Re: [boost] Proposal for moving Boost to CMake

Subject: Re: [boost] Proposal for moving Boost to CMake
From: Gary Furnish (gfurnish_at_[hidden])
Date: 2017-06-19 20:57:42

a user-config.jam has to exist in one of several defined places, $HOME
or $BOOST_BUILD_PATH.  This is incompatible with wanting a scripted
environment.  Building everything in one go prohibits you from using a
separate install prefix for each compiler, which is needed to build a
separate root directory for each tool chain you might have.  With
CMake I literally just set the Compiler and compiler flags from the
command line (-DCMAKE_CXX_COMPILER=whatever, etc).  With boost, I'm
not even sure how to do it.  I think there is some undocumented
feature to let you put a custom jam file in some random directory and
then use some undocumented flag to somehow point b2 to use that
directory to look for your jam file/build in.  So I think it might
somehow be possible to write a script to write a jam file for each
compiler I want to use in a build directory and somehow do an out of
tree build for boost in that directory pointing at that jam file.  I
don't know the magic steps to invoke for it.  If it exists its
certainly not documented.  I test an internal code base with > 9
compiler configurations(from source) for the entire dependency chain.
Just adding features to a jam manually is not an option; everything
should be automateable.  Anything not automateable gets broken.

On Mon, Jun 19, 2017 at 12:28 PM, Daniel James via Boost
<boost_at_[hidden]> wrote:
> On 19 June 2017 at 01:53, Gary Furnish via Boost <boost_at_[hidden]> wrote:
>> For whatever its worth as a user who sometimes contributes patches to
>> fix bugs, I don't use the system compiler and instead use scripts to
>> test different builds of internal code (clang, clang with various
>> sanitizers and options, different versions of gcc, etc).  This is such
>> a pain with boost build because of the difficulty of automating
>> building multiple copies with custom compilers and flags with the same
>> source tree.  In cmake this is easy, you just change some command line
>> flags, something trivial in scripts.  In Boost, I think I got it
>> working once using undocumented features after spending several hours
>> looking around at docs, source code(!), and stack overflow.  I now
>> automatically just don't use boost
>> libraries that aren't header only.  I would rather rewrite code than
>> fight with the build process. That is a bad state of affairs.
>
> That's odd, that's one thing I've always found easier with boost build
> than any other build system. You add a target to your user-config.jam,
> such as:
>
> using gcc : sanitize : g++ -fsanitize=address ;
>
> Then run the build using something like 'b2 gcc-sanitize'. I think
> there's some way of specifying flags at the command line, but I find
> it's easier just to set up a number of configurations in the
> configuration file. So when developing unordered, if I want to run the
> insert tests, I might do something like this:
>
> cd libs/unordered/test
> b2 -q insert_tests gcc gcc-std11 clang clang-std14
>
> I have no idea how to do the same thing with cmake. As far as I'm
> aware with cmake you have to set up multiple build directories for
> each variant of each project. I've found it a real pain for building
> projects like libc++.
>
> Just to make it clear, I'm far from an expert in boost build, and
> struggle with many other aspects. But I've never found cmake to be the
> land of milk and honey that I hear so much about. I'm also more than a
> bit fed up of cleaning up after other people's grand projects.
>
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