# rustc CWE-407 Wave-2 Deep Scan — CLEAN (beyond 0001–0004)

**Scan date:** 2026-03-29
**Target:** rust-lang/rust (rustc compiler)
**Prior defects:** rustc-0001 (evalstack swap-remove), rustc-0002 (evalstack),
  rustc-0003 (is_target_feature_call_safe Vec scan), rustc-0004 (finalize_imports
  ambiguity_errors Vec scan)
**Crates scanned this wave:**
- `compiler/rustc_resolve/src/` (imports.rs, late.rs, macros.rs, build_reduced_graph.rs,
  rustdoc.rs, check_unused.rs, diagnostics.rs, ident.rs)
- `compiler/rustc_trait_selection/src/` (select/mod.rs, select/candidate_assembly.rs,
  solve/fulfill.rs, dyn_compatibility.rs)
- `compiler/rustc_borrowck/src/` (diagnostics/conflict_errors.rs, polonius/constraints.rs,
  diagnostics/outlives_suggestion.rs)
- `compiler/rustc_middle/src/` (dep_graph/graph.rs, ty/inhabitedness/inhabited_predicate.rs,
  ty/mod.rs, ty/print/pretty.rs)
- `compiler/rustc_passes/src/dead.rs`
- `compiler/rustc_hir_typeck/src/` (fn_ctxt/arg_matrix.rs, fn_ctxt/checks.rs, pat.rs,
  fallback.rs, coercion.rs)
- `compiler/rustc_ast_lowering/src/` (expr.rs, asm.rs, delegation.rs)
- `compiler/rustc_codegen_ssa/src/` (target_features.rs, mir/mod.rs, back/link.rs)

## Findings

### rustc_passes/dead.rs — ignore_variant_stack: Vec<DefId>
`ignore_variant_stack.contains(&ctor_def_id)` at lines 141, 153. This Vec is a
push/truncate scope stack that holds variants from a single match arm's pattern
(`pat.necessary_variants()`). It is bounded by the nesting depth of the match arm
being analyzed, not by the total number of enum variants in the crate. In practice
it never exceeds a handful of entries. Not a CWE-407 defect.

### rustc_middle/dep_graph/graph.rs — TaskDeps::reads: EdgesVec
`task_deps.reads.contains(&dep_node_index)` at line 494. This is an intentional
deliberate hybrid: the code uses a linear scan only for `reads.len() <= LINEAR_SCAN_MAX`
(= 16), then switches to a `read_set: FxHashSet` for larger lists. The constant
LINEAR_SCAN_MAX is chosen so the linear scan is cheaper than a hash lookup for small
sizes. Hybrid dedup is a known optimization pattern, not a defect.

### rustc_middle/ty/inhabitedness/inhabited_predicate.rs — eval_stack: SmallVec<[Ty; 1]>
`eval_stack.contains(&t)` at lines 109, 127. This is a DFS cycle-detection stack
during type inhabitedness checking. The stack depth equals the type nesting depth,
which is bounded in well-formed code. Not a hot path.

### rustc_hir_typeck/fn_ctxt/arg_matrix.rs — stack: Vec<usize>
`stack.contains(&j)` at line 270, inside a cycle-detection loop over argument
compatibility. The stack grows to the length of the compatibility cycle (at most
the number of mismatched arguments). This only runs when argument reordering is
diagnosed, which is an error-reporting path. Not a hot compilation path.

### rustc_hir_typeck/pat.rs — variant_field_idents: Vec<Ident>
`variant_field_idents.contains(&field.ident)` at line 2409, called inside
`.map()` over `fields.iter()`. This is O(F×V) where F = fields in pattern and
V = fields in variant. However, this function (`struct_fn_arg_suggestions`) is
only called to generate a diagnostic suggestion string when a struct pattern is
wrong. Pure error-reporting path.

### rustc_ast_lowering/expr.rs — legacy_args_idx: &[usize]
`legacy_args_idx.contains(&idx)` at lines 452, 473. Called inside loops over
`args.iter()`. Only runs inside `invalid_expr_error`, which is only called when a
legacy const-generic argument error is emitted. Error-reporting path only.

### rustc_codegen_ssa/target_features.rs — RUSTC_SPECIFIC_FEATURES: &[&str]
`RUSTC_SPECIFIC_FEATURES.contains(&base_feature)` at lines 172, 179. The
`RUSTC_SPECIFIC_FEATURES` slice is a small compile-time constant (currently 3 entries:
`crt-static`, `relocation-model`, `code-model`). O(1) in practice.

### All other contains() calls in scanned crates
Resolved to `FxHashSet`, `FxIndexSet`, `BTreeSet`, `HashSet`, bitset types
(`LocalDefIdSet`, `BitSet`), range checks, or flag bitmask tests (`contains()` on
`CodegenFnAttrFlags` is a bitmask AND, O(1)). All O(1).

### Previously-found hot-path patterns (rustc-0001 through rustc-0004)
These defects were found and patched in prior scans. No recurrence detected:
- `evalstack` in `rustc_const_eval` now uses swap_remove instead of index-walking
- `is_target_feature_call_safe` now uses `HashSet`
- `finalize_imports` ambiguity_errors scan now uses a counter

## Conclusion

No new CWE-407 defects found beyond rustc-0001 through rustc-0004. All remaining
`contains()` calls in the scanned hot-path crates use hash-backed structures, bitmask
checks, or are in bounded/error-only paths.
