# Nim — CWE-407 Diamond Recursion Scan: CLEAN

## Scan Date
2026-03-29

## Targets Checked

### 1. Object type inheritance (`isObjectSubtype`, `sigmatch.nim`)
- **File:** `compiler/sigmatch.nim`, lines 619–636
- **Mechanism:** Single-inheritance `while t != nil: t = t.baseClass` chain.
  Nim objects have exactly one parent — no diamond possible.
- **Result:** CLEAN (single-parent chain, O(D) linear).

### 2. Concept matching (`concepts.nim`)
- **File:** `compiler/concepts.nim`
- **Guard:** `MatchCon` carries `marker: initHashSet[ConceptTypePair]()` —
  used to prevent infinite recursion in mutual-concept matching.
- **`conceptsMatch`:** Compares concept bodies structurally; `processConcept`
  uses the HashSet marker for cycle detection.
- **Result:** CLEAN — HashSet visited guard present.

### 3. Module dependency tracking (`deps.nim`)
- **File:** `compiler/deps.nim`, lines 282–286
- **Guard:** `seenFiles = initHashSet[string]()` with `containsOrIncl`.
- **Result:** CLEAN.

### 4. Type traversal in `types.nim`
- **File:** `compiler/types.nim`, line 1352
- Uses `seen = initIntSet()` with `containsOrIncl(seen, result.id)` for type
  alias chain traversal.
- **Result:** CLEAN.

### 5. AST cycle detection (`trees.nim`)
- **File:** `compiler/trees.nim`, `cyclicTreeAux`
- Uses `visited: seq[PNode]` (a stack, not a set) with linear `for v in visited: if v == n`
  check — O(V) per node, O(V²) total.
- **However:** This is DFS stack semantics (push on enter, pop on exit), correct for
  cycle detection in trees. `cyclicTree` is only called from `vm.nim` after macro
  expansion to validate the output — not in a hot compilation path.
- N is bounded by macro output AST size, not by type hierarchy depth. Not a diamond
  recursion issue.
- **Result:** Not CWE-407 (bounded, correct algorithm for stack-based DFS).

## Conclusion

No CWE-407 diamond recursion defects found in Nim. Object inheritance is single-parent;
concept matching uses a HashSet guard; module dependency tracking uses a HashSet.
