Re: [libgpiod][WIP PATCH 0/2] Convert the build from autotools to meson

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Wed, Dec 07, 2022 at 08:34:20AM +1030, Andrew Jeffery wrote:
> On Wed, 7 Dec 2022, at 01:24, Andy Shevchenko wrote:
> > On Mon, Dec 05, 2022 at 07:55:29PM +0100, Bartosz Golaszewski wrote:
> >> On Mon, Dec 5, 2022 at 2:22 PM Andrew Jeffery <andrew@xxxxxxxx> wrote:

...

> >> > Meson defaults to using ninja as its backend, and automatically exploits
> >> > ccache[2] when available to keep repeated builds speedy.
> >
> > ...which is a bad idea for a clean build.
> >
> >> It does show! Full rebuild with autotools:
> >> 
> >> real 0m43,902s
> >> user 2m40,010s
> >> sys 0m20,172s
> >> 
> >> Full rebuild with meson:
> >> 
> >> real 0m10,001s
> >> user 1m1,334s
> >> sys 0m12,205s
> >> 
> >> More than 4x faster now.
> >
> > And risk to have a badly formed binaries (yes, very little risk, but > 0).
> >
> >> > [2] https://ccache.dev/
> >
> > ccache has downside of its own use. If we have a common storage for ccache --
> > the collision is just matter of time (yes, have seen that in real life).
> >
> > OTOH requiring per-project ccache storage makes a little sense for the end user
> > as they quite likely won't rebuild it many times.
> 
> Valid points. However I think they're addressed by:
> 
> 1. Not installing ccache on the system, or
> 2. Overriding the auto-detection behaviour of `meson setup ...` 
> 
> Regarding 2, you can specify the CC and CXX environment variables to force its hand:
> 
> ```
> $ command -v ccache
> /usr/bin/ccache
> $ CC=cc CXX=c++ meson setup -Dbindings=cxx build
> The Meson build system
> Version: 0.63.0
> ...
> C compiler for the host machine: cc (gcc 12.2.0 "cc (Ubuntu 12.2.0-3ubuntu1) 12.2.0")
> ...
> C++ compiler for the host machine: c++ (gcc 12.2.0 "c++ (Ubuntu 12.2.0-3ubuntu1) 12.2.0")
> ...
> ```
> 
> Compared to the default behaviour:
> 
> ```
> $ meson setup -Dbindings=cxx build
> The Meson build system
> Version: 0.63.0
> ...
> C compiler for the host machine: ccache cc (gcc 12.2.0 "cc (Ubuntu 12.2.0-3ubuntu1) 12.2.0")
> ...
> C++ compiler for the host machine: ccache c++ (gcc 12.2.0 "c++ (Ubuntu 12.2.0-3ubuntu1) 12.2.0")
> ...
> ```
> 
> This use of the CC and CXX variables is covered in the documentation:
> 
> https://mesonbuild.com/Feature-autodetection.html#ccache

Right, my point that ccache should be opt-in and not opt-out.
For example, Buidroot project has ccache support (as opt-in).

-- 
With Best Regards,
Andy Shevchenko