working copy: start defining a trait for a locked working copy

As with the `WorkingCopy` trait, this just contains some trivial
methods for now.

cli/src/cli_util.rs

@@ -63,7 +63,7 @@ use jj_lib::revset::{
 use jj_lib::settings::{ConfigResultExt as _, UserSettings};
 use jj_lib::transaction::Transaction;
 use jj_lib::tree::TreeMergeError;
-use jj_lib::working_copy::WorkingCopy;
+use jj_lib::working_copy::{LockedWorkingCopy, WorkingCopy};
 use jj_lib::workspace::{
     LockedWorkspace, Workspace, WorkspaceInitError, WorkspaceLoadError, WorkspaceLoader,
 };

cli/src/commands/mod.rs

@@ -48,6 +48,7 @@ use jj_lib::revset_graph::{
 };
 use jj_lib::rewrite::{back_out_commit, merge_commit_trees, rebase_commit, DescendantRebaser};
 use jj_lib::settings::UserSettings;
+use jj_lib::working_copy::LockedWorkingCopy;
 use jj_lib::workspace::Workspace;
 use jj_lib::{conflicts, file_util, revset};
 use maplit::{hashmap, hashset};

lib/src/local_working_copy.rs

@@ -59,7 +59,7 @@ use crate::repo_path::{FsPathParseError, RepoPath, RepoPathComponent, RepoPathJo
 use crate::settings::HumanByteSize;
 use crate::store::Store;
 use crate::tree::Tree;
-use crate::working_copy::WorkingCopy;
+use crate::working_copy::{LockedWorkingCopy, WorkingCopy};
 
 #[cfg(unix)]
 type FileExecutableFlag = bool;
@@ -1580,17 +1580,21 @@ pub struct LockedLocalWorkingCopy {
     tree_state_dirty: bool,
 }
 
-impl LockedLocalWorkingCopy {
-    /// The operation at the time the lock was taken
-    pub fn old_operation_id(&self) -> &OperationId {
+impl LockedWorkingCopy for LockedLocalWorkingCopy {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn old_operation_id(&self) -> &OperationId {
         &self.old_operation_id
     }
 
-    /// The tree at the time the lock was taken
-    pub fn old_tree_id(&self) -> &MergedTreeId {
+    fn old_tree_id(&self) -> &MergedTreeId {
         &self.old_tree_id
     }
+}
 
+impl LockedLocalWorkingCopy {
     pub fn reset_watchman(&mut self) -> Result<(), SnapshotError> {
         self.wc
             .tree_state_mut()

lib/src/working_copy.rs

@@ -18,6 +18,7 @@
 use std::any::Any;
 use std::path::Path;
 
+use crate::backend::MergedTreeId;
 use crate::op_store::{OperationId, WorkspaceId};
 
 /// The trait all working-copy implementations must implement.
@@ -38,3 +39,15 @@ pub trait WorkingCopy {
     /// The operation this working copy was most recently updated to.
     fn operation_id(&self) -> &OperationId;
 }
+
+/// A working copy that's being modified.
+pub trait LockedWorkingCopy {
+    /// Should return `self`. For down-casting purposes.
+    fn as_any(&self) -> &dyn Any;
+
+    /// The operation at the time the lock was taken
+    fn old_operation_id(&self) -> &OperationId;
+
+    /// The tree at the time the lock was taken
+    fn old_tree_id(&self) -> &MergedTreeId;
+}

lib/src/workspace.rs

@@ -39,7 +39,7 @@ use crate::repo::{
 };
 use crate::settings::UserSettings;
 use crate::submodule_store::SubmoduleStore;
-use crate::working_copy::WorkingCopy;
+use crate::working_copy::{LockedWorkingCopy, WorkingCopy};
 
 #[derive(Error, Debug)]
 pub enum WorkspaceInitError {