git sync: Setup scaffolding

* First commit that just sets up scaffolding.
* `jj git sync` is hidden as it's not yet ready.


Issue: #1039

cli/src/commands/git/mod.rs

@@ -20,6 +20,7 @@ pub mod init;
 pub mod push;
 pub mod remote;
 pub mod submodule;
+pub mod sync;
 
 use clap::Subcommand;
 
@@ -39,6 +40,8 @@ use self::remote::cmd_git_remote;
 use self::remote::RemoteCommand;
 use self::submodule::cmd_git_submodule;
 use self::submodule::GitSubmoduleCommand;
+use self::sync::cmd_git_sync;
+use self::sync::GitSyncArgs;
 use crate::cli_util::CommandHelper;
 use crate::cli_util::WorkspaceCommandHelper;
 use crate::command_error::user_error_with_message;
@@ -61,6 +64,8 @@ pub enum GitCommand {
     Remote(RemoteCommand),
     #[command(subcommand, hide = true)]
     Submodule(GitSubmoduleCommand),
+    #[command(hide = true)]
+    Sync(GitSyncArgs),
 }
 
 pub fn cmd_git(
@@ -77,6 +82,7 @@ pub fn cmd_git(
         GitCommand::Push(args) => cmd_git_push(ui, command, args),
         GitCommand::Remote(args) => cmd_git_remote(ui, command, args),
         GitCommand::Submodule(args) => cmd_git_submodule(ui, command, args),
+        GitCommand::Sync(args) => cmd_git_sync(ui, command, args),
     }
 }
 

cli/src/commands/git/sync.rs

@@ -0,0 +1,48 @@
+use crate::cli_util::CommandHelper;
+use crate::ui::Ui;
+/// Sync the local JJ repo to specified Git remote branch(es).
+///
+/// The sync command will first fetch from the Git remote, then
+/// rebase all local changes onto the appropriate updated
+/// heads that were fetched.
+///
+/// Changes that are made empty by the rebase are dropped.
+#[derive(clap::Args, Clone, Debug)]
+pub struct GitSyncArgs {
+    /// Rebase only the specified branches.
+    ///
+    /// Note that this value affects only the rebase behaviour, as
+    /// the fetch behaviour always fetches all branches.
+    ///
+    /// By default, the specified name matches exactly. Use `glob:` prefix to
+    /// expand `*` as a glob. The other wildcard characters aren't supported.
+    #[arg(long, short, alias="bookmark", default_value = "glob:*", value_parser = StringPattern::parse)]
+    pub branch: Vec<StringPattern>,
+    /// Fetch from all remotes
+    ///
+    /// By default, the fetch will only use remotes configured in the `git.fetch`
+    /// section of the config.
+    ///
+    /// When specified, --all-remotes causes the fetch to use all remotes known
+    /// to the underlying git repo.
+    #[arg(long, default_value = "false")]
+    pub all_remotes: bool,
+}
+
+pub fn cmd_git_sync(
+    ui: &mut Ui,
+    command: &CommandHelper,
+    args: &GitSyncArgs,
+) -> Result<(), CommandError> {
+    let mut workspace_command = command.workspace_helper(ui)?;
+    let guard = tracing::debug_span!("git.sync.pre-fetch").entered();
+    drop(guard);
+    let guard = tracing::debug_span!("git.sync.fetch").entered();
+    drop(guard);
+    let guard = tracing::debug_span!("git.sync.post-fetch").entered();
+    drop(guard);
+    let guard = tracing::debug_span!("git.sync.rebase").entered();
+    drop(guard);
+
+    Ok(())
+}