[gentoo-portage-dev] dep resolution weirdness

[George Shapovalov]

Hi guys.

I am quite confused by the following:

aldar ~ # emerge -puD world --tree
These are the packages that would be merged, in reverse order:
Calculating world dependencies... done!
[nomerge      ] dev-ada/cbind-6.0
[nomerge      ]  virtual/gnat-4.1
[ebuild     UD]   dev-lang/gnat-gcc-4.1.1 [4.1.2]

aldar ~ # emerge -puD cbind --tree
These are the packages that would be merged, in reverse order:
Calculating dependencies... done!

(or, for that matter:
aldar gnat # e -puD virtual/gnat
These are the packages that would be merged, in order:
Calculating dependencies... done!
)

Here, cbind is an Ada library that needs gnat - the Ada compiler, so it 
DEPENDs (and RDEPENDs) on a virtual which provides the choice of gnat-gcc or 
gnat-gpl compiler(s). These can be installed side by side (using 
toolchain-like eclass to manage location and eselect module for choosing the 
active one) whence the virtual.

The relevant dependency lines are here:
dev-ada/cbind:   DEPEND="virtual/gnat"

virtual/gnat-4.1: 
RDEPEND="=dev-lang/gnat-gcc-4.1*"
DEPEND=""

(and virtual/gnat-3.4:
RDEPEND="|| ( =dev-lang/gnat-gcc-3.4*
    =dev-lang/gnat-gpl-3.4* )"
DEPEND=""
although it looks like this one is not considered in this particular case)


As you see emerge -uD world wants to downgrade gnat for some reason (which is 
wrong), while emerge -uD cbind (or any other Ada library that has similar 
dependencies) does not (which is right).

So, what is going on here? Is this a problem with specifying dependencies? If 
so, how should I fix this? Is this a portage bug? A stale cache? I would like 
to get this fixed or worked around in some way apparently :). (I just issued 
an update to gnat-gcc and hit this. Oh, and ~dev-lang/gnat-gcc-4.1 as RDEPEND 
in virtual/gnat does not work at all (just, as I understand, it should not)).

George
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