API/jsi/jsi/CMakeLists.txt:15-24 chooses jsi's compile flags off the
compiler ID string:
set(jsi_compile_flags "")
if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" OR
"${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
list(APPEND jsi_compile_flags "-Wno-non-virtual-dtor")
elseif ("${CMAKE_CXX_COMPILER_ID}" MATCHES "MSVC")
# Turn on Error Handling in MSVC, otherwise objects are not destructed
# when they go out of scope due to exceptions.
list(APPEND jsi_compile_flags "/EHsc")
endif()Under clang-cl the ID is Clang, so the first branch is taken and the
/EHsc at :22 — whose comment says exactly why it is needed — is never
reached. That matters because clang-cl targets the MSVC ABI and defaults to
exceptions off, so jsi.cpp fails to compile:
jsi.cpp(113,5): error: cannot use 'throw' with exceptions disabled (x11)
FAILED: .../jsi/CMakeFiles/jsi.dir/jsi.cpp.obj
CMake's MSVC variable is true for clang-cl and is the test that expresses
the intent here ("this compiler is targeting the MSVC ABI"); the ID string is
not.
This is filed separately from the hermes_update_cxx_flags /
/EHsc-strip issue (#2173) on purpose. jsi is the one target in the tree that never
goes through hermes_update_cxx_flags, so fixing that function would not fix
this file. It is the same mistake in a second, independent place.
Repro
git clone https://github.com/facebook/hermes.git hermes-static
cd hermes-static
git checkout 5cee10abc93667ea5538caecaf0a457c66fa5bdc
call "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars64.bat"
set CLANGCL=C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/Llvm/x64/bin/clang-cl.exe
cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release ^
-DCMAKE_C_COMPILER="%CLANGCL%" -DCMAKE_CXX_COMPILER="%CLANGCL%" ^
-DHERMES_ENABLE_TEST_SUITE=OFF -DHERMES_ENABLE_NAPI=OFF
(HERMES_ENABLE_TEST_SUITE=OFF and HERMES_ENABLE_NAPI=OFF only shorten the
build; neither is load-bearing for the failure below.) Then:
cmake --build build --target jsi
Expected: compiles. Actual: eleven cannot use 'throw' with exceptions disabled
in API/jsi/jsi/jsi.cpp.
To see the choice itself rather than its consequence, add
message(STATUS "jsi flags: ${jsi_compile_flags}") after :23 — it prints
-Wno-non-virtual-dtor under clang-cl, with no /EHsc.
Environment
Windows 11 Pro 10.0.26200, x86-64
CMake 3.31.6-msvc6 (the one Visual Studio 2022 ships), Ninja 1.13.2
Visual Studio 2022 Community
> clang-cl --version
clang version 19.1.5
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\Llvm\x64\bin
Proposed fix (one line)
Change the elseif at API/jsi/jsi/CMakeLists.txt:19 to test CMake's MSVC
variable rather than the compiler ID string — i.e. elseif (MSVC) — so any
MSVC-ABI compiler, clang-cl included, gets the /EHsc the comment above it asks
for. (If the -Wno-non-virtual-dtor is still wanted for clang-cl, the two are
not exclusive and both can be appended.)
Related issues
Where this came from
Measured while embedding static_h as the second runtime of a native game host on Windows (the repository is private at the time of filing, so no links). The workaround used downstream is a directory-scope /EHsc in the consuming project, chosen over target_compile_options(jsi PRIVATE /EHsc) precisely because the per-target fix covered this file and left four others failing (#2173). No file under the Hermes checkout was edited.
API/jsi/jsi/CMakeLists.txt:15-24choosesjsi's compile flags off thecompiler ID string:
Under clang-cl the ID is
Clang, so the first branch is taken and the/EHscat:22— whose comment says exactly why it is needed — is neverreached. That matters because clang-cl targets the MSVC ABI and defaults to
exceptions off, so
jsi.cppfails to compile:CMake's
MSVCvariable is true for clang-cl and is the test that expressesthe intent here ("this compiler is targeting the MSVC ABI"); the ID string is
not.
This is filed separately from the
hermes_update_cxx_flags//EHsc-strip issue (#2173) on purpose.jsiis the one target in the tree that nevergoes through
hermes_update_cxx_flags, so fixing that function would not fixthis file. It is the same mistake in a second, independent place.
Repro
(
HERMES_ENABLE_TEST_SUITE=OFFandHERMES_ENABLE_NAPI=OFFonly shorten thebuild; neither is load-bearing for the failure below.) Then:
Expected: compiles. Actual: eleven
cannot use 'throw' with exceptions disabledin
API/jsi/jsi/jsi.cpp.To see the choice itself rather than its consequence, add
message(STATUS "jsi flags: ${jsi_compile_flags}")after:23— it prints-Wno-non-virtual-dtorunder clang-cl, with no/EHsc.Environment
Proposed fix (one line)
Change the
elseifatAPI/jsi/jsi/CMakeLists.txt:19to test CMake'sMSVCvariable rather than the compiler ID string — i.e.
elseif (MSVC)— so anyMSVC-ABI compiler, clang-cl included, gets the
/EHscthe comment above it asksfor. (If the
-Wno-non-virtual-dtoris still wanted for clang-cl, the two arenot exclusive and both can be appended.)
Related issues
hermes_update_cxx_flags//EHsc-strip issue incmake/modules/Hermes.cmake,static_h: the tree cannot be compiled with clang-cl — CMake's/EHscis stripped andhermes_update_cxx_flagsreplaces it with GCC spellings clang-cl ignores #2173, is the same mistake in the other place; fixing either alone leaves the tree failing.Where this came from
Measured while embedding
static_has the second runtime of a native game host on Windows (the repository is private at the time of filing, so no links). The workaround used downstream is a directory-scope/EHscin the consuming project, chosen overtarget_compile_options(jsi PRIVATE /EHsc)precisely because the per-target fix covered this file and left four others failing (#2173). No file under the Hermes checkout was edited.