Breakage from grub-mkconfig changes for grub-file

[Colin Watson <cjwatson@ubuntu.com>]

ec824e0f2a399ce2ab3a2e3353d372a236595059 introduced extensive changes to
grub-mkconfig, which among other things arranged to run all but a
hardcoded list of grub.d scripts once for each of several platforms with
their output enclosed in an "if" block.  I do not feel that this change
was well-thought-out, and I think it should be rethought or reverted
before 2.02.  I didn't see anything about it here in advance - did I
miss a thread?

The problems I have with it are illustrated by its effects on the Debian
patch.  I must emphasise that I don't think this is unique to the case
of distributions with non-trivial patch sets, and that it's also likely
to affect users who have made reasonable changes to /etc/grub.d/ locally
(as they're entitled to do); distributions are just a useful
early-warning system here.

  1) Awkward hardcoded list; poor configurability

  00_header, 30_os-prober, 40_custom, and 41_custom are run only once.
  The Debian patch set has an additional script which is not
  platform-dependent and should be run only once, namely
  05_debian_theme, so I had to add another case here.  Users will surely
  have other such files; not only do they have to know on upgrade that
  they need to take care of this, but they have no recourse that doesn't
  involve editing $prefix/bin/grub-mkconfig, which is not a file that
  should normally be edited by the system administrator; changes to that
  file will not normally persist on upgrades.

  This should be redesigned so that there is some way to declare in a
  grub.d script that it requires multi-platform support and should be
  run multiple times.  (It *must* be this way round so that upgrades
  work properly.)

  2) Strange ad-hoc platform names

  The platform names used in grub-mkconfig (x86 i386-xen-pae x86_64-xen
  mips mipsel sparc64 powerpc ia64 arm arm64) are not the same as the
  platform names used in the GRUB build system, but yet they're exported
  across the interface to /etc/grub.d/ as GRUB_PLATFORM.  This is messy
  and confusing, and it's not clear what promises we make about future
  changes here.

  We should rationalise this before issuing anything as part of a stable
  release, perhaps by adopting the same target_cpu/platform terminology
  used in the build system.  Furthermore, if we made the namespaces
  match up then it would be fairly straightforward to only run grub.d
  scripts for platforms for which we have installed GRUB modules, which
  seems as though it would be sensible.

  3) Breaks function definitions

  In the GRUB script language, "function" is only permitted at the top
  level.  This may be an oversight since bash doesn't share this
  restriction and GRUB script generally tries to look like bash;
  nevertheless it exists today.  Part of the Debian patch set causes
  10_linux to emit a function definition, which now causes a syntax
  error.

  I think my preferred fix here would be to implement functions other
  than at the top level, but it seems a bit rash to try to cram that
  into 2.02.

  4) Smaller bugs

  Aside from the bug fixed in 77ec462a568fc9c89ef45e960bf33b5de73140fb,
  I'm pretty sure that the condition for the "x86" platform is buggy;
  shouldn't it have an extra "-a" in there?  This sort of thing makes me
  worried about the level of testing these changes have had.

The grub-file tool seems reasonable and useful to me, but can we just
revert the grub-mkconfig parts of these changes until after 2.02 so that
the effects of these interface changes can be considered more carefully?
It looks like it was part of a new feature rather than a bug-fix.

I noticed this while testing Debian packages of 2.02~beta1.
Unfortunately, I don't think I can salvage this into something I can
upload without extensive interface changes of the sort that I'm not
comfortable making downstream.

Thanks,

-- 
Colin Watson                                       [cjwatson@ubuntu.com]