[gentoo-user] What is the difference between emerge's --changed-deps=y and @changed-deps?

[Morgan Wesström]

On a freshly updated system (emerge -uDN @world):

"emerge @changed-deps" wants to reinstall 0 packages.

"emerge -u --changed-deps=y" wants to reinstall 24 packages.

"emerge -uD --changed-deps=y" wants to reinstall 181 packages.

A couple of years ago there was a build breakage in Portage because, as I
understood it at the time, some developer changed the dependencies in an
existing ebuild without bumping its revision level. The solution was to use
--changed-deps=y to catch these occurrences and I've been using it in my
regular update routine since then. But as you can see in the third example
above, it usually wants to reinstall hundreds of packages that doesn't have any
updated versions and I'm wondering if this is working as intended. I have a
hard time believing that gentoo devs are pushing changes to existing ebuilds in
such numbers on a regular basis without bumping the revision level.

Some time ago I became aware that Portage now has a @changed-deps set, which I
assumed was accomplishing the same thing, but it doesn't produce the same
result as --changed-deps=y - usually just a dozen reinstalls or so.

Can someone please elaborate on what's going on here, what the difference is
between --changed-deps=y and @changed-deps, if that difference is intended and
what the recommended update procedure is these days to catch these and other
kinds of inconsistencies in Portage?

Regards
Morgan

[Lee K]

Don't know if it's relevant or not but recently upstream deprecated the
"KERNEL" USE flag, resulting in many rebuilds for packages.

[hitachi303]

Am 10.01.22 um 07:44 schrieb Lee K:

I don't think so. "N" should have taken care of this.

from the man:
--newuse, -N Tells emerge to include installed packages where USE flags
have changed since compilation. [...]

[hitachi303]

Am 10.01.22 um 01:59 schrieb Morgan Wesström:

On my system most of this is related to build time dependencies.

#emerge -Duav --reinstall changed-use --changed-deps=y --with-bdeps=n @world
Total: 10 packages (10 reinstalls)

#emerge -Duav --reinstall changed-use --changed-deps=y --with-bdeps=y @world
Total: 131 packages (131 reinstalls)

[Morgan Wesström]

> Don't know if it's relevant or not but recently upstream deprecated the
> "KERNEL" USE flag, resulting in many rebuilds for packages.
>

Thank you, Lee, but that was just a coincidental change. The changed-deps
behaviour has been going on since I've started using it in my update routine
several years ago. It's a little tiresome when emerge wants to recompile
libreoffice and firefox every time I update my system and I'd like to
understand in more detail what these parameters do so I can judge the necessity
of using them to keep my installation in a consistent state.

Regards
Morgan