Homebrew Boost 1.78 breaks external signer configure #24413

Test on macOS 12.2.1 against the master branch. #24397 doesn't fix it.

brew info boost
boost: stable 1.78.0 (bottled), HEAD
...
./configure --enable-external-signer
...
checking for boostlib >= 1.64.0 (106400)... yes
checking whether Boost.Process can be used... no
configure: error: External signing is not supported for this Boost version

It does work with boost 1.76 (there was no 1.77 release in home-brew):

brew install boost@1.76
...
LDFLAGS="-L/usr/local/opt/boost@1.76/lib" CPPFLAGS="-I/usr/local/opt/boost@1.76/include" ./configure --enable-external-signer
...
checking for boostlib >= 1.64.0 (106400)... yes
checking whether Boost.Process can be used... yes
...
Options used to compile and link:
  external signer = yes

There's nothing in the release notes about Boost.Process for either 1.77 or 1.78.

The Homebrew formula changes are nothing but a trivial version and hash bump.

The configure check is failing because of this issue: https://github.com/boostorg/process/issues/235

configure:32793: checking whether Boost.Process can be used
configure:32806: g++ -std=c++17 -o conftest -g -O2  -DHAVE_BUILD_INFO -DMAC_OSX -DOBJC_OLD_DISPATCH_PROTOTYPES=0 -DPROVIDE_FUZZ_MAIN_FUNCTION  -Wl,-headerpad_max_install_names -Wl,-dead_strip -Wl,-dead_strip_dylibs conftest.cpp  >&5
In file included from conftest.cpp:77:
In file included from /usr/local/include/boost/process.hpp:24:
In file included from /usr/local/include/boost/process/async_system.hpp:22:
In file included from /usr/local/include/boost/process/child.hpp:22:
In file included from /usr/local/include/boost/process/detail/execute_impl.hpp:24:
/usr/local/include/boost/process/detail/posix/executor.hpp:156:36: error: non-constant-expression cannot be narrowed from type 'unsigned long' to 'int' in initializer list [-Wc++11-narrowing]
        int data[2] = {ec.value(), len + 1};
                                   ^~~~~~~
/usr/local/include/boost/process/detail/posix/executor.hpp:156:36: note: insert an explicit cast to silence this issue
        int data[2] = {ec.value(), len + 1};
                                   ^~~~~~~
                                   static_cast<int>( )
1 error generated.

Ok, we should probably just document the workaround and point to this issue for when the upstream fix is ready and released.

Fixed in #24415.

Interesting that "macOS 12 native" CI task still install boost 1.76.0.

Probably because it doesn't run brew update (which is very slow).

It might make sense to have the CI run brew update && brew upgrade on the master branch one per month, or something like that. Or manually reset the cache on that schedule. cc @MarcoFalke

It might make sense to have the CI run brew update && brew upgrade on the master branch one per month, or something like that. Or manually reset the cache on that schedule. cc @MarcoFalke

Related: https://github.com/cirruslabs/cirrus-ci-docs/issues/878

[-Wc++11-narrowing]

Why is this warning being treated as an error in the configure check?

Did you perhaps set C*FLAGS to include -Werror explicitly?

Why is this warning being treated as an error in the configure check?

It's being treated as an error because Clang treats it as an error:

int main() {
	auto a = 10.0;
	int b = {a + 1};
	return 0;
}

If I compile this with LLVM Clang 13.0.1:

/usr/local/opt/llvm/bin/clang++ --version               
Homebrew clang version 13.0.1
...
/usr/local/opt/llvm/bin/clang++ -std=c++17 narrowing.cpp                                                                  
narrowing.cpp:3:11: error: type 'double' cannot be narrowed to 'int' in initializer list [-Wc++11-narrowing]
        int b = {a + 1};
                 ^~~~~
narrowing.cpp:3:11: note: insert an explicit cast to silence this issue
        int b = {a + 1};
                 ^~~~~
                 static_cast<int>( )
1 error generated.

or Apple Clang 13:

clang++ --version               
Apple clang version 13.0.0 (clang-1300.0.29.30)
...
clang++ -std=c++17 narrowing.cpp
narrowing.cpp:3:11: error: type 'double' cannot be narrowed to 'int' in initializer list [-Wc++11-narrowing]
        int b = {a + 1};
                 ^~~~~
narrowing.cpp:3:11: note: insert an explicit cast to silence this issue
        int b = {a + 1};
                 ^~~~~
                 static_cast<int>( )
1 error generated.

GCC 11 warns but does not error:

/usr/local/opt/gcc@11/bin/gcc-11 --version               
gcc-11 (Homebrew GCC 11.2.0_3) 11.2.0
...
/usr/local/opt/gcc@11/bin/gcc-11 -std=c++17 narrowing.cpp
narrowing.cpp: In function 'int main()':
narrowing.cpp:3:20: warning: narrowing conversion of '(a + (double)1)' from 'double' to 'int' [-Wnarrowing]
    3 |         int b = {a + 1};
      |                  ~~^~~

There's no user error here, unless it's an error to install a newer compiler.

Interesting that there are no issues with upgrading boost from 1.76 to 1.78 on macOS arm64 (assuming ##24521).