Verification Loop

Project-aware verification for Elixir/Phoenix. Reads mix.exs and .check.exs to discover tools, test commands, and custom aliases before running anything.

Iron Laws

1. Discover before running — Read mix.exs first; never run mix credo if credo isn't a dependency
2. Prefer ex_check — If :ex_check + .check.exs exists, mix check replaces individual steps
3. Prefer project aliases — If mix ci or composite alias exists, use it over individual steps
4. Run in order — Later steps assume earlier ones pass
5. Ask before E2E tests — Unit tests run automatically; E2E/integration tests need user confirmation
6. NEVER report success without showing actual command output — "should work" is not verification

Step 0: Project Discovery (ALWAYS FIRST)

Read mix.exs — extract deps/0, aliases/0, and cli/0 (for preferred_envs). Also check for .check.exs. See ${CLAUDE_SKILL_DIR}/references/project-discovery.md for full patterns.

Discover tools (deps): :credo, :dialyxir, :sobelow, :ex_check, :excoveralls, :boundary

Discover test commands (aliases + deps):

• Unit: mix test (always), or custom alias like mix test.with_coverage
• E2E: mix playwright.test, mix cypress.run, or similar (check preferred_envs for MIX_ENV)
• Fast E2E: mix playwright.run (skips setup — for re-runs)

Discover composite runner: If .check.exs exists, read it — mix check may handle compile, format, credo, test, dialyzer, sobelow, and more.

Report discovery:

Project tools: compile ✓ | format ✓ | credo ✓ | dialyzer ✓ | sobelow ✓ | ex_check ✓
Test commands: mix test (unit) | mix playwright.test (E2E, MIX_ENV=int_test)
Composite runner: mix check (.check.exs covers: compiler, formatter, credo, dialyzer, sobelow, tests)
Strategy: Running `mix check` then asking about E2E

Verification Sequence

Before using any discovered alias or composite command, confirm it runs:

1. Check the dependency is in mix.lock (not just mix.exs) — deps may not be fetched
2. Run the command — if it fails with "command not found" or dependency error, fall back to individual steps
3. Log the fallback: "mix check failed (ex_check not installed?), falling back to individual steps"

If ex_check installed + .check.exs exists: Try mix check. If it fails, fall back to individual steps.

If composite alias found (e.g., mix ci, mix precommit): Try it. If it fails, fall back to individual steps.

Otherwise (or after fallback): Run individual steps, skipping unavailable tools.

Step 1: Compile

mix compile --warnings-as-errors — always

Elixir 1.20+ (OTP 27+): the compiler's built-in type checker emits type violations / verified bugs as warnings, so --warnings-as-errors now fails the build on them — no Dialyzer needed. If a previously-green build fails after a 1.20 bump, suspect a newly-detected type violation, not a regression. Read the message literally (accepted vs supplied type); it is almost always a real bug. See elixir-idioms/references/elixir-120-type-system.md.

Step 2: Format

mix format --check-formatted — always (auto-fix with mix format if fails)

Step 3: Credo

mix credo --strict — if :credo in deps, else skip

Step 4: Test

mix test --trace — use project test alias if available

Step 5: Dialyzer

mix dialyzer — if :dialyxir in deps, pre-PR only

Step 6: Sobelow

mix sobelow --config — if :sobelow in deps

Skip unavailable tools with: "Credo: ⏭ Not installed"

Step 7: Additional Test Offer

After core verification passes, check if project has additional test commands (E2E, integration, coverage). Ask the user:

Core verification passed. Additional test commands available:
1. mix playwright.test (E2E, MIX_ENV=int_test) — ~5min
2. mix test.with_coverage (unit + coverage report)
Run any of these? [1/2/both/skip]

Respect preferred_envs / cli/0 for correct MIX_ENV on each command.

Quick Reference

Step	Command	Condition
Discovery	Read mix.exs + .check.exs	Always first
Composite	mix check	If :ex_check installed
Compile	mix compile --warnings-as-errors	Always
Format	mix format --check-formatted	Always
Credo	mix credo --strict	:credo in deps
Test	mix test --trace	Always (use alias if exists)
Dialyzer	mix dialyzer	:dialyxir in deps, pre-PR
Sobelow	mix sobelow --config	:sobelow in deps
E2E/Extra	Ask user	If additional test commands found

Usage

1. Run /phx:verify — discovery happens automatically
2. Core checks run in order, adapted to project
3. After pass, offered additional test commands (E2E, coverage)
4. Commit only after all chosen checks pass