[LLVMdev] RFC: Timeline for deprecating the autoconf build system?

[Steven Stewart-Gallus]

Hello, thank you for the thoughts.

> Have you seen the docs for CMake3.0 [1] (see cmake-buildsystem
> especially)? They certainly aren't perfect but they are considerably
> better than what was there before.

Okay, the documentation has come a long way since 3.0 although it
still needs a bit of polish.

> I wouldn't say that much "important functionality is plain lacking",
> it probably just isn't documented that well.

See the following.

> Installation prefix is set using the CMAKE_INSTALL_PREFIX cache
> variable. You can set it at configure time,
> 
> $ cmake -DCMAKE_INSTALL_PREFIX=$HOME/root/usr/local  /path/to/llvm/src

Correct, but I cannot set it as a default in a configuration file so I
need to specify it for every single package that I compile every time
I configure it. I think this a very basic and obvious feature that
CMake should support.

> I'm don't think it's necessary to set the rpath. If you read [2]
> you'll see that you can just run the binaries in the build tree and
> they have rpath set correctly (the installed binaries have rpath
> removed)

I do in fact need to set the rpath so that I can link to a higher
version of GCC's C++ standard library implementation installed there
as LLVM does not build against an older version of GCC.

> As mentioned above you can override the installation directory
> whenever you like (but it may trigger a rebuild).

> but it may trigger a rebuild

Yeah, that's not what I want.

> But you know you can
> do this right?
> 
> $ make install DESTDIR=/some/path/

That's not the same behaviour at all!
DESTDIR="$HOME/root/usr/local/stow/llvm" installs to
"$HOME/root/usr/local/stow/llvm/$HOME/root/usr/local" instead of
"$HOME/root/usr/local/stow/llvm" which is silly.

> The documentation is probably the biggest problem. I actually quite
> liked CMake (apart from its syntax and variable scoping rules) once
> I understood the bits I needed to understand.  I probably have a
> very different perspective from many though given that I used CMake
> first and then tried autotools afterwards (I'll be honest... I don't
> like it very much).

The fundamental difference between Autotools and CMake is that they
are built for different users. CMake is built for the modern developer
in 2014 on Linux, Windows, Mac OS X or FreeBSD. Autotools is primarily
built for the Free Software enthusiast university student in 1980 who
is compiling a package on his University's Unix like server (which
could be any of many different ones). As such, Autotools is
horrendously difficult for the developer to use but when used properly
is extremely portable and easy to use for the university student who
compiles the project.

Thank you,
Steven Stewart-Gallus