phxtrace

# Call Tracing Build call trees showing how functions are reached from entry points. ## Iron Laws - Never Violate These 1. **Always use `mix xref callers` first** - It's authoritative; grep is fallback only 2. **Stop at entry points** - Controllers, LiveView callbacks, Oban workers, GenServer callbacks 3. **Track visited MFAs** - Prevent infinite loops from circular calls 4. **Extract argument patterns** - Just knowing "who calls" isn't enough; HOW they call matters 5. **Max depth 10** - Deeper trees indicate architectural issues, not useful traces ## When to Build Call Tree (Use Proactively) | Condition | Why Call Tree Helps | |-----------|---------------------| | Unexpected nil/value at runtime | Trace where the value originates | | Bug can't reproduce locally | See all entry points that reach the code | | Changing function signature | Find all callers and their argument patterns | | Incomplete stack trace | Get full path context | | "Where does X come from?" | Visual answer to data flow question | ## Quick Trace Run `mix xref callers MyApp.Accounts.update_user/2` to find all callers. Then read the reported locations to see argument patterns. ## Entry Points (Stop Here) | Pattern | Type | |---------|------| | `def mount/3`, `def handle_event/3` | LiveView | | `def index/2`, `def show/2`, `def create/2` | Controller | | `def perform(%Oban.Job{})` | Oban Worker | | `def handle_call/3`, `def handle_cast/2` | GenServer | ## Delegate to call-tracer Agent For full recu...