wasm: support the wasm32-unknown-emscripten target (#8281)

.github/workflows/ci.yml

@@ -19,6 +19,8 @@ env:
   rust_nightly: nightly-2025-10-12
   # Pin a specific miri version
   rust_miri_nightly: nightly-2026-06-29
+  rust_emscripten_nightly: nightly-2026-08-17
+  emsdk_version: '6.0.8'
   rust_clippy: '1.88'
   # When updating this, also update:
   # - README.md
@@ -1193,6 +1195,59 @@ jobs:
           RUSTFLAGS: --cfg tokio_unstable
           CARGO_TARGET_WASM32_WASIP2_RUNNER: wasmtime run -Sinherit-network
 
+  wasm32-unknown-emscripten:
+    name: test tokio for wasm32-unknown-emscripten
+    needs: basics
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ env.rust_stable }}
+          targets: wasm32-unknown-emscripten
+
+      - name: Install Emscripten
+        uses: mymindstorm/setup-emsdk@v14
+        with:
+          version: ${{ env.emsdk_version }}
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 26
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Install cargo-hack
+        uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-hack
+
+      - name: Check tokio feature matrix for emscripten
+        run: cargo hack check -p tokio --each-feature --exclude-features full,net,process,signal,rt-multi-thread,io-uring,taskdump,schedule-latency --target wasm32-unknown-emscripten
+        working-directory: tokio
+
+      - name: Test tokio for emscripten
+        run: cargo test -p tokio --target wasm32-unknown-emscripten --features "rt,time,sync,macros,fs,io-util,io-std,test-util" --tests
+        working-directory: tokio
+        env:
+          CARGO_TARGET_WASM32_UNKNOWN_EMSCRIPTEN_RUNNER: node
+          RUSTFLAGS: "-Dwarnings -Clink-args=-sALLOW_MEMORY_GROWTH=1 -Clink-args=-sEXIT_RUNTIME=1 -Clink-args=-sSTACK_SIZE=1048576"
+
+      - name: Install Rust ${{ env.rust_emscripten_nightly }}
+        uses: dtolnay/rust-toolchain@nightly
+        with:
+          toolchain: ${{ env.rust_emscripten_nightly }}
+          targets: wasm32-unknown-emscripten
+          components: rust-src
+
+      - name: Test tokio multi-thread runtime for emscripten (pthreads)
+        run: cargo +${{ env.rust_emscripten_nightly }} test -Zbuild-std=std,panic_abort -p tokio --target wasm32-unknown-emscripten --features "rt,rt-multi-thread,time,sync,macros" --test rt_multi_thread_emscripten
+        working-directory: tokio
+        env:
+          CARGO_TARGET_WASM32_UNKNOWN_EMSCRIPTEN_RUNNER: node
+          RUSTFLAGS: "-Dwarnings -Ctarget-feature=+atomics,+bulk-memory,+mutable-globals -Clink-args=-pthread -Clink-args=-sPTHREAD_POOL_SIZE=8 -Clink-args=-sINITIAL_MEMORY=134217728 -Clink-args=-sEXIT_RUNTIME=1 -Clink-args=-sSTACK_SIZE=1048576"
+
   check-external-types:
     name: check-external-types (${{ matrix.os }})
     needs: basics