Build and test wasm on MacOS in CI

The default clang installation provided in MacOS does not work. We fixed
 this locally by installing clang via llvm through brew and setting the
 CC and AR env variables to point at the new clang installation.The CI
 MacOS image seems to already have llvm installed so we did not need to
 install llvm on the CI.

See rust-bitcoin/rust-secp256k1#254 for more
details

.github/workflows/rust.yml

@@ -29,21 +29,29 @@ jobs:
           DO_BENCH: true
         run: ./contrib/test.sh
 
-  wasm_pack:
+  wasm:
     name: Stable - Docs / WebAssembly Build
-    runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust:
-          - stable
+        target: [ x86_64-unknown-linux-gnu, x86_64-apple-darwin ]
+        include:
+          - target: x86_64-unknown-linux-gnu
+            os: ubuntu-latest
+            cc: clang-9
+            ar: ar
+          - target: x86_64-apple-darwin
+            os: macos-latest
+            cc: /usr/local/opt/llvm/bin/clang
+            ar: /usr/local/opt/llvm/bin/llvm-ar
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v2
       - name: Checkout Toolchain
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: ${{ matrix.rust }}
+          toolchain: stable
           override: true
       - name: Building docs
         env:
@@ -54,18 +62,10 @@ jobs:
       - name: Running WASM build
         env:
           DO_WASM: true
+          CC: ${{ matrix.cc }}
+          AR: ${{ matrix.ar }}
         run: ./contrib/test.sh
 
-  build_wasm:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: stable
-          target: wasm32-unknown-unknown
-      - run: cargo build --target wasm32-unknown-unknown --features global-context,use-serde,use-rand
-
   Tests:
     name: Tests
     strategy:

Cargo.toml

@@ -45,3 +45,6 @@ bitcoin_hashes = "0.9"
 [target.wasm32-unknown-unknown.dev-dependencies]
 wasm-bindgen-test = "0.3"
 rand = { version = "0.6", features = ["wasm-bindgen"] }
+
+[lib]
+crate-type = ["cdylib", "rlib"]

contrib/test.sh

@@ -53,8 +53,8 @@ fi
 # Webassembly stuff
 if [ "$DO_WASM" = true ]; then
     clang --version &&
-    CC=clang-9 wasm-pack build &&
-    CC=clang-9 wasm-pack test --node;
+    wasm-pack build &&
+    wasm-pack test --node;
 fi
 
 # Address Sanitizer