[RFC] pkg-kde-tools: auto-injections of dependencies

[Norbert Preining]

Hi all

I would like to ask your comments concerning the following MR:
https://salsa.debian.org/qt-kde-team/pkg-kde-tools/-/merge_requests/5

Next is the text of the MR, and below it some technical explanation and
usage for locked upgrade of Plasma.

***** Text of the MR starts here *****************
Aim of this MR is to allow for auto-injection of plasma-base dependencies
(as discussed on IRC and mailing list) by doing the following:

- add a new script `dh_injectdependencies` which can add arbitrary
  dependencies like 
    `dh_injectdependencies breaks: "plasma-base (>= 5.22)" depends: "plasma-base (>= 5.21)"`
- add a DebHelper sequence `injectdependencies` so that one can use it with `--with`
- add a `plasma.mk` makefile snippet that auto-computes the correct versions and inject them.

As an example, I changed one Plasma package `debian/rules` file to:
- add
	include /usr/share/pkg-kde-tools/qt-kde-team/1/plasma.mk
- add `Breaks: ${misc:Breaks}` to each binary package stanza
- add `injectdependencies` to the `--with` list

In total it starts as:
```
include /usr/share/pkg-kde-tools/qt-kde-team/1/plasma.mk

%:
        dh $@ --with kf5,pkgkde_symbolshelper,injectdependencies --buildsystem kf5 --without build_stamp
```


With that, each binary package gets (for version 5.20.3) additional
```
Depends: plasma-base (>= 5.20)
Breaks: plasma-base (>= 5.21)
```

The above changes have to be done only once, and new versions will
automatically pick up the correct major.minor dep/break.


Questions
==========

I had contemplated putting the code of the injectsequences into the
kf5 sequence (Debhelper), it only adds a call to dh_injectsequences
before `dh_gencontrol`, and without an override it does nothing.
By that, no addition to the `--with` code is necessary. What do other
think about this approach?

Another thing to ponder is renaming the script to `dh_injectrels` or
`dh_injectrelations`.
**** End of MR text *********************

Concerning implementations:

- few stuff for building the package

- dh_injectdependencies is rather simple, it loops over all binary
  packages and adds the given packages to the respective variables.
  We use ${misc:Depends} (which is commonly used), but add in the
  same way ${misc:Relation} for each relation between packages
  (${misc:Breaks} etc ...)

- the Debhelper sequence injectdependencies simply adds a call to
  dh_injectdependencies *before* dh_gencontrol
	insert_before("dh_gencontrol", "dh_injectdependencies");
  Without and explicit override, this is a noop.

- finally the plasma auto detection magic in qt-kde-team/1/plasma.mk
  This uses /usr/share/dpkg/pkg-info.mk for getting DEB_VERSION_UPSTREAM
  and compute the Major and Minor and Patchlevel version from it.
  As a special case, if the patchlevel >= 70 (eg 5.20.70) we use
  the next minor version (-> 5.21).
  Then it adds a override_dh_injectdependencies with breaks on
  the next version of plasma-base, and depends on the current version
  of plasma-base

The NEW package plasma-base
(https://salsa.debian.org/qt-kde-team/kde/plasma-base)
currently breaks against all plasma packages << 5.20 to ensure that
all Plasma packages are updated together to new releases.

The idea is that we can keep plasma-base at the previous version, and
thus ensure that the new packages cannot be partially installed, and
only bump plasma-base when all packages are ready. This way a concerted
update will be done.

All plasma packages have in their git repo now a branch "dh-plasma" that
adds the necessary ${misc:Breaks} and debian/rules adaptions to build
with these new dependencies.

I have tested all binary packages one by one so that 
- install version from unstable
- update only the one binary package to 5.20.3
  this will make apt update several other packages, too
- check that no package remains at 5.19 level


Please let me know what you think about this approach.

Thanks

Norbert

--
PREINING Norbert                              https://www.preining.info
Accelia Inc. + IFMGA ProGuide + TU Wien + JAIST + TeX Live + Debian Dev
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