# UNDF: UNDF-2026-000000267
# rustc deeper scan — fulfill.rs CLEAN

**Scan date:** 2026-03-27
**File scanned:**
- `compiler/rustc_trait_selection/src/traits/fulfill.rs`

## Findings

### `fulfill.rs` — CLEAN
`FulfillProcessor::needs_process_obligation` contains:
```rust
_ => (|| {
    for &infer_var in stalled_on {
        if self.selcx.infcx.ty_or_const_infer_var_changed(infer_var) {
            return true;
        }
    }
    false
})()
```
`stalled_on` is a `Vec<TyOrConstInferVar>` representing inference variables a
single obligation is waiting on. This is a scan of one obligation's stall vars —
not a scan of a global registry inside an outer loop over all obligations.
The rustc team already documented and optimized this path (the comment notes
it outperforms `.any()` for small vecs, and the common case of `len == 1` is
handled by a separate fast branch).

`skippable_obligations` uses `take_while` on a single `stalled_on` element —
also intentionally bounded.

No CWE-407 defect.

## Conclusion
`fulfill.rs` is CLEAN beyond previously patched defects.
`rustc-0004` (imports.rs ambiguity_errors Vec scan) remains the only new
defect found in this deeper rustc scan.
