# generic-witness-maybe-abi

> Shared generic optional witness dispatch has incompatible mandatory bigint/byte-array payload guards; profile-specific compatibility review.

Canonical: https://nightshade.dicksonwu.xyz/rules/generic-witness-maybe-abi.html
Release: Nightshade 0.1.1 (v0.1.1)

| Field | Value |
| --- | --- |
| Rule ID | `generic-witness-maybe-abi` |
| Severity | low |
| Confidence | low |
| Maturity | experimental |
| Selection | Opt-in |
| Policy intent | not required |
| Default enabled | no |
| Category | Other active opt-ins / Privacy and cryptographic derivations |
| Engine facts used | resolved-source-references, canonical-generic-specializations, resolved-types |
| Release | v0.1.1 |

## Selection and scope

Not selected by default. Select it with `--detectors` or the `detectors` list in nightshade.json. Either one replaces profile selection, so list every rule you want.

```sh
./.nightshade/node_modules/.bin/nightshade ./contracts --detectors generic-witness-maybe-abi
./.nightshade/node_modules/.bin/nightshade detector show generic-witness-maybe-abi
```

The first command runs only this rule; `--detectors` takes a comma-separated list. The second prints the rule's metadata from your installed version.

Severity is review priority. It does not express exploitability or impact. Confidence is detector metadata, not a probability. All built-in rules are experimental.

Compiler scope: the engine supports the pinned profiles 0.28.0, 0.29.0, 0.30.0, 0.31.1, 0.33.0-rc.2, 0.34.0, 0.35.0-rc.1 and 0.35.0, with ZKIR2 by default. Support for this rule can be narrower; the rule documentation below states any narrower scope.

## Corpus checks

Synthetic corpus checks for this rule in the 0.1.1 proof run. A check counts only with compiler acceptance and complete analysis.

| Positive detected | Corrected quiet | Lookalike quiet | Other negative quiet | Incomplete |
| ---: | ---: | ---: | ---: | ---: |
| 1/1 | 1/1 | 1/1 | 0/0 | 0 |

No deviations were recorded for this rule.

These are behavior checks on synthetic fixtures, not a precision or recall estimate. See [evaluation](https://nightshade.dicksonwu.xyz/evaluation.md#synthetic-corpus).

## Rule documentation

From https://github.com/DicksonWu654/nightshade/blob/v0.1.1/docs/detectors/generic-witness-maybe-abi.md at v0.1.1.

Availability: **opt-in ABI compatibility review**, no policy required.
Severity/confidence: **low/high**. Select with
`--detectors generic-witness-maybe-abi`.

Under Compact **0.34.0/ZKIR2**, concrete specializations of one generic witness
dispatch to the same host method without a generic type argument. When its result
is the canonical standard-library `Maybe<T>`, the generated wrapper checks
`value` even when `is_some` is false. A bigint payload and a byte-array payload
cannot use one fixed absent-result placeholder. This rule reports the static
signature relationship, with the declaration, conflicting return types and
source reference sites grouped into one finding per canonical witness template.

```compact
import CompactStandardLibrary;
witness lookup<T>(key: Bytes<4>): Maybe<T>;
export circuit getNumber(key: Bytes<4>): Maybe<Uint<64>> {
  return disclose(lookup<Uint<64>>(key));
}
export circuit getBytes(key: Bytes<4>): Maybe<Bytes<32>> {
  return disclose(lookup<Bytes<32>>(key));
}
```

A shared host handler may distinguish keys, private state, call order or other
context and return the correct typed payload. **This is not evidence that the
handler fails.** Review absent-result handling and the generated witness
signatures. Use distinct host witness names when incompatible result
representations should have independent handlers. `Uint<64>` and `Field` are a
quiet lookalike because their ordinary payload guards both accept `0n`.

The rule requires identical concrete parameter types and known disjoint
bigint/byte-array result representations. Resolved import/type aliases retain
identity; separate concrete module instances and different witness declarations
are kept separate. It describes the entry-reachable source/schema graph, including
constant-dead references and zero-iteration callbacks whose wrappers the qualified
compiler retains. It does not assert a successful invocation or proof feasibility.

The compiler-only distinct-module probe also emits one shared host method spelling.
This initial rule groups only one canonical template: a quiet distinct-instance
control is a scope negative, not evidence of separate dispatch or ABI safety.

## Suppress a match

If a match is intentional, suppress it on the line before with the exact rule ID and a reason of at least eight characters:

```compact
// nightshade-disable-next-line generic-witness-maybe-abi -- Reason this match is intentional
```

Diagnostics cannot be suppressed, and an unmatched directive for a selected rule makes analysis incomplete. See [configuration](https://nightshade.dicksonwu.xyz/configuration.md#suppress-an-intentional-match) for fingerprint suppressions and baselines.

## References

- [Rule source document at v0.1.1](https://github.com/DicksonWu654/nightshade/blob/v0.1.1/docs/detectors/generic-witness-maybe-abi.md)
- [Catalog entry in rules.json](https://nightshade.dicksonwu.xyz/rules.json)
- [All rules](https://nightshade.dicksonwu.xyz/rules.md#privacy-and-cryptographic-derivations)
- [Limitations](https://nightshade.dicksonwu.xyz/limitations.md)