libs/textwrap/no_line_continuations

libs/textwrap/ick.toml

@@ -1,3 +1,10 @@
+[[rule]]
+name = "no_line_continuations"
+impl = "python"
+scope = "file"
+inputs = ["*.py"]
+deps = ["libcst"]
+
 [[rule]]
 name = "use_textwrap_in_tests"
 impl = "python"

libs/textwrap/no_line_continuations.py

@@ -0,0 +1,86 @@
+"""Ick rule: flag line-continuation backslashes inside textwrap.dedent strings."""
+import re
+import sys
+from pathlib import Path
+
+import libcst as cst
+from libcst.metadata import PositionProvider, QualifiedNameProvider
+
+
+_LINE_CONT_RE = re.compile(r'(\\+)\n')
+
+
+def _has_line_continuation(raw_value: str) -> bool:
+    """Return True if the raw string source has a line-continuation backslash after the first line.
+
+    The pattern ``\"\"\"\\`` (continuation right after the opening triple-quote) is
+    explicitly allowed; it's only continuations on subsequent lines that break dedent.
+    """
+    prefix_len = len(raw_value) - len(raw_value.lstrip("rRbBfFuU"))
+    content_start = prefix_len + 3  # skip prefix + opening triple-quote
+
+    for m in _LINE_CONT_RE.finditer(raw_value):
+        if len(m.group(1)) % 2 == 0:
+            continue
+        if m.start() == content_start:
+            continue  # """\  at the very start is fine
+        return True
+    return False
+
+
+class LineContinuationChecker(cst.CSTVisitor):
+    METADATA_DEPENDENCIES = (QualifiedNameProvider, PositionProvider)
+
+    def __init__(self) -> None:
+        self.issues: list[int] = []
+
+    def visit_Call(self, node: cst.Call) -> None:
+        names = self.get_metadata(QualifiedNameProvider, node.func, set())
+        if not any(qn.name == "textwrap.dedent" for qn in names):
+            return
+        if not node.args:
+            return
+        arg = node.args[0]
+        if arg.keyword is not None:
+            return
+        str_node = arg.value
+        if not isinstance(str_node, cst.SimpleString):
+            return
+        value = str_node.value
+        prefix = value[:len(value) - len(value.lstrip("rRbBfFuU"))]
+        prefix_lower = prefix.lower()
+        if "r" in prefix_lower:
+            return  # raw strings: backslash is literal, not a line continuation
+        if "b" in prefix_lower:
+            return  # bytes strings: textwrap.dedent doesn't accept bytes
+        stripped = value[len(prefix):]
+        if not (stripped.startswith('"""') or stripped.startswith("'''")):
+            return
+        if _has_line_continuation(value):
+            pos = self.get_metadata(PositionProvider, node)
+            self.issues.append(pos.start.line)
+
+
+def main() -> None:
+    exit_status = 0
+    for path_str in sys.argv[1:]:
+        path = Path(path_str)
+        src = path.read_bytes()
+        try:
+            module = cst.parse_module(src)
+        except cst.ParserSyntaxError:
+            continue
+
+        checker = LineContinuationChecker()
+        wrapper = cst.metadata.MetadataWrapper(module)
+        wrapper.visit(checker)
+
+        for lineno in checker.issues:
+            print(f"{path_str}:{lineno}: line-continuation backslash in textwrap.dedent string")
+            exit_status = 99
+
+    sys.exit(exit_status)
+
+
+if __name__ == "__main__":
+    main()

libs/textwrap/tests/no_line_continuations/basic/input/example.py

@@ -0,0 +1,6 @@
+import textwrap
+
+x = textwrap.dedent("""
+    first line \
+    second line
+""")

libs/textwrap/tests/no_line_continuations/basic/output/output.txt

@@ -0,0 +1 @@
+example.py:3: line-continuation backslash in textwrap.dedent string

libs/textwrap/tests/no_line_continuations/from_import/input/example.py

@@ -0,0 +1,6 @@
+from textwrap import dedent as tw_dedent
+
+x = tw_dedent("""
+    first line \
+    second line
+""")

libs/textwrap/tests/no_line_continuations/from_import/output/output.txt

@@ -0,0 +1 @@
+example.py:3: line-continuation backslash in textwrap.dedent string

libs/textwrap/tests/no_line_continuations/start_ok/input/example.py

@@ -0,0 +1,6 @@
+import textwrap
+
+x = textwrap.dedent("""\
+    hello
+    world
+""")