Explore introducing `semgrep` to enforce stricter coding guidelines

[tnull]

Recent bugs and discussions highlighted that we may want to enforce some stricter (automated) code checks.

In particular, we may want to introduce semgrep to:

• Require any non-lock()ing unwrap() to be accompanied by a // safety: comment.
• Disallow usage of SystemTime::now / Instant::now / Instant::elapsed_since to maintain WASM compatibility.

Similar approaches are currently applied by other projects in the rust-bitcoin ecosystem, related usages are for example:

• Introduce semgrep rust-bitcoin/rust-bech32#153
• https://github.com/fedimint/fedimint/blob/master/.config/semgrep.yaml

(cc @tcharding)

[tcharding]

@dpc should be credited with finding semgrep not me :)

Require any non-lock()ing unwrap() to be accompanied by a // safety: comment.

Could disallow any non-lock()ing unwraps altogether and use expect. Not sure how you could whitelist unit tests though, not doing so might be annoying. (In rust-bitcoin we have an (unwritten) no-unwrap outside of unit tests policy.

[dpc]

Not sure how you could whitelist unit tests though, not doing so might be annoying.

Ban unwrap, except in functions that have #[test]? Not perfect but better than nothing.

[tcharding]

Simple now I read it.