Chore: Pin ruff rule selection

[ModeSevenIndustrialSolutions]

Why

This repo runs the ruff hook with no ruff configuration, so it applies whatever ruff's default rule set happens to be. That default is not stable across releases — verified directly:

$ ruff 0.15.22 check --show-settings --isolated
 59 rules across  2 categories (E, F)

$ ruff 0.16.0 check --show-settings --isolated
413 rules across 38 categories

A 7× expansion in a patch-level bump. The routine autoupdate that crossed it broke 15 repos in this org simultaneously on untouched code — including this one, where #146 is blocked on 5 violations.

What

[lint]
select = ["E", "W", "F", "I", "B", "C4", "UP"]
ignore = ["E501", "B008"]

Not invented — this is the de facto house style, a superset in 13 of the 16 org repos that already pin their rules.

A standalone .ruff.toml because this repo has no pyproject.toml.

Selecting these categories switches every other rule off — that is the point. Adopting them becomes a deliberate, reviewed change rather than a side effect of a version bump.

line-length and target-version are left unset on purpose — both would change behaviour rather than pin it (target-version alters which pyupgrade rules fire). Standardising those is separate work.

Effect on #146

All 5 blocking violations fall outside the pinned set and cease to exist:

Rule	Count	In core-7?
EXE001	2	No — EXE not selected
PIE810	1	No — PIE not selected
BLE001	1	No — BLE not selected
SIM115	1	No — SIM not selected

The last two were the ones needing a judgement call: BLE001 wraps a tomllib.load, and SIM115 flags the emit() helper's conditional file handle (open(...) if target else sys.stdout), which already has correct try/finally cleanup and simply cannot be expressed as a plain context manager. This removes the need to contort either.

Validation

• No code changes needed — verified clean under the pinned set with ruff 0.16.0 against the files the hook selects
• ruff check --show-settings confirms enabled categories drop from 38 to B C E F I UP W
• pre-commit run --all-files → all hooks pass

[Copilot]

Pull request overview

Adds an explicit Ruff configuration file to pin the enabled lint rule set, preventing Ruff’s evolving defaults from causing unexpected lint failures on version bumps.

Changes:

• Introduces .ruff.toml with an explicit [lint].select set (E, W, F, I, B, C4, UP) and targeted ignores (E501, B008).
• Adds lint.per-file-ignores for tests/**/*.py to reduce test-only noise when the selected ruleset is widened later.

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[tykeal]

🤖 Dependamerge
Approved this pull request ✅

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

.ruff.toml:41

• The file currently ends with a whitespace-only line, which will be flagged by the existing trailing-whitespace pre-commit hook. Remove the trailing whitespace/extra blank line so the repo stays clean under pre-commit.

"tests/**/*.py" = ["S101", "ARG", "PLR0913", "PLR0917", "PLR2004"]

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (2)

.ruff.toml:18

• The comment text "Pinning does not decline the unselected rules" is misleading/awkward here: with a select list, Ruff disables all unselected rules, so this can read as if unselected rules still run. Reword to make it explicit that unselected rules are switched off, and that adding more rules later is a deliberate config change.

# Pinning does not decline the unselected rules.  It makes adopting them
# a deliberate, reviewed change instead of a side effect of a version
# bump.

.ruff.toml:24

• "de-facto" is typically written as "de facto" (no hyphen) in standard usage, including attributive use.

# The de-facto standard across this organisation: present as a superset