Lint unstable floating point computations

[llogiq]

Something along the lines of Herbie for Haskell, but without the auto-fixing – perhaps we can port the transformations to give (very) good suggestions.

[mcarton]

Hi I loved the idea and I've been working on this recently, it's not finished yet but I think it's ready to talk about it and it's usable. I think it's much bigger than any lint in clippy, it also needs a database, an optional configuration file and can optionally use an external program (herbie-inout) too so I'm not just making a PR here, but if you think it could be integrated that'd be awesome.

[Manishearth]

I'm fine with this being a separate lint, really :smile: . I have a defunct project, rust-Wall, which is meant to reexport lints from basically all the lint crates, except so far there is only one with universally-useful lints (clippy), so it never got used. We could reexport there and revive it.

Why does it need a database?

[mcarton]

The database contains cached expression replacements eg. (a*a + b*b).sqrt() → a.hypot(b). It's required because Herbie is too slow to re-analyze every expressions every time. Also Herbie is quite difficult to install and requires a specific, not up-to-date, version of some esoteric language I forgot the name of. I've had to install it in docker. But with a pre-filled database, the installation is not required. The database format is the same as for Haskell's plugin, so they can be shared. Nice to hear about rust-Wall, it's a shame there are no more lints (or not, maybe every one is just collaborating here :smile:).

[Manishearth]

We could probably use rust-phf to in-memory that database? figure out a hashable representation for it and go!

[Manishearth]

Everyone is just collaborating here :smile: When I created rust-Wall clippy was small and I didn't expect it to be the One True home for lints

[mcarton]

I think we should keep the database, using rust-phf we could not cache new expression replacements as they are discovered by Herbie as it's a compile time thing.

[Manishearth]

Isn't the discovery thing slow? Perhaps we could build up a good database by merging all the existing Haskell-Herbie stuff and running the slow rust-herbie on a ton of crates in the ecosystem?

[mcarton]

Currently I've only used the database from Haskell-Herbie but I plan to run it on “a ton of crates in the ecosystem” of course :smile: If you guys have ideas of crates I've opened an issue to list them: https://github.com/mcarton/rust-herbie-lint/issues/2.

[Manishearth]

fyi you're getting some well-deserved publicity here :smile:

[gnzlbg]

I'd like this lint to be available in clippy; otherwise it just doesn't get used.

Are there any other lints that could benefit from a dependency onHerbie or Z3 ? Maybe having these as dependencies won't pay off initially, but as more lints use them the cost can be amortized over time.