Don't modify empty files if unchanged

nathanjmcdougall · nathanjmcdougall · commit 5dfd1cb57a26 · 2025-07-25T15:23:16.000+12:00
diff --git a/src/usethis/_integrations/file/yaml/io_.py b/src/usethis/_integrations/file/yaml/io_.py
@@ -474,7 +474,12 @@ def edit_yaml(
         except YAMLError as err:
             msg = f"Error reading '{yaml_path}':\n{err}"
             raise YAMLDecodeError(msg) from None
+
+    start_empty = not yaml_document.content
     yield yaml_document
+    if start_empty and not yaml_document.content:
+        # No change
+        return
     yaml_document.roundtripper.dump(yaml_document.content, stream=yaml_path)
 
 
diff --git a/src/usethis/_integrations/pre_commit/io_.py b/src/usethis/_integrations/pre_commit/io_.py
@@ -62,7 +62,7 @@ def edit_pre_commit_config_yaml() -> Generator[PreCommitConfigYAMLDocument, None
 
 def _validate_config(ruamel_content: YAMLLiteral) -> JsonSchemaForPreCommitConfigYaml:
     if isinstance(ruamel_content, CommentedMap) and not ruamel_content:
-        ruamel_content["repos"] = []
+        ruamel_content = CommentedMap({"repos": []})
 
     try:
         return JsonSchemaForPreCommitConfigYaml.model_validate(ruamel_content)
diff --git a/tests/usethis/_integrations/pre_commit/test_pre_commit_io_.py b/tests/usethis/_integrations/pre_commit/test_pre_commit_io_.py
@@ -30,7 +30,7 @@ def test_unchanged(self, tmp_path: Path):
         # Assert
         assert (tmp_path / ".pre-commit-config.yaml").read_text() == content_str
 
-    def test_empty_is_valid(self, tmp_path: Path):
+    def test_start_with_empty_file(self, tmp_path: Path):
         # Arrange
         (tmp_path / ".pre-commit-config.yaml").write_text("")
 
@@ -43,3 +43,14 @@ def test_empty_is_valid(self, tmp_path: Path):
 
         # Assert
         assert (tmp_path / ".pre-commit-config.yaml").read_text() == "repos: []\n"
+
+    def test_empty_valid_but_unchanged(self, tmp_path: Path):
+        # Arrange
+        (tmp_path / ".pre-commit-config.yaml").write_text("")
+
+        # Act
+        with change_cwd(tmp_path), edit_pre_commit_config_yaml():
+            pass
+
+        # Assert
+        assert (tmp_path / ".pre-commit-config.yaml").read_text() == ""
