ADR-0018: Dual MIT or Apache-2.0 license

• Status: Accepted
• Date: 2026-09-06

Context

ADR-0001 licensed the independent port MIT, matching zlob's own terms. The Ferramenta family review of 2026-09 (decision D5 in sebastian-software/ferramenta#6) settled on MIT OR Apache-2.0 for every family crate that is not itself a port of a differently licensed original. That pairing is the Rust ecosystem's default: MIT keeps the permissive terms this project started from, and Apache-2.0 adds an express patent grant and a contribution clause that corporate consumers ask for. Publishing under only one of the two makes Ferralk the odd dependency in a graph where nearly everything else offers both.

Cargo packages a crate directory, not the repository root, so a license file that only exists at the root is missing from the published .crate tarball.

Decision

Both published crates carry license = "MIT OR Apache-2.0"; a consumer picks either license. The copyright holder is Sebastian Software GmbH. LICENSE-MIT and LICENSE-APACHE live at the repository root and, byte for byte, in crates/ferralk/ and crates/ferralk-glob/; the doctest harness asserts the copies stay identical.

This supersedes the license sentence of ADR-0001. The rest of that decision — independent port, no drop-in claim, zlob credited in the README and NOTICE — is unchanged, and the terms of any third-party notice a ported file carries are unaffected by the license this project offers for its own work.

Consequences

• Contributions are offered under both licenses; a contributor who cannot grant one of them cannot contribute, which is the price of the pairing.
• The Apache-2.0 patent grant now covers consumers, which is the practical reason the family chose the pair.
• Any future port of third-party source keeps its original notice next to the ported file and in NOTICE, exactly as ADR-0001 requires.
• The allowed licenses of the dependency graph are enforced separately, by the deny.toml allow-list rather than by this decision.