B2 compilation failure on Cygwin

[Lastique]

Running tools/build/src/engine/build.sh on Cygwin and Cygwin64 fails with the attached log.

build.log

[grafikrobot]

Looks like cygwin doesn't properly simulate Unix contrary to its claims.

[Lastique]

Well, I don't think it's 100% compatible or will ever be. But these errors make me think of a missing include somewhere.

[Lastique]

For example, readlink is present in sys/unistd.h, guarded with #if __BSD_VISIBLE || __POSIX_VISIBLE >= 200112 || __XSI_VISIBLE >= 4. sys/unistd.h is included from unistd.h and the macro checks require _BSD_SOURCE, _POSIX_C_SOURCE >= 200112, _XOPEN_SOURCE >= 500, defined(_XOPEN_SOURCE) && defined(_XOPEN_SOURCE_EXTENDED) or _GNU_SOURCE. I think, it's one of these macros you may be missing.

[Lastique]

In terms of POSIX, it seems you're using mutually exclusive sets of system calls. I tried compiling with _XOPEN_SOURCE=700, but, for example, alphasort is conditioned on __POSIX_VISIBLE >= 200809 and vfork is __XSI_VISIBLE >= 4 && __POSIX_VISIBLE < 200809.

Compiling with _GNU_SOURCE or _BSD_SOURCE succeeds.

[pdimov]

Is -std=c++11 being used? Cygwin requires -std=gnu++11 if I'm not mistaken.

[pdimov]

That is, POSIX functions are not enabled under Cygwin unless -std=gnu++11 is used. (Or nothing, as the default for 7.4 is -std=gnu++14.)

[Lastique]

It uses -std=c++11. But I haven't noticed any checks for C++ version or GNU extensions in the preprocessor checks.

I know Solaris headers are broken a similar way, though. They require different versions of _XOPEN_SOURCE depending on whether you're building in C++03 or C++11 mode.

[pdimov]

__STRICT_ANSI__ is checked a number of times in sys/features.h.

[grafikrobot]

Is the conclusion on this that I should be using -std=gnu11 on Cygwin?

[pdimov]

Either that, or nothing; Cygwin has gcc 7 at the moment, which defaults to -std=gnu++14.

[grafikrobot]

I'd rather be explicit to reduce the risk of someone adding a post 11 dependency.