GitFetch API: Refactor jj git clone to use new GitFetch api directly.

* Make the new `GitFetch` api public.
* Rewrite all tests that used `git::fetch*` to use the new API.
  One interesting artifact of the new API is that it holds onto a reference
  of the `tx.repo_mut()`, so the GitFetch object needs to fall go of scope
  completely before we can make any other mutable calls to `tx`.
* Delete the `git::fetch_and_get_default_branch`

cli/src/commands/git/clone.rs

@@ -20,6 +20,7 @@ use std::path::PathBuf;
 
 use jj_lib::config::ConfigNamePathBuf;
 use jj_lib::git;
+use jj_lib::git::GitFetch;
 use jj_lib::git::GitFetchError;
 use jj_lib::git::GitFetchStats;
 use jj_lib::repo::Repo;
@@ -220,27 +221,34 @@ fn do_git_clone(
     git_repo.remote(remote_name, source).unwrap();
     let mut fetch_tx = workspace_command.start_transaction();
 
-    let stats = with_remote_git_callbacks(ui, None, |cb| {
-        git::fetch_and_get_default_branch(
+    let stats = with_remote_git_callbacks(ui, None, |cb| -> Result<GitFetchStats, CommandError> {
+        let git_settings = command.settings().git_settings();
+        let mut git_fetch = GitFetch::new(
             fetch_tx.repo_mut(),
             &git_repo,
-            remote_name,
-            &[StringPattern::everything()],
-            cb,
-            &command.settings().git_settings(),
-            depth,
-        )
-    })
-    .map_err(|err| match err {
-        GitFetchError::NoSuchRemote(_) => {
-            panic!("shouldn't happen as we just created the git remote")
-        }
-        GitFetchError::GitImportError(err) => CommandError::from(err),
-        GitFetchError::InternalGitError(err) => map_git_error(err),
-        GitFetchError::InvalidBranchPattern => {
-            unreachable!("we didn't provide any globs")
-        }
+            &git_settings,
+            git::fetch_options(cb, depth),
+        );
+
+        let default_branch = git_fetch
+            .fetch(&[StringPattern::everything()], remote_name)
+            .map_err(|err| match err {
+                GitFetchError::NoSuchRemote(_) => {
+                    panic!("shouldn't happen as we just created the git remote")
+                }
+                GitFetchError::GitImportError(err) => CommandError::from(err),
+                GitFetchError::InternalGitError(err) => map_git_error(err),
+                GitFetchError::InvalidBranchPattern => {
+                    unreachable!("we didn't provide any globs")
+                }
+            })?;
+        let import_stats = git_fetch.import_refs()?;
+        Ok(GitFetchStats {
+            default_branch,
+            import_stats,
+        })
     })?;
+
     print_git_import_stats(ui, fetch_tx.repo(), &stats.import_stats, true)?;
     fetch_tx.finish(ui, "fetch from git remote into empty repo")?;
     Ok((workspace_command, stats))

lib/src/git.rs

@@ -1229,7 +1229,7 @@ pub enum GitFetchError {
     InternalGitError(#[from] git2::Error),
 }
 
-fn fetch_options(
+pub fn fetch_options(
     callbacks: RemoteCallbacks<'_>,
     depth: Option<NonZeroU32>,
 ) -> git2::FetchOptions<'_> {
@@ -1251,7 +1251,7 @@ struct FetchedBranches {
     remote: String,
 }
 
-struct GitFetch<'a> {
+pub struct GitFetch<'a> {
     mut_repo: &'a mut MutableRepo,
     git_repo: &'a git2::Repository,
     git_settings: &'a GitSettings,
@@ -1260,7 +1260,7 @@ struct GitFetch<'a> {
 }
 
 impl<'a> GitFetch<'a> {
-    fn new(
+    pub fn new(
         mut_repo: &'a mut MutableRepo,
         git_repo: &'a git2::Repository,
         git_settings: &'a GitSettings,
@@ -1275,7 +1275,7 @@ impl<'a> GitFetch<'a> {
         }
     }
 
-    fn fetch(
+    pub fn fetch(
         &mut self,
         branch_names: &[StringPattern],
         remote_name: &str,
@@ -1378,55 +1378,6 @@ pub struct GitFetchStats {
     pub import_stats: GitImportStats,
 }
 
-#[tracing::instrument(skip(mut_repo, git_repo, callbacks))]
-pub fn fetch_and_get_default_branch(
-    mut_repo: &mut MutableRepo,
-    git_repo: &git2::Repository,
-    remote_name: &str,
-    branch_names: &[StringPattern],
-    callbacks: RemoteCallbacks<'_>,
-    git_settings: &GitSettings,
-    depth: Option<NonZeroU32>,
-) -> Result<GitFetchStats, GitFetchError> {
-    let mut git_fetch = GitFetch::new(
-        mut_repo,
-        git_repo,
-        git_settings,
-        fetch_options(callbacks, depth),
-    );
-    let default_branch = git_fetch.fetch(branch_names, remote_name)?;
-    let import_stats = git_fetch.import_refs()?;
-    let stats = GitFetchStats {
-        default_branch,
-        import_stats,
-    };
-    Ok(stats)
-}
-
-pub fn fetch(
-    mut_repo: &mut MutableRepo,
-    git_repo: &git2::Repository,
-    remote_name: &str,
-    branch_names: &[StringPattern],
-    callbacks: RemoteCallbacks<'_>,
-    git_settings: &GitSettings,
-    depth: Option<NonZeroU32>,
-) -> Result<GitFetchStats, GitFetchError> {
-    let mut git_fetch = GitFetch::new(
-        mut_repo,
-        git_repo,
-        git_settings,
-        fetch_options(callbacks, depth),
-    );
-    git_fetch.fetch(branch_names, remote_name)?;
-    let import_stats = git_fetch.import_refs()?;
-    let stats = GitFetchStats {
-        default_branch: None,
-        import_stats,
-    };
-    Ok(stats)
-}
-
 #[derive(Error, Debug, PartialEq)]
 pub enum GitPushError {
     #[error("No git remote named '{0}'")]