Indicate that a final newline was added in --diff (#1897) (#1897)

[etc/vim.git] / src / black / __init__.py

diff --git a/src/black/__init__.py b/src/black/__init__.py
index 0b734adca565e507aa3ed1daeec4cf49b1fcb61f..c1907d9b1f10dd47a19d30df5686d9885fda4fdb 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -6425,14 +6425,14 @@ def assert_stable(src: str, dst: str, mode: Mode) -> None:
 
 
 @mypyc_attr(patchable=True)
-def dump_to_file(*output: str) -> str:
+def dump_to_file(*output: str, ensure_final_newline: bool = True) -> str:
     """Dump `output` to a temporary file. Return path to the file."""
     with tempfile.NamedTemporaryFile(
         mode="w", prefix="blk_", suffix=".log", delete=False, encoding="utf8"
     ) as f:
         for lines in output:
             f.write(lines)
-            if lines and lines[-1] != "\n":
+            if ensure_final_newline and lines and lines[-1] != "\n":
                 f.write("\n")
     return f.name
 
@@ -6450,11 +6450,20 @@ def diff(a: str, b: str, a_name: str, b_name: str) -> str:
     """Return a unified diff string between strings `a` and `b`."""
     import difflib
 
-    a_lines = [line + "\n" for line in a.splitlines()]
-    b_lines = [line + "\n" for line in b.splitlines()]
-    return "".join(
-        difflib.unified_diff(a_lines, b_lines, fromfile=a_name, tofile=b_name, n=5)
-    )
+    a_lines = [line for line in a.splitlines(keepends=True)]
+    b_lines = [line for line in b.splitlines(keepends=True)]
+    diff_lines = []
+    for line in difflib.unified_diff(
+        a_lines, b_lines, fromfile=a_name, tofile=b_name, n=5
+    ):
+        # Work around https://bugs.python.org/issue2142
+        # See https://www.gnu.org/software/diffutils/manual/html_node/Incomplete-Lines.html
+        if line[-1] == "\n":
+            diff_lines.append(line)
+        else:
+            diff_lines.append(line + "\n")
+            diff_lines.append("\\ No newline at end of file\n")
+    return "".join(diff_lines)
 
 
 def cancel(tasks: Iterable["asyncio.Task[Any]"]) -> None: