[PATCH 1/2] build: fail if explicitly requested lib is unbuildable

[Bruce Richardson]

On Fri, Sep 01, 2023 at 04:30:56PM +0200, David Marchand wrote:
> On Fri, Sep 1, 2023 at 4:29 PM David Marchand <david.marchand at redhat.com> wrote:
> >
> > On Fri, Sep 1, 2023 at 4:23 PM Bruce Richardson
> > <bruce.richardson at intel.com> wrote:
> > >
> > > When the user passes a list of desired libraries to build via the
> > > "enable_libs" option, the expectation is that those libraries should be
> > > part of the build. However, if those libs have either external or
> > > internal dependencies, they still may be silently disabled, for example:
> > > running "meson setup -Denable_libs=security build" will successfully
> > > run, but the security lib will not be configured as "cryptodev" is
> > > missing.
> > >
> > > We can fix this by setting a flag to indicate when the libraries are
> > > specified via an enable_libs flag. If so, then we error out when a
> > > library is unbuildable, giving a suitable error message. For the above
> > > example case, the "meson setup" run fails with:
> > >
> > > Message: Disabling security [lib/security]: missing internal dependency "cryptodev"
> > >
> > > lib/meson.build:218:16: ERROR: Problem encountered: Cannot build explicitly requested lib "security".
> > >         Please add missing dependency "cryptodev" to "enable_libs" option
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> >
> > I remember setting a enable_drivers=net/af_xdp on a system lacking
> > libbpf-devel and not getting warned about its absence.
> > So I suspect enable_drivers is affected by the same issue.
> 
> Arf sorry, did not see it was a two patch series :-).
> 
No problem.

At least your response confirms to me that this is indeed a common issue,
that could do with a solution. As I explain in patch 2, fixing for drivers
is a little trickier than for libs, as for drivers we really need to take
account of wildcards to avoid breaking people's existing builds. [Or, at
minimum, my own builds! :-)].

BTW: while we could look to handle wildcards for libs, I think their use is
probably much more limited there, and I decided to go with the simplest
possible solution instead.

/Bruce