Composer Upgrade

Composer Upgrade

Upgrade Workflow

Follow this sequence when upgrading a PHP project:

1. Check for security issues → composer audit — fixes here are highest priority
2. Identify what's outdated → composer outdated --format=json
3. Prioritize — packages with CVEs AND outdated go first; see [references/audit.md](references/audit.md)
4. Diagnose blockers → composer why-not vendor/package version — note any sub-packages blocking the update
5. Trace dependencies → composer why vendor/package
6. Update packages → composer update vendor/package — if blocked, include identified blockers: composer update vendor/package blocker/one blocker/two
7. Test
8. Harden constraints → composer bump (applications only)
9. Re-audit → composer audit to confirm all advisories are resolved

See [references/commands.md](references/commands.md) for full flag reference, including global flags for non-interactive use (--no-interaction --no-progress --no-ansi). See [references/upgrade-workflow.md](references/upgrade-workflow.md) for detailed strategies, including merge conflict resolution. See [references/audit.md](references/audit.md) for security audit details, severity tiers, and how to build a prioritized package list.

Resolving composer.lock Merge Conflicts

When composer.lock has a merge conflict, use scripts/diff_lock.py to compare both sides and generate the commands needed to reconcile them.

During an active merge conflict:

# Compare HEAD vs MERGE_HEAD automatically and output composer commands
python3 scripts/diff_lock.py --conflict

# Human-readable summary of what changed
python3 scripts/diff_lock.py --conflict --format=summary

Compare any two branches or files:

python3 scripts/diff_lock.py main:composer.lock feature-branch:composer.lock
python3 scripts/diff_lock.py HEAD:composer.lock MERGE_HEAD:composer.lock
python3 scripts/diff_lock.py old.lock new.lock

The script outputs composer require / composer remove commands that move packages from the source state to the target state. Run the generated commands, then commit the result.

See [references/upgrade-workflow.md](references/upgrade-workflow.md) — "Workflow: Merge Conflict in composer.lock" — for the full step-by-step process.

Core Commands

See [references/commands.md](references/commands.md) for full flag reference and version constraint quick reference.

composer outdated

composer outdated --format=json           # preferred when parsing output (fewer tokens)
composer outdated --direct --format=json  # only direct deps

Red = major bump (breaking changes likely). Yellow = minor/patch (safe). ! = not semver-safe.

composer why-not

composer why-not vendor/package 2.0      # what prevents this upgrade
composer why-not php 8.2                 # what blocks a PHP version bump

Output shows the dependency chain: which packages require conflicting versions.

composer why

composer why vendor/package              # which installed packages depend on this one

composer update

composer update vendor/package --no-interaction --no-progress --no-ansi
composer update vendor/package --dry-run --no-interaction --no-ansi   # preview first

# If blocked, first identify which sub-dependencies are preventing the update:
composer why-not vendor/package 2.0
# Then include only those specific blockers in the update command:
composer update vendor/package blocker/one blocker/two --no-interaction --no-progress --no-ansi

Common Patterns

"Why can't I update X?"

composer why-not vendor/package 3.0

Read the output to find which package constrains it, then check if that constraining package itself can be updated.

"What's blocking my PHP version upgrade?"

composer why-not php 8.2

Lists every package that lacks a php: ^8.2 constraint, sorted by most blocking.

"Safe incremental upgrade"

Prefer updating direct dependencies one at a time with --dry-run first:

composer update vendor/package --dry-run --no-interaction --no-ansi
composer update vendor/package --no-interaction --no-progress --no-ansi

If blocked, use composer why-not to identify the specific packages preventing the update, then include only those in the update command:

composer why-not vendor/package 2.0
# → reveals blocker/one and blocker/two are preventing the update
composer update vendor/package blocker/one blocker/two --no-interaction --no-progress --no-ansi

Bumping a major version constraint

Prefer composer require over hand-editing composer.json — it updates the constraint and resolves the lock in one step:

composer require vendor/package:"^3.0" --dry-run --no-interaction --no-ansi
composer require vendor/package:"^3.0" --no-interaction --no-progress --no-ansi

For risky upgrades (auth, permissions, database layers), use a dual constraint to test before committing:

# Allow both old and new major versions while testing
composer require vendor/package:"^2.5.0|^3.0" --no-interaction --no-progress --no-ansi
# If tests pass, lock in the new version:
composer require vendor/package:"^3.0" --no-interaction --no-progress --no-ansi

See [references/upgrade-workflow.md](references/upgrade-workflow.md) — "Techniques for Major Version Upgrades" — for more detail.

Hardening constraints after upgrading (applications)

composer bump                  # raise lower bounds in composer.json to installed versions
composer bump --dev-only       # only require-dev (safe for libraries too)

Before: "symfony/console": "^6.0" → After: "symfony/console": "^6.4.3" (the ^ is preserved, so future minor/patch upgrades still work).

See [references/commands.md](references/commands.md) for auto-bump config and full flag reference.

> Applications only: Do not run composer bump (without --dev-only) on libraries — it narrows constraints in ways that break downstream consumers.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: peterfox
• Source: peterfox/agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.