object_id: extract ObjectId trait and macros to separate module

I'm going to add a prefix resolution method to OpStore, but OpStore is
unrelated to the index. I think ObjectId, HexPrefix, and PrefixResolution can
be extracted to this module.

cli/src/cli_util.rs

@@ -30,7 +30,7 @@ use clap::builder::{NonEmptyStringValueParser, TypedValueParser, ValueParserFact
 use clap::{Arg, ArgAction, ArgMatches, Command, FromArgMatches};
 use indexmap::{IndexMap, IndexSet};
 use itertools::Itertools;
-use jj_lib::backend::{BackendError, ChangeId, CommitId, MergedTreeId, ObjectId};
+use jj_lib::backend::{BackendError, ChangeId, CommitId, MergedTreeId};
 use jj_lib::commit::Commit;
 use jj_lib::git::{
     FailedRefExport, FailedRefExportReason, GitConfigParseError, GitExportError, GitImportError,
@@ -42,6 +42,7 @@ use jj_lib::hex_util::to_reverse_hex;
 use jj_lib::id_prefix::IdPrefixContext;
 use jj_lib::matchers::{EverythingMatcher, Matcher, PrefixMatcher};
 use jj_lib::merged_tree::MergedTree;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_heads_store::{self, OpHeadResolutionError};
 use jj_lib::op_store::{OpStoreError, OperationId, WorkspaceId};
 use jj_lib::op_walk::OpsetEvaluationError;

cli/src/commands/abandon.rs

@@ -14,7 +14,7 @@
 
 use std::io::Write;
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use tracing::instrument;
 
 use crate::cli_util::{

cli/src/commands/backout.rs

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::rewrite::back_out_commit;
 use tracing::instrument;
 

cli/src/commands/branch.rs

@@ -19,8 +19,9 @@ use std::str::FromStr;
 
 use clap::builder::NonEmptyStringValueParser;
 use itertools::Itertools;
-use jj_lib::backend::{CommitId, ObjectId};
+use jj_lib::backend::CommitId;
 use jj_lib::git;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::{RefTarget, RemoteRef};
 use jj_lib::repo::Repo;
 use jj_lib::revset::{self, RevsetExpression};

cli/src/commands/checkout.rs

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use tracing::instrument;
 
 use crate::cli_util::{join_message_paragraphs, CommandError, CommandHelper, RevisionArg};

cli/src/commands/chmod.rs

@@ -13,8 +13,9 @@
 // limitations under the License.
 
 use itertools::Itertools;
-use jj_lib::backend::{ObjectId, TreeValue};
+use jj_lib::backend::TreeValue;
 use jj_lib::merged_tree::MergedTreeBuilder;
+use jj_lib::object_id::ObjectId;
 use tracing::instrument;
 
 use crate::cli_util::{user_error, CommandError, CommandHelper, RevisionArg};

cli/src/commands/commit.rs

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::rewrite::merge_commit_trees;
 use tracing::instrument;

cli/src/commands/debug.rs

@@ -17,9 +17,9 @@ use std::fmt::Debug;
 use std::io::Write as _;
 
 use clap::Subcommand;
-use jj_lib::backend::ObjectId;
 use jj_lib::default_index::{AsCompositeIndex as _, DefaultIndexStore, DefaultReadonlyIndex};
 use jj_lib::local_working_copy::LocalWorkingCopy;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::working_copy::WorkingCopy;
 use jj_lib::{op_walk, revset};

cli/src/commands/describe.rs

@@ -14,7 +14,7 @@
 
 use std::io::{self, Read, Write};
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use tracing::instrument;
 
 use crate::cli_util::{join_message_paragraphs, CommandError, CommandHelper, RevisionArg};

cli/src/commands/diffedit.rs

@@ -14,8 +14,8 @@
 
 use std::io::Write;
 
-use jj_lib::backend::ObjectId;
 use jj_lib::matchers::EverythingMatcher;
+use jj_lib::object_id::ObjectId;
 use jj_lib::rewrite::merge_commit_trees;
 use tracing::instrument;
 

cli/src/commands/edit.rs

@@ -14,7 +14,7 @@
 
 use std::io::Write;
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use tracing::instrument;
 
 use crate::cli_util::{CommandError, CommandHelper, RevisionArg};

cli/src/commands/git.rs

@@ -23,11 +23,12 @@ use std::{fmt, fs, io};
 
 use clap::{ArgGroup, Subcommand};
 use itertools::Itertools;
-use jj_lib::backend::{ObjectId, TreeValue};
+use jj_lib::backend::TreeValue;
 use jj_lib::git::{
     self, parse_gitmodules, GitBranchPushTargets, GitFetchError, GitFetchStats, GitPushError,
 };
 use jj_lib::git_backend::GitBackend;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::RefTarget;
 use jj_lib::refs::{
     classify_branch_push_action, BranchPushAction, BranchPushUpdate, TrackingRefPair,

cli/src/commands/move.rs

@@ -13,7 +13,7 @@
 // limitations under the License.
 
 use clap::ArgGroup;
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::rewrite::merge_commit_trees;
 use tracing::instrument;

cli/src/commands/operation.rs

@@ -17,7 +17,7 @@ use std::slice;
 
 use clap::Subcommand;
 use itertools::Itertools as _;
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::OperationId;
 use jj_lib::op_walk;
 use jj_lib::repo::Repo;

cli/src/commands/rebase.rs

@@ -19,8 +19,9 @@ use std::sync::Arc;
 use clap::ArgGroup;
 use indexmap::IndexSet;
 use itertools::Itertools;
-use jj_lib::backend::{CommitId, ObjectId};
+use jj_lib::backend::CommitId;
 use jj_lib::commit::Commit;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::{ReadonlyRepo, Repo};
 use jj_lib::revset::{RevsetExpression, RevsetIteratorExt};
 use jj_lib::rewrite::{rebase_commit, rebase_commit_with_options, EmptyBehaviour, RebaseOptions};

cli/src/commands/resolve.rs

@@ -16,8 +16,9 @@ use std::collections::BTreeMap;
 use std::io::Write;
 
 use itertools::Itertools;
-use jj_lib::backend::{ObjectId, TreeValue};
+use jj_lib::backend::TreeValue;
 use jj_lib::merge::MergedTreeValue;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo_path::RepoPathBuf;
 use tracing::instrument;
 

cli/src/commands/restore.rs

@@ -14,7 +14,7 @@
 
 use std::io::Write;
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::rewrite::{merge_commit_trees, restore_tree};
 use tracing::instrument;
 

cli/src/commands/split.rs

@@ -13,7 +13,7 @@
 // limitations under the License.
 use std::io::Write;
 
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::rewrite::merge_commit_trees;
 use tracing::instrument;

cli/src/commands/squash.rs

@@ -13,7 +13,7 @@
 // limitations under the License.
 
 use clap::parser::ValueSource;
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::revset;
 use tracing::instrument;
 

cli/src/commands/unsquash.rs

@@ -12,8 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use jj_lib::backend::ObjectId;
 use jj_lib::matchers::EverythingMatcher;
+use jj_lib::object_id::ObjectId;
 use jj_lib::rewrite::merge_commit_trees;
 use tracing::instrument;
 

cli/src/commands/workspace.rs

@@ -18,8 +18,8 @@ use std::io::Write;
 
 use clap::Subcommand;
 use itertools::Itertools;
-use jj_lib::backend::ObjectId;
 use jj_lib::file_util;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::WorkspaceId;
 use jj_lib::repo::Repo;
 use jj_lib::rewrite::merge_commit_trees;

cli/src/commit_templater.rs

@@ -18,10 +18,11 @@ use std::io;
 use std::rc::Rc;
 
 use itertools::Itertools as _;
-use jj_lib::backend::{ChangeId, CommitId, ObjectId as _};
+use jj_lib::backend::{ChangeId, CommitId};
 use jj_lib::commit::Commit;
 use jj_lib::hex_util::to_reverse_hex;
 use jj_lib::id_prefix::IdPrefixContext;
+use jj_lib::object_id::ObjectId as _;
 use jj_lib::op_store::{RefTarget, WorkspaceId};
 use jj_lib::repo::Repo;
 use jj_lib::{git, rewrite};

cli/src/diff_util.rs

@@ -19,7 +19,7 @@ use std::ops::Range;
 
 use futures::{try_join, Stream, StreamExt};
 use itertools::Itertools;
-use jj_lib::backend::{BackendResult, ObjectId, TreeValue};
+use jj_lib::backend::{BackendResult, TreeValue};
 use jj_lib::commit::Commit;
 use jj_lib::conflicts::{materialize_tree_value, MaterializedTreeValue};
 use jj_lib::diff::{Diff, DiffHunk};
@@ -27,6 +27,7 @@ use jj_lib::files::DiffLine;
 use jj_lib::matchers::Matcher;
 use jj_lib::merge::MergedTreeValue;
 use jj_lib::merged_tree::{MergedTree, TreeDiffStream};
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::repo_path::{RepoPath, RepoPathBuf};
 use jj_lib::settings::{ConfigResultExt as _, UserSettings};

cli/src/merge_tools/builtin.rs

@@ -4,12 +4,13 @@ use std::sync::Arc;
 
 use futures::{StreamExt, TryStreamExt};
 use itertools::Itertools;
-use jj_lib::backend::{BackendError, FileId, MergedTreeId, ObjectId, TreeValue};
+use jj_lib::backend::{BackendError, FileId, MergedTreeId, TreeValue};
 use jj_lib::diff::{find_line_ranges, Diff, DiffHunk};
 use jj_lib::files::{self, ContentHunk, MergeResult};
 use jj_lib::matchers::Matcher;
 use jj_lib::merge::Merge;
 use jj_lib::merged_tree::{MergedTree, MergedTreeBuilder};
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo_path::{RepoPath, RepoPathBuf};
 use jj_lib::store::Store;
 use pollster::FutureExt;

cli/src/operation_templater.rs

@@ -15,7 +15,7 @@
 use std::io;
 
 use itertools::Itertools as _;
-use jj_lib::backend::ObjectId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::{OperationId, OperationMetadata};
 use jj_lib::operation::Operation;
 use jj_lib::repo::ReadonlyRepo;

cli/tests/test_git_import_export.rs

@@ -14,7 +14,8 @@
 use std::path::Path;
 
 use itertools::Itertools as _;
-use jj_lib::backend::{CommitId, ObjectId as _};
+use jj_lib::backend::CommitId;
+use jj_lib::object_id::ObjectId as _;
 
 use crate::common::TestEnvironment;
 

lib/src/backend.rs

@@ -26,75 +26,10 @@ use thiserror::Error;
 
 use crate::content_hash::ContentHash;
 use crate::merge::Merge;
+use crate::object_id::{id_type, ObjectId};
 use crate::repo_path::{RepoPath, RepoPathComponent, RepoPathComponentBuf};
 use crate::signing::SignResult;
 
-pub trait ObjectId {
-    fn new(value: Vec<u8>) -> Self;
-    fn object_type(&self) -> String;
-    fn from_bytes(bytes: &[u8]) -> Self;
-    fn as_bytes(&self) -> &[u8];
-    fn to_bytes(&self) -> Vec<u8>;
-    fn from_hex(hex: &str) -> Self;
-    fn hex(&self) -> String;
-}
-
-macro_rules! id_type {
-    ($vis:vis $name:ident) => {
-        content_hash! {
-            #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
-            $vis struct $name(Vec<u8>);
-        }
-        $crate::backend::impl_id_type!($name);
-    };
-}
-
-macro_rules! impl_id_type {
-    ($name:ident) => {
-        impl std::fmt::Debug for $name {
-            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
-                f.debug_tuple(stringify!($name)).field(&self.hex()).finish()
-            }
-        }
-
-        impl crate::backend::ObjectId for $name {
-            fn new(value: Vec<u8>) -> Self {
-                Self(value)
-            }
-
-            fn object_type(&self) -> String {
-                stringify!($name)
-                    .strip_suffix("Id")
-                    .unwrap()
-                    .to_ascii_lowercase()
-                    .to_string()
-            }
-
-            fn from_bytes(bytes: &[u8]) -> Self {
-                Self(bytes.to_vec())
-            }
-
-            fn as_bytes(&self) -> &[u8] {
-                &self.0
-            }
-
-            fn to_bytes(&self) -> Vec<u8> {
-                self.0.clone()
-            }
-
-            fn from_hex(hex: &str) -> Self {
-                Self(hex::decode(hex).unwrap())
-            }
-
-            fn hex(&self) -> String {
-                hex::encode(&self.0)
-            }
-        }
-    };
-}
-
-pub(crate) use {id_type, impl_id_type};
-
 id_type!(pub CommitId);
 id_type!(pub ChangeId);
 id_type!(pub TreeId);

lib/src/default_index/composite.rs

@@ -26,8 +26,9 @@ use super::entry::{
 };
 use super::readonly::ReadonlyIndexSegment;
 use super::rev_walk::RevWalk;
-use crate::backend::{ChangeId, CommitId, ObjectId};
+use crate::backend::{ChangeId, CommitId};
 use crate::index::{HexPrefix, Index, PrefixResolution};
+use crate::object_id::ObjectId;
 use crate::revset::{ResolvedExpression, Revset, RevsetEvaluationError};
 use crate::store::Store;
 use crate::{default_revset_engine, hex_util};

lib/src/default_index/entry.rs

@@ -20,7 +20,8 @@ use std::hash::{Hash, Hasher};
 use smallvec::SmallVec;
 
 use super::composite::{CompositeIndex, IndexSegment};
-use crate::backend::{ChangeId, CommitId, ObjectId};
+use crate::backend::{ChangeId, CommitId};
+use crate::object_id::ObjectId;
 
 /// Global index position.
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Hash)]

lib/src/default_index/mod.rs

@@ -43,8 +43,9 @@ mod tests {
     use super::entry::SmallIndexPositionsVec;
     use super::mutable::MutableIndexSegment;
     use super::*;
-    use crate::backend::{ChangeId, CommitId, ObjectId};
+    use crate::backend::{ChangeId, CommitId};
     use crate::index::{HexPrefix, Index, PrefixResolution};
+    use crate::object_id::ObjectId;
 
     /// Generator of unique 16-byte ChangeId excluding root id
     fn change_id_generator() -> impl FnMut() -> ChangeId {

lib/src/default_index/mutable.rs

@@ -32,10 +32,11 @@ use tempfile::NamedTempFile;
 use super::composite::{AsCompositeIndex, CompositeIndex, IndexSegment};
 use super::entry::{IndexPosition, LocalPosition, SmallIndexPositionsVec};
 use super::readonly::{DefaultReadonlyIndex, ReadonlyIndexSegment};
-use crate::backend::{ChangeId, CommitId, ObjectId};
+use crate::backend::{ChangeId, CommitId};
 use crate::commit::Commit;
 use crate::file_util::persist_content_addressed_temp_file;
 use crate::index::{HexPrefix, Index, MutableIndex, PrefixResolution, ReadonlyIndex};
+use crate::object_id::ObjectId;
 use crate::revset::{ResolvedExpression, Revset, RevsetEvaluationError};
 use crate::store::Store;
 

lib/src/default_index/readonly.rs

@@ -29,9 +29,10 @@ use thiserror::Error;
 use super::composite::{AsCompositeIndex, CompositeIndex, IndexSegment};
 use super::entry::{IndexPosition, LocalPosition, SmallIndexPositionsVec};
 use super::mutable::DefaultMutableIndex;
-use crate::backend::{ChangeId, CommitId, ObjectId};
+use crate::backend::{ChangeId, CommitId};
 use crate::default_revset_engine;
 use crate::index::{HexPrefix, Index, MutableIndex, PrefixResolution, ReadonlyIndex};
+use crate::object_id::ObjectId;
 use crate::revset::{ResolvedExpression, Revset, RevsetEvaluationError};
 use crate::store::Store;
 

lib/src/default_index/store.rs

@@ -27,13 +27,14 @@ use thiserror::Error;
 
 use super::mutable::DefaultMutableIndex;
 use super::readonly::{DefaultReadonlyIndex, ReadonlyIndexLoadError, ReadonlyIndexSegment};
-use crate::backend::{BackendError, BackendInitError, CommitId, ObjectId};
+use crate::backend::{BackendError, BackendInitError, CommitId};
 use crate::commit::CommitByCommitterTimestamp;
 use crate::dag_walk;
 use crate::file_util::{persist_content_addressed_temp_file, IoResultExt as _, PathError};
 use crate::index::{
     Index, IndexReadError, IndexStore, IndexWriteError, MutableIndex, ReadonlyIndex,
 };
+use crate::object_id::ObjectId;
 use crate::op_store::{OpStoreError, OperationId};
 use crate::operation::Operation;
 use crate::store::Store;

lib/src/default_revset_engine.rs

@@ -999,8 +999,9 @@ fn has_diff_from_parent(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::backend::{ChangeId, CommitId, ObjectId};
+    use crate::backend::{ChangeId, CommitId};
     use crate::default_index::DefaultMutableIndex;
+    use crate::object_id::ObjectId;
 
     /// Generator of unique 16-byte ChangeId excluding root id
     fn change_id_generator() -> impl FnMut() -> ChangeId {

lib/src/git.rs

@@ -26,9 +26,10 @@ use itertools::Itertools;
 use tempfile::NamedTempFile;
 use thiserror::Error;
 
-use crate::backend::{BackendError, CommitId, ObjectId};
+use crate::backend::{BackendError, CommitId};
 use crate::commit::Commit;
 use crate::git_backend::GitBackend;
+use crate::object_id::ObjectId;
 use crate::op_store::{RefTarget, RefTargetOptionExt, RemoteRef, RemoteRefState};
 use crate::refs::BranchPushUpdate;
 use crate::repo::{MutableRepo, Repo};

lib/src/git_backend.rs

@@ -32,12 +32,13 @@ use thiserror::Error;
 use crate::backend::{
     make_root_commit, Backend, BackendError, BackendInitError, BackendLoadError, BackendResult,
     ChangeId, Commit, CommitId, Conflict, ConflictId, ConflictTerm, FileId, MergedTreeId,
-    MillisSinceEpoch, ObjectId, SecureSig, Signature, SigningFn, SymlinkId, Timestamp, Tree,
-    TreeId, TreeValue,
+    MillisSinceEpoch, SecureSig, Signature, SigningFn, SymlinkId, Timestamp, Tree, TreeId,
+    TreeValue,
 };
 use crate::file_util::{IoResultExt as _, PathError};
 use crate::lock::FileLock;
 use crate::merge::{Merge, MergeBuilder};
+use crate::object_id::ObjectId;
 use crate::repo_path::{RepoPath, RepoPathComponentBuf};
 use crate::settings::UserSettings;
 use crate::stacked_table::{

lib/src/id_prefix.rs

@@ -21,9 +21,10 @@ use std::rc::Rc;
 use itertools::Itertools as _;
 use once_cell::unsync::OnceCell;
 
-use crate::backend::{ChangeId, CommitId, ObjectId};
+use crate::backend::{ChangeId, CommitId};
 use crate::hex_util;
 use crate::index::{HexPrefix, PrefixResolution};
+use crate::object_id::ObjectId;
 use crate::repo::Repo;
 use crate::revset::{DefaultSymbolResolver, RevsetExpression};
 
@@ -445,7 +446,8 @@ fn unwrap_as_short_key<const N: usize>(key_bytes: &[u8]) -> &[u8; N] {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::backend::{ChangeId, ObjectId};
+    use crate::backend::ChangeId;
+    use crate::object_id::ObjectId;
 
     #[derive(Clone, Copy, Eq, PartialEq)]
     struct Position(usize);

lib/src/index.rs

@@ -20,8 +20,9 @@ use std::sync::Arc;
 
 use thiserror::Error;
 
-use crate::backend::{CommitId, ObjectId};
+use crate::backend::CommitId;
 use crate::commit::Commit;
+use crate::object_id::ObjectId;
 use crate::op_store::OperationId;
 use crate::operation::Operation;
 use crate::revset::{ResolvedExpression, Revset, RevsetEvaluationError};

lib/src/lib.rs

@@ -47,6 +47,7 @@ pub mod lock;
 pub mod matchers;
 pub mod merge;
 pub mod merged_tree;
+pub mod object_id;
 pub mod op_heads_store;
 pub mod op_store;
 pub mod op_walk;

lib/src/local_backend.rs

@@ -28,12 +28,13 @@ use tempfile::NamedTempFile;
 
 use crate::backend::{
     make_root_commit, Backend, BackendError, BackendResult, ChangeId, Commit, CommitId, Conflict,
-    ConflictId, ConflictTerm, FileId, MergedTreeId, MillisSinceEpoch, ObjectId, SecureSig,
-    Signature, SigningFn, SymlinkId, Timestamp, Tree, TreeId, TreeValue,
+    ConflictId, ConflictTerm, FileId, MergedTreeId, MillisSinceEpoch, SecureSig, Signature,
+    SigningFn, SymlinkId, Timestamp, Tree, TreeId, TreeValue,
 };
 use crate::content_hash::blake2b_hash;
 use crate::file_util::persist_content_addressed_temp_file;
 use crate::merge::MergeBuilder;
+use crate::object_id::ObjectId;
 use crate::repo_path::{RepoPath, RepoPathComponentBuf};
 
 const COMMIT_ID_LENGTH: usize = 64;

lib/src/local_working_copy.rs

@@ -42,7 +42,7 @@ use thiserror::Error;
 use tracing::{instrument, trace_span};
 
 use crate::backend::{
-    BackendError, FileId, MergedTreeId, MillisSinceEpoch, ObjectId, SymlinkId, TreeId, TreeValue,
+    BackendError, FileId, MergedTreeId, MillisSinceEpoch, SymlinkId, TreeId, TreeValue,
 };
 use crate::commit::Commit;
 use crate::conflicts::{self, materialize_tree_value, MaterializedTreeValue};
@@ -56,6 +56,7 @@ use crate::matchers::{
 };
 use crate::merge::{Merge, MergeBuilder, MergedTreeValue};
 use crate::merged_tree::{MergedTree, MergedTreeBuilder};
+use crate::object_id::ObjectId;
 use crate::op_store::{OperationId, WorkspaceId};
 use crate::repo_path::{RepoPath, RepoPathBuf, RepoPathComponent};
 use crate::settings::HumanByteSize;

lib/src/merge.rs

@@ -28,8 +28,9 @@ use itertools::Itertools;
 use smallvec::{smallvec_inline, SmallVec};
 
 use crate::backend;
-use crate::backend::{BackendError, FileId, ObjectId, TreeId, TreeValue};
+use crate::backend::{BackendError, FileId, TreeId, TreeValue};
 use crate::content_hash::ContentHash;
+use crate::object_id::ObjectId;
 use crate::repo_path::RepoPath;
 use crate::store::Store;
 use crate::tree::Tree;

lib/src/object_id.rs

@@ -0,0 +1,81 @@
+// Copyright 2020-2024 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![allow(missing_docs)]
+
+pub trait ObjectId {
+    fn new(value: Vec<u8>) -> Self;
+    fn object_type(&self) -> String;
+    fn from_bytes(bytes: &[u8]) -> Self;
+    fn as_bytes(&self) -> &[u8];
+    fn to_bytes(&self) -> Vec<u8>;
+    fn from_hex(hex: &str) -> Self;
+    fn hex(&self) -> String;
+}
+
+macro_rules! id_type {
+    ($vis:vis $name:ident) => {
+        content_hash! {
+            #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
+            $vis struct $name(Vec<u8>);
+        }
+        $crate::object_id::impl_id_type!($name);
+    };
+}
+
+macro_rules! impl_id_type {
+    ($name:ident) => {
+        impl std::fmt::Debug for $name {
+            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+                f.debug_tuple(stringify!($name)).field(&self.hex()).finish()
+            }
+        }
+
+        impl crate::object_id::ObjectId for $name {
+            fn new(value: Vec<u8>) -> Self {
+                Self(value)
+            }
+
+            fn object_type(&self) -> String {
+                stringify!($name)
+                    .strip_suffix("Id")
+                    .unwrap()
+                    .to_ascii_lowercase()
+                    .to_string()
+            }
+
+            fn from_bytes(bytes: &[u8]) -> Self {
+                Self(bytes.to_vec())
+            }
+
+            fn as_bytes(&self) -> &[u8] {
+                &self.0
+            }
+
+            fn to_bytes(&self) -> Vec<u8> {
+                self.0.clone()
+            }
+
+            fn from_hex(hex: &str) -> Self {
+                Self(hex::decode(hex).unwrap())
+            }
+
+            fn hex(&self) -> String {
+                hex::encode(&self.0)
+            }
+        }
+    };
+}
+
+pub(crate) use {id_type, impl_id_type};

lib/src/op_store.rs

@@ -22,9 +22,10 @@ use itertools::Itertools as _;
 use once_cell::sync::Lazy;
 use thiserror::Error;
 
-use crate::backend::{id_type, CommitId, ObjectId, Timestamp};
+use crate::backend::{CommitId, Timestamp};
 use crate::content_hash::ContentHash;
 use crate::merge::Merge;
+use crate::object_id::{id_type, ObjectId};
 
 content_hash! {
     #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]

lib/src/op_walk.rs

@@ -22,8 +22,8 @@ use std::sync::Arc;
 use itertools::Itertools as _;
 use thiserror::Error;
 
-use crate::backend::ObjectId as _;
 use crate::index::HexPrefix;
+use crate::object_id::ObjectId as _;
 use crate::op_heads_store::{OpHeadResolutionError, OpHeadsStore};
 use crate::op_store::{OpStore, OpStoreError, OpStoreResult, OperationId};
 use crate::operation::Operation;

lib/src/refs.rs

@@ -205,7 +205,7 @@ pub fn classify_branch_push_action(targets: TrackingRefPair) -> BranchPushAction
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::backend::ObjectId;
+    use crate::object_id::ObjectId;
     use crate::op_store::RemoteRefState;
 
     fn new_remote_ref(target: RefTarget) -> RemoteRef {

lib/src/repo.rs

@@ -30,7 +30,7 @@ use tracing::instrument;
 use self::dirty_cell::DirtyCell;
 use crate::backend::{
     Backend, BackendError, BackendInitError, BackendLoadError, BackendResult, ChangeId, CommitId,
-    MergedTreeId, ObjectId, SigningFn,
+    MergedTreeId, SigningFn,
 };
 use crate::commit::{Commit, CommitByCommitterTimestamp};
 use crate::commit_builder::CommitBuilder;
@@ -40,6 +40,7 @@ use crate::file_util::{IoResultExt as _, PathError};
 use crate::git_backend::GitBackend;
 use crate::index::{HexPrefix, Index, IndexStore, MutableIndex, PrefixResolution, ReadonlyIndex};
 use crate::local_backend::LocalBackend;
+use crate::object_id::ObjectId;
 use crate::op_heads_store::{self, OpHeadResolutionError, OpHeadsStore};
 use crate::op_store::{
     OpStore, OpStoreError, OperationId, RefTarget, RemoteRef, RemoteRefState, WorkspaceId,

lib/src/revset_graph.rs

@@ -296,7 +296,7 @@ mod tests {
     use renderdag::{Ancestor, GraphRowRenderer, Renderer as _};
 
     use super::*;
-    use crate::backend::ObjectId;
+    use crate::object_id::ObjectId;
 
     fn id(c: char) -> CommitId {
         let d = u8::try_from(c).unwrap();

lib/src/rewrite.rs

@@ -22,12 +22,13 @@ use itertools::Itertools;
 use pollster::FutureExt;
 use tracing::instrument;
 
-use crate::backend::{BackendError, BackendResult, CommitId, MergedTreeId, ObjectId};
+use crate::backend::{BackendError, BackendResult, CommitId, MergedTreeId};
 use crate::commit::Commit;
 use crate::dag_walk;
 use crate::index::Index;
 use crate::matchers::{Matcher, Visit};
 use crate::merged_tree::{MergedTree, MergedTreeBuilder};
+use crate::object_id::ObjectId;
 use crate::op_store::RefTarget;
 use crate::repo::{MutableRepo, Repo};
 use crate::repo_path::RepoPath;

lib/src/settings.rs

@@ -21,9 +21,10 @@ use chrono::DateTime;
 use rand::prelude::*;
 use rand_chacha::ChaCha20Rng;
 
-use crate::backend::{ChangeId, Commit, ObjectId, Signature, Timestamp};
+use crate::backend::{ChangeId, Commit, Signature, Timestamp};
 use crate::fmt_util::binary_prefix;
 use crate::fsmonitor::FsmonitorKind;
+use crate::object_id::ObjectId;
 use crate::signing::SignBehavior;
 
 #[derive(Debug, Clone)]

lib/src/simple_op_heads_store.rs

@@ -18,8 +18,8 @@ use std::fmt::{Debug, Formatter};
 use std::fs;
 use std::path::{Path, PathBuf};
 
-use crate::backend::ObjectId;
 use crate::lock::FileLock;
+use crate::object_id::ObjectId;
 use crate::op_heads_store::{OpHeadsStore, OpHeadsStoreLock};
 use crate::op_store::OperationId;
 

lib/src/simple_op_store.rs

@@ -24,10 +24,11 @@ use prost::Message;
 use tempfile::NamedTempFile;
 use thiserror::Error;
 
-use crate::backend::{CommitId, MillisSinceEpoch, ObjectId, Timestamp};
+use crate::backend::{CommitId, MillisSinceEpoch, Timestamp};
 use crate::content_hash::blake2b_hash;
 use crate::file_util::persist_content_addressed_temp_file;
 use crate::merge::Merge;
+use crate::object_id::ObjectId;
 use crate::op_store::{
     OpStore, OpStoreError, OpStoreResult, Operation, OperationId, OperationMetadata, RefTarget,
     RemoteRef, RemoteRefState, RemoteView, View, ViewId, WorkspaceId,
@@ -528,8 +529,9 @@ mod tests {
     use maplit::{btreemap, hashmap, hashset};
 
     use super::*;
-    use crate::backend::{CommitId, MillisSinceEpoch, ObjectId, Timestamp};
+    use crate::backend::{CommitId, MillisSinceEpoch, Timestamp};
     use crate::content_hash::blake2b_hash;
+    use crate::object_id::ObjectId;
     use crate::op_store::{OperationMetadata, RefTarget, WorkspaceId};
 
     fn create_view() -> View {

lib/src/tree.rs

@@ -24,12 +24,12 @@ use thiserror::Error;
 use tracing::instrument;
 
 use crate::backend::{
-    BackendError, ConflictId, FileId, ObjectId, TreeEntriesNonRecursiveIterator, TreeEntry, TreeId,
-    TreeValue,
+    BackendError, ConflictId, FileId, TreeEntriesNonRecursiveIterator, TreeEntry, TreeId, TreeValue,
 };
 use crate::files::MergeResult;
 use crate::matchers::{EverythingMatcher, Matcher};
 use crate::merge::{trivial_merge, Merge, MergedTreeValue};
+use crate::object_id::ObjectId;
 use crate::repo_path::{RepoPath, RepoPathBuf, RepoPathComponent, RepoPathComponentsIter};
 use crate::store::Store;
 use crate::{backend, files};

lib/tests/test_commit_builder.rs

@@ -12,9 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use jj_lib::backend::{ChangeId, MillisSinceEpoch, ObjectId, Signature, Timestamp};
+use jj_lib::backend::{ChangeId, MillisSinceEpoch, Signature, Timestamp};
 use jj_lib::matchers::EverythingMatcher;
 use jj_lib::merged_tree::DiffSummary;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::repo_path::{RepoPath, RepoPathBuf};
 use jj_lib::settings::UserSettings;

lib/tests/test_git.rs

@@ -20,9 +20,7 @@ use std::{fs, thread};
 use assert_matches::assert_matches;
 use git2::Oid;
 use itertools::Itertools;
-use jj_lib::backend::{
-    BackendError, ChangeId, CommitId, MillisSinceEpoch, ObjectId, Signature, Timestamp,
-};
+use jj_lib::backend::{BackendError, ChangeId, CommitId, MillisSinceEpoch, Signature, Timestamp};
 use jj_lib::commit::Commit;
 use jj_lib::commit_builder::CommitBuilder;
 use jj_lib::git;
@@ -31,6 +29,7 @@ use jj_lib::git::{
     GitRefUpdate, RefName, SubmoduleConfig,
 };
 use jj_lib::git_backend::GitBackend;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::{BranchTarget, RefTarget, RemoteRef, RemoteRefState};
 use jj_lib::refs::BranchPushUpdate;
 use jj_lib::repo::{MutableRepo, ReadonlyRepo, Repo};

lib/tests/test_id_prefix.rs

@@ -13,10 +13,11 @@
 // limitations under the License.
 
 use itertools::Itertools;
-use jj_lib::backend::{CommitId, MillisSinceEpoch, ObjectId, Signature, Timestamp};
+use jj_lib::backend::{CommitId, MillisSinceEpoch, Signature, Timestamp};
 use jj_lib::id_prefix::IdPrefixContext;
 use jj_lib::index::HexPrefix;
 use jj_lib::index::PrefixResolution::{AmbiguousMatch, NoMatch, SingleMatch};
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::revset::RevsetExpression;
 use testutils::{TestRepo, TestRepoBackend};

lib/tests/test_index.rs

@@ -16,7 +16,7 @@ use std::fs;
 use std::sync::Arc;
 
 use assert_matches::assert_matches;
-use jj_lib::backend::{CommitId, ObjectId as _};
+use jj_lib::backend::CommitId;
 use jj_lib::commit::Commit;
 use jj_lib::commit_builder::CommitBuilder;
 use jj_lib::default_index::{
@@ -24,6 +24,7 @@ use jj_lib::default_index::{
     DefaultMutableIndex, DefaultReadonlyIndex, IndexPosition,
 };
 use jj_lib::index::Index as _;
+use jj_lib::object_id::ObjectId as _;
 use jj_lib::repo::{MutableRepo, ReadonlyRepo, Repo};
 use jj_lib::settings::UserSettings;
 use testutils::test_backend::TestBackend;

lib/tests/test_local_working_copy.rs

@@ -26,11 +26,12 @@ use std::path::Path;
 use std::sync::Arc;
 
 use itertools::Itertools;
-use jj_lib::backend::{MergedTreeId, ObjectId, TreeId, TreeValue};
+use jj_lib::backend::{MergedTreeId, TreeId, TreeValue};
 use jj_lib::fsmonitor::FsmonitorKind;
 use jj_lib::local_working_copy::LocalWorkingCopy;
 use jj_lib::merge::Merge;
 use jj_lib::merged_tree::MergedTreeBuilder;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::{OperationId, WorkspaceId};
 use jj_lib::repo::{ReadonlyRepo, Repo};
 use jj_lib::repo_path::{RepoPath, RepoPathBuf, RepoPathComponent};

lib/tests/test_operations.rs

@@ -18,7 +18,8 @@ use std::sync::Arc;
 
 use assert_matches::assert_matches;
 use itertools::Itertools as _;
-use jj_lib::backend::{CommitId, ObjectId};
+use jj_lib::backend::CommitId;
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_walk::{self, OpsetEvaluationError, OpsetResolutionError};
 use jj_lib::operation::Operation;
 use jj_lib::repo::{ReadonlyRepo, Repo};

lib/tests/test_revset.rs

@@ -21,11 +21,12 @@ use std::path::Path;
 
 use assert_matches::assert_matches;
 use itertools::Itertools;
-use jj_lib::backend::{ChangeId, CommitId, MillisSinceEpoch, ObjectId, Signature, Timestamp};
+use jj_lib::backend::{ChangeId, CommitId, MillisSinceEpoch, Signature, Timestamp};
 use jj_lib::commit::Commit;
 use jj_lib::git;
 use jj_lib::git_backend::GitBackend;
 use jj_lib::index::{HexPrefix, PrefixResolution};
+use jj_lib::object_id::ObjectId;
 use jj_lib::op_store::{RefTarget, RemoteRef, RemoteRefState, WorkspaceId};
 use jj_lib::repo::Repo;
 use jj_lib::repo_path::RepoPath;

lib/testutils/src/lib.rs

@@ -22,13 +22,14 @@ use std::sync::{Arc, Once};
 use itertools::Itertools;
 use jj_lib::backend::{
     self, Backend, BackendInitError, ChangeId, CommitId, FileId, MergedTreeId, MillisSinceEpoch,
-    ObjectId, Signature, Timestamp, TreeValue,
+    Signature, Timestamp, TreeValue,
 };
 use jj_lib::commit::Commit;
 use jj_lib::commit_builder::CommitBuilder;
 use jj_lib::git_backend::GitBackend;
 use jj_lib::local_backend::LocalBackend;
 use jj_lib::merged_tree::MergedTree;
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo::{MutableRepo, ReadonlyRepo, Repo, RepoLoader, StoreFactories};
 use jj_lib::repo_path::{RepoPath, RepoPathBuf};
 use jj_lib::settings::UserSettings;

lib/testutils/src/test_backend.rs

@@ -22,8 +22,9 @@ use std::sync::{Arc, Mutex, MutexGuard, OnceLock};
 use async_trait::async_trait;
 use jj_lib::backend::{
     make_root_commit, Backend, BackendError, BackendResult, ChangeId, Commit, CommitId, Conflict,
-    ConflictId, FileId, ObjectId, SecureSig, SigningFn, SymlinkId, Tree, TreeId,
+    ConflictId, FileId, SecureSig, SigningFn, SymlinkId, Tree, TreeId,
 };
+use jj_lib::object_id::ObjectId;
 use jj_lib::repo_path::{RepoPath, RepoPathBuf};
 
 const HASH_LENGTH: usize = 10;