Ccache depend mode

[Luboš Luňák]

On Thursday 09 of May 2019, Rene Engelhard wrote:
> On Tue, May 07, 2019 at 11:32:12AM +0200, Luboš Luňák wrote:
> > - We use -MMD, which exludes system headers (or even our externals, since
> > for those we use -isystem too). This means that ccache could give
> > incorrect hits if those headers change. That may seem bad, but I think
> > it's unlikely to cause problems in practice, for several reasons:
> >  * System headers rarely change.
>
> They change all the time.
>
> >  * If they change, it's generally a binary compatible change.
>
> No? There's many versions of the same compatible header where the header
> stays the same?
>
> You seem to only think of people only developing on their stable, not
> changing distro.
>
> People often build stuff for their distros (as distro packagers, where
> this stuff *does* change - and that also compatibly because said new update
> affected someting else or a specific header of even the same header but
> compatibly.
>
> In development times, I upgrade my unstable chroot daily (and whatever
> changed in unstable changes there, too. That includes system libs/headers
> and compilers and whatever.)

 Fair enough, but does that actually change anything about what I said? Most 
people do not develop on a rolling distro, so in the usual case still system 
headers rarely change. And if your case is different, then the setup already 
doesn't suit it perfectly. You already have missing make dependencies, and 
now the same setup also needs --enable-ccache=nodepend.

-- 
 Luboš Luňák
 l.lunak at collabora.com