pre-commit: check generated DBC files (#692)

.pre-commit-config.yaml

@@ -42,3 +42,10 @@ repos:
         - --force
         - --quiet
         - -j4
+-   repo: local
+    hooks:
+    -   id: generator
+        name: dbc generator
+        entry: generator/test_generator.py
+        language: script
+        pass_filenames: false

generator/test_generator.py

@@ -11,7 +11,11 @@ def test_generator():
 
     ignore = [f for f in os.listdir(opendbc_root) if not f.endswith('_generated.dbc')]
     comp = filecmp.dircmp(opendbc_root, d, ignore=ignore)
-    assert len(comp.diff_files) == 0, f"Different files: {comp.diff_files}"
+
+    err = "Generated DBC mismatch\n\n"
+    err += f"Different files: {comp.diff_files}\n\n"
+    err += "Run opendbc/generator/generator.py to regenerate DBC files."
+    assert len(comp.diff_files) == 0, err
 
 
 if __name__ == "__main__":