Support building on webassembly

[detrumi]

It would be great if proptest could be built on WASM. Slightly related to #47 but more specific, since proptest can almost be compiled to webassembly already.

I'm already disabling the default forking feature, to avoid the rusty-fork dependency.

The only thing blocking building proptest on webassembly is these few lines, importing std::os::unix inside a #[cfg(not(target_os = "windows"))] block.

Could the osstring_invalid_string function be constrained more, by excluding wasm32 for example? Or maybe there's a better solution to avoid using std::os::unix on all non-windows targets?

[matklad]

A possible solution here would be to split proptest into two crates:

• a proptest-traits, which exposes strategy trait and related machinery. This part could be strictly pure & platform-independent I think?
• proptest-runner, which allows one to actually run property test, maintaining a failure database, etc.

EDIT: this would help because we depend on prop-test in a non-optional way to define an "Arbitrary" instance for text edits. It would be totally fine if the actual tests work on Linux/Windows/Mac.

[AltSysrq]

I gated the code you deleted behind a cfg check in 0.9.2, so I think it should be working for you now.

split proptest into two crates

Unfortunately, the two are rather intertwined — even the basic public API requires Strategy to know about TestRunner and vice versa.

[lastmjs]

Were any of you able to get proptest to compile for WebAssembly? I am running into this error:

error[E0433]: failed to resolve: use of undeclared crate or module `imp`
  --> /home/lastmjs/.cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/wait-timeout-0.2.0/src/lib.rs:66:9
   |
66 |         imp::wait_timeout(self, dur)
   |         ^^^ use of undeclared crate or module `imp

[lastmjs]

I turned off all features except for std, and it now compiles.

Have you had success actually getting proptest to run? I keep getting a panic when trying to create a runner: Panicked at 'not supported on this platform', library/std/src/sys/wasm/../unsupported/os.rs:76:5

[RReverser]

^ that's about how far I got too, with a more precise message in a few places:

panicked at 'condvar wait not supported', library/std/src/sys/wasm/../unsupported/locks/condvar.rs:23:9

[mlodato517]

🤦 Just saw #270

Ignore

I tried a minimal reproduction with wasm-pack and wasm_bindgen_test like:

proptest! {
    #[wasm_bindgen_test]
    fn some_test(num: u32) { assert_eq!(num, num); }
}

And ran into three failures:

• Two were usages of Instant::now in runner.rs. Not sure if those can/should be grouped under the timeout feature. If so, that'd be convenient and I'd happy to PR that.
• The other one was env vars in the config and I have no idea what to do about that 😅

Neither of these address the more niche cases like condvar mentioned above but maybe we can iteratively approach WASM support by handling something like that minimal reproduction first? Happy to help if anyone has bandwidth to offer any guidance!