Skip newline before python docstring

Docstrings are defined in PEP 257 as "A docstring is a string literal
that occurs as the first statement in a module, function, class, or
method definition." When reuse adds a header, it forcibly adds a
space before the docstring violating this principle.

When the style is set to Python and the first line in the file is a
docstring, do not add a space between the license and the docstring.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>

AUTHORS.rst

@@ -144,3 +144,4 @@ Contributors
 - Skyler Grey <sky@a.starrysky.fyi>
 - Emil Velikov <emil.l.velikov@gmail.com>
 - Linnea Gräf <nea@nea.moe>
+- Charlie Jenkins <charlie@rivosinc.com>

changelog.d/changed/removed-space-before-docstring.md

@@ -0,0 +1,2 @@
+- To conform to PEP 257, do not put a space before a docstring at the beginning
+  of python formatted files. (#1136)

src/reuse/header.py

@@ -9,6 +9,7 @@
 # SPDX-FileCopyrightText: 2022 Florian Snow <florian@familysnow.net>
 # SPDX-FileCopyrightText: 2022 Yaman Qalieh
 # SPDX-FileCopyrightText: 2022 Carmen Bianca Bakker <carmenbianca@fsfe.org>
+# SPDX-FileCopyrightText: 2025 Charles Jenkins <charlie@rivosinc.com>
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
@@ -39,6 +40,7 @@
 DEFAULT_TEMPLATE = _ENV.get_template("default_template.jinja2")
 
 _NEWLINE_PATTERN = re.compile(r"\n", re.MULTILINE)
+_DOCSTRING_PATTERN = re.compile(r'^""".*"""', re.MULTILINE)
 
 
 class _TextSections(NamedTuple):
@@ -215,6 +217,20 @@ def _extract_shebang(prefix: str, text: str) -> tuple[str, str]:
     return (shebang, text)
 
 
+def _get_separator(style: Type[CommentStyle], text: str) -> str:
+    """Define separator between the license and the body of the text."""
+    separator = "\n"
+
+    if style == PythonCommentStyle:
+        # PEP 257 requires that docstrings are the first line of the file, so
+        # there must not be a space after the license.
+        docstring = _DOCSTRING_PATTERN.match(text)
+        if docstring:
+            separator = ""
+
+    return separator
+
+
 # pylint: disable=too-many-arguments
 def find_and_replace_header(
     text: str,
@@ -289,7 +305,7 @@ def find_and_replace_header(
     if before.strip():
         new_text = f"{before.rstrip()}\n\n{new_text}"
     if after.strip():
-        new_text = f"{new_text}\n{after.lstrip()}"
+        new_text = f"{new_text}{_get_separator(style, after)}{after.lstrip()}"
     return new_text
 
 
@@ -335,5 +351,5 @@ def add_new_header(
     if shebang.strip():
         new_text = f"{shebang.rstrip()}\n\n{new_text}"
     if text.strip():
-        new_text = f"{new_text}\n{text.lstrip()}"
+        new_text = f"{new_text}{_get_separator(style, text)}{text.lstrip()}"
     return new_text

tests/test_header.py

@@ -228,6 +228,26 @@ def test_find_and_replace_no_header():
     )
 
 
+def test_find_and_replace_no_header_docstring():
+    """Given text with docstring and no without header, add a header."""
+    info = ReuseInfo({"GPL-3.0-or-later"}, {"SPDX-FileCopyrightText: Jane Doe"})
+    text = '"""docstring"""'
+    expected = cleandoc(
+        """
+        # SPDX-FileCopyrightText: Jane Doe
+        #
+        # SPDX-License-Identifier: GPL-3.0-or-later
+        \"\"\"docstring\"\"\"
+        """
+    )
+
+    assert (
+        find_and_replace_header(text, info)
+        == add_new_header(text, info)
+        == expected
+    )
+
+
 def test_find_and_replace_verbatim():
     """Replace a header with itself."""
     info = ReuseInfo()
@@ -459,4 +479,21 @@ def test_find_and_replace_preserve_newline():
     assert find_and_replace_header(text, info) == text
 
 
+def test_find_and_replace_preserve_no_newline_docstring():
+    """If the file content doesn't have a newline and has a docstring,
+    don't add a newline."""
+
+    info = ReuseInfo()
+    text = cleandoc(
+        """
+            # SPDX-FileCopyrightText: Jane Doe
+            #
+            # SPDX-License-Identifier: GPL-3.0-or-later
+            \"\"\"docstring\"\"\"
+            """
+    )
+
+    assert find_and_replace_header(text, info) == text
+
+
 # REUSE-IgnoreEnd