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Fix #155: switch WASM builds from legacy Asyncify to JSPI
cmake/Emscripten.cmake set both -fwasm-exceptions (compile + link) and -sASYNCIFY=1 (per-target link), and recent emsdk releases hard-fail the combination in wasm-opt with `__asyncify_get_call_index does not exist`, breaking the wasm.yml workflow. JSPI (JavaScript Promise Integration) is the upstream-recommended replacement for legacy Asyncify and is compatible with native WebAssembly exception handling, so the per-target flag now reads -sJSPI=1 and the no-longer-relevant myproject_WASM_ASYNCIFY_STACK_SIZE cache variable is dropped. A new CMake-script regression test stubs the target/global option commands, includes Emscripten.cmake under EMSCRIPTEN=TRUE, and asserts that the legacy flags are gone, JSPI is emitted, and -fwasm-exceptions remains.
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Lines changed: 142 additions & 5 deletions

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‎cmake/Emscripten.cmake‎

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@@ -42,8 +42,6 @@ if(EMSCRIPTEN)
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"Initial WASM memory in bytes (default: 32MB)")
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set(myproject_WASM_PTHREAD_POOL_SIZE "4" CACHE STRING
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"Pthread pool size for WASM builds (default: 4)")
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set(myproject_WASM_ASYNCIFY_STACK_SIZE "65536" CACHE STRING
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"Asyncify stack size in bytes (default: 64KB)")
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# For Emscripten WASM builds, FTXUI requires pthreads and native exception handling
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# Set these flags early so they propagate to all dependencies
@@ -89,9 +87,11 @@ function(myproject_configure_wasm_target target)
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"-sUSE_PTHREADS=1"
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"-sPROXY_TO_PTHREAD=1"
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"-sPTHREAD_POOL_SIZE=${myproject_WASM_PTHREAD_POOL_SIZE}"
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# Enable asyncify for emscripten_sleep and async operations
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"-sASYNCIFY=1"
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"-sASYNCIFY_STACK_SIZE=${myproject_WASM_ASYNCIFY_STACK_SIZE}"
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# Enable JSPI (JavaScript Promise Integration) for emscripten_sleep
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# and other async operations. JSPI is the modern replacement for
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# legacy Asyncify (-sASYNCIFY=1) and, unlike Asyncify, is compatible
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# with native WebAssembly exception handling (-fwasm-exceptions).
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"-sJSPI=1"
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# Memory configuration
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"-sALLOW_MEMORY_GROWTH=1"
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"-sINITIAL_MEMORY=${myproject_WASM_INITIAL_MEMORY}"

‎test/CMakeLists.txt‎

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@@ -34,6 +34,15 @@ add_test(
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COMMAND ${CMAKE_COMMAND} -P
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${CMAKE_CURRENT_SOURCE_DIR}/cmake/test_sanitizers_non_apple_includes_leak.cmake)
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# CMake-script regression test for cmake/Emscripten.cmake (issue #155):
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# the legacy `-sASYNCIFY=1` flag is incompatible with `-fwasm-exceptions`
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# under modern emsdk; the WASM target must use the JSPI replacement.
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add_test(
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NAME cmake.emscripten.modern_async
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COMMAND ${CMAKE_COMMAND}
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-DTEST_TMP_DIR=${CMAKE_CURRENT_BINARY_DIR}/test_emscripten_modern_async
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-P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/test_emscripten_modern_async.cmake)
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# Provide a test to verify that the version being reported from the application
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# matches the version given to CMake. This will be important once you package
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# your program. Real world shows that this is the kind of simple mistake that is easy

‎test/cmake/test_emscripten_modern_async.cmake‎

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@@ -0,0 +1,128 @@
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#[[
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Regression test for #155: WASM builds were broken because
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cmake/Emscripten.cmake combined two flags that newer Emscripten releases
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reject in the same translation unit:
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* -fwasm-exceptions (set via add_compile_options / add_link_options)
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* -sASYNCIFY=1 (set via target_link_options on each WASM target)
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The link step ended in `wasm-opt` with
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`Fatal: Module::getFunction: __asyncify_get_call_index does not exist`
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because the legacy Asyncify transformation is incompatible with native
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WebAssembly exception handling.
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Per the issue ("Prefer the modern replacement features") the project
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should use JSPI (JavaScript Promise Integration) instead, which is the
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upstream-recommended replacement for legacy Asyncify and works alongside
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-fwasm-exceptions.
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This test simulates an EMSCRIPTEN configuration, stubs the CMake commands
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that touch real targets, includes Emscripten.cmake, and asserts that:
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1. The legacy `-sASYNCIFY=1` flag is NOT emitted (regression guard).
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2. The legacy `-sASYNCIFY_STACK_SIZE` flag is NOT emitted (irrelevant
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for JSPI).
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3. The modern `-sJSPI=1` flag IS emitted on the WASM target.
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4. `-fwasm-exceptions` is still active on the global compile/link
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options so native EH continues to be used.
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]]
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cmake_minimum_required(VERSION 3.21)
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set(EMSCRIPTEN TRUE)
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# Use the real source tree so EXISTS checks against the shell template pass
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# and Emscripten.cmake's input templates resolve correctly.
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set(CMAKE_SOURCE_DIR "${CMAKE_CURRENT_LIST_DIR}/../..")
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# Caller (CTest) supplies an out-of-tree scratch dir via -DTEST_TMP_DIR=...;
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# fall back to the platform temp dir when the script is invoked manually.
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if(NOT DEFINED TEST_TMP_DIR OR TEST_TMP_DIR STREQUAL "")
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set(TEST_TMP_DIR "$ENV{TMPDIR}")
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if(TEST_TMP_DIR STREQUAL "")
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set(TEST_TMP_DIR "/tmp")
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endif()
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set(TEST_TMP_DIR "${TEST_TMP_DIR}/cmake_template_test_emscripten_modern_async")
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endif()
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set(CMAKE_BINARY_DIR "${TEST_TMP_DIR}")
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file(MAKE_DIRECTORY "${CMAKE_BINARY_DIR}")
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set(CAPTURE_FILE "${CMAKE_BINARY_DIR}/captured_options.txt")
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file(WRITE "${CAPTURE_FILE}" "")
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# Capture global compile / link options emitted at module-include time.
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function(add_compile_options)
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file(APPEND "${CAPTURE_FILE}" "ADD_COMPILE_OPTIONS:${ARGN}\n")
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endfunction()
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function(add_link_options)
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file(APPEND "${CAPTURE_FILE}" "ADD_LINK_OPTIONS:${ARGN}\n")
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endfunction()
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# Capture per-target link options. Drop the leading <target> <scope> args
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# so the captured payload is easy to grep.
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function(target_link_options)
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set(_args "${ARGN}")
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list(REMOVE_AT _args 0 1)
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file(APPEND "${CAPTURE_FILE}" "TARGET_LINK_OPTIONS:${_args}\n")
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endfunction()
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# Stub out the rest of the target-affecting commands so script mode
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# doesn't try to look up a real CMake target.
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function(target_compile_definitions)
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endfunction()
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function(get_target_property var target prop)
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set(${var} "${target}" PARENT_SCOPE)
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endfunction()
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function(set_target_properties)
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endfunction()
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function(add_custom_command)
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endfunction()
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function(configure_file)
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endfunction()
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function(set_property)
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endfunction()
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include("${CMAKE_CURRENT_LIST_DIR}/../../cmake/Emscripten.cmake")
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myproject_configure_wasm_target(
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fake_wasm_target
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TITLE "Fake"
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DESCRIPTION "Fake WASM target for regression test #155")
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file(READ "${CAPTURE_FILE}" captures)
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message(STATUS "Captured Emscripten options:\n${captures}")
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if(captures MATCHES "ASYNCIFY=1")
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message(
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FATAL_ERROR
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"Legacy -sASYNCIFY=1 must not be emitted: it is incompatible with "
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"-fwasm-exceptions and breaks WASM linking (#155). Captured:\n${captures}")
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endif()
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if(captures MATCHES "ASYNCIFY_STACK_SIZE")
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message(
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FATAL_ERROR
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"-sASYNCIFY_STACK_SIZE is only meaningful for legacy Asyncify and "
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"should be removed alongside -sASYNCIFY=1 (#155). Captured:\n${captures}")
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endif()
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if(NOT captures MATCHES "-sJSPI=1")
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message(
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FATAL_ERROR
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"Expected modern -sJSPI=1 flag (replacement for legacy Asyncify) on "
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"the WASM target (#155). Captured:\n${captures}")
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endif()
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if(NOT captures MATCHES "-fwasm-exceptions")
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message(
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FATAL_ERROR
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"-fwasm-exceptions must remain enabled for WASM builds; the fix "
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"for #155 should switch async support, not disable native EH. "
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"Captured:\n${captures}")
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endif()

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