Matthew Phillips (Nov 20 2023 at 18:13): Matthew Phillips (Nov 20 2023 at 18:13):Hello, I tried running the hello world, wanting to create a wasm output, ./roc build --target wasm32 but got this error:
I was expecting this file to exist:
/Users/matthew/.cache/roc/packages/github.com/roc-lang/basic-cli/releases/download/0.5.0/Cufzl36_SnJ4QbOoEmiJ5dIpUxBvdB3NEySvuH82Wio/host.zig
However, it was not there!
Matthew Phillips (Nov 20 2023 at 18:14):The help suggests that using --target wasm32 should not assume prebuilt, but that doesn't seem to be the case. Any advice?
Notification Bot (Nov 20 2023 at 18:14):2 messages were moved here from #beginners > my from time to time feedback about Roc by Anton.
Anton (Nov 20 2023 at 18:22):Hi @Matthew Phillips,
The basic-cli platform does not support targeting wasm. That's because a lot of basic-cli functions can't work in a wasm/browser context, like reading from stdin. We should have a better error message for this case though.
You may want to checkout this wasm platform.
Can you share what you would like to build/test with wasm?
Anton (Nov 20 2023 at 18:22):That may help us guide you better.
Matthew Phillips (Nov 20 2023 at 18:23):Ah ok thank you. So the idea is you use a different cli when building to wasm?
Anton (Nov 20 2023 at 18:24):A different platform to be specific.
Matthew Phillips (Nov 20 2023 at 18:24):Hm, ok I think the problem is I don't know what "platform" is yet
Matthew Phillips (Nov 20 2023 at 18:24):so i'll read that page
Matthew Phillips (Nov 20 2023 at 18:26):ok, so the pf in the app config defines the platform? So I just need to swap that out? Will try it.
Matthew Phillips (Nov 20 2023 at 18:29):Do you need a zig file to use wasm?
Anton (Nov 20 2023 at 18:29):Yes, I believe so
Anton (Nov 20 2023 at 18:31):I recommend downloading this platform locally and following along with the README
Matthew Phillips (Nov 20 2023 at 18:32):ok, i'll test that out, thanks
Anton (Nov 20 2023 at 18:32):So I just need to swap that out?
Different platforms work with different types and provide different functionality so in most cases it will not be possible to swap out the platform without changing anything else.
Anton (Nov 20 2023 at 18:32):I have to go now, but other people should be able to help out :)
Matthew Phillips (Nov 20 2023 at 18:33):Oh, well it's already included in the nightly.
Matthew Phillips (Nov 20 2023 at 18:33):Thanks @Anton
Matthew Phillips (Nov 20 2023 at 18:35):I get a compiler error. Getting closer!
Matthew Phillips (Nov 20 2023 at 18:36):I think it's because I have the wrong version of zig installed.
Matthew Phillips (Nov 20 2023 at 18:37):Fixing that part now.
Matthew Phillips (Nov 20 2023 at 18:40):Now installing Rust...
Matthew Phillips (Nov 20 2023 at 18:45)::hammer: Rebuilding platform...
An internal compiler expectation was broken.
This is definitely a compiler bug.
Please file an issue here: https://github.com/roc-lang/roc/issues/new/choose
thread 'main' panicked at 'cannot find wasi-libc.a', crates/compiler/build/src/link.rs:133:5
Matthew Phillips (Nov 20 2023 at 18:45):rustc --version
rustc 1.74.0 (79e9716c9 2023-11-13)
Matthew Phillips (Nov 20 2023 at 18:45):zig version
0.11.0
Matthew Phillips (Nov 20 2023 at 18:54):app "rocLovesWebAssembly"
packages { pf: "./examples/platform-switching/web-assembly-platform/main.roc" }
imports []
provides [main] to pf
main = "Roc <3 Web Assembly!\n"
Brendan Hansknecht (Nov 20 2023 at 19:00):My guess is that we build that file but have failed to include it in the nightly releases. So the platform works if the compiler is built from source, but not if it is downloaded from nightly.
Matthew Phillips (Nov 20 2023 at 19:08):Ok, might try that
Matthew Phillips (Nov 20 2023 at 19:28):If you run cargo build where are the binaries? I'm not familiar with rust conventions
Ayaz Hafiz (Nov 20 2023 at 19:30):target/debug/roc (or target/release/roc if you built with --release)
Matthew Phillips (Nov 20 2023 at 19:30):Perfect, thanks
Matthew Phillips (Nov 20 2023 at 19:31):woohoo, it all works now
Brendan Hansknecht (Nov 20 2023 at 19:32):I'll file a bug for that
Brendan Hansknecht (Nov 20 2023 at 19:32):Should definitely work for nightly too
Brendan Hansknecht (Nov 20 2023 at 19:36): Matthew Phillips (Nov 20 2023 at 19:37):Not sure if this is another bug or I did something wrong:
LinkError: WebAssembly.instantiate(): Import #2 module="wasi_snapshot_preview1" function="random_get": function import requires a callable
That's in the browser.
Matthew Phillips (Nov 20 2023 at 19:40):Yeah, i think that's a bug too
Matthew Phillips (Nov 20 2023 at 19:41):I would guess that's just the example missing that function
Matthew Phillips (Nov 20 2023 at 19:41):But I don't see anything in the repo about "random_get"
Matthew Phillips (Nov 20 2023 at 19:43): random_get(v) {
return Math.random();
}
Adding this to the importObj fixed it. I assume this is not right though!
Matthew Phillips (Nov 20 2023 at 19:44):good enough to unblock me, for now.
Brendan Hansknecht (Nov 20 2023 at 19:48):Hmm. So I think I see the real issue, this is compiling for wasi, which is web assembly not in the browser. I think it should be compiling for just wasm without any extra wasi stuff.
Matthew Phillips (Nov 20 2023 at 19:49):ah yeah that makes sense
Matthew Phillips (Nov 20 2023 at 19:53):That problems means the binary size is a little larger than it would normally be
Matthew Phillips (Nov 20 2023 at 19:54):not that it's big currently or anything
Last updated: Jul 26 2025 at 12:14 UTC