End every written file with a newline

file_utils.py

@@ -142,7 +142,21 @@ def get_existing_files_content(build_folder, existing_files):
     return existing_files_content
 
 
+def ensure_final_newline(content: str) -> str:
+    """Ends non-empty text with a newline, as linters expect (e.g. RuboCop, ESLint eol-last, Ruff W292)."""
+    if content and not content.endswith("\n"):
+        return content + "\n"
+    return content
+
+
 def store_response_files(target_folder, response_files, existing_files):
+    """Writes the files returned by the API to target_folder. None content deletes the file.
+
+    Every written file ends with a newline - whole-file rewrites come back from the API without one. The
+    added newline is also written back into response_files, so callers that diff response_files against
+    the folder afterwards see exactly what is on disk. Content is written byte-for-byte, without newline
+    translation, so the disk matches response_files on every platform.
+    """
     for file_name in response_files:
         full_file_name = os.path.join(target_folder, file_name)
 
@@ -156,9 +170,11 @@ def store_response_files(target_folder, response_files, existing_files):
 
             continue
 
+        response_files[file_name] = ensure_final_newline(response_files[file_name])
+
         os.makedirs(os.path.dirname(full_file_name), exist_ok=True)
 
-        with open(full_file_name, "w", encoding="utf-8") as f:
+        with open(full_file_name, "w", encoding="utf-8", newline="") as f:
             f.write(response_files[file_name])
 
         if file_name not in existing_files:

tests/test_file_utils.py

@@ -3,7 +3,9 @@
 
 import pytest
 
-from file_utils import load_linked_resources, store_response_files
+import file_utils
+from diff_utils import get_code_diff
+from file_utils import get_existing_files_content, load_linked_resources, store_response_files
 from plain2code_exceptions import UnsupportedBase64Content, UnsupportedResourceType
 from plain2code_utils import MAX_BASE64_BLOB_LENGTH
 
@@ -82,11 +84,91 @@ def test_load_linked_resources_real_base64_image_raises(template_dir):
 
 
 def test_store_response_files_writes_unicode_as_utf8(template_dir):
-    # Content with a non-cp1252 character (📍 U+1F4CD) must be written as UTF-8
-    # regardless of the platform's default text encoding (e.g. cp1252 on Windows).
-    content = "Location 📍 marker"
+    """A non-cp1252 character (📍 U+1F4CD) is written as UTF-8, whatever the platform's default encoding."""
+    content = "Location 📍 marker\n"
     store_response_files(template_dir, {"notes.md": content}, [])
 
     file_path = os.path.join(template_dir, "notes.md")
     with open(file_path, "rb") as f:
         assert f.read().decode("utf-8") == content
+
+
+def _read_bytes(folder, file_name):
+    """Returns a file's content exactly as stored on disk, without newline translation."""
+    with open(os.path.join(folder, file_name), "rb") as f:
+        return f.read().decode("utf-8")
+
+
+@pytest.mark.parametrize(
+    "content, expected",
+    [
+        ("class Foo\nend", "class Foo\nend\n"),
+        ("class Foo\nend\n", "class Foo\nend\n"),
+        ("class Foo\nend\n\n", "class Foo\nend\n\n"),
+        ("class Foo\r\nend\r\n", "class Foo\r\nend\r\n"),
+        ("", ""),
+    ],
+)
+def test_store_response_files_ends_every_text_file_with_a_newline(template_dir, content, expected):
+    """A missing final newline is added, as linters such as RuboCop, ESLint and Ruff require.
+
+    An existing final newline is not doubled, and empty content stays empty.
+    """
+    store_response_files(template_dir, {"app/foo.rb": content}, [])
+
+    assert _read_bytes(template_dir, "app/foo.rb") == expected
+
+
+def test_store_response_files_hands_back_the_content_it_wrote(template_dir):
+    """response_files holds the content as written, so diffs taken after storing match the disk.
+
+    The fix journal and the conformance fixes handed to the unit tests fixer take such diffs.
+    """
+    response_files = {"app/foo.rb": "class Foo\nend", "app/bar.rb": "class Bar\nend\n"}
+
+    store_response_files(template_dir, response_files, [])
+
+    assert response_files == {"app/foo.rb": "class Foo\nend\n", "app/bar.rb": "class Bar\nend\n"}
+
+
+def test_rewriting_a_file_without_its_final_newline_does_not_change_it(template_dir):
+    """A rewrite that drops only the final newline leaves the file byte-identical and produces no diff."""
+    existing_files = store_response_files(template_dir, {"app/foo.rb": "class Foo\nend\n"}, [])
+    existing_files_content = get_existing_files_content(template_dir, existing_files)
+
+    rewrite = {"app/foo.rb": "class Foo\nend"}
+    store_response_files(template_dir, rewrite, existing_files)
+
+    assert get_existing_files_content(template_dir, existing_files) == existing_files_content
+    assert get_code_diff(rewrite, existing_files_content) == {}
+
+
+def test_store_response_files_still_deletes_a_file_whose_content_is_none(template_dir):
+    """None content still deletes the file and removes it from existing_files, and is not turned into a newline."""
+    existing_files = store_response_files(template_dir, {"app/foo.rb": "class Foo\nend\n"}, [])
+
+    response_files = {"app/foo.rb": None}
+    store_response_files(template_dir, response_files, existing_files)
+
+    assert not os.path.exists(os.path.join(template_dir, "app/foo.rb"))
+    assert existing_files == []
+    assert response_files == {"app/foo.rb": None}
+
+
+def test_store_response_files_writes_the_same_bytes_where_text_mode_writes_crlf(template_dir, monkeypatch):
+    """Files hold exactly the normalized content even where text mode writes CRLF line endings (native Windows)."""
+    # Imported here: isort 8 and isort 9 disagree on which section a top-level `import _pyio` belongs to.
+    import _pyio
+
+    # Python's reference io (_pyio) takes its line separator from os.linesep, so here it translates like Windows.
+    monkeypatch.setattr(os, "linesep", "\r\n")
+    monkeypatch.setattr(file_utils, "open", _pyio.open, raising=False)
+    with _pyio.open(os.path.join(template_dir, "probe.txt"), "w") as probe:
+        probe.write("\n")
+    assert _read_bytes(template_dir, "probe.txt") == "\r\n"
+
+    response_files = {"app/foo.rb": "class Foo\nend", "app/bar.rb": "class Bar\r\nend\r\n"}
+    store_response_files(template_dir, response_files, [])
+
+    assert _read_bytes(template_dir, "app/foo.rb") == response_files["app/foo.rb"] == "class Foo\nend\n"
+    assert _read_bytes(template_dir, "app/bar.rb") == response_files["app/bar.rb"] == "class Bar\r\nend\r\n"