Bug #119238 Compilation error with clang 20

Submitted:	27 Oct 2025 7:31	Modified:	9 Jun 13:52
Reporter:	Laurynas Biveinis (OCA)	Email Updates:
Status:	Open	Impact on me:	None
Category:	MySQL Server: Compiling	Severity:	S3 (Non-critical)
Version:	8.0.45	OS:	MacOS (26.0.1)
Assigned to:		CPU Architecture:	ARM

Description:
CMake options: -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DFORCE_UNSUPPORTED_COMPILER=ON -DBUILD_CONFIG=mysql_release -DCMAKE_BUILD_TYPE=Release -DMYSQL_MAINTAINER_MODE=ON -DWITH_SYSTEM_LIBS=ON -DWITH_NDBCLUSTER_STORAGE_ENGINE=OFF -DDOWNLOAD_BOOST=ON -DWITH_BOOST=(path) -DFORCE_COLORED_OUTPUT=ON -DCMAKE_CXX_FLAGS=-g -DCMAKE_CXX_FLAGS_DEBUG=-g -DCMAKE_CXX_FLAGS_RELEASE=-O2 -DNDEBUG -g

with Homebrew-installed LLVM 20 result in

FAILED: [code=1] router/src/harness/src/CMakeFiles/harness_stdx.dir/stdx/filesystem.cc.o
/opt/homebrew/opt/llvm@20/bin/clang++ -DBOOST_NO_CXX98_FUNCTION_BASE -DHAVE_TLSv13 -DLZ4_DISABLE_DEPRECATE_WARNINGS -D_USE_MATH_DEFINES -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Dharness_stdx_EXPORTS -I/Users/laurynas/vilniusdb/mysql-8.0.44/_build-release-llvm-20 -I/Users/laurynas/vilniusdb/mysql-8.0.44/_build-release-llvm-20/include -I/Users/laurynas/vilniusdb/mysql-8.0.44 -I/Users/laurynas/vilniusdb/mysql-8.0.44/include -I/Users/laurynas/vilniusdb/mysql-8.0.44/_build-release-llvm-20/router -I/Users/laurynas/vilniusdb/mysql-8.0.44/_build-release-llvm-20/router/include -I/Users/laurynas/vilniusdb/mysql-8.0.44/router/src/harness/src/../include -I/Users/laurynas/vilniusdb/mysql-8.0.44/router/src/harness/src -I/Users/laurynas/vilniusdb/mysql-8.0.44/_build-release-llvm-20/router/src/harness/src/../include -isystem /Users/laurynas/vilniusdb/mysql-8.0.44/extra/rapidjson/include -isystem /opt/homebrew/opt/openssl@1.1/include -isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/editline -isystem /opt/homebrew/include -std=c++17 -fno-omit-frame-pointer -ftls-model=initial-exec -g -Wall -Wextra -Wformat-security -Wvla -Wundef -Wmissing-format-attribute -Woverloaded-virtual -Wcast-qual -Wno-null-conversion -Wno-unused-private-field -Wconditional-uninitialized -Wdeprecated -Wno-deprecated-declarations -Wno-shorten-64-to-32 -Wextra-semi -Wheader-hygiene -Wnon-virtual-dtor -Wundefined-reinterpret-cast -Wrange-loop-analysis -Winconsistent-missing-destructor-override -Winconsistent-missing-override -Wshadow-field -Werror -ffunction-sections -fdata-sections -O2 -DNDEBUG -g -arch arm64 -fPIC -fcolor-diagnostics -MD -MT router/src/harness/src/CMakeFiles/harness_stdx.dir/stdx/filesystem.cc.o -MF router/src/harness/src/CMakeFiles/harness_stdx.dir/stdx/filesystem.cc.o.d  --language=c++  -o router/src/harness/src/CMakeFiles/harness_stdx.dir/stdx/filesystem.cc.o -c /Users/laurynas/vilniusdb/mysql-8.0.44/router/src/harness/src/stdx/filesystem.cc
In file included from /Users/laurynas/vilniusdb/mysql-8.0.44/router/src/harness/src/stdx/filesystem.cc:40:
/Users/laurynas/vilniusdb/mysql-8.0.44/router/src/harness/src/../include/mysql/harness/stdx/expected.h:74:8: error: 'is_default_constructible' cannot be specialized: Users are not allowed to specialize this standard library entity [-Winvalid-specialization]
   74 | struct is_default_constructible<std::unique_ptr<T, void (*)(T *)>>
      |        ^
/opt/homebrew/Cellar/llvm@20/20.1.8/bin/../include/c++/v1/__type_traits/is_constructible.h:51:29: note: marked 'no_specializations' here
   51 | struct _LIBCPP_TEMPLATE_VIS _LIBCPP_NO_SPECIALIZATIONS is_default_constructible
      |                             ^
/opt/homebrew/Cellar/llvm@20/20.1.8/bin/../include/c++/v1/__config:1177:9: note: expanded from macro '_LIBCPP_NO_SPECIALIZATIONS'
 1177 |       [[_Clang::__no_specializations__("Users are not allowed to specialize this standard library entity")]]
      |         ^

How to repeat:
See above

The build completes with -Wno-invalid-specialization

8.4.7 is not affected

Same with 8.0.45

Same with 8.0.46 with current XCode

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