Fix #666: TSAN builds don't actually use threads

TSAN builds did not explicitly enable MULTITHREAD_SUPPORT_ENABLED, so they
relied on the CMake default. This adds -DMULTITHREAD_SUPPORT_ENABLED=ON to
both TSAN jobs and expands the CI matrix to cover threading on/off with
Debug/Release for Linux, macOS, and Windows MSVC. Also excludes async-dependent
.chai tests from non-threaded builds and adds a Threading_Config_Test to verify
the threading configuration is correct in both modes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -9,17 +9,18 @@ on:
 
 jobs:
   linux:
-    name: Linux GCC ${{ matrix.build_type }}
+    name: Linux GCC ${{ matrix.build_type }} threads=${{ matrix.multithread }}
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
         build_type: [Debug, Release]
+        multithread: [ON, OFF]
     steps:
       - uses: actions/checkout@v4
 
       - name: Configure
-        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }}
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DMULTITHREAD_SUPPORT_ENABLED=${{ matrix.multithread }}
 
       - name: Build
         run: cmake --build build -j
@@ -28,17 +29,18 @@ jobs:
         run: ctest --test-dir build --output-on-failure
 
   macos:
-    name: macOS AppleClang ${{ matrix.build_type }}
+    name: macOS AppleClang ${{ matrix.build_type }} threads=${{ matrix.multithread }}
     runs-on: macos-latest
     strategy:
       fail-fast: false
       matrix:
         build_type: [Debug, Release]
+        multithread: [ON, OFF]
     steps:
       - uses: actions/checkout@v4
 
       - name: Configure
-        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }}
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DMULTITHREAD_SUPPORT_ENABLED=${{ matrix.multithread }}
 
       - name: Build
         run: cmake --build build -j
@@ -85,17 +87,18 @@ jobs:
         run: ctest --test-dir build --output-on-failure
 
   windows:
-    name: Windows MSVC ${{ matrix.build_type }}
+    name: Windows MSVC ${{ matrix.build_type }} threads=${{ matrix.multithread }}
     runs-on: windows-latest
     strategy:
       fail-fast: false
       matrix:
         build_type: [Debug, Release]
+        multithread: [ON, OFF]
     steps:
       - uses: actions/checkout@v4
 
       - name: Configure
-        run: cmake -B build
+        run: cmake -B build -DMULTITHREAD_SUPPORT_ENABLED=${{ matrix.multithread }}
 
       - name: Build
         run: cmake --build build --config ${{ matrix.build_type }} -j
@@ -114,7 +117,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Configure
-        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_THREAD_SANITIZER=ON
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_THREAD_SANITIZER=ON -DMULTITHREAD_SUPPORT_ENABLED=ON
 
       - name: Build
         run: cmake --build build -j
@@ -133,7 +136,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Configure
-        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_THREAD_SANITIZER=ON
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_THREAD_SANITIZER=ON -DMULTITHREAD_SUPPORT_ENABLED=ON
 
       - name: Build
         run: cmake --build build -j

CMakeLists.txt

@@ -292,6 +292,15 @@ endif()
 file(GLOB UNIT_TESTS RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}/unittests/ ${CMAKE_CURRENT_SOURCE_DIR}/unittests/*.chai ${CMAKE_CURRENT_SOURCE_DIR}/unittests/3.x/*.chai)
 list(SORT UNIT_TESTS)
 
+if(NOT MULTITHREAD_SUPPORT_ENABLED)
+  list(REMOVE_ITEM UNIT_TESTS
+    async_engine_lifetime.chai
+    future.chai
+    list_push_front.chai
+    move_async.chai
+  )
+endif()
+
 file(GLOB PERFORMANCE_TESTS RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}/performance_tests/ ${CMAKE_CURRENT_SOURCE_DIR}/performance_tests/*.chai)
 list(SORT PERFORMANCE_TESTS)
 
@@ -430,6 +439,10 @@ if(BUILD_TESTING)
     target_link_libraries(emscripten_eval_test ${LIBS})
     add_test(NAME Emscripten_Eval_Test COMMAND emscripten_eval_test)
 
+    add_executable(threading_config_test unittests/threading_config_test.cpp)
+    target_link_libraries(threading_config_test ${LIBS})
+    add_test(NAME Threading_Config_Test COMMAND threading_config_test)
+
     install(TARGETS test_module RUNTIME DESTINATION bin LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}/chaiscript")
   endif()
 endif()

unittests/threading_config_test.cpp

@@ -0,0 +1,26 @@
+#include <chaiscript/chaiscript.hpp>
+
+int main() {
+#ifndef CHAISCRIPT_NO_THREADS
+  // When threading is enabled, verify that async() is registered and functional
+  chaiscript::ChaiScript chai;
+  const auto result = chai.eval<int>(R"(
+    var f = async(fun() { return 42; });
+    f.get();
+  )");
+  if (result != 42) {
+    return EXIT_FAILURE;
+  }
+#else
+  // When threading is disabled, verify that async() is NOT registered
+  chaiscript::ChaiScript chai;
+  try {
+    chai.eval("async(fun() { return 0; })");
+    return EXIT_FAILURE;
+  } catch (const std::exception &) {
+    // Expected: async should not exist
+  }
+#endif
+
+  return EXIT_SUCCESS;
+}