Don't reproduce frozen stages with --force

dvc/stage/__init__.py

@@ -422,6 +422,13 @@ def reproduce(self, interactive=False, **kwargs) -> Optional["Stage"]:
         allow_missing = kwargs.get("allow_missing", False)
         pull = kwargs.get("pull", False)
         upstream = kwargs.pop("upstream", None)
+        if self.frozen and not self.is_import:
+            # `dvc freeze` documents a frozen stage as always treated as
+            # unchanged, so `--force` must not reproduce it. The command is
+            # skipped in `run()` either way, but reproducing re-saves the stage
+            # and rewrites its dependency hashes in dvc.lock. Falling through to
+            # the checks below still lets it restore missing outputs.
+            force = False
         if force:
             pass
         # Skip stages with missing data if otherwise unchanged

tests/func/repro/test_repro.py

@@ -17,7 +17,7 @@
 from dvc.stage.exceptions import StageFileDoesNotExistError, StageNotFound
 from dvc.testing import matchers as M
 from dvc.utils.fs import remove
-from dvc.utils.serialize import modify_yaml
+from dvc.utils.serialize import load_yaml, modify_yaml
 from dvc_data.hashfile.hash import file_md5
 
 
@@ -56,6 +56,21 @@ def test_repro_frozen(tmp_dir, dvc, run_copy):
     assert stages == [data_stage, stage0]
 
 
+def test_repro_frozen_force(tmp_dir, dvc, run_copy):
+    """Check that `--force` doesn't rewrite a frozen stage's dependency hashes"""
+    tmp_dir.dvc_gen("data", "foo")
+    run_copy("data", "stage0", name="copy-data-stage0")
+    run_copy("stage0", "stage1", name="copy-data-stage1")
+
+    dvc.freeze("copy-data-stage1")
+    frozen_before = load_yaml("dvc.lock")["stages"]["copy-data-stage1"]
+
+    tmp_dir.gen("stage0", "bar")
+
+    assert dvc.reproduce("copy-data-stage1", force=True) == []
+    assert load_yaml("dvc.lock")["stages"]["copy-data-stage1"] == frozen_before
+
+
 def test_downstream(tmp_dir, dvc):
     # The dependency graph should look like this:
     #