CI: install wasm zlib + HDF5 into the Emscripten sysroot

The Emscripten/WASM jobs were red: HDF5's own static build failed with
"Could NOT find ZLIB ... non-existent target ZLIB::ZLIB". Emscripten restricts
find_package() to CMAKE_FIND_ROOT_PATH (= the sysroot), so a custom-prefix
-DZLIB_ROOT / CMAKE_PREFIX_PATH is silently ignored (the same static-HDF5
packaging gap #1894 works around downstream).

Install the static zlib + HDF5 into the active Emscripten sysroot (em-config
CACHE), as library_builders.sh does, so find_package(ZLIB)/find_package(HDF5)
locate them with no extra hints -- in the HDF5 dep build, the openPMD configure,
and the Pyodide wheel build alike. Also pin setup-emsdk to 'latest' ('5.0.3' is
Pyodide's fork tag and silently fell back to emsdk main).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ax3l

.github/ci/wasm_deps.sh

@@ -5,16 +5,18 @@
 # License: LGPLv3+
 #
 # Cross-compile openPMD-api's static C/C++ dependencies (zlib + HDF5) for
-# wasm32-emscripten into the prefix given as $1 (put on CMAKE_PREFIX_PATH).
+# wasm32-emscripten and install them into the active Emscripten sysroot, where a
+# later find_package() locates them: Emscripten restricts find_package to
+# CMAKE_FIND_ROOT_PATH (= the sysroot), so a custom prefix is silently ignored.
 # Flags mirror the Pyodide wheel builder (library_builders.sh) so the test build
 # matches the shipped wheel; the co-load-only -fvisibility=hidden is omitted here
 # (the test executables are standalone, not side modules).
 #
-# Requires an active Emscripten SDK on PATH (emcmake/emcc).
+# Requires an active Emscripten SDK on PATH (emcmake/emcc/em-config).
 
 set -eu -o pipefail
 
-PREFIX="${1:?usage: wasm_deps.sh <install-prefix>}"
+PREFIX="$(em-config CACHE)/sysroot"
 ZLIB_VERSION="${ZLIB_VERSION:-1.3.1}"
 HDF5_VERSION="${HDF5_VERSION:-1.14.6}"
 

.github/workflows/wasm.yml

@@ -23,15 +23,16 @@ jobs:
       with:
         node-version: '22'
 
-    # Keep the Emscripten version aligned with Pyodide's as it advances.
+    # Latest stable Emscripten (the standalone C++ suite is version-tolerant;
+    # Pyodide's exact toolchain is exercised by the pyodide-python job below).
     - name: Emscripten SDK
       uses: mymindstorm/setup-emsdk@v14
       with:
-        version: '5.0.3'
+        version: 'latest'
         actions-cache-folder: 'emsdk-cache'
 
     - name: Static wasm dependencies (zlib + HDF5)
-      run: bash .github/ci/wasm_deps.sh "${GITHUB_WORKSPACE}/wasm-deps"
+      run: bash .github/ci/wasm_deps.sh
 
     # CMAKE_CROSSCOMPILING_EMULATOR=node -> ctest runs each test binary via node.
     # NODERAWFS gives the test binaries the real filesystem (HDF5/JSON file I/O);
@@ -47,7 +48,6 @@ jobs:
           -DopenPMD_BUILD_EXAMPLES=OFF                                       \
           -DHDF5_USE_STATIC_LIBRARIES=ON                                     \
           -DZLIB_USE_STATIC_LIBS=ON                                          \
-          -DCMAKE_PREFIX_PATH="${GITHUB_WORKSPACE}/wasm-deps"                \
           -DCMAKE_CROSSCOMPILING_EMULATOR=node                              \
           -DCMAKE_C_FLAGS="-sSUPPORT_LONGJMP=wasm"                          \
           -DCMAKE_CXX_FLAGS="-fwasm-exceptions -sSUPPORT_LONGJMP=wasm"      \
@@ -92,14 +92,13 @@ jobs:
       env:
         CIBW_BUILD: "cp314-pyodide_wasm32"
         CIBW_TEST_SKIP: "*"
-        CIBW_BEFORE_BUILD_PYODIDE: "bash .github/ci/wasm_deps.sh /tmp/wasm-deps"
+        CIBW_BEFORE_BUILD_PYODIDE: "bash .github/ci/wasm_deps.sh"
         CIBW_ENVIRONMENT_PYODIDE: >
           openPMD_CMAKE_openPMD_USE_HDF5='ON'
           openPMD_CMAKE_openPMD_USE_ADIOS2='OFF'
           openPMD_USE_MPI='OFF'
           HDF5_USE_STATIC_LIBRARIES='ON'
           ZLIB_USE_STATIC_LIBS='ON'
-          CMAKE_PREFIX_PATH='/tmp/wasm-deps'
 
     # Load the wheel in a Pyodide venv (runs Python in node) and execute the full
     # unittest suite. Test.py reads sample data from ../samples relative to its