commit: migrate remaining uses of Commit::tree_id() and delete it

cli/src/commands/mod.rs

@@ -3108,7 +3108,7 @@ don't make any changes, then the operation will be aborted.
         .mut_repo()
         .rewrite_commit(command.settings(), &commit)
         .set_parents(vec![first_commit.id().clone()])
-        .set_tree(commit.tree_id().clone())
+        .set_tree_id(commit.merged_tree_id().clone())
         .generate_new_change_id()
         .set_description(second_description)
         .write()?;

lib/src/commit.rs

@@ -20,7 +20,7 @@ use std::hash::{Hash, Hasher};
 use std::sync::Arc;
 
 use crate::backend;
-use crate::backend::{BackendError, ChangeId, CommitId, MergedTreeId, Signature, TreeId};
+use crate::backend::{BackendError, ChangeId, CommitId, MergedTreeId, Signature};
 use crate::merged_tree::MergedTree;
 use crate::repo_path::RepoPath;
 use crate::store::Store;
@@ -113,12 +113,6 @@ impl Commit {
         self.store.get_root_tree(&self.data.root_tree)
     }
 
-    // TODO(#1624): delete when all callers have been updated to support tree-level
-    // conflicts
-    pub fn tree_id(&self) -> &TreeId {
-        self.data.root_tree.as_legacy_tree_id()
-    }
-
     pub fn merged_tree_id(&self) -> &MergedTreeId {
         &self.data.root_tree
     }
@@ -148,7 +142,7 @@ impl Commit {
     pub fn is_discardable(&self) -> bool {
         if self.description().is_empty() {
             if let [parent_commit] = &*self.parents() {
-                return self.tree_id() == parent_commit.tree_id();
+                return self.merged_tree_id() == parent_commit.merged_tree_id();
             }
         }
         false

lib/src/default_revset_engine.rs

@@ -884,7 +884,7 @@ fn has_diff_from_parent(
     let parents = commit.parents();
     if let [parent] = parents.as_slice() {
         // Fast path: no need to load the root tree
-        let unchanged = commit.tree_id() == parent.tree_id();
+        let unchanged = commit.merged_tree_id() == parent.merged_tree_id();
         if matcher.visit(&RepoPath::root()) == Visit::AllRecursively {
             return !unchanged;
         } else if unchanged {

lib/tests/test_init.rs

@@ -14,6 +14,7 @@
 
 use std::path::{Path, PathBuf};
 
+use jj_lib::backend::MergedTreeId;
 use jj_lib::git_backend::GitBackend;
 use jj_lib::op_store::WorkspaceId;
 use jj_lib::repo::Repo;
@@ -123,7 +124,10 @@ fn test_init_checkout(use_git: bool) {
         .get_wc_commit_id(&WorkspaceId::default())
         .unwrap();
     let wc_commit = repo.store().get_commit(wc_commit_id).unwrap();
-    assert_eq!(wc_commit.tree_id(), repo.store().empty_tree_id());
+    assert_eq!(
+        *wc_commit.merged_tree_id(),
+        MergedTreeId::Legacy(repo.store().empty_tree_id().clone())
+    );
     assert_eq!(
         wc_commit.store_commit().parents,
         vec![repo.store().root_commit_id().clone()]

lib/tests/test_mut_repo.rs

@@ -58,7 +58,10 @@ fn test_checkout(use_git: bool) {
         .mut_repo()
         .check_out(ws_id.clone(), &settings, &wc_commit_parent)
         .unwrap();
-    assert_eq!(wc_commit.tree_id(), wc_commit_parent.tree_id());
+    assert_eq!(
+        wc_commit.merged_tree_id(),
+        wc_commit_parent.merged_tree_id()
+    );
     assert_eq!(wc_commit.parents().len(), 1);
     assert_eq!(wc_commit.parents()[0].id(), wc_commit_parent.id());
     let repo = tx.commit();