Fix WASM build issues, improve test coverage and improve cmake files

* Ensure compiler.usethread=0 is set before compilation in single-threaded WASM builds
* Explicitly enable exceptions for the single-threaded WASM module
* Test the single-threaded module in addition to the multi-threaded module in internal and external CI
* Consolidate wasm/tests/CMakeLists.txt into wasm/CMakeLists.txt, fixing the single-threaded benchmark test build which was missing shared linker flags

PiperOrigin-RevId: 901149728
Change-Id: If4946e29e5116610782d218906cf3f5940c1cdd0

.github/workflows/build_steps.sh

@@ -212,25 +212,28 @@ build_test_wasm() {
     echo "Building and testing WASM bindings..."
     source emsdk/emsdk_env.sh
     export PATH="$(pwd)/node_modules/.bin:$PATH"
-
-    echo "Building Multi-Threaded version..."
+    echo "Build MuJoCo with Emscripten (Multi-Threaded)..."
     emcmake cmake -B build_wasm_mt \
         -DCMAKE_INTERPROCEDURAL_OPTIMIZATION:BOOL=OFF \
         -DMUJOCO_WASM_THREADS=ON \
         $WASM_CMAKE_ARGS
     cmake --build build_wasm_mt --parallel $(nproc)
 
+    echo "Run bindings tests for Multi-Threaded version..."
+    npm run test --prefix ./wasm
+
     echo "Moving Multi-Thread version under mt subfolder..."
     mkdir -p wasm/dist/mt
     mv wasm/dist/mujoco.* wasm/dist/mt/
 
-    echo "Building Single-Threaded version..."
+    echo "Build MuJoCo with Emscripten (Single-Threaded)..."
     emcmake cmake -B build_wasm_st \
         -DCMAKE_INTERPROCEDURAL_OPTIMIZATION:BOOL=OFF \
         -DMUJOCO_WASM_THREADS=OFF \
         $WASM_CMAKE_ARGS
     cmake --build build_wasm_st --parallel $(nproc)
 
+    echo "Run bindings tests for Single-Threaded version..."
     npm run test --prefix ./wasm
 }
 

CMakeLists.txt

@@ -132,9 +132,6 @@ endif()
 
 if(EMSCRIPTEN)
   add_subdirectory(wasm)
-  if(MUJOCO_BUILD_TESTS_WASM)
-    add_subdirectory(wasm/tests)
-  endif()
 endif()
 
 

src/user/user_model.cc

@@ -4967,6 +4967,20 @@ void mjCModel::ResolveKeyframes(const mjModel* m) {
 }
 
 void mjCModel::TryCompile(mjModel*& m, mjData*& d, const mjVFS* vfs) {
+#if defined(__EMSCRIPTEN__) && !defined(MUJOCO_WASM_THREADS)
+  // The MuJoCo compiler defaults to usethread=1, which causes it to try to
+  // create pthreads for compilation. In the single-threaded WASM build, this
+  // crashes because there is no threading support, so we disable threading on
+  // the internal compiler struct (not the spec) to avoid permanently mutating
+  // the spec (which would cause usethread="false" to appear in a saved XML).
+  struct ScopedDisableThreading {
+    mjtByte& ref;
+    mjtByte saved;
+    explicit ScopedDisableThreading(mjtByte& r) : ref(r), saved(r) { ref = 0; }
+    ~ScopedDisableThreading() { ref = saved; }
+  } disable_usethread(compiler.usethread);
+#endif
+
   // check if nan test works
   double test = mjNAN;
   if (mjuu_defined(test)) {

wasm/CMakeLists.txt

@@ -22,16 +22,14 @@ include_directories(${PROJECT_SOURCE_DIR})
 
 link_directories(${CMAKE_BINARY_DIR}/lib)
 
-file(GLOB MUJOCO_WASM_FILES
-    "codegen/generated/*.cc"
-    "unpack.cc"
-)
+# Set Emscripten compile flags.
+# -fexceptions is required for val::throw_() (used by ThrowMujocoErrorToJS) to
+# actually throw a JS exception. Without it, Emscripten compiles throw as a
+# no-op. In the MT build, -pthread implicitly enables exception support, but
+# the ST build needs it set explicitly here.
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
 
-if(NOT MUJOCO_WASM_FILES)
-    message(FATAL_ERROR "No source files found in codegen/generated/")
-endif()
-
-# Set Emscripten linker flags
+# Set Emscripten linker flags shared by all WASM targets.
 set(EMCC_LINKER_FLAGS
     "--bind"
     "-s ASSERTIONS=1"
@@ -42,9 +40,9 @@ set(EMCC_LINKER_FLAGS
     "-s EXPORTED_RUNTIME_METHODS=['ccall','cwrap','FS','MEMFS']"
     "-s EXPORT_NAME=loadMujoco"
     "-s DISABLE_EXCEPTION_CATCHING=0"
+    "-fexceptions"
     "-gsource-map"
     "-g"
-    "--emit-tsd mujoco.d.ts"
 )
 if(MUJOCO_WASM_THREADS)
     list(APPEND EMCC_LINKER_FLAGS
@@ -53,7 +51,28 @@ if(MUJOCO_WASM_THREADS)
     )
     add_definitions(-DMUJOCO_WASM_THREADS)
 endif()
-string (REPLACE ";" " " EMCC_LINKER_FLAGS_STR "${EMCC_LINKER_FLAGS}")
+
+# Common link libraries for all WASM targets. The mujoco library is linked as a
+# whole archive to avoid losing plugin registration such as obj_decoder and
+# stl_decoder.
+set(MUJOCO_WASM_LINK_LIBRARIES
+    -Wl,--whole-archive mujoco -Wl,--no-whole-archive
+    ccd lodepng tinyxml2 qhullstatic_r
+)
+
+# --- Main WASM bindings target ---
+
+file(GLOB MUJOCO_WASM_FILES
+    "codegen/generated/*.cc"
+    "unpack.cc"
+)
+
+if(NOT MUJOCO_WASM_FILES)
+    message(FATAL_ERROR "No source files found in codegen/generated/")
+endif()
+
+set(MUJOCO_WASM_LINKER_FLAGS ${EMCC_LINKER_FLAGS} "--emit-tsd mujoco.d.ts")
+string(REPLACE ";" " " MUJOCO_WASM_LINKER_FLAGS_STR "${MUJOCO_WASM_LINKER_FLAGS}")
 
 add_executable(mujoco_wasm ${MUJOCO_WASM_FILES})
 
@@ -61,15 +80,36 @@ add_executable(mujoco_wasm ${MUJOCO_WASM_FILES})
 # `mujoco` library target, but emit artifacts named `mujoco.*` by setting the
 # output name. Also apply the emscripten linker flags to the wasm target.
 set_target_properties(mujoco_wasm PROPERTIES
-    LINK_FLAGS "${EMCC_LINKER_FLAGS_STR}"
+    LINK_FLAGS "${MUJOCO_WASM_LINKER_FLAGS_STR}"
     OUTPUT_NAME "mujoco"
 )
 
-# Link the mujoco library as a whole archive to avoid losing plugin
-# registration such as obj_decoder and stl_decoder.
-target_link_libraries(mujoco_wasm PRIVATE
-    -Wl,--whole-archive mujoco -Wl,--no-whole-archive
-    ccd lodepng tinyxml2 qhullstatic_r
-)
+target_link_libraries(mujoco_wasm PRIVATE ${MUJOCO_WASM_LINK_LIBRARIES})
 
 install(TARGETS mujoco_wasm DESTINATION ${DIVISIBLE_INSTALL_BIN_DIR})
+
+# --- Benchmark target ---
+
+if(MUJOCO_BUILD_TESTS_WASM)
+    file(GLOB MUJOCO_WASM_BENCHMARK_FILES
+        "tests/benchmark_test.cc"
+        "unpack.cc"
+    )
+
+    if(NOT MUJOCO_WASM_BENCHMARK_FILES)
+        message(FATAL_ERROR "No benchmark source files found")
+    endif()
+
+    set(BENCHMARK_LINKER_FLAGS ${EMCC_LINKER_FLAGS} "--emit-tsd mujoco_wasm_benchmark.d.ts")
+    string(REPLACE ";" " " BENCHMARK_LINKER_FLAGS_STR "${BENCHMARK_LINKER_FLAGS}")
+
+    add_executable(mujoco_wasm_benchmark ${MUJOCO_WASM_BENCHMARK_FILES})
+
+    set_target_properties(mujoco_wasm_benchmark PROPERTIES
+        LINK_FLAGS "${BENCHMARK_LINKER_FLAGS_STR}"
+    )
+
+    target_link_libraries(mujoco_wasm_benchmark PRIVATE ${MUJOCO_WASM_LINK_LIBRARIES})
+
+    install(TARGETS mujoco_wasm_benchmark DESTINATION ${DIVISIBLE_INSTALL_BIN_DIR})
+endif()

wasm/tests/CMakeLists.txt

@@ -1,63 +0,0 @@
-# Copyright 2025 DeepMind Technologies Limited
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/wasm/dist")
-
-set(CMAKE_INSTALL_PREFIX ${PROJECT_SOURCE_DIR}/wasm)
-
-include_directories(${PROJECT_SOURCE_DIR}/include)
-include_directories(${PROJECT_SOURCE_DIR}/src)
-include_directories(${PROJECT_SOURCE_DIR})
-
-link_directories(${CMAKE_BINARY_DIR}/lib)
-
-file(GLOB MUJOCO_WASM_FILES
-    "benchmark_test.cc"
-    "../unpack.cc"
-)
-
-if(NOT MUJOCO_WASM_FILES)
-    message(FATAL_ERROR "No source files found")
-endif()
-
-# Set Emscripten linker flags
-set(EMCC_LINKER_FLAGS
-    "--bind"
-    "-pthread"
-    "-s PTHREAD_POOL_SIZE=navigator.hardwareConcurrency"
-    "-s ASSERTIONS=1"
-    "-s ALLOW_MEMORY_GROWTH=1"
-    "-s EXPORT_ES6=1"
-    "-s MODULARIZE=1"
-    "-s FORCE_FILESYSTEM=1"
-    "-s EXPORTED_RUNTIME_METHODS=['ccall','cwrap','FS','MEMFS']"
-    "-s EXPORT_NAME=loadMujoco"
-    "-gsource-map"
-    "-g"
-    "--emit-tsd mujoco_wasm_benchmark.d.ts"
-)
-string (REPLACE ";" " " EMCC_LINKER_FLAGS_STR "${EMCC_LINKER_FLAGS}")
-
-add_executable(mujoco_wasm_benchmark ${MUJOCO_WASM_FILES})
-
-set_target_properties(mujoco_wasm_benchmark PROPERTIES LINK_FLAGS "${EMCC_LINKER_FLAGS_STR}")
-
-# Link the mujoco library as a whole archive to avoid losing plugin
-# registration such as obj_decoder and stl_decoder.
-target_link_libraries(mujoco_wasm_benchmark PRIVATE
-    -Wl,--whole-archive mujoco -Wl,--no-whole-archive
-    ccd lodepng tinyxml2 qhullstatic_r
-)
-
-install(TARGETS mujoco_wasm_benchmark DESTINATION ${DIVISIBLE_INSTALL_BIN_DIR})