Bug #18823: _Bool not defined for C++

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 3.2.0dev (2022-06-12T17:35:26Z master 8158f05e72)
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[michals (Michal Suchánek)]

When a _Bool argument is added to rb_fd_select ruby cannot be compiled on

VisualStudio 2022
VisualStudio 2019

gcc-5
gcc-4.8

clang-5
clang-4
clang-3.9

c++98 (llvm 14)
c++2a (llvm 14)

which suggests that if defined(HAVE_STDBOOL_H) && (__cplusplus >= 201103L) in include/ruby/internal/stdbool.h may not be a great way to detect that C++ has bool, especially on Visual Studio.

[michals (Michal Suchánek)]

Apparently for MSVC to report the correct c++ version it needs the /Zc:__cplusplus flag.

I don't know where to inject this flag, though.

The other failure cases are probably really obsolete.

[mame (Yusuke Endoh)]

• Status changed from Open to Feedback

When a _Bool argument is added to rb_fd_select

I cannot understand what do you mean. Could you elaborate how to reproduce your issue and show the error log?

[michals (Michal Suchánek)]

I added a _Bool argument as part of other development which prevents ruby from building on older compiler versions and VS - eg. https://github.com/ruby/ruby/commit/6c72653d98c36c2a816bfff4e4e9b1c451154a9e

[michals (Michal Suchánek)]

generating cxxanyargs-x64-mswin64_140.def
compiling ../../../../src/ext/-test-/cxxanyargs/cxxanyargs.cpp
cxxanyargs.cpp
D:\a\ruby\ruby\src\include\ruby/internal/intern/select/win32.h(213): error C2061: syntax error: identifier '_Bool'
D:\a\ruby\ruby\src\include\ruby/internal/intern/select.h(84): error C2061: syntax error: identifier '_Bool'
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\bin\HostX64\x64\cl.EXE"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: 'cd' : return code '0x2'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\bin\HostX64\x64\nmake.EXE"' : return code '0x2'

Run ../src/configure -C ${default_configure} ${append_configure} --with-gcc="${default_cc} ${append_cc}" --enable-shared
configure: creating cache config.cache
checking for ruby... /usr/bin/ruby
made symlink config.guess to .downloaded-cache/config.guess
made symlink config.sub to .downloaded-cache/config.sub
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking target system type... x86_64-pc-linux-gnu
checking for llvm-ar-14... llvm-ar-14
checking for clang++-14... clang++-14
checking for llvm-nm-14... llvm-nm-14
checking for llvm-objcopy-14... llvm-objcopy-14
checking for llvm-objdump-14... llvm-objdump-14
checking for llvm-ranlib-14... llvm-ranlib-14
checking for llvm-strip-14... llvm-strip-14
checking for gcc... clang-14 
...
compiling ../../../../src/ext/-test-/debug/init.c
In file included from ../../../../src/ext/-test-/cxxanyargs/cxxanyargs.cpp:1:
In file included from ../../../../src/include/ruby/ruby.h:193:
In file included from ../../../../src/include/ruby/intern.h:54:
In file included from ../../../../src/include/ruby/internal/intern/select.h:35:
../../../../src/include/ruby/internal/intern/select/largesize.h:179:127: error: unknown type name '_Bool'
int rb_fd_select(int nfds, rb_fdset_t *rfds, rb_fdset_t *wfds, rb_fdset_t *efds ,rb_fdset_t *errfds, struct timeval *timeout, _Bool select);
                                                                                                                              ^
In file included from ../../../../src/ext/-test-/cxxanyargs/cxxanyargs.cpp:1:
In file included from ../../../../src/include/ruby/ruby.h:193:
In file included from ../../../../src/include/ruby/intern.h:54:
../../../../src/include/ruby/internal/intern/select.h:84:134: error: unknown type name '_Bool'
int rb_thread_fd_select(int nfds, rb_fdset_t *rfds, rb_fdset_t *wfds, rb_fdset_t *efds ,rb_fdset_t *errfds, struct timeval *timeout, _Bool select);
                                                                                                                                     ^
2 errors generated.

[mame (Yusuke Endoh)]

• Status changed from Feedback to Rejected

michals (Michal Suchánek) wrote in #note-3:

I added a _Bool argument as part of other development which prevents ruby from building on older compiler versions and VS - eg. https://github.com/ruby/ruby/commit/6c72653d98c36c2a816bfff4e4e9b1c451154a9e

I think include/ruby/internal/stdbool.h defines "bool", not "_Bool".

BTW, I don't know of any actual examples that uses "bool" in the public API signature. I guess it is defined just for internal.

[michals (Michal Suchánek)]

include/ruby/internal/stdbool.h defines _Bool, and in most cases just uses bool defined by the runtime.

I have no idea how there would even be _Bool if not defined there.

_Bools is used in bigdecimal and detected in extconf so it's not strictly internal.

Also rb_fd_select does not sound like public API and is not used by the bundled extensions but might be used by something like eventmachine.

Extensions do get the internal headers included, though. Hence the error when _Bool is used in function prototypes in one of these internal headers.

[mame (Yusuke Endoh)]

michals (Michal Suchánek) wrote in #note-6:

include/ruby/internal/stdbool.h defines _Bool, and in most cases just uses bool defined by the runtime.

No. C99 defines "_Bool" as an intrinsic type, and C's stdbool.h defines "bool" as an alias to "_Bool". See the specification of the C language and https://pubs.opengroup.org/onlinepubs/009696799/basedefs/stdbool.h.html .

include/ruby/internal/stdbool.h attempts to define "bool" in C89, C99, and C++. C++ provides "bool" as an intrinsic type, so the header does almost nothing.

BTW, I am a little baffled by a bug report like "ruby does not compile if I modify its source code".

[michals (Michal Suchánek)]

Thanks for the clarification.

I see that ruby core uses bool pretty consistently, and _Bool is used only in a few places.

Not sure where I copied it from.