`API/jsi/jsi/CMakeLists.txt` tests `CMAKE_CXX_COMPILER_ID MATCHES "MSVC"`, so clang-cl gets neither branch's flags

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

• #1247 (2024), where the maintainers said Static Hermes would support Windows "only via Clang" — i.e. clang-cl is the intended Windows compiler, and this file's test excludes it.
• The hermes_update_cxx_flags / /EHsc-strip issue in cmake/modules/Hermes.cmake, #2173, is the same mistake in the other place; fixing either alone leaves the tree failing.

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.