depends_lib, depends_build, depends_run, oh my

[markd at macports.org]

Oops.  Resending to the list with the correct address minus the cc's.

>Have various dependency questions here. I couldn't find info on this  
>in the new guide.
>
>Why do we have depends_lib, depends_build and depends_run? Why not  
>just a single "depends"? Why does it matter which phase requires the  
>other software? Isn't it enough to know that the other software is  
>required at some point, and so MacPorts should install that other  
>software first?
>
>What are these three keywords supposed to denote? I thought  
>"depends_lib" was for libraries a program links with (e.g. gettext),  
>"depends_build" was for things only the build system needs (e.g.  
>pkgconfig) and "depends_run" was for binaries that need to be present  
>at runtime (e.g. I have no idea).

I have the same questions.  I would really like to get accurate
information on this into the new guide.  The only section of the old guide
relating to it that I can find is not helpful: 
http://geeklair.net/macports_guide/ch03.html#additional%20options

The portfile.7 has more (pasted below), but is there any real functional
difference between these?  It seems llike they are functionally the same
in practice and ports listed as dependencies all get installed before any
phases of a port are begun.  Were the three distinguished for some future
use not yet implemented?  Can someone explain this so it can be documented?

Mark


     depends_build
         List of dependencies to check before build, destroot, install, and
         package targets.
         Type: optional
         Example:
               depends_build port:autoconf

     depends_run
         List of dependencies to check before destroot, install and package
         targets.
         Type: optional
         Example:
               depends_run port:bash

     depends_lib
         List of dependencies to check before configure, build, destroot,
         install, and package targets.
         Type: optional
         Example:
               depends_lib port:libfetch