ci: add musl build step

Author: ptondereau

.github/workflows/build.yml

@@ -91,6 +91,7 @@ jobs:
         rust: [stable, nightly]
         clang: ["15", "17"]
         phpts: [ts, nts]
+        target: [gnu, musl]
         exclude:
           # ext-php-rs requires nightly Rust when on Windows.
           - os: windows-latest
@@ -101,11 +102,23 @@ jobs:
             clang: "15"
           - os: windows-latest
             clang: "15"
+          # musl only supported on Linux with stable Rust
+          - os: windows-latest
+            target: musl
+          - os: macos-latest
+            target: musl
+          - target: musl
+            rust: nightly
     env:
       CARGO_TERM_COLOR: always
     steps:
       - name: Checkout code
         uses: actions/checkout@v5
+      - name: Install musl toolchain
+        if: matrix.target == 'musl'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y musl-tools musl-dev
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
@@ -118,6 +131,9 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
           components: rustfmt, clippy
+      - name: Add musl target
+        if: matrix.target == 'musl'
+        run: rustup target add x86_64-unknown-linux-musl
       - run: rustup show
       - name: Cache cargo dependencies
         uses: Swatinem/rust-cache@v2
@@ -162,13 +178,17 @@ jobs:
       - name: Build
         env:
           EXT_PHP_RS_TEST: ""
-        run: cargo build --release --features closure,anyhow,runtime --workspace
+          RUSTFLAGS: ${{ matrix.target == 'musl' && '-C target-feature=-crt-static' || '' }}
+          CC: ${{ matrix.target == 'musl' && 'musl-gcc' || 'gcc' }}
+        run: cargo build --release --features closure,anyhow,runtime --workspace ${{ matrix.target == 'musl' && '--target x86_64-unknown-linux-musl' || '' }}
       # Test
       - name: Test inline examples
         # Macos fails on unstable rust. We skip the inline examples test for now.
         if: "!(contains(matrix.os, 'macos') && matrix.rust == 'nightly')"
-        run: cargo test --release --workspace --features closure,anyhow,runtime --no-fail-fast
-
+        env:
+          RUSTFLAGS: ${{ matrix.target == 'musl' && '-C target-feature=-crt-static' || '' }}
+          CC: ${{ matrix.target == 'musl' && 'musl-gcc' || 'gcc' }}
+        run: cargo test --release --workspace --features closure,anyhow,runtime --no-fail-fast ${{ matrix.target == 'musl' && '--target x86_64-unknown-linux-musl' || '' }}
   test-embed:
     name: Test with embed
     runs-on: ubuntu-latest

README.md

@@ -126,6 +126,22 @@ best resource at the moment. This can be viewed at [docs.rs].
     1.57 at the time of writing.
 - Clang 5.0 or later.
 
+### Alpine Linux (musl) Requirements
+
+Building for Alpine Linux (musl libc) is supported on stable Rust with the following
+requirements:
+
+- Install musl toolchain: `sudo apt-get install musl-tools musl-dev`
+- Add musl target: `rustup target add x86_64-unknown-linux-musl`
+- Build with dynamic linking flag:
+  ```bash
+  RUSTFLAGS="-C target-feature=-crt-static" \
+    cargo build --target x86_64-unknown-linux-musl
+  ```
+
+**Note**: Building for musl requires dynamic CRT linking (`-crt-static` flag) to produce
+the `cdylib` output required for PHP extensions.
+
 ### Windows Requirements
 
 - Extensions can only be compiled for PHP installations sourced from