clockworklabs/SpacetimeDB · error · anyhow::Error

wasm-bindgen detected. It seems like either you or a crate…

Error message

wasm-bindgen detected.

It seems like either you or a crate in your dependency tree is depending on
wasm-bindgen. wasm-bindgen is only for webassembly modules that target the web
platform, and will not work in the context of SpacetimeDB.

To find the offending dependency, run `cargo tree -i wasm-bindgen`. Try checking
its cargo features for 'js' or 'web' or 'wasm-bindgen' to see if there's a way
to disable it.

What it means

After compiling the module, check_for_issues decodes the resulting .wasm with wasmbin and inspects its import section for wasm-bindgen signatures. wasm-bindgen generates JS-bridge imports that only resolve inside a browser host; SpacetimeDB's runtime cannot supply them, so such a module would trap at instantiation. The CLI therefore rejects the artifact at build/publish time and points you at cargo tree to find the culprit in your dependency graph.

Solutions

1. Run `cargo tree -i wasm-bindgen` (same target/features as the module build) to see which dependency pulls it in
2. Disable the offending feature in Cargo.toml: `default-features = false` or turn off its `js`/`web`/`wasm-bindgen` features
3. Replace the crate with a wasm-neutral or no_std alternative
4. Rebuild and publish

Example fix

# before (Cargo.toml) -- default features pull wasm-bindgen
some-util = "1.0"

# after
some-util = { version = "1.0", default-features = false }
# verify: cargo tree -i wasm-bindgen  -> should report not found

#!/usr/bin/env bash
# fail CI if wasm-bindgen enters the module graph
cargo tree -i wasm-bindgen >/dev/null 2>&1 \
  && { echo 'wasm-bindgen detected in dependency tree' >&2; exit 1; } \
  || true

When it happens

Trigger: Publishing a module whose dependency tree pulls in wasm-bindgen when compiled for wasm32-unknown-unknown -- e.g. a dependency with `js`, `web`, or `wasm-bindgen` cargo features enabled by default, or web-oriented library code reused inside the module.

Common situations: Reusing crypto/serialization/utility code from a web project; a crate that switches to a wasm-bindgen backend on wasm32 targets unless default features are disabled; adding a dependency without auditing its wasm feature set.

Related errors

• getrandom usage detected. It seems like either you or a…
• AddColumns: table ` ` not found in new module def
• AddConstraint: ` ` not found in new module def
• AddRowLevelSecurity: RLS
• AddSequence: ` ` not found in new module def

AI-assisted analysis of clockworklabs/SpacetimeDB@6dee26c6ef (2026-08-20). Data as JSON: /api/errors/eec4500f25ff63f6. Report an issue: GitHub.

Appendix: source

Thrown at crates/cli/src/tasks/rust.rs:120

    }
    let artifact = artifact.context("no artifact found?")?;
    let artifact = artifact.filenames.into_iter().next().context("no wasm?")?;

    check_for_issues(artifact.as_ref())?;

    Ok(artifact.into())
}

fn check_for_issues(artifact: &Path) -> anyhow::Result<()> {
    // if this fails for some reason, just let it fail elsewhere
    let Ok(file) = fs::File::open(artifact) else {
        return Ok(());
    };
    let Ok(module) = wasmbin::Module::decode_from(&mut io::BufReader::new(file)) else {
        return Ok(());
    };
    if has_wasm_bindgen(&module) {
        anyhow::bail!(
            "wasm-bindgen detected.\n\
             \n\
             It seems like either you or a crate in your dependency tree is depending on\n\
             wasm-bindgen. wasm-bindgen is only for webassembly modules that target the web\n\
             platform, and will not work in the context of SpacetimeDB.\n\
             \n\
             To find the offending dependency, run `cargo tree -i wasm-bindgen`. Try checking\n\
             its cargo features for 'js' or 'web' or 'wasm-bindgen' to see if there's a way\n\
             to disable it."
        )
    }
    if has_getrandom(&module) {
        anyhow::bail!(
            "getrandom usage detected.\n\
             \n\
             It seems like either you or a crate in your dependency tree is depending on\n\
             the `getrandom` crate for random number generation. getrandom is the default\n\
             randomness source for the `rand` crate, and is used when you call\n\

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