fix: keep tab-width compensation local to each docstring

src/docformatter/format.py

@@ -1071,12 +1071,6 @@ def _do_format_docstring(  # noqa PLR0911
             # Something probably isn't right with the splitting.
             return docstring
 
-        # Compensate for textwrap counting each tab in indentation as 1
-        # character.
-        tab_compensation = indentation.count("\t") * (self.args.tab_width - 1)
-        self.args.wrap_summaries -= tab_compensation
-        self.args.wrap_descriptions -= tab_compensation
-
         if description:
             return self._do_format_multiline_docstring(
                 indentation,
@@ -1114,12 +1108,16 @@ def _do_format_oneline_docstring(
         str
             The formatted docstring.
         """
+        # Keep tab compensation local to this docstring.
+        wrap_length = self.args.wrap_summaries - indentation.count("\t") * (
+            self.args.tab_width - 1
+        )
         if self.args.make_summary_multi_line:
             beginning = f"{open_quote}\n{indentation}"
             ending = f'\n{indentation}"""'
             summary_wrapped = _wrappers.do_wrap_summary(
                 _strings.do_normalize_summary(contents, self.args.non_cap),
-                wrap_length=self.args.wrap_summaries,
+                wrap_length=wrap_length,
                 initial_indent=indentation,
                 subsequent_indent=indentation,
             ).strip()
@@ -1129,7 +1127,7 @@ def _do_format_oneline_docstring(
                 open_quote
                 + _strings.do_normalize_summary(contents, self.args.non_cap)
                 + '"""',
-                wrap_length=self.args.wrap_summaries,
+                wrap_length=wrap_length,
                 initial_indent=indentation,
                 subsequent_indent=indentation,
             ).strip()
@@ -1165,6 +1163,7 @@ def _do_format_multiline_docstring(
         str
             The formatted docstring.
         """
+        tab_compensation = indentation.count("\t") * (self.args.tab_width - 1)
         # Compensate for triple quotes by temporarily prepending 3 spaces.
         # This temporary prepending is undone below.
         initial_indent = (
@@ -1173,14 +1172,14 @@ def _do_format_multiline_docstring(
         pre_summary = "\n" + indentation if self.args.pre_summary_newline else ""
         summary = _wrappers.do_wrap_summary(
             _strings.do_normalize_summary(summary, self.args.non_cap),
-            wrap_length=self.args.wrap_summaries,
+            wrap_length=self.args.wrap_summaries - tab_compensation,
             initial_indent=initial_indent,
             subsequent_indent=indentation,
         ).lstrip()
         description = _wrappers.do_wrap_description(
             description,
             indentation=indentation,
-            wrap_length=self.args.wrap_descriptions,
+            wrap_length=self.args.wrap_descriptions - tab_compensation,
             force_wrap=self.args.force_wrap,
             strict=self.args.non_strict,
             rest_sections=self.args.rest_section_adorns,

tests/formatter/test_tab_wrapping_state.py

@@ -0,0 +1,103 @@
+"""Keep tab-width compensation local to each formatted docstring."""
+
+import ast
+import copy
+import sys
+
+import pytest
+
+from docformatter import Formatter
+
+
+@pytest.mark.integration
+@pytest.mark.parametrize(
+    "args",
+    [
+        ["--tab-width", "4", "--wrap-summaries", "40", "--wrap-descriptions", "40", ""],
+        [
+            "--tab-width",
+            "8",
+            "--wrap-summaries",
+            "40",
+            "--wrap-descriptions",
+            "40",
+            "--make-summary-multi-line",
+            "",
+        ],
+        [
+            "--tab-width",
+            "4",
+            "--wrap-summaries",
+            "40",
+            "--wrap-descriptions",
+            "40",
+            "--black",
+            "",
+        ],
+        ["--tab-width", "4", "--wrap-summaries", "0", "--wrap-descriptions", "40", ""],
+        ["--tab-width", "4", "--wrap-summaries", "40", "--wrap-descriptions", "0", ""],
+        ["--tab-width", "4", "--wrap-summaries", "0", "--wrap-descriptions", "0", ""],
+    ],
+)
+@pytest.mark.parametrize("indentation", ["\t", "\t\t"])
+@pytest.mark.parametrize("with_description", [False, True])
+def test_tab_wrapping_is_independent_of_previous_docstrings(
+    args, test_args, indentation, with_description
+):
+    """Repeated docstrings and files must not consume the configured wrap widths."""
+    widths = (test_args.wrap_summaries, test_args.wrap_descriptions)
+    summary = "Return the requested value with several words in the summary."
+    docstring = '"""' + summary
+    if with_description:
+        docstring += (
+            "\n\n"
+            + indentation
+            + "Describe the returned value with enough words to require wrapping."
+            + "\n"
+            + indentation
+        )
+    docstring += '"""'
+    source = f"def function_0():\n{indentation}{docstring}\n{indentation}pass\n\n"
+    original_args = copy.copy(test_args)
+    formatter = Formatter(test_args, sys.stderr, sys.stdin, sys.stdout)
+
+    expected = formatter._do_format_code(source)
+    assert (test_args.wrap_summaries, test_args.wrap_descriptions) == widths
+    ast.parse(expected)
+    assert all(
+        line.startswith(indentation) for line in expected.splitlines()[1:] if line
+    )
+    if all(width > 0 for width in widths):
+        assert all(
+            len(line.expandtabs(test_args.tab_width)) <= min(widths)
+            for line in expected.splitlines()
+        )
+    if widths[0] == 0:
+        assert summary in expected
+    if with_description and widths[1] == 0:
+        assert (
+            "Describe the returned value with enough words to require wrapping."
+            in expected
+        )
+    assert formatter._do_format_code(expected) == expected
+    # The same Formatter is reused when processing multiple files.
+    assert formatter._do_format_code(source) == expected
+
+    repeated_source = "".join(
+        source.replace("function_0", f"function_{i}") for i in range(13)
+    )
+    repeated_expected = "".join(
+        expected.replace("function_0", f"function_{i}") for i in range(13)
+    )
+    formatted = formatter._do_format_code(repeated_source)
+    assert formatted == repeated_expected
+    ast.parse(formatted)
+    assert formatter._do_format_code(formatted) == formatted
+    assert (test_args.wrap_summaries, test_args.wrap_descriptions) == widths
+
+    # A preceding tab-indented file must not affect a space-indented file.
+    space_source = source.replace("\t", "    ")
+    fresh_formatter = Formatter(original_args, sys.stderr, sys.stdin, sys.stdout)
+    assert formatter._do_format_code(space_source) == fresh_formatter._do_format_code(
+        space_source
+    )