Support wasm32-unknown-unknown

[vivekvpandya]

Using evercrypt with Substrate (no_std and target = wasm32-unknown-unknown)

I am trying to build evercrypt-sys with following change to enable wasm32-unknown-unknown target .

diff --git a/evercrypt-sys/build.rs b/evercrypt-sys/build.rs
index a02144b..88bd25f 100644
--- a/evercrypt-sys/build.rs
+++ b/evercrypt-sys/build.rs
@@ -330,6 +330,9 @@ fn main() {
             .set_hacl_src_dir("msvc-compatible"),
         // TODO: Which Android versions do we want to support?
         "aarch64-linux-android" => panic!("Target '{:?}' is not supported yet.", target),
+        "wasm32-unknown-unknown" => {
+            cfg.set_cross_config_flags(vec!["-target", "wasm32-unknown-unknown"])
+        }
         _ => panic!("Target '{:?}' is not supported yet.", target),
     };

And my build command is: cargo test --target wasm32-unknown-unknown
I am getting following error. (I have glibc-devel package install on my Fedora)

   Compiling evercrypt-sys v0.0.8 (/home/vivek/dev/evercrypt-rust/evercrypt-sys)
error: failed to run custom build command for `evercrypt-sys v0.0.8 (/home/vivek/dev/evercrypt-rust/evercrypt-sys)`
Caused by:
  process didn't exit successfully: `/home/vivek/dev/evercrypt-rust/evercrypt-sys/target/debug/build/evercrypt-sys-5c5394f05cb975ec/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=wrapper.h
  cargo:rerun-if-changed=hacl-star
  build_config: BuildConfig { hacl_src_dir: "gcc-compatible", cross: true, config_flags: ["-target", "wasm32-unknown-unknown"], make_flags: [], env: {}, lib_name: "evercrypt", windows: false }
  out_path: "/home/vivek/dev/evercrypt-rust/evercrypt-sys/target/wasm32-unknown-unknown/debug/build/evercrypt-sys-5b180f46e6e63781/out"
  hacl_src_path: "/home/vivek/dev/evercrypt-rust/evercrypt-sys/target/wasm32-unknown-unknown/debug/build/evercrypt-sys-5b180f46e6e63781/out/hacl-star/dist/gcc-compatible"

  --- stderr
  /home/vivek/dev/evercrypt-rust/evercrypt-sys/target/wasm32-unknown-unknown/debug/build/evercrypt-sys-5b180f46e6e63781/out/hacl-star/dist/gcc-compatible/libintvector.h:4:10: fatal error: 'sys/types.h' file not found
  /home/vivek/dev/evercrypt-rust/evercrypt-sys/target/wasm32-unknown-unknown/debug/build/evercrypt-sys-5b180f46e6e63781/out/hacl-star/dist/gcc-compatible/libintvector.h:4:10: fatal error: 'sys/types.h' file not found, err: true
  thread 'main' panicked at 'Unable to generate bindings: ()', build.rs:272:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace```

Please help on this

[franziskuskiefer]

Thanks for taking a look at evercrypt @vivekvpandya
Currently neither the Rust crate nor hacl* itself supports wasm. hacl* has a separate wasm support (there are JS bindings).
There are two options for supporting wasm

1. compile the hacl* C to wasm for the Rust wasm target
2. use the hacl* wasm code generated from kremlin directly in the Rust wasm target

The latter is probably the preferable approach but requires different bindings than evercrypt-sys.