rand 0.6+ panic when using wasm-bindgen

[dandry]

I'm familiar with the #616 issue, however I still experience this problem while using rand 0.6.5 and wasm-bindgen 0.2.45.

The source code:

extern crate rand;
use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn test() {
   let mut rng = rand::thread_rng();
}

Cargo.toml

[package]
name = "mgr-rust-wasm"
version = "0.1.0"
authors = ["Dandry<[email protected]>"]
edition = "2018"

[lib]
crate-type = ["cdylib", "rlib"]

[features]
default = ["console_error_panic_hook"]

[dependencies]
wasm-bindgen = "0.2.45"
rand = "0.6.5"

# The `console_error_panic_hook` crate provides better debugging of panics by
# logging them with `console.error`. This is great for development, but requires
# all the `std::fmt` and `std::panicking` infrastructure, so isn't great for
# code size when deploying.
console_error_panic_hook = { version = "0.1.1", optional = true }

# `wee_alloc` is a tiny allocator for wasm that is only ~1K in code size
# compared to the default allocator's ~10K. It is slower than the default
# allocator, however.
#
# Unfortunately, `wee_alloc` requires nightly Rust when targeting wasm for now.
wee_alloc = { version = "0.4.2", optional = true }

[dev-dependencies]
wasm-bindgen-test = "0.2.45"

[profile.release]
# Tell `rustc` to optimize for small code size.
opt-level = "s"

Executing the test() function in JS results in panic:

Uncaught RuntimeError: unreachable
at __rust_start_panic (wasm-function[171]:1)
at rust_panic (wasm-function[99]:31)
at std::panicking::rust_panic_with_hook::h5d8808384a53a826 (wasm-function[32]:303)
at std::panicking::continue_panic_fmt::h821bed92a14cf5d5 (wasm-function[53]:114)
at std::panicking::begin_panic_fmt::h83a0a8c60964976b (wasm-function[71]:94)
at rand::rngs::thread::THREAD_RNG_KEY::__init::{{closure}}::h0b4a20f36b746721 (wasm-function[74]:80)
at rand::rngs::thread::THREAD_RNG_KEY::__init::h91a64631d4c9d99e (wasm-function[40]:217)
at <std::thread::local::LocalKey>::try_with::ha7869471de61cfad (wasm-function[30]:53)
at <std::thread::local::LocalKey>::with::h8ab2ea0937eaef49 (wasm-function[81]:19)
at rand::rngs::thread::thread_rng::h18a8bb12b6ca765b (wasm-function[153]:6)

EDIT: Maybe it's worth mentioning that I'm using Manjaro Linux.

[dandry]

It turns out that my Cargo.toml configuration was wrong and I missed use rand::Rng; in my source code.
The following is correct in Cargo.toml:

rand = { version = "0.6.5", features = ["wasm-bindgen"] }

Sorry for wasting your time. This issue can be closed.

[dhardy]

Yes, we require specification of a feature flag for WASM.

Not sure why the error message is so terrible, but the code for Rand 0.7 is already totally different so there isn't much incentive to investigate further.

[yixing-liu]

I had the same error message with version "0.6.5" and "0.7". I added features =["wasm-bindgen"] .
This is my error message:

bootstrap.js:5 Error importing `index.js`: RuntimeError: unreachable
    at __rust_start_panic (wasm-function[171]:1)
    at rust_panic (wasm-function[101]:31)
    at std::panicking::rust_panic_with_hook::h12b7239ed4348eae (wasm-function[24]:303)
    at std::panicking::continue_panic_fmt::hfbe042bfacb6a5d7 (wasm-function[51]:114)
    at std::panicking::begin_panic_fmt::hb49e9d7f7ff6a73d (wasm-function[70]:94)
    at rand::rngs::thread::THREAD_RNG_KEY::__init::{{closure}}::h8d38765b7916ab20 (wasm-function[69]:90)
    at rand::rngs::thread::THREAD_RNG_KEY::__init::h217fcb2d71e66af8 (wasm-function[49]:100)
    at std::thread::local::LocalKey<T>::try_with::h673d3027270a955d (wasm-function[14]:54)
    at std::thread::local::LocalKey<T>::with::h1a224dc51f4b1570 (wasm-function[79]:19)
    at rand::rngs::thread::thread_rng::h659b4c6634f4c979 (wasm-function[108]:10)

I am using WSL Ubuntu LTS 18. I don't think this should matter, though.

[dhardy]

@yixing-liu minimal example please, and also test whether the same happens when using the getrandom crate directly.

[josephlr]

Note that if you're trying to reproduce this only using getrandom v0.2 the feature has been renamed to "js". So you'll need to have:

[dependencies]
getrandom = { version = "0.2", features = ["js"] }

[clay53]

I just want to note that the error message is still terrible. I can open a separate issue if that'd be appreciated.

[dhardy]

Regarding Rand v0.6? Sorry, we have limited (human) resources, and investigating poor error messages for (very) outdated versions is not a good use of what we have. Unless you wish to make a PR yourself, in which case please go ahead.

[clay53]

Oh sorry, v0.7