working_copy: allow load_working_copy() to return error

It's reasonable for a `WorkingCopy` implementation to want to return
an error. `LocalWorkingCopyFactory` doesn't because it loads all data
lazily. The VFS-based one at Google wants to be able to return an
error, however.

cli/examples/custom-working-copy/main.rs

@@ -191,12 +191,12 @@ impl WorkingCopyFactory for ConflictsWorkingCopyFactory {
         store: Arc<Store>,
         working_copy_path: PathBuf,
         state_path: PathBuf,
-    ) -> Box<dyn WorkingCopy> {
-        Box::new(ConflictsWorkingCopy::load(
+    ) -> Result<Box<dyn WorkingCopy>, WorkingCopyStateError> {
+        Ok(Box::new(ConflictsWorkingCopy::load(
             store,
             working_copy_path,
             state_path,
-        ))
+        )))
     }
 }
 

cli/src/cli_util.rs

@@ -1504,6 +1504,7 @@ jj git init --colocate",
             err @ SignInitError::UnknownBackend(_),
         )) => user_error(err),
         WorkspaceLoadError::StoreLoadError(err) => internal_error(err),
+        WorkspaceLoadError::WorkingCopyState(err) => internal_error(err),
         WorkspaceLoadError::NonUnicodePath | WorkspaceLoadError::Path(_) => user_error(err),
     }
 }

lib/src/local_working_copy.rs

@@ -1706,8 +1706,12 @@ impl WorkingCopyFactory for LocalWorkingCopyFactory {
         store: Arc<Store>,
         working_copy_path: PathBuf,
         state_path: PathBuf,
-    ) -> Box<dyn WorkingCopy> {
-        Box::new(LocalWorkingCopy::load(store, working_copy_path, state_path))
+    ) -> Result<Box<dyn WorkingCopy>, WorkingCopyStateError> {
+        Ok(Box::new(LocalWorkingCopy::load(
+            store,
+            working_copy_path,
+            state_path,
+        )))
     }
 }
 

lib/src/working_copy.rs

@@ -81,7 +81,7 @@ pub trait WorkingCopyFactory {
         store: Arc<Store>,
         working_copy_path: PathBuf,
         state_path: PathBuf,
-    ) -> Box<dyn WorkingCopy>;
+    ) -> Result<Box<dyn WorkingCopy>, WorkingCopyStateError>;
 }
 
 /// A working copy that's being modified.

lib/src/workspace.rs

@@ -72,6 +72,8 @@ pub enum WorkspaceLoadError {
     #[error("Repo path could not be interpreted as Unicode text")]
     NonUnicodePath,
     #[error(transparent)]
+    WorkingCopyState(#[from] WorkingCopyStateError),
+    #[error(transparent)]
     Path(#[from] PathError),
 }
 
@@ -503,13 +505,14 @@ impl WorkspaceLoader {
         &self,
         store: &Arc<Store>,
         working_copy_factories: &WorkingCopyFactories,
-    ) -> Result<Box<dyn WorkingCopy>, StoreLoadError> {
+    ) -> Result<Box<dyn WorkingCopy>, WorkspaceLoadError> {
         let working_copy_factory = self.get_working_copy_factory(working_copy_factories)?;
-        Ok(working_copy_factory.load_working_copy(
+        let working_copy = working_copy_factory.load_working_copy(
             store.clone(),
             self.workspace_root.to_owned(),
             self.working_copy_state_path.to_owned(),
-        ))
+        )?;
+        Ok(working_copy)
     }
 }