compile with clang 20.1.0 error: 'lifetimebound' attribute cannot be applied to a....

[marakew]

[5/6] D:\LLVM-20.x.x-win64\bin\clang++.exe  -isystem D:/msvc/VC/Tools/MSVC/14.43.34808/include -isystem D:/msvc/V
C/Tools/MSVC/14.43.34808/atlmfc/include -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/ucr
t" -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/shared" -isystem "D:/Program Files (x86)
/Windows Kits/10/Include/10.0.18362.0/um" -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/w
inrt" -O3 -DNDEBUG -std=c++20 -Xclang -flto-visibility-public-std -D_MT -Xclang --dependent-lib=libcmt -MD -MT CM
akeFiles/demo.dir/main.cpp.obj -MF CMakeFiles\demo.dir\main.cpp.obj.d @CMakeFiles\demo.dir\main.cpp.obj.modmap -o
 CMakeFiles/demo.dir/main.cpp.obj -c D:/T60/test/CMake_Modules/main.cpp
FAILED: CMakeFiles/demo.dir/main.cpp.obj
D:\LLVM-20.x.x-win64\bin\clang++.exe  -isystem D:/msvc/VC/Tools/MSVC/14.43.34808/include -isystem D:/msvc/VC/Tool
s/MSVC/14.43.34808/atlmfc/include -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/ucrt" -is
ystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/shared" -isystem "D:/Program Files (x86)/Windo
ws Kits/10/Include/10.0.18362.0/um" -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/winrt"
-O3 -DNDEBUG -std=c++20 -Xclang -flto-visibility-public-std -D_MT -Xclang --dependent-lib=libcmt -MD -MT CMakeFil
es/demo.dir/main.cpp.obj -MF CMakeFiles\demo.dir\main.cpp.obj.d @CMakeFiles\demo.dir\main.cpp.obj.modmap -o CMake
Files/demo.dir/main.cpp.obj -c D:/T60/test/CMake_Modules/main.cpp
In module 'MyModule' imported from D:/T60/test/CMake_Modules/main.cpp:1:
D:/msvc/VC/Tools/MSVC/14.43.34808/include\utility:784:6: error: 'lifetimebound' attribute cannot be applied to a
parameter of a function that returns void; did you mean 'lifetime_capture_by(X)'
  784 | void as_const(const _Ty&&) = delete;
      |      ^
1 error generated.
ninja: build stopped: subcommand failed.

microsoft/STL#5271 (comment)

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: John Doe (marakew)

``` [5/6] D:\LLVM-20.x.x-win64\bin\clang++.exe -isystem D:/msvc/VC/Tools/MSVC/14.43.34808/include -isystem D:/msvc/V C/Tools/MSVC/14.43.34808/atlmfc/include -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/ucr t" -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/shared" -isystem "D:/Program Files (x86) /Windows Kits/10/Include/10.0.18362.0/um" -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/w inrt" -O3 -DNDEBUG -std=c++20 -Xclang -flto-visibility-public-std -D_MT -Xclang --dependent-lib=libcmt -MD -MT CM akeFiles/demo.dir/main.cpp.obj -MF CMakeFiles\demo.dir\main.cpp.obj.d @CMakeFiles\demo.dir\main.cpp.obj.modmap -o CMakeFiles/demo.dir/main.cpp.obj -c D:/T60/test/CMake_Modules/main.cpp FAILED: CMakeFiles/demo.dir/main.cpp.obj D:\LLVM-20.x.x-win64\bin\clang++.exe -isystem D:/msvc/VC/Tools/MSVC/14.43.34808/include -isystem D:/msvc/VC/Tool s/MSVC/14.43.34808/atlmfc/include -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/ucrt" -is ystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/shared" -isystem "D:/Program Files (x86)/Windo ws Kits/10/Include/10.0.18362.0/um" -isystem "D:/Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/winrt" -O3 -DNDEBUG -std=c++20 -Xclang -flto-visibility-public-std -D_MT -Xclang --dependent-lib=libcmt -MD -MT CMakeFil es/demo.dir/main.cpp.obj -MF CMakeFiles\demo.dir\main.cpp.obj.d @CMakeFiles\demo.dir\main.cpp.obj.modmap -o CMake Files/demo.dir/main.cpp.obj -c D:/T60/test/CMake_Modules/main.cpp In module 'MyModule' imported from D:/T60/test/CMake_Modules/main.cpp:1: D:/msvc/VC/Tools/MSVC/14.43.34808/include\utility:784:6: error: 'lifetimebound' attribute cannot be applied to a parameter of a function that returns void; did you mean 'lifetime_capture_by(X)' 784 | void as_const(const _Ty&&) = delete; | ^ 1 error generated. ninja: build stopped: subcommand failed. ```

microsoft/STL#5271 (comment)

[frederick-vs-ja]

31b0be4 (https://reviews.llvm.org/D141744) and #114203 are possibly related.

[kamrann]

I've run into this too since somewhere around a couple of months back on trunk. It appears to be specifically a problem when using C++ 20 modules. I hit the error when building my project using modules (just for my own code, not import std); the same project without modules is building successfully.

[hypengw]

Same on libstdc++ 14.2.1.

[cor3ntin]

@ilya-biryukov @bricknerb

[ilya-biryukov]

We should only apply the attribute to as_const if it does not return void, I will send a patch. The problem is here:

llvm-project/clang/lib/Sema/SemaAttr.cpp

Line 229 in 0f2fb2b

case Builtin::BIas_const:

It also seems weird to make this a hard error, I propose to downgrade that to a warning. Failing all builds seems too harsh for this, those who care about these kinds of things probably already pass -Werror
@cor3ntin, does that sound reasonable or are there reasons to keep this an error? also @bricknerb @usx95 in case you have thoughts on this.

[ilya-biryukov]

@cor3ntin this problem is in the latest Clang release, right? Should we have a new minor release with this fix?
(IIUC, Clang can't compile any file that has #include <utility> from Microsoft's STL, this seems like a major issue)