lib: make git support optional via crate feature

I've wanted to make the Git support optional for a long time. However,
since everyone uses the Git backend (and we want to support it even in
the custom binary at Google), there hasn't been much practical reason
to make Git support optional.

Since we now use jj-lib on the server at Google, it does make sense to
have the server not include Git support. In addition to making the
server binary smaller, it would make it easier for us (jj team at
Googlle) to prove that our server is not affected by some libgit2 or
Gitoxide vulnerability. But to be honest, neither of those problems
have come up, so it's more of an excuse to make the Git support
optional at this point.

It turned out to be much simpler than I expected to make Git support
in the lib crate optional. We have done a pretty good job of keeping
Git-related logic separated there.

If we make Git support optional in the lib crate, it's going to make
it a bit harder to move logic from the CLI crate into the lib crate
(as we have planned to do). Maybe that's good, though, since it helps
remind us to keep Git-related logic separated.

.github/workflows/build.yml

@@ -76,6 +76,20 @@ jobs:
       env:
         RUST_BACKTRACE: 1
 
+  build-no-git:
+    name: Build jj-lib without Git support
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29
+
+    - name: Install Rust
+      uses: dtolnay/rust-toolchain@1482605bfc5719782e1267fd0c0cc350fe7646b8
+      with:
+        toolchain:  1.76
+    - name: Build
+      run: cargo build -p jj-lib --no-default-features --verbose
+
   check-protos:
     name: Check protos
     runs-on: ubuntu-latest

lib/Cargo.toml

@@ -42,8 +42,8 @@ config = { workspace = true }
 digest = { workspace = true }
 either = { workspace = true }
 futures = { workspace = true }
-git2 = { workspace = true }
-gix = { workspace = true }
+git2 = { workspace = true, optional = true }
+gix = { workspace = true, optional = true }
 glob = { workspace = true }
 hex = { workspace = true }
 ignore = { workspace = true }
@@ -91,7 +91,8 @@ testutils = { workspace = true }
 tokio = { workspace = true, features = ["full"] }
 
 [features]
-default = []
+default = ["git"]
+git = ["dep:git2", "dep:gix"]
 vendored-openssl = ["git2/vendored-openssl"]
 watchman = ["dep:tokio", "dep:watchman_client"]
 testing = []

lib/src/lib.rs

@@ -44,7 +44,9 @@ pub mod fileset;
 mod fileset_parser;
 pub mod fmt_util;
 pub mod fsmonitor;
+#[cfg(feature = "git")]
 pub mod git;
+#[cfg(feature = "git")]
 pub mod git_backend;
 pub mod gitignore;
 pub mod gpg_signing;

lib/src/repo.rs

@@ -37,7 +37,6 @@ use crate::commit_builder::CommitBuilder;
 use crate::default_index::{DefaultIndexStore, DefaultMutableIndex};
 use crate::default_submodule_store::DefaultSubmoduleStore;
 use crate::file_util::{IoResultExt as _, PathError};
-use crate::git_backend::GitBackend;
 use crate::index::{ChangeIdIndex, Index, IndexStore, MutableIndex, ReadonlyIndex};
 use crate::local_backend::LocalBackend;
 use crate::object_id::{HexPrefix, ObjectId, PrefixResolution};
@@ -378,9 +377,14 @@ impl Default for StoreFactories {
             LocalBackend::name(),
             Box::new(|_settings, store_path| Ok(Box::new(LocalBackend::load(store_path)))),
         );
+        #[cfg(feature = "git")]
         factories.add_backend(
-            GitBackend::name(),
-            Box::new(|settings, store_path| Ok(Box::new(GitBackend::load(settings, store_path)?))),
+            crate::git_backend::GitBackend::name(),
+            Box::new(|settings, store_path| {
+                Ok(Box::new(crate::git_backend::GitBackend::load(
+                    settings, store_path,
+                )?))
+            }),
         );
         #[cfg(feature = "testing")]
         factories.add_backend(

lib/src/revset.rs

@@ -43,7 +43,7 @@ pub use crate::revset_parser::{
 };
 use crate::store::Store;
 use crate::str_util::StringPattern;
-use crate::{dsl_util, git, revset_parser};
+use crate::{dsl_util, revset_parser};
 
 /// Error occurred during symbol resolution.
 #[derive(Debug, Error)]
@@ -1313,7 +1313,8 @@ pub fn walk_revs<'index>(
 fn resolve_remote_branch(repo: &dyn Repo, name: &str, remote: &str) -> Option<Vec<CommitId>> {
     let view = repo.view();
     let target = match (name, remote) {
-        ("HEAD", git::REMOTE_NAME_FOR_LOCAL_GIT_REPO) => view.git_head(),
+        #[cfg(feature = "git")]
+        ("HEAD", crate::git::REMOTE_NAME_FOR_LOCAL_GIT_REPO) => view.git_head(),
         (name, remote) => &view.get_remote_branch(name, remote).target,
     };
     target
@@ -1605,7 +1606,17 @@ fn resolve_commit_ref(
             let commit_ids = repo
                 .view()
                 .remote_branches_matching(branch_pattern, remote_pattern)
-                .filter(|&((_, remote_name), _)| remote_name != git::REMOTE_NAME_FOR_LOCAL_GIT_REPO)
+                .filter(|&((_, remote_name), _)| {
+                    #[cfg(feature = "git")]
+                    {
+                        remote_name != crate::git::REMOTE_NAME_FOR_LOCAL_GIT_REPO
+                    }
+                    #[cfg(not(feature = "git"))]
+                    {
+                        let _ = remote_name;
+                        true
+                    }
+                })
                 .flat_map(|(_, remote_ref)| remote_ref.target.added_ids())
                 .cloned()
                 .collect();

lib/src/simple_op_store.rs

@@ -36,7 +36,7 @@ use crate::op_store::{
     OpStore, OpStoreError, OpStoreResult, Operation, OperationId, OperationMetadata, RefTarget,
     RemoteRef, RemoteRefState, RemoteView, View, ViewId, WorkspaceId,
 };
-use crate::{dag_walk, git, op_store};
+use crate::{dag_walk, op_store};
 
 // BLAKE2b-512 hash length in bytes
 const OPERATION_ID_LENGTH: usize = 64;
@@ -528,8 +528,11 @@ fn branch_views_from_proto_legacy(
                 // than deleted but yet-to-be-pushed local branch. Alternatively, we could read
                 // git.auto-local-branch setting here, but that wouldn't always work since the
                 // setting could be toggled after the branch got merged.
+                #[cfg(feature = "git")]
                 let is_git_tracking =
-                    remote_branch.remote_name == git::REMOTE_NAME_FOR_LOCAL_GIT_REPO;
+                    remote_branch.remote_name == crate::git::REMOTE_NAME_FOR_LOCAL_GIT_REPO;
+                #[cfg(not(feature = "git"))]
+                let is_git_tracking = false;
                 let default_state = if is_git_tracking || local_target.is_present() {
                     RemoteRefState::Tracking
                 } else {
@@ -578,13 +581,21 @@ fn migrate_git_refs_to_remote(view: &mut View) {
             git_view.branches.insert(name.to_owned(), remote_ref);
         }
     }
-    view.remote_views
-        .insert(git::REMOTE_NAME_FOR_LOCAL_GIT_REPO.to_owned(), git_view);
+    #[cfg(feature = "git")]
+    {
+        view.remote_views.insert(
+            crate::git::REMOTE_NAME_FOR_LOCAL_GIT_REPO.to_owned(),
+            git_view,
+        );
 
-    // jj < 0.9 might have imported refs from remote named "git"
-    let reserved_git_ref_prefix = format!("refs/remotes/{}/", git::REMOTE_NAME_FOR_LOCAL_GIT_REPO);
-    view.git_refs
-        .retain(|name, _| !name.starts_with(&reserved_git_ref_prefix));
+        // jj < 0.9 might have imported refs from remote named "git"
+        let reserved_git_ref_prefix = format!(
+            "refs/remotes/{}/",
+            crate::git::REMOTE_NAME_FOR_LOCAL_GIT_REPO
+        );
+        view.git_refs
+            .retain(|name, _| !name.starts_with(&reserved_git_ref_prefix));
+    }
 }
 
 fn ref_target_to_proto(value: &RefTarget) -> Option<crate::protos::op_store::RefTarget> {

lib/src/workspace.rs

@@ -23,10 +23,9 @@ use std::sync::Arc;
 
 use thiserror::Error;
 
-use crate::backend::{Backend, BackendInitError, MergedTreeId};
+use crate::backend::{BackendInitError, MergedTreeId};
 use crate::commit::Commit;
-use crate::file_util::{self, IoResultExt as _, PathError};
-use crate::git_backend::{canonicalize_git_repo_path, GitBackend};
+use crate::file_util::{IoResultExt as _, PathError};
 use crate::local_backend::LocalBackend;
 use crate::local_working_copy::{LocalWorkingCopy, LocalWorkingCopyFactory};
 use crate::op_store::{OperationId, WorkspaceId};
@@ -157,36 +156,44 @@ impl Workspace {
 
     /// Initializes a workspace with a new Git backend and bare Git repo in
     /// `.jj/repo/store/git`.
+    #[cfg(feature = "git")]
     pub fn init_internal_git(
         user_settings: &UserSettings,
         workspace_root: &Path,
     ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
-        let backend_initializer: &BackendInitializer =
-            &|settings, store_path| Ok(Box::new(GitBackend::init_internal(settings, store_path)?));
+        let backend_initializer: &BackendInitializer = &|settings, store_path| {
+            Ok(Box::new(crate::git_backend::GitBackend::init_internal(
+                settings, store_path,
+            )?))
+        };
         let signer = Signer::from_settings(user_settings)?;
         Self::init_with_backend(user_settings, workspace_root, backend_initializer, signer)
     }
 
     /// Initializes a workspace with a new Git backend and Git repo that shares
     /// the same working copy.
+    #[cfg(feature = "git")]
     pub fn init_colocated_git(
         user_settings: &UserSettings,
         workspace_root: &Path,
     ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
         let backend_initializer = |settings: &UserSettings,
                                    store_path: &Path|
-         -> Result<Box<dyn Backend>, _> {
+         -> Result<Box<dyn crate::backend::Backend>, _> {
             // TODO: Clean up path normalization. store_path is canonicalized by
             // ReadonlyRepo::init(). workspace_root will be canonicalized by
             // Workspace::new(), but it's not yet here.
             let store_relative_workspace_root =
                 if let Ok(workspace_root) = workspace_root.canonicalize() {
-                    file_util::relative_path(store_path, &workspace_root)
+                    crate::file_util::relative_path(store_path, &workspace_root)
                 } else {
                     workspace_root.to_owned()
                 };
-            let backend =
-                GitBackend::init_colocated(settings, store_path, &store_relative_workspace_root)?;
+            let backend = crate::git_backend::GitBackend::init_colocated(
+                settings,
+                store_path,
+                &store_relative_workspace_root,
+            )?;
             Ok(Box::new(backend))
         };
         let signer = Signer::from_settings(user_settings)?;
@@ -197,33 +204,38 @@ impl Workspace {
     ///
     /// The `git_repo_path` usually ends with `.git`. It's the path to the Git
     /// repo directory, not the working directory.
+    #[cfg(feature = "git")]
     pub fn init_external_git(
         user_settings: &UserSettings,
         workspace_root: &Path,
         git_repo_path: &Path,
     ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
-        let backend_initializer =
-            |settings: &UserSettings, store_path: &Path| -> Result<Box<dyn Backend>, _> {
-                // If the git repo is inside the workspace, use a relative path to it so the
-                // whole workspace can be moved without breaking.
-                // TODO: Clean up path normalization. store_path is canonicalized by
-                // ReadonlyRepo::init(). workspace_root will be canonicalized by
-                // Workspace::new(), but it's not yet here.
-                let store_relative_git_repo_path = match (
-                    workspace_root.canonicalize(),
-                    canonicalize_git_repo_path(git_repo_path),
-                ) {
-                    (Ok(workspace_root), Ok(git_repo_path))
-                        if git_repo_path.starts_with(&workspace_root) =>
-                    {
-                        file_util::relative_path(store_path, &git_repo_path)
-                    }
-                    _ => git_repo_path.to_owned(),
-                };
-                let backend =
-                    GitBackend::init_external(settings, store_path, &store_relative_git_repo_path)?;
-                Ok(Box::new(backend))
+        let backend_initializer = |settings: &UserSettings,
+                                   store_path: &Path|
+         -> Result<Box<dyn crate::backend::Backend>, _> {
+            // If the git repo is inside the workspace, use a relative path to it so the
+            // whole workspace can be moved without breaking.
+            // TODO: Clean up path normalization. store_path is canonicalized by
+            // ReadonlyRepo::init(). workspace_root will be canonicalized by
+            // Workspace::new(), but it's not yet here.
+            let store_relative_git_repo_path = match (
+                workspace_root.canonicalize(),
+                crate::git_backend::canonicalize_git_repo_path(git_repo_path),
+            ) {
+                (Ok(workspace_root), Ok(git_repo_path))
+                    if git_repo_path.starts_with(&workspace_root) =>
+                {
+                    crate::file_util::relative_path(store_path, &git_repo_path)
+                }
+                _ => git_repo_path.to_owned(),
             };
+            let backend = crate::git_backend::GitBackend::init_external(
+                settings,
+                store_path,
+                &store_relative_git_repo_path,
+            )?;
+            Ok(Box::new(backend))
+        };
         let signer = Signer::from_settings(user_settings)?;
         Self::init_with_backend(user_settings, workspace_root, &backend_initializer, signer)
     }