view: also merge git_heads when merging views

I don't know if I had just forgotten to merge `git_heads` when I added
it to the view object, but it seems like it should be merged just like
refs.

lib/src/repo.rs

@@ -37,6 +37,7 @@ use crate::op_store::{
     BranchTarget, OpStore, OperationId, OperationMetadata, RefTarget, WorkspaceId,
 };
 use crate::operation::Operation;
+use crate::refs::merge_ref_targets;
 use crate::rewrite::DescendantRebaser;
 use crate::settings::{RepoSettings, UserSettings};
 use crate::simple_op_heads_store::SimpleOpHeadsStore;
@@ -1022,6 +1023,17 @@ impl MutableRepo {
                 other_target.as_ref(),
             );
         }
+
+        if let Some(new_git_head) = merge_ref_targets(
+            self.index.as_index_ref(),
+            self.view().git_head(),
+            base.git_head(),
+            other.git_head(),
+        ) {
+            self.set_git_head(new_git_head);
+        } else {
+            self.clear_git_head();
+        }
     }
 
     /// Finds and records commits that were rewritten or abandoned between

lib/tests/test_view.rs

@@ -462,8 +462,7 @@ fn test_merge_views_git_heads() {
         removes: vec![tx0_head.id().clone()],
         adds: vec![tx1_head.id().clone(), tx2_head.id().clone()],
     };
-    // TODO: Should be equal
-    assert_ne!(repo.view().git_head(), Some(&expected_git_head));
+    assert_eq!(repo.view().git_head(), Some(&expected_git_head));
 }
 
 fn commit_transactions(settings: &UserSettings, txs: Vec<Transaction>) -> Arc<ReadonlyRepo> {