Symfony Branch Cascade Merge

Merges each maintained branch into the next one, from oldest to newest.

Progress checklist

• Step 0: Pre-flight checks
• Step 1: Fetch maintained branches and pull them
• Step 2: Cascade merge loop

Confirmation rule

Whenever the skill says "Wait for confirmation", treat anything other than an explicit affirmative as no: stop and ask the user how they want to proceed.

Step 0 — Pre-flight checks

git status --porcelain --untracked-files=no

If any output, stop:

"The working tree is not clean. Please commit or stash your changes first."

Step 1 — Fetch maintained branches and pull them

1a. Get the branch list

curl -s https://symfony.com/releases.json

Read maintained_versions. It is already sorted oldest → newest (e.g. ["6.4", "7.4", "8.0", "8.1"]). Store as BRANCHES.

1b. Pull every branch

For each branch in BRANCHES:

git checkout <branch>
git pull --ff-only origin <branch>

Using --ff-only ensures local branches haven't diverged from origin. If the pull fails, stop and report the error.

Step 2 — Cascade merge loop

For each consecutive pair (SOURCE, TARGET) in BRANCHES:

2a. Merge

git checkout <TARGET>
composer up
git merge <SOURCE>

Three outcomes are possible:

• Already up-to-date: print "✓ <TARGET> already up-to-date with <SOURCE>" and skip to the next pair.
• Clean merge (no conflicts): git creates the merge commit automatically. Proceed directly to step 2c.
• Conflicts: proceed to step 2b.

2b. Resolve conflicts (only when git reports conflicts)

List conflicts:

git diff --name-only --diff-filter=U

Read each conflicted file, resolve it, then git add it. When all are resolved:

git commit --no-edit

Conflict resolution rules

Structural divergence across major versions

A newer major may have removed deprecated classes, attributes, or config formats (e.g. TaggedLocator, XML DI config), raised the minimum PHP version, or refactored shared logic into a trait or a new utility class. When merging across such a boundary:

• Remove test methods marked @group legacy / #[Group('legacy')] for deprecations the new major dropped, and any test/fixture/import that references a removed symbol (otherwise it fatals on the TARGET).
• Each major raises the minimum PHP (min PHP per branch in releases.json min_php_requirements: 6.4=8.1, 7.4=8.2, 8.0=8.4). Code merged from SOURCE that branches on or polyfills a PHP below the TARGET's minimum (\PHP_VERSION_ID < ... guards, or function_exists() / class_exists() fallbacks for now-always-available symbols) is dead on the TARGET and can be collapsed to the modern path. The TARGET usually dropped it already, so prefer its version; clean up only where SOURCE's old-PHP code lands somewhere the TARGET had not simplified.
• Prefer the TARGET branch's approach for any refactored idiom.
• Fastest sanity check: look at how the downstream branch (one already past this divergence, e.g. 8.2 while resolving on 8.0) resolved the same files, and match it.

After resolving, show git diff HEAD~1 (first parent of the merge commit, i.e. the previous TARGET state) and wait for the user to confirm the resolution looks correct before proceeding.

2c. Run tests for affected components

Extract component, bridge, and bundle names from changed files:

git diff --name-only HEAD~1..HEAD

Paths look like src/Symfony/{Component,Bridge,Bundle}/<NAME>/.... Deduplicate, then run tests for each:

./phpunit src/Symfony/Component/<NAME>
./phpunit src/Symfony/Bridge/<NAME>
./phpunit src/Symfony/Bundle/<NAME>

For files under src/Symfony/Contracts/, run the single shared test suite:

./phpunit src/Symfony/Contracts

Ignore files outside these directories (root configs, .github/, etc.): they don't have component-level test suites.

If tests fail or report PHPUnit deprecations (the PHPUnit version may differ between branches), first check whether the failure is pre-existing: run the same test on the TARGET branch before the merge (git stash && git checkout HEAD~1 or check CI). Only fix failures introduced by the merge:

1. Analyze and fix the code, including any PHPUnit deprecation notices.
2. Commit the fix: [<ComponentName>] Fix merge conflict resolution.
3. Re-run failing tests until green and deprecation-free.

Report any pre-existing failures to the user without attempting to fix them.

2c-bis. Run the repo's static-analysis / hardening checks

If the repo ships custom static analysis (this one has .github/sa-tools/ with PHPStan rules and check-hardening-tests.php), the merge carries those rules into the TARGET, where they now apply to the TARGET's own code. Newer-branch code can trip rules the SOURCE introduced but never had to satisfy. Run them:

php .github/sa-tools/check-hardening-tests.php
# and the custom PHPStan rules, as wired in .github/workflows/static-analysis.yml

Fix the branch-specific gaps (e.g. add ['allowed_classes' => …] to a bare unserialize(), add an instanceof \Stringable guard to a string-property __unserialize(), or add the missing regression test). These gaps are not introduced by the merge, but the merge makes the checks apply — so they must be green before pushing. Confirm scope with the user before a large hardening pass.

Beware false positives: untracked nested vendor/ dirs and the local PHP extension set (a missing extension falls back to a possibly-outdated polyfill) can produce findings/failures that do not exist on a clean checkout / CI.

2d. Ask for confirmation before pushing

Show:

Merge: <SOURCE> → <TARGET>
Affected: <component list>
Tests: all passing

Commits since origin/<TARGET>:
git log --oneline origin/<TARGET>..<TARGET>

Ready to push? (yes / no)

Wait for confirmation. The user may make changes themselves before confirming.

2e. Push and continue

git push origin <TARGET>

If the push fails, stop and report the error.

Print "✓ <SOURCE> → <TARGET> done." and continue to the next pair.

Final summary

All merges complete:
  6.4 → 7.4  ✓
  7.4 → 8.0  ✓
  8.0 → 8.1  ✓

Gotchas

• CHANGELOG.md conflicts are the most common; entries must be kept from both sides, never dropped.
• A merge can introduce test failures even without conflicts, because behavior from the older branch may be incompatible with newer code. Always run tests.
• A clean (no-conflict) merge still needs verification, not just a commit: auto-merged test metadata (docblock vs attribute), security-guard slot indices, and CI version pins can each be wrong even when git reports no conflict.
• Some components have slow test suites. Only run tests for components with changed files, not the entire project.

Error handling

• Never force-push or rewrite history.
• Never use --no-verify on commits.
• Never auto-recover from a failed git push or git pull. Stop and hand control back to the user.
• Never parallelize the cascade or run branches concurrently (e.g. via subagents): each merge depends on the previous one and shares the git working tree. Run strictly oldest to newest, one at a time.