Is evalexpr compatible for WASM builds?

[TimeTravelPenguin]

I am working on a Typst plugin. I decided to try evalexpr because I need a way to send "functions" for evaluation from Typst to the WASM plugin, and the only feasible way to do this is via strings. Thus, evalexpr allows me to evaluate computations in this way.

After some attempts, I have not been able to successfully use this package, and I am not entirely sure why. I suspect it is not compatible with WASM or, at the very least, with whatever protocol Typst uses for its plugin system.

When I attempt to use my compiled plugin, I get a Typst error:

plugin panicked: wasm `unreachable` instruction executed

Would you have any idea as to what the issue may be? Do you have any suggestions for alternate packages?

Thanks

[ISibboI]

Are you using any feature flags of evalexpr? Because if you don't, then evalexpr has no dependencies and should compile on almost any target. If you do, I think rand needs some extra config to work on wasm-unknown-unknown. Google rust rand wasm-unknown-unknown or something, I think there is even an official guide out there about how to compilte rand for wasm-unknown-unknown.

Let me know if it works, otherwise, please create a minimal failing example.

[TimeTravelPenguin]

Ah, I think I have worked out the issue. I am not too familiar with this sort of thing, but the issue seems to be the use of HashMap.

I see that using hashbrown's HashMap works, but not std::collections::HashMap.

Edit: also, for extra clarification, I was not using any default features.

[ISibboI]

I see, thanks. Didn't know that HashMap was incompatible with wasm. I'll leave this issue open, because maybe I'll add a feature flag that makes this crate build and work with `wasm-unknown-unknown` at some point in the future.

…

On Tue, Jul 7, 2026 at 9:22 AM Phillip Smith ***@***.***> wrote: *TimeTravelPenguin* left a comment (ISibboI/evalexpr#201) <#201 (comment)> Ah, I think I have worked out the issue. I am not too familiar with this sort of thing, but the issue seems to be the use of HashMap. I see that using hashbrown's HashMap works, but not std::collections::HashMap. — Reply to this email directly, view it on GitHub <#201?email_source=notifications&email_token=AASATXSWKH35KGLMN3MLEWD5DSJKNA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOJQGA3TQMJYG4ZKM4TFMFZW63VGMFZXG2LHN2SWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#issuecomment-4900781872>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AASATXVYQQG7W6MBBF4ZK4T5DSJKNAVCNFSNUABFKJSXA33TNF2G64TZHMYTONRUHA2TIMZXHNEXG43VMU5TIOBSGUZTIMBYHE4KC5QC> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/AASATXTTF62HOLK4EAU3NMT5DSJKNA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOJQGA3TQMJYG4ZKM4TFMFZW63VGMFZXG2LHN2SWK5TFNZ2KUZTPN52GK4S7NFXXG> and Android <https://github.com/notifications/mobile/android/AASATXTAXSMGPR3V4YD2XST5DSJKNA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOJQGA3TQMJYG4ZKM4TFMFZW63VGMFZXG2LHN2SWK5TFNZ2K4ZTPN52GK4S7MFXGI4TPNFSA>. Download it today! You are receiving this because you were assigned.Message ID: ***@***.***>

[TimeTravelPenguin]

Hmm, I think your understanding is correct. My plugin was targeting wasm32-wasip1. I should be able to revert to wasm32-unknown-unknown. Honestly, I didn't realise that would cause this issue.