-al"]);
+    insta::assert_snapshot!(stdout, @"user-alias");
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["--", "jj", "repo-al"]);
+    insta::assert_snapshot!(stdout, @"repo-alias");
+
+    // make sure --repository flag is respected
+    let stdout = test_env.jj_cmd_success(
+        test_env.env_root(),
+        &[
+            "--",
+            "jj",
+            "--repository",
+            repo_path.to_str().unwrap(),
+            "repo-al",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @"repo-alias");
+}