RFC: less chatty system builds

[David Chisnall]

On 16 Dec 2013, at 21:35, Dimitry Andric <dim at FreeBSD.org> wrote:

> In any case, if anything like this is implemented, I would really prefer
> something like CMake does, e.g. give you a percentage counter that
> provides some information about how 'far' the build is progressing.

I haven't seen this for a while, because I now use ninja exclusively for building any projects that use CMake.  The output of Ninja is pretty close to my ideal for a build system, and so I'd recommend that anyone hacking on this look at it.  It looks something like this while building:

$ ninja
[1/22] Building CXX object lib/Target/Mips/AsmParser/CMakeFiles/LLVMMipsAsmParser.dir/MipsAsmParser.cpp.o

The [1/22] part is a counter of the number of build steps done and updates in place.  The 'Building CXX object ...' part tells you what the current rule is and what it's being applied to.  This is only approximate, as it usually does parallel builds, but it gives you some idea of what's happening.

If a command produces warning output but exits with success, then that command's output is dumped to stdout (explicitly serialised by Ninja so that it's never interleaved with another command's output).  

If a command exits with a failure condition, then Ninja dumps the exact command line that was used, along with all of the output, and then stops.  Another side benefit is that Ninja always uses absolute paths for invoking the commands and for arguments, and so you can always just re-run that single failing command.

Oh, and when I do a build of LLVM/Clang on my laptop using Ninja, it takes about 3-5 minutes, whereas when I do it with our build system it takes about 15.  When I do it on a 24-core server, it takes less than two minutes with Ninja and with ours it takes about 15 (no speedup over my laptop).  I'd therefore suggest that there might be more pressing things that need fixing with our antiquated build infrastructure than the prettiness of the output...

David