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WASM Compatibility (no bindings) #35

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@HarryR HarryR commented Sep 18, 2025 •
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When building for WASM targets we don't want to generate the bindings As compiling the project e.g. via wasm-pack, complains "stddef.h" isn't found.

We solve this by a feature flag "c_bindings", which will be enabled on non-wasm targets by default, thus when included in a project being built for wasm it will compile and work as expected when we use the library directly.

I also flagged the timer code in graph.rs as that's not compatible with wasm.

Example output without this patch:

$ make pkg/wasm_example.js
wasm-pack build --target web
[INFO]: 🎯  Checking for the Wasm target...
[INFO]: 🌀  Compiling to Wasm...
warning: patch for `circom-witnesscalc` uses the features mechanism. default-features and features will not take effect because the patch dependency does not support this mechanism
   Compiling circom-witnesscalc v0.2.2 (/src/circom-witnesscalc)
error: failed to run custom build command for `circom-witnesscalc v0.2.2 (/src/circom-witnesscalc)`

Caused by:
  process didn't exit successfully: `/src/circuits/target/release/build/circom-witnesscalc-f66e624381c95aa5/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=protos/messages.proto
  cargo:rerun-if-changed=protos/vm.proto
  cargo:rerun-if-env-changed=TARGET
  cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS_wasm32-unknown-unknown
  cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS_wasm32_unknown_unknown
  cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS
  cargo:rerun-if-changed=include/graph_witness.h

  --- stderr
  include/graph_witness.h:1:10: fatal error: 'stddef.h' file not found

  thread 'main' panicked at /src/circom-witnesscalc/build.rs:36:14:
  Unable to generate bindings: ClangDiagnostic("include/graph_witness.h:1:10: fatal error: 'stddef.h' file not found\n")
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Error: Compiling your crate to WebAssembly failed
Caused by: Compiling your crate to WebAssembly failed
Caused by: failed to execute `cargo build`: exited with exit status: 101
  full command: cd "/src/circuits" && "cargo" "build" "--lib" "--release" "--target" "wasm32-unknown-unknown"
make: *** [Makefile:32: pkg/wasm_example.js] Error 1

Example output with this patch:

...
    Finished `release` profile [optimized] target(s) in 4.56s
[INFO]: ⬇️  Installing wasm-bindgen...
[INFO]: Optimizing wasm binaries with `wasm-opt`...
[INFO]: Optional fields missing from Cargo.toml: 'description', 'repository', and 'license'. These are not necessary, but recommended
[INFO]: ✨   Done in 9.62s
[INFO]: 📦   Your wasm pkg is ready to publish at /src/circuits/pkg.

One note, in Cargo.toml, I took this approach:

[features]
default = []
print_opcode = []
c_bindings = []

# Target-specific defaults - only enable c_bindings for non-WASM
[target.'cfg(not(target_arch = "wasm32"))'.features]
default = ["c_bindings"]

Because I'm using [patch.crates-io] in the test project to override the dependency, and I can't set default-features = false this way, so I ... defaulted it in a target-specific way.

@HarryR
WASM Compatibility (no bindings)
1dad169 
When building for WASM targets we don't want to generate the bindings
As compiling the project e.g. via wasm-pack, complains "stddef.h" isn't found.

We solve this by a feature flag "c_bindings", which will be enabled on non-wasm
targets by default, thus when included in a project being built for wasm it
will compile and work as expected when we use the library directly.

I also flagged the timer code in graph.rs as that's not compatible with wasm.
@HarryR
Add --syms (like --r1cs), remove inputs_file (unused)
40cfe1e
@demonsh demonsh requested a review from olomix September 25, 2025 10:34
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@HarryR
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