debian/README.source

   1 Document by Luca Bruno & Sylvestre Ledru
   2
   3 This source package is unfortunately quite tricky and with
   4 several cutting edges, due to the complexity of rust-lang
   5 bootstrapping system and the high rate of language changes
   6 still ongoing.
   7
   8 We try to describe here inner packaging details and the
   9 reasons behind them.
  10
  11
  12 Bootstrapping
  13 =============
  14
  15 This package is composed of two upstream tarballs:
  16  * the rust-lang source
  17  * a minimal stage0 to start bootstrapping the system
  18
  19 This is an interim solution, in the long term we plan to have
  20 rust bootstrap itself from an installed copy. However, we are
  21 currently forced to ship a stage0.
  22
  23 We have to that way, because:
  24  * upstream periodically snapshots stage0. This happens multiple times
  25    between releases, so it is not currently possible to bootstrap using
  26    (only) released versions
  27  * requirements are pretty tight, and when a language feature change
  28    rustc cannot self-bootstrap (you need a stage0 before the change,
  29    which support the old set of features)
  30  * stage0 are in strictly-chained linear series. This means we cannot
  31    miss even a single snapshot, otherwise next bootstrap could fail.
  32    Moreover, also due to first point above, bootstrapping across
  33    non-adjacent snapshots/packages won't work
  34
  35 On the other hand:
  36  * stage0 is directly generated by the same infrastructure that
  37    packages the source tarball
  38  * Mozilla upstream directly provides it, and at least has some point
  39    you have to trust it in order to break the boostrap cycle
  40  * builds are automated, and public build logs can be inspected at
  41    http://buildbot.rust-lang.org/builders/snap3-linux
  42  * snapshot artifacts have to be manually approved by upstream, and
  43    are identified by the SHA1 of the resulting content
  44
  45 Things should improve as the language is being stabilized.
  46 We will re-evaluate this choice after 1.0.
  47
  48
  49 Embedded libraries
  50 ==================
  51
  52 This source package embeds several external libraries (foeked and managed
  53 by rust upstream as git submodules).
  54 In early stages, many more libraries were forked/emebedded but we are steadily
  55 progressing in splitting them out.
  56
  57 Here below the remaining ones, with the technical reasons.
  58
  59  * jemalloc from https://github.com/rust-lang/jemalloc
  60    -> system-wide one can't be used due to rust using a "je_" prefix.
  61
  62    This is intentional upstream design and won't change soon, see:
  63     - https://github.com/rust-lang/rust/pull/18678
  64     - http://smallcultfollowing.com/babysteps/blog/2014/11/14/allocators-in-rust/
  65
  66  * compiler-rt from https://github.com/rust-lang/compiler-rt
  67    -> system-wide compiler-rt fails during linkage
  68
  69    Bug reported upstream, still to be fixed, see:
  70     - https://github.com/rust-lang/rust/issues/15054
  71     - https://github.com/rust-lang/rust/issues/15708
  72
  73 As a summary, we plan to:
  74  * keep embedding jemalloc (probably forever)
  75  * work with upstream to fix compiler-rt linkage soon.
  76
  77  -- Sylvestre Ledru <sylvestre@debian.org>  Fri, 27 Mar 2015 14:27:12 +0100
  78