[gentoo-dev] why doesn't readline-6 install libreadline.so symlink?

[Andrey Grozin]

I'm using portage-2.2_pre*. After upgrading to sys-libs/readline-6.0, 
portage (naturally) kept /lib/libreadline.so.5 -> /lib/libreadline.so.5.2, 
because a lot of programs needed it. I did emerge @preserved-rebuild, and 
only one binary using libreadline.so.5.2 left: /usr/bin/gp, the 
interactive interpreter of sci-mathematics/pari. Re-emerging it does not 
help: headers from readline-6 are used, but the program links wirh 
libreadline.so.5.2. I thought something is wrong in the pari's configure. 
This package does not use autoconf, but a hand-written Configure script. 
It seems all right. Then I found that /lib/libreadline.so symlink still 
points to libreadline.so.5. This confuses the pari's Configure. I made it 
to point to libreadline.so.6 by hand, and re-emerged pari. OK, gp now 
links with libreadline.so.6.0. Why doesn't readline-6.0 ebuild install 
this symlink?

After this re-emerging of pari, portage said

!!! existing preserved libs:
>>> package: sys-libs/readline-6.0_p3
  *  - /lib/libreadline.so
  *      used by /usr/bin/M2 (sci-mathematics/Macaulay2-1.2-r3)
  *      used by /usr/bin/Singular-3-0-4 (sci-mathematics/singular-3.0.4.4)
  *      used by /usr/bin/asy (media-gfx/asymptote-1.86)
  *      used by 111 other files

I already re-emerged these packages (at least, 3 shown) as a part of 
emerging @preserved-rebuild after upgrading readline, and they were not in 
the @preserved-rebuild set before I changed the libreadline.so symlink. 
Does this mean that all of these packages used libreadline.so -> 
libreadline.so.5? This is not good. I'm going to emerge @preserved-rebuild 
again, to be sure that my system is in a self-consistent state.

It seems that keeping libreadline.so -> libreadline.so.5 after merging 
readline-6.0 and unmerging readline-5.2 is a bad idea.

Andrey