[Bug 1920804] Re: Apt does not seem to automatically consider non-candidates when resolving deps

[Dimitri John Ledkov]

As per private conversation, it's not a bug but a feature to only
consider candidates by default.

** Changed in: apt (Ubuntu)
       Status: New => Won't Fix

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https://bugs.launchpad.net/bugs/1920804

Title:
  Apt does not seem to automatically consider non-candidates when
  resolving deps

Status in apt package in Ubuntu:
  Won't Fix

Bug description:
  # apt show sbuild-build-depends-main-dummy
  Package: sbuild-build-depends-main-dummy
  Version: 0.invalid.0
  Maintainer: Debian buildd-tools Developers <buildd-tools-devel at lists.alioth.debian.org>
  Installed-Size: unknown
  Depends: debhelper (>= 9), debhelper-compat (= 12), dpkg-dev (>= 1.17.14), python3, cargo (>= 0.40.0), rustc (= 1.49.0+dfsg1+llvm-0ubuntu1), libstd-rust-dev (= 1.49.0+dfsg1+llvm-0ubuntu1), libstd-rust-1.49 (= 1.49.0+dfsg1+llvm-0ubuntu1), cmake (>= 3.0) | cmake3, pkg-config, zlib1g-dev, zlib1g-dev, liblzma-dev, autotools-dev, m4, ninja-build, binutils (>= 2.26) | binutils-2.26, git, procps, gdb (>= 7.12), build-essential, fakeroot, libssl-dev
  Conflicts: gdb-minimal (<< 8.1-0ubuntu6), libstd-rust-1.50, libstd-rust-dev (>= 1.50.0), rustc (>= 1.50.0)
  Download-Size: 1096 B
  APT-Sources: copy:/build/rustc-Csm90L/resolver-AFxnMU/apt_archive ./ Packages
  Description: Dummy package to satisfy dependencies with apt - created by sbuild
   This package was created automatically by sbuild and should never appear on
   a real system. You can safely remove it.

  # apt-cache policy libstd-rust-dev rustc
  libstd-rust-dev:
    Installed: (none)
    Candidate: 1.50.0+dfsg1+llvm-0ubuntu1
    Version table:
       1.50.0+dfsg1+llvm-0ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu hirsute/universe amd64 Packages
       1.49.0+dfsg1+llvm-0ubuntu1 500
          500 http://ppa.launchpad.net/ci-train-ppa-service/4491/ubuntu hirsute/main amd64 Packages
  rustc:
    Installed: (none)
    Candidate: 1.50.0+dfsg1+llvm-0ubuntu1
    Version table:
       1.50.0+dfsg1+llvm-0ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu hirsute/universe amd64 Packages
       1.49.0+dfsg1+llvm-0ubuntu1 500
          500 http://ppa.launchpad.net/ci-train-ppa-service/4491/ubuntu hirsute/main amd64 Packages

  # apt install sbuild-build-depends-main-dummy
  Reading package lists... Done
  Building dependency tree... Done
  Reading state information... Done
  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:

  The following packages have unmet dependencies:
   sbuild-build-depends-main-dummy : Depends: cargo (>= 0.40.0) but it is not going to be installed
                                     Depends: rustc (= 1.49.0+dfsg1+llvm-0ubuntu1) but it is not going to be installed
                                     Depends: libstd-rust-dev (= 1.49.0+dfsg1+llvm-0ubuntu1) but it is not going to be installed
  E: Unable to correct problems, you have held broken packages.

  But:

  # apt install sbuild-build-depends-main-dummy rustc=1.49.0+dfsg1+llvm-0ubuntu1 libstd-rust-dev=1.49.0+dfsg1+llvm-0ubuntu1
  Reading package lists... Done
  Building dependency tree... Done
  Reading state information... Done
  The following additional packages will be installed:
    autoconf automake autopoint autotools-dev bsdextrautils cargo cmake cmake-data debhelper debugedit dh-autoreconf dh-strip-nondeterminism dwz file gdb gettext gettext-base git git-man
    groff-base intltool-debian libarchive-zip-perl libarchive13 libbabeltrace1 libboost-regex1.74.0 libcurl4 libdebhelper-perl libdebuginfod-common libdebuginfod1 liberror-perl
    libfile-stripnondeterminism-perl libgit2-1.1 libhttp-parser2.9 libipt2 libjsoncpp24 liblua5.2-0 liblzma-dev libmagic-mgc libmagic1 libmbedcrypto3 libmbedtls12 libmbedx509-0
    libpipeline1 libpopt0 libpython3.9 librhash0 librpmio9 libsigsegv2 libsource-highlight-common libsource-highlight4v5 libssh2-1 libssl-dev libstd-rust-1.49 libsub-override-perl libtool
    libuchardet0 libuv1 m4 man-db ninja-build pkg-config po-debconf ucf zlib1g-dev
  Suggested packages:
    autoconf-archive gnu-standards autoconf-doc cargo-doc cmake-doc dh-make rpm-i18n gdb-doc gdbserver gettext-doc libasprintf-dev libgettextpo-dev git-daemon-run | git-daemon-sysvinit
    git-doc git-el git-email git-gui gitk gitweb git-cvs git-mediawiki git-svn groff lrzip liblzma-doc libssl-doc libtool-doc gfortran | fortran95-compiler gcj-jdk m4-doc apparmor less
    www-browser libmail-box-perl rust-doc rust-src lld-11
  Recommended packages:
    libc-dbg curl | wget | lynx less ssh-client libarchive-cpio-perl libltdl-dev libmail-sendmail-perl rust-gdb | rust-lldb
  The following NEW packages will be installed:
    autoconf automake autopoint autotools-dev bsdextrautils cargo cmake cmake-data debhelper debugedit dh-autoreconf dh-strip-nondeterminism dwz file gdb gettext gettext-base git git-man
    groff-base intltool-debian libarchive-zip-perl libarchive13 libbabeltrace1 libboost-regex1.74.0 libcurl4 libdebhelper-perl libdebuginfod-common libdebuginfod1 liberror-perl
    libfile-stripnondeterminism-perl libgit2-1.1 libhttp-parser2.9 libipt2 libjsoncpp24 liblua5.2-0 liblzma-dev libmagic-mgc libmagic1 libmbedcrypto3 libmbedtls12 libmbedx509-0
    libpipeline1 libpopt0 libpython3.9 librhash0 librpmio9 libsigsegv2 libsource-highlight-common libsource-highlight4v5 libssh2-1 libssl-dev libstd-rust-1.49 libstd-rust-dev
    libsub-override-perl libtool libuchardet0 libuv1 m4 man-db ninja-build pkg-config po-debconf rustc sbuild-build-depends-main-dummy ucf zlib1g-dev
  0 upgraded, 67 newly installed, 0 to remove and 0 not upgraded.
  Need to get 103 MB of archives.
  After this operation, 472 MB of additional disk space will be used.
  Do you want to continue? [Y/n]

  Is fine.

  It feels that apt should be automatically considering non-candidate
  versions, if the version constraints demand that, when installing the
  sbuild generated dummy package which converts debian/control build-
  depends into depends.

  Apt itself seems to do everything right, and I do wonder that maybe we
  should stop doing this whole thing with custom archive & a deb to
  install build-dep, and instead implement to use `apt build-dep` in
  sbuild to install build-deps. But I don't see enough flags in `apt
  build-dep` to consider B-D & B-C and then sometimes also choose to
  consider -Arch & -Indep variants. Also not sure if build profiles are
  considered correctly.

  Oh and apt build-dep ./ on the debian/control that generated above
  dummy dependency package just worked fine.

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