Skip to content

Fall back to the default configuration when sources share no project root - #5386

Merged
cobaltt7 merged 5 commits into
psf:mainfrom
shashb27:fix/5379-no-common-project-root
Sep 24, 2026
Merged

Fall back to the default configuration when sources share no project root#5386
cobaltt7 merged 5 commits into
psf:mainfrom
shashb27:fix/5379-no-common-project-root

Conversation

@shashb27

@shashb27 shashb27 commented Sep 3, 2026 •
edited by cobaltt7
Loading

Copy link
Copy Markdown
Contributor

Description

Closes #5379
Closes #5422

Fixes the crash in #5379: when the given sources share no common parent directory — for example, they live on different drives on Windows — find_project_root raised ValueError: max() iterable argument is empty during CLI startup, before any file was formatted.

This implements the option @cobaltt7 preferred in the issue discussion: treat the situation as no config found rather than an error.

  • find_project_root returns (None, None) when the sources' parent sets do not intersect, instead of crashing.
  • No project-level pyproject.toml is discovered in that case; the user-level config applies as usual, otherwise Black's defaults are used.
  • A warning is printed (No project root could be identified: ... Pass --config ... or --quiet ...), silenced by passing --config explicitly or by --quiet. (The issue comment mentioned a --silent flag; Black's closest equivalent is --quiet.)
  • Formatting continues.

One structural point that the "no config found" framing alone doesn't cover: the project root is not used only for config discovery — it also anchors gitignore handling, --exclude/--force-exclude matching, and the symlink-outside-root guard in get_sources/gen_python_files, and child.relative_to(root) can never work across drives with a single root. So when no common root exists, this PR falls back to a per-source root: each top-level source (its directory, for files) acts as the root for its own discovery/exclusion handling. Same-drive invocations are completely unchanged.

Note #5385 implements the alternative route from the same comment (a usage error). Whichever route the maintainers prefer is fine by me — the per-source-root fallback here is also what lets formatting continue when --config is passed explicitly, which that comment asked for from the error route as well. Happy to rebase, adjust, or reshape this PR either way.

Checklist

  • The change is adequately tested (new tests cover the (None, None) return, config discovery skipping the project root, the warning and its --config/--quiet gating, and end-to-end formatting with per-source roots; verified on Windows against real cross-drive paths, where the original crash reproduces on main).

Refs #5379

shashb27 and others added 3 commits September 2, 2026 22:39
@shashb27
Fall back to the default configuration when sources share no project …
1b8ea88 
…root

Sources on different Windows drives share no common parent directory,
so find_project_root crashed with 'ValueError: max() iterable argument
is empty' during CLI startup. Following the approach preferred in the
issue discussion, find_project_root now returns (None, None) for such
inputs: no project configuration is discovered, a warning pointing at
--config / --quiet is emitted, and formatting continues, with each
source serving as its own root for exclusion, symlink, and gitignore
handling.

Refs psf#5379
@shashb27
Add changelog entry for psf#5386
7987b37
@pre-commit-ci
[pre-commit.ci] auto fixes from pre-commit.com hooks
b8a3bb7 
for more information, see https://pre-commit.ci
This was referenced Sep 3, 2026
Closed
Closed
@github-actions

github-actions Bot commented Sep 16, 2026 •
edited
Loading

Copy link
Copy Markdown
Contributor

diff-shades results comparing this PR (84fdd7c) to main (2b96e28):

--preview style: no changes

--stable style: no changes

What is this? | Workflow run | diff-shades documentation

cobaltt7
cobaltt7 reviewed Sep 21, 2026
View reviewed changes
Comment thread CHANGES.md Resolved
@cobaltt7

cobaltt7 commented Sep 24, 2026

Copy link
Copy Markdown
Collaborator

Thank you!

@cobaltt7
cobaltt7 merged commit 8d5a2d9 into psf:main Sep 24, 2026
57 checks passed
luketainton pushed a commit to luketainton/luke_instant-msg-api that referenced this pull request Oct 5, 2026
renovate[bot] @luketainton
chore(deps): update dependency black to <26.10.1,>=26.10.0 (#290)
5cf1d34 
This PR contains the following updates:

| Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
| [black](https://github.com/psf/black) ([changelog](https://github.com/psf/black/blob/main/CHANGES.md)) | `<26.5.2,>=26.5.1` → `<26.10.1,>=26.10.0` | ![age](https://developer.mend.io/api/mc/badges/age/pypi/black/26.10.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/black/26.5.1/26.10.0?slim=true) |

---

### Release Notes

<details>
<summary>psf/black (black)</summary>

### [`v26.10.0`](https://github.com/psf/black/blob/HEAD/CHANGES.md#Version-26100)

[Compare Source](psf/black@26.5.1...26.10.0)

##### Stable style

- `--line-ranges` no longer inserts an empty line after a docstring when the range
  covers only the docstring itself ([#&#8203;5312](psf/black#5312))
- Fix `# fmt: skip` on a bracketed ternary turning the surrounding tuple into a call
  ([#&#8203;5464](psf/black#5464))
- Fix crash when `# fmt: skip` is placed on a one-line function or class with PEP 695
  type parameters ([#&#8203;5429](psf/black#5429))
- Fix an inline comment after the closing bracket of optional parentheses being moved
  inside the parentheses when the parenthesized expression contains own-line comments
  ([#&#8203;5395](psf/black#5395))
- Fix unparseable output when `# fmt: skip` is placed on a bracket of an `if`, `while`,
  `for`, or `with` header ([#&#8203;5401](psf/black#5401), [#&#8203;5405](psf/black#5405))
- Fix crash when formatting parenthesized expressions with multiple inline comments and
  `# fmt: skip` ([#&#8203;5414](psf/black#5414))
- Fix parsing Jupyter notebook assignment magics when non-ASCII characters appear
  earlier on the line ([#&#8203;5381](psf/black#5381))
- Preserve blank lines that come immediately before a `# fmt: on` comment ([#&#8203;5300](psf/black#5300))
- Keep the parentheses around the target of an annotated assignment (e.g.
  `(x): int = 5`), which prevent CPython from including the name in `__annotations__`
  ([#&#8203;5321](psf/black#5321))
- Stop treating a t-string in docstring position as a docstring (e.g. `t"  spam  "` as
  the first statement of a module, class or function) ([#&#8203;5287](psf/black#5287))
- Fix unparseable output for a t-string whose replacement field contains a quote (e.g.
  `t'\'{a["b"]}\''`) ([#&#8203;5265](psf/black#5265))
- Fix unparseable output for a triple-quoted string whose body ends in an
  already-escaped double quote (e.g. `'''\'''\"'''`) ([#&#8203;5262](psf/black#5262))
- Fix `--skip-magic-trailing-comma` dropping the trailing comma from a split
  single-element tuple used as a lambda parameter default ([#&#8203;5246](psf/black#5246))
- Fix unstable formatting when an inline comment sits on optional parentheses (e.g. a
  parenthesized assert message) ([#&#8203;5241](psf/black#5241))
- Fix `--skip-magic-trailing-comma` dropping the trailing comma of a one-element
  subscript (`a[x,]`) when the line is long enough to be split and contains a power
  operator ([#&#8203;5272](psf/black#5272))
- Fix crash when a standalone comment sits between tokens of a comprehension or lambda
  ([#&#8203;5144](psf/black#5144))
- Fix inline comments on a bracket inside a comprehension being dropped ([#&#8203;5330](psf/black#5330))
- Respect the magic trailing comma in a PEP 695 type parameter list containing a
  `*TypeVarTuple` or `**ParamSpec` ([#&#8203;5244](psf/black#5244))
- Fix crash when a comment-only `# fmt: off`/`# fmt: on` block is followed by a `with`
  statement after another standalone comment ([#&#8203;5189](psf/black#5189))
- Fix a crash when splitting `case case if ...` match patterns at very small line
  lengths ([#&#8203;5147](psf/black#5147))
- Fix multiline docstring indentation when leading tabs are used inside indented
  docstrings ([#&#8203;5148](psf/black#5148))
- Respect `# fmt: skip` on a line that opens a bracket (e.g.
  `from x import (  # fmt: skip`) when a standalone comment is among the bracket's
  contents ([#&#8203;5161](psf/black#5161))
- Fix an AST safety error when separate `# type: ignore` comments in a parenthesized
  attribute chain were merged onto one physical line ([#&#8203;5297](psf/black#5297))
- Preserve comments and blank lines outside requested ranges when formatting with
  `--line-ranges` ([#&#8203;5175](psf/black#5175))
- Fix crash when `# fmt: skip` is used on one-line `async def`, `async with`, and
  `async for` statements containing a semicolon ([#&#8203;5311](psf/black#5311))
- Stop converting form feeds or other similar characters in docstrings into newlines
  ([#&#8203;5461](psf/black#5461))
- Fix `--skip-source-first-line` turning the skipped line's CRLF ending into `\r\r\n`
  when reformatting a file with CRLF line endings ([#&#8203;5438](psf/black#5438))

##### Preview style

##### New preview features

- Add missing blank lines after classes whose last method has an ellipsis body ([#&#8203;5439](psf/black#5439))
- Split only the brackets holding a magic trailing comma when more trailers follow them
  (e.g. stop splitting inside the `[2]` of `[1,][2](3)`) ([#&#8203;5448](psf/black#5448))
- Keep dictionary keys containing operators together on one line when the value can be
  wrapped onto a new line instead ([#&#8203;5435](psf/black#5435))
- Remove redundant parentheses around individual variables in unpacking targets (e.g.
  `for (x), (y) in points:` becomes `for x, y in points:`) ([#&#8203;5416](psf/black#5416))
- Normalize uppercase `T` prefixes on t-strings to lowercase ([#&#8203;5425](psf/black#5425))
- Remove redundant parentheses around generator expressions ([#&#8203;5304](psf/black#5304), [#&#8203;5369](psf/black#5369))
- Preserve two blank lines before a top-level class starting inside a `# fmt: off` block
  after an import ([#&#8203;5238](psf/black#5238))
- Fix unnecessary parentheses around short right-hand expressions in indexed assignments
  (e.g. `x[key] = expr`) ([#&#8203;5095](psf/black#5095))
- Parenthesize tuple expressions in `yield` statements for consistency with function
  calls and returns ([#&#8203;5170](psf/black#5170))
- Stop splitting between a variable and its operator (`not in`, `==`, `is`, ...) when
  the right-hand side is a bracketed expression, and instead split inside the brackets
  ([#&#8203;5135](psf/black#5135))
- In `.pyi` stub files, enforce a blank line after a function or method that has a
  docstring-only body when another comment or statement follows it ([#&#8203;5158](psf/black#5158))

##### Updates to existing preview features

- Fix crash in stub files when `# fmt: skip` is placed on a function in a group of
  same-name decorated functions (e.g. `@overload`s or a property setter) ([#&#8203;5430](psf/black#5430))
- Keep the parentheses around a lambda used as the iterable of a comprehension (e.g.
  `[x for x in (lambda: 0) if x]`) ([#&#8203;5176](psf/black#5176), [#&#8203;5200](psf/black#5200))

##### Updates to existing unstable features

- Do not treat multi-line expressions with merged strings and trailing `# type: ignore`
  comments as single-line unsplittable expressions ([#&#8203;5466](psf/black#5466))
- Fix duplicated inline comment when stripping the parentheses around a string or
  merging a backslash-continued string on the same line ([#&#8203;5449](psf/black#5449))
- Split long stringified return annotations even when the function has parameters
  ([#&#8203;5427](psf/black#5427))
- Don't hug brackets when doing so would join two `# type: ignore` comments onto one
  line ([#&#8203;5271](psf/black#5271))
- Fix a crash when `# type: ignore` is lost during formatting of a long parenthesized
  string ([#&#8203;5329](psf/black#5329))
- Fix only the first part of an implicitly concatenated unmergeable string (e.g.
  `r"..." r"..."`) being wrapped in parentheses ([#&#8203;5434](psf/black#5434))

##### Configuration

- Add support for `NO_COLOR` environment variable to disable ANSI output ([#&#8203;5129](psf/black#5129))
- Remove spurious target version warning when runtime version is included in a
  `--target-version` flag ([#&#8203;5167](psf/black#5167))
- Fix `--force-exclude` not excluding files whose path contains `..` (e.g.
  `black ../generated/file.py` run from a subdirectory) ([#&#8203;5471](psf/black#5471))
- Fall back to the default configuration, with a warning, when the given sources share
  no common project root (e.g. they are on different drives on Windows) instead of
  crashing ([#&#8203;5386](psf/black#5386))
- Fix loading a stale cached `pyproject.toml` path when `--code` is used from different
  working directories in the same process ([#&#8203;5152](psf/black#5152))
- Add validation for `--line-ranges` values ([#&#8203;5107](psf/black#5107))
- Ignore empty cache files instead of raising an `EOFError` ([#&#8203;5192](psf/black#5192))
- Reject non-string `include` and `force-exclude` values in `pyproject.toml` ([#&#8203;5193](psf/black#5193))
- Validate `BLACK_NUM_WORKERS` values and report invalid values as usage errors instead
  of crashing ([#&#8203;5211](psf/black#5211))
- Ignore permission errors when reading cache ([#&#8203;5258](psf/black#5258))

##### Packaging

- Reduce the size of Linux standalone binaries by stripping debug symbols during the
  PyInstaller release build ([#&#8203;5223](psf/black#5223))
- Black is now released using GitHub
  [Immutable Releases](https://docs.github.com/code-security/concepts/supply-chain-security/immutable-releases)
  ([#&#8203;5296](psf/black#5296))

##### Performance

- Fix superlinear runtime growth with the number of input files ([#&#8203;5450](psf/black#5450))
- Improve performance on strings containing many consecutive backslashes ([#&#8203;5163](psf/black#5163))
- Improve performance on files with many `# fmt: skip`/`# fmt: off`/`# fmt: on` comments
  ([#&#8203;5169](psf/black#5169), [#&#8203;5190](psf/black#5190), [#&#8203;5232](psf/black#5232))
- Improve performance on long calls and collections ([#&#8203;5177](psf/black#5177))
- Improve performance on multiline strings inside large collections (e.g. a dict literal
  with triple-quoted strings as values) ([#&#8203;5188](psf/black#5188))
- Improve performance on files with many soft keywords (e.g. `match`/`case` blocks)
  ([#&#8203;5186](psf/black#5186))
- Improve performance on long semicolon-separated statements (in the stable style) and
  large dict literals (in `--preview`) ([#&#8203;5184](psf/black#5184))
- Improve performance of `--line-ranges` on files with many sibling blocks (a long
  `if`/`elif` chain, a `match` with many cases, or many top-level definitions) ([#&#8203;5213](psf/black#5213))
- Improve performance on deeply nested bracketed expressions ([#&#8203;5171](psf/black#5171), [#&#8203;5242](psf/black#5242))
- Improve performance on lists and subscripts holding one long expression without
  operators (e.g. a long run of implicitly concatenated strings inside `[]`) ([#&#8203;5239](psf/black#5239))
- Improve performance on deeply chained operations (e.g. a long `a ** b ** c ** ...`
  chain) ([#&#8203;5235](psf/black#5235))
- Improve performance on long `if`/`elif` chains and other compound statements with many
  clauses ([#&#8203;5322](psf/black#5322))
- Improve performance of `string_processing`:
  - when merging implicitly concatenated f-strings containing long string literals
    ([#&#8203;5165](psf/black#5165))
  - when merging long implicitly concatenated strings ([#&#8203;5173](psf/black#5173), [#&#8203;5194](psf/black#5194))
  - when rewriting large nodes (e.g. `"%s ..." % (a, b, c, ...)`) ([#&#8203;5178](psf/black#5178), [#&#8203;5199](psf/black#5199), [#&#8203;5220](psf/black#5220))
  - when splitting long string literals ([#&#8203;5183](psf/black#5183))

##### Output

- Report parser failures using editor-friendly `path:line:column` locations ([#&#8203;5237](psf/black#5237))
- Fix crash when writing formatted code or diffs to a `sys.stdout` that has no `buffer`
  attribute (e.g. in Jupyter notebooks) ([#&#8203;5411](psf/black#5411))
- Report parse failures on Black's own output as internal errors ([#&#8203;5383](psf/black#5383))

##### *Blackd*

- Return HTTP 400 instead of 500 when the `X-Python-Variant` header is empty or has an
  empty entry (e.g. a trailing comma) ([#&#8203;5428](psf/black#5428))
- Allow optional whitespace around comma-separated versions and `pyi` in the
  `X-Python-Variant` header ([#&#8203;5441](psf/black#5441))

##### Integrations

- Remove unused `migrate-black` script ([#&#8203;5319](psf/black#5319))
- Support PEP 440 version specifiers in `tool.black.required-version` for the GitHub
  Action ([#&#8203;5399](psf/black#5399))
- Add outputs (`is_formatted`, `change_count`, `same_count`, `failure_count`) to GitHub
  Action runs ([#&#8203;5408](psf/black#5408))

##### Documentation

- Document `vim-python-pep8-indent`, which provides an `indentexpr` for Black-style
  insert-mode indentation ([#&#8203;5288](psf/black#5288))

</details>

---

### Configuration

📅 **Schedule**: (UTC)

- Branch creation
  - At any time (no schedule defined)
- Automerge
  - At any time (no schedule defined)

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Mend Renovate CLI](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0NC4xMzIuNSIsInVwZGF0ZWRJblZlciI6IjQ0LjEzMi41IiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJ0eXBlL2RlcGVuZGVuY2llcyJdfQ==-->

Reviewed-on: https://git.tainton.uk/luke/instant-msg-api/pulls/290
Co-authored-by: renovate[bot] <renovate-bot@git.tainton.uk>
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@cobaltt7 cobaltt7 cobaltt7 left review comments

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

find_project_root raises ValueError for sources on different Windows drives

2 participants

@shashb27 @cobaltt7