exp save: Include LOCK_FILE

dvc/repo/experiments/executor/base.py

@@ -265,6 +265,7 @@ def save(
         force: bool = False,
         include_untracked: Optional[List[str]] = None,
     ) -> ExecutorResult:
+        from dvc.dvcfile import LOCK_FILE
         from dvc.repo import Repo
 
         exp_hash: Optional[str] = None
@@ -283,6 +284,10 @@ def save(
         include_untracked.extend(
             dvc.index._plot_sources  # pylint: disable=protected-access
         )
+        # dvc repro automatically stages dvc.lock. Running redundant `git add`
+        # on it causes an error when exiting the detached head context.
+        if LOCK_FILE in dvc.scm.untracked_files():
+            include_untracked.append(LOCK_FILE)
 
         try:
             stages = dvc.commit([], force=True, relink=False)

tests/func/experiments/test_save.py

@@ -134,5 +134,22 @@ def test_untracked_top_level_files_are_included_in_exp(tmp_dir, scm, dvc):
     dvc.reproduce(stage.addressing)
     exp = dvc.experiments.save()
     fs = scm.get_fs(exp)
-    for file in ["metrics.json", "params.yaml", "plots.csv"]:
+    for file in ["metrics.json", "params.yaml", "plots.csv", "dvc.lock"]:
         assert fs.exists(file)
+
+
+def test_untracked_dvclock_is_included_in_exp(tmp_dir, scm, dvc):
+    stage = dvc.stage.add(
+        cmd="echo foo",
+        name="foo",
+    )
+    scm.add_commit(["dvc.yaml"], message="add dvc.yaml")
+    dvc.reproduce(stage.addressing)
+
+    # dvc.reproduce automatically stages `dvc.lock`
+    # force it to be untracked
+    scm.reset()
+
+    exp = dvc.experiments.save()
+    fs = scm.get_fs(exp)
+    assert fs.exists("dvc.lock")