[Buildroot] [PATCH] core/graph-depends: add option to graph reverse dependencies

[Yann E. MORIN <yann.morin.1998@free.fr>]

Thomas, All,

On 2016-10-25 23:04 +0200, Thomas Petazzoni spake thusly:
> On Sun, 23 Oct 2016 19:19:44 +0200, Yann E. MORIN wrote:
> > Now that we can dump the reverse dependencies of a package, add the
> > ability to graph those.
[--SNIP--]
> I've applied, thanks. However, our logic that gets rid of "redundant"
> dependencies also has the consequence of creating some graphs that are
> quite weird.
> 
> I tested a configuration where I enabled python and libglib2, both of
> which depend on libffi. When you do:
> 
> $ make libffi-show-rdepends
> 
> You get as expected "libglib2 python"
> 
> However, when you do
> 
> $ make libffi-graph-rdepends
> 
> The resulting graph is a bit weird. You would expect something like
> this:
> 
>            libffi
>        ------/ \------
>        |             |
>     libglib2       python

make BR2_GRAPH_DEPS_OPTS='--transitive -d1' libffi-graph-rdepends
would give you the expected graph.

But using options is not what you want. ;-)

> But instead, what you get is:
> 
>   libffi
>     /\
>     ||
>    python
>     /\
>     ||
>  util-linux
>     /\
>     ||
>   libglib2
> 
> Because indeed libglib2 depends on util-linux, and util-linux can
> optionally build python bindings and therefore depend on python.
> 
> Not sure what we can do about this: keeping all dependencies was really
> creating huge and unreadable graphs.

Well, that's the crux of the issue: keeping the whole graph is quickly
unworkable with even non-complex configurations.

Maybe what we should stress is that the graph-depends and graph-rdepends
display the build-order dependencies.

But yes, the apparent discrepancies between foo-show-rdepends and
foo-graph-rdepends can look weird on first sight, but both are correct.

Regards,
Yann E. MORIN.

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