Add Github action to run SwiftFormat

[SkylerGodfrey]

Looking to add in SwiftFormat to the project: https://github.com/nicklockwood/SwiftFormat?tab=readme-ov-file#github-actions

[jjpritzl]

Proposal: Use Xcode's built-in swift-format instead of third-party SwiftFormat

Rather than pulling in a third-party tool, we can use Apple's swift-format that ships with Xcode — no extra dependencies needed. It's available via xcrun swift-format.

Recommended approach

Use both of the following together:

1. A local pre-commit git hook that auto-formats Swift files before each commit (fast developer feedback loop).
2. A GitHub Action that runs swift-format lint on PRs as a CI safety net.

Note: This complements the existing SwiftLint workflow — SwiftLint enforces style/linting rules, while swift-format handles code formatting. They work well side by side.

---

1. .swift-format config

Add a .swift-format file at the repo root. Here's a starting point — the team should discuss and customize values like lineLength:

{
  "version": 1,
  "lineLength": 200,
  "indentation": {
    "spaces": 4
  }
}

2. GitHub Action (CI safety net)

.github/workflows/swift-format.yml:

name: swift-format

on:
  pull_request:
    paths:
      - '.github/workflows/swift-format.yml'
      - '.swift-format'
      - '**/*.swift'

permissions:
  contents: read

jobs:
  swift-format:
    runs-on: macos-latest
    steps:
      - uses: actions/checkout@v4
      - name: Lint with swift-format
        run: xcrun swift-format lint --strict -r -p .

3. Local pre-commit hook

git-hooks/pre-commit.swift-format:

#!/bin/bash
RED='\033[0;31m'
GREEN='\033[0;32m'
NC='\033[0m'

echo -e "${GREEN}Running swift-format...${NC}"

REPO_ROOT=$(git rev-parse --show-toplevel)
xcrun swift-format --in-place -r -p "$REPO_ROOT"
FAILED=$?

if [ $FAILED -ne 0 ]; then
    echo -e "${RED}Commit rejected: Swift formatting failed${NC}"
    exit 1
fi

echo -e "${GREEN}✓ Swift files were formatted${NC}"
exit 0

Install with:

ln -sf ../../git-hooks/pre-commit.swift-format .git/hooks/pre-commit

---

Rollout strategy

1. First commit — Run xcrun swift-format --in-place -r -p . across the entire codebase and commit the result as a single, dedicated commit containing only formatting changes. This keeps git blame clean.
2. Separate commit(s) — Add the .swift-format config, GitHub Action workflow, pre-commit hook, and any README updates in their own commit(s), separate from the formatting changes.