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

["Andrew Jeffery" <andrew@xxxxxxxx>]

Hi Andy,

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

Andrew