# Elixir — CWE-407 Diamond Recursion Scan: CLEAN

## Scan Date
2026-03-29

## Targets Checked

### 1. Behaviour/callback verification (`Module.Behaviour`)
- **File:** `lib/elixir/lib/module/behaviour.ex`, `check_behaviours_and_impls`
- **Mechanism:** Calls `behaviour.behaviour_info(:callbacks)` — returns a precomputed
  list from the compiled BEAM module. No recursive traversal of the behaviour graph.
- **Result:** CLEAN.

### 2. Protocol consolidation (`lib/elixir/lib/protocol.ex`)
- **Mechanism:** Protocol dispatch uses `__impl__/1` which is compiled into the
  protocol module as a direct function call — O(1) dispatch.
- `Protocol.consolidate/2` iterates `impls` list linearly — no recursive traversal.
- **Result:** CLEAN.

### 3. Import deduplication (Erlang layer, `elixir_import.erl`)
- **File:** `lib/elixir/src/elixir_import.erl`, `ensure_no_duplicates` (line 225)
- `lists:member({Name, Arity}, Acc)` in a fold — O(N²) over import list.
- **N is bounded:** import lists are typically ≤100 entries per module, no diamond
  graph structure. This is a minor quadratic scan, not an exponential diamond defect.
- **Result:** Not CWE-407 (bounded, not graph-recursive).

### 4. Macro expansion / `@impl` checking
- **File:** `lib/elixir/lib/module/parallel_checker.ex`
- `defining?/2` uses `Enum.any?` over a waiting list — bounded by concurrent module
  compilation queue, not a type hierarchy depth.
- **Result:** CLEAN for diamond recursion.

### 5. Erlang runtime module loading
- Elixir relies on Erlang/OTP module loading which tracks loaded modules in a
  global `code_server` ETS table — O(1) lookup.
- **Result:** CLEAN.

## Conclusion

No CWE-407 diamond recursion defects found in Elixir. Behaviour callbacks use
precomputed BEAM metadata; protocol dispatch is compiled to direct calls; module
loading uses ETS-backed sets.
