Fix crash on docstrings ending with "\ "

CHANGES.md

@@ -4,6 +4,8 @@
 
 #### _Black_
 
+- Fix crash on docstrings ending with "\ ". (#2142)
+
 - Reflect the `--skip-magic-trailing-comma` and `--experimental-string-processing` flags
   in the name of the cache file. Without this fix, changes in these flags would not take
   effect if the cache had already been populated. (#2131)

src/black/__init__.py

@@ -2179,7 +2179,13 @@ def visit_STRING(self, leaf: Leaf) -> Iterator[Line]:
                 indent = " " * 4 * self.current_line.depth
                 docstring = fix_docstring(docstring, indent)
             else:
-                docstring = docstring.strip()
+                new_docstring = docstring.strip()
+                # If the docstring ended with "\ ", stripping away the space
+                # will be a syntax error. Just put the trailing space back.
+                if new_docstring.endswith("\\"):
+                    docstring = docstring.lstrip()
+                else:
+                    docstring = new_docstring
 
             if docstring:
                 # Add some padding if the docstring starts / ends with a quote mark.

tests/data/docstring.py

@@ -158,6 +158,10 @@ def docstring_with_inline_tabs_and_tab_indentation():
 	"""
 	pass
 
+
+def backslash_space():
+    """\ """
+
 # output
 
 class MyClass:
@@ -316,3 +320,7 @@ def docstring_with_inline_tabs_and_tab_indentation():
     line ends with some tabs
     """
     pass
+
+
+def backslash_space():
+    """\ """