git init: add revset alias for trunk() when intializing with existing git repository

CHANGELOG.md

@@ -20,8 +20,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   individually instead of being passed a directory by setting
   `merge-tools.$TOOL.diff-invocation-mode="file-by-file"` in config.toml.
 
-* `jj git clone` adds the default branch of the remote as repository
+* `jj git clone` and `jj git init` with an existing git repository adds the
-  settings for `revset-aliases."trunk()"`.`
+  default branch of the remote as repository settings for
+  `revset-aliases."trunk()"`.`
 
 ### Fixed bugs
 

cli/src/commands/git/init.rs

@@ -16,6 +16,7 @@ use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
+use jj_lib::git::{parse_git_ref, RefName};
 use jj_lib::repo::{ReadonlyRepo, Repo};
 use jj_lib::workspace::Workspace;
 use jj_lib::{file_util, git};
@@ -23,8 +24,9 @@ use jj_lib::{file_util, git};
 use crate::cli_util::{print_trackable_remote_branches, start_repo_transaction, CommandHelper};
 use crate::command_error::{user_error_with_hint, user_error_with_message, CommandError};
 use crate::commands::git::maybe_add_gitignore;
+use crate::config::{write_config_value_to_file, ConfigNamePathBuf};
 use crate::git_util::{
-    is_colocated_git_workspace, print_failed_git_export, print_git_import_stats,
+    get_git_repo, is_colocated_git_workspace, print_failed_git_export, print_git_import_stats,
 };
 use crate::ui::Ui;
 
@@ -152,6 +154,7 @@ pub fn do_init(
             let mut workspace_command = command.for_loaded_repo(ui, workspace, repo)?;
             maybe_add_gitignore(&workspace_command)?;
             workspace_command.maybe_snapshot(ui)?;
+            maybe_set_repository_level_trunk_alias(ui, workspace_command.repo())?;
             if !workspace_command.working_copy_shared_with_git() {
                 let mut tx = workspace_command.start_transaction();
                 jj_lib::git::import_head(tx.mut_repo())?;
@@ -210,3 +213,33 @@ fn init_git_refs(
     )?;
     Ok(repo)
 }
+
+// Set repository level `trunk()` alias to the default branch for "origin".
+pub fn maybe_set_repository_level_trunk_alias(
+    ui: &Ui,
+    repo: &Arc<ReadonlyRepo>,
+) -> Result<(), CommandError> {
+    let git_repo = get_git_repo(repo.store())?;
+    if let Ok(reference) = git_repo.find_reference("refs/remotes/origin/HEAD") {
+        if let Some(reference_name) = reference.symbolic_target() {
+            if let Some(RefName::RemoteBranch {
+                branch: default_branch,
+                ..
+            }) = parse_git_ref(reference_name)
+            {
+                let config_path = repo.repo_path().join("config.toml");
+                write_config_value_to_file(
+                    &ConfigNamePathBuf::from_iter(["revset-aliases", "trunk()"]),
+                    &format!("{default_branch}@origin"),
+                    &config_path,
+                )?;
+                writeln!(
+                    ui.status(),
+                    "Setting the revset alias \"trunk()\" to \"{default_branch}@origin\"",
+                )?;
+            }
+        };
+    };
+
+    Ok(())
+}

cli/tests/test_git_init.rs

@@ -148,6 +148,65 @@ fn test_git_init_external(bare: bool) {
     }
 }
 
+#[test_case(false; "full")]
+#[test_case(true; "bare")]
+fn test_git_init_external_import_trunk(bare: bool) {
+    let test_env = TestEnvironment::default();
+    let git_repo_path = test_env.env_root().join("git-repo");
+    let git_repo = init_git_repo(&git_repo_path, bare);
+
+    // Add remote branch "trunk" for remote "origin", and set it as "origin/HEAD"
+    let oid = git_repo
+        .find_reference("refs/heads/my-branch")
+        .unwrap()
+        .target()
+        .unwrap();
+    git_repo
+        .reference("refs/remotes/origin/trunk", oid, false, "")
+        .unwrap();
+    git_repo
+        .reference_symbolic(
+            "refs/remotes/origin/HEAD",
+            "refs/remotes/origin/trunk",
+            false,
+            "",
+        )
+        .unwrap();
+
+    let (stdout, stderr) = test_env.jj_cmd_ok(
+        test_env.env_root(),
+        &[
+            "git",
+            "init",
+            "repo",
+            "--git-repo",
+            git_repo_path.to_str().unwrap(),
+        ],
+    );
+    insta::allow_duplicates! {
+        insta::assert_snapshot!(stdout, @"");
+        insta::assert_snapshot!(stderr, @r###"
+        Done importing changes from the underlying Git repo.
+        Setting the revset alias "trunk()" to "trunk@origin"
+        Working copy now at: sqpuoqvx f6950fc1 (empty) (no description set)
+        Parent commit      : mwrttmos 8d698d4a my-branch trunk@origin | My commit message
+        Added 1 files, modified 0 files, removed 0 files
+        Initialized repo in "repo"
+        "###);
+    }
+
+    // "trunk()" alias should be set to remote "origin"'s default branch "trunk"
+    let stdout = test_env.jj_cmd_success(
+        &test_env.env_root().join("repo"),
+        &["config", "list", "--repo", "revset-aliases.\"trunk()\""],
+    );
+    insta::allow_duplicates! {
+    insta::assert_snapshot!(stdout, @r###"
+    revset-aliases."trunk()" = "trunk@origin"
+    "###);
+    }
+}
+
 #[test]
 fn test_git_init_external_non_existent_directory() {
     let test_env = TestEnvironment::default();

docs/revsets.md

@@ -362,9 +362,9 @@ for a comprehensive list.
   tried. If more than one potential trunk commit exists, the newest one is
   chosen. If none of the branches exist, the revset evaluates to `root()`.
 
-  When working with an existing Git repository (via `jj git clone`),
+  When working with an existing Git repository (via `jj git clone` or
-  `trunk()` will be overridden at the repository level to the default branch of
+  `jj git init`), `trunk()` will be overridden at the repository level
-  the remote.
+  to the default branch of the remote `origin`.
 
   You can [override](./config.md) this as appropriate. If you do, make sure it
   always resolves to exactly one commit. For example:

lib/src/git.rs

@@ -62,7 +62,7 @@ impl fmt::Display for RefName {
     }
 }
 
-fn parse_git_ref(ref_name: &str) -> Option<RefName> {
+pub fn parse_git_ref(ref_name: &str) -> Option<RefName> {
     if let Some(branch_name) = ref_name.strip_prefix("refs/heads/") {
         // Git CLI says 'HEAD' is not a valid branch name
         (branch_name != "HEAD").then(|| RefName::LocalBranch(branch_name.to_string()))