fix: preserve the indentation characters of the original code

src/docformatter/format.py

@@ -575,6 +575,45 @@ def _get_unmatched_start_end_indices(
     return (_start_row, _start_col), (_end_row, _end_col)
 
 
+class _Untokenizer(tokenize.Untokenizer):
+    __line = ""
+
+    def untokenize(self, iterable):
+        def _remember_line(tokens):
+            for tok in tokens:
+                self.__prev_line, self.__line = self.__line, tok[4]
+                yield tok
+
+        return super().untokenize(_remember_line(iterable))
+
+    def add_backslash_continuation(self, start):
+        """Add backslash continuation characters if the row has increased
+        without encountering a newline token.
+
+        This also inserts the correct amount of whitespace before the backslash.
+        """
+        row_offset = start[0] - self.prev_row
+        if row_offset == 0:
+            return
+
+        newline = "\r\n" if self.__prev_line.endswith("\r\n") else "\n"
+        line = self.__prev_line.rstrip("\\\r\n")
+        ws = line[len(line.rstrip()):]
+        self.tokens.append(ws + f"\\{newline}" * row_offset)
+        self.prev_col = 0
+
+    def add_whitespace(self, start, line=""):
+        row, col = start
+        if row < self.prev_row or row == self.prev_row and col < self.prev_col:
+            raise ValueError("start ({},{}) precedes previous end ({},{})"
+                             .format(row, col, self.prev_row, self.prev_col))
+        self.add_backslash_continuation(start)
+        col_offset = col - self.prev_col
+        if col_offset:
+            line = line or self.__line
+            self.tokens.append(line[self.prev_col : col])
+
+
 class FormatResult:
     """Possible exit codes."""
 
@@ -753,7 +792,9 @@ def _do_add_formatted_docstring(
         blank_line_count : int
             The number of blank lines to add after the docstring.
         """
-        _indent = " " * token.start[1] if docstring_type != "module" else ""
+        _indent = (
+            token.line[: token.start[1]] if docstring_type != "module" else ""
+        )
         _formatted = self._do_format_docstring(_indent, token.string)
         _line = _indent + _formatted
 
@@ -817,7 +858,9 @@ def _do_add_unformatted_docstring(
         docstring_type : str
             The type of the docstring (e.g., module, class, function, attribute).
         """
-        _indent = " " * token.start[1] if docstring_type != "module" else ""
+        _indent = (
+            token.line[: token.start[1]] if docstring_type != "module" else ""
+        )
         _line = _indent + token.string
         _new_token = tokenize.TokenInfo(
             type=tokenize.STRING,
@@ -916,7 +959,7 @@ def _do_format_code(self, source: str) -> str:
 
             # Perform docstring rewriting
             self._do_rewrite_docstring_blocks(tokens)
-            _code = tokenize.untokenize(self.new_tokens)
+            _code = _Untokenizer().untokenize(self.new_tokens)
 
             return _strings.do_normalize_line_endings(
                 _code.splitlines(True), _original_newline

tests/_data/string_files/do_format_code.toml

@@ -170,6 +170,27 @@ expected='''def foo():
 	if True:
 	    x = 1'''
 
+[wrapped_indentation]
+source='''def foo():
+	"""This is a very, very, very long docstring that should really be reformatted nicely by docformatter."""
+	if True:
+		x = 1'''
+expected='''def foo():
+	"""This is a very, very, very long docstring that should really be reformatted
+	nicely by docformatter."""
+	if True:
+		x = 1'''
+
+[preserve_whitespace]
+source='''def foo(
+	bar
+):
+	pass'''
+expected='''def foo(
+	bar
+):
+	pass'''
+
 [escaped_newlines]
 source='''def foo():
     """

tests/formatter/test_do_format_code.py

@@ -72,6 +72,8 @@
         ("non_docstring", NO_ARGS),
         ("tabbed_indentation", NO_ARGS),
         ("mixed_indentation", NO_ARGS),
+        ("wrapped_indentation", NO_ARGS),
+        ("preserve_whitespace", NO_ARGS),
         ("escaped_newlines", NO_ARGS),
         ("code_comments", NO_ARGS),
         ("inline_comment", NO_ARGS),