tests/test-strict.t

streamclone: define first iteration of version 2 of stream format

(This patch is based on a first draft from Gregory Szorc, with deeper rework)

Version 1 of the stream clone format was invented many years ago and suffers
from a few deficiencies:

1) Filenames are stored in store-encoded (on filesystem) form rather than in
   their internal form. This makes future compatibility with new store
   filename encodings more difficult.
2) File entry "headers" consist of a newline of the file name followed by the
   string file size. Converting strings to integers is avoidable overhead. We
   can't store filenames with newlines (manifests have this limitation as
   well, so it isn't a major concern). But the big concern here is the
   necessity for readline(). Scanning for newlines means reading ahead and
   that means extra buffer allocations and slicing (in Python) and this makes
   performance suffer.
3) Filenames aren't compressed optimally. Filenames should be compressed well
   since there is a lot of repeated data. However, since they are scattered
   all over the stream (with revlog data in between), they typically fall
   outside the window size of the compressor and don't compress.
4) It can only exchange stored based content, being able to exchange caches
   too would be nice.
5) It is limited to a stream-based protocol and isn't suitable for an on-disk
   format for general repository reading because the offset of individual file
   entries requires scanning the entire file to find file records.

As part of enabling streaming clones to work in bundle2, #2 proved to have a
significant negative impact on performance. Since bundle2 provides the
opportunity to start fresh, Gregory Szorc figured he would take the
opportunity to invent a new streaming clone data format.

The new format devised in this series addresses #1, #2, and #4. It punts on #3
because it was complex without yielding a significant gain and on #5 because
devising a new store format that "packs" multiple revlogs into a single
"packed revlog" is massive scope bloat. However, this v2 format might be
suitable for streaming into a "packed revlog" with minimal processing. If it
works, great. If not, we can always invent stream format when it is needed.

This patch only introduces the bases of the format. We'll get it usable through
bundle2 first, then we'll extend the format in future patches to bring it to its
full potential (especially #4).

  $ hg init

  $ echo a > a
  $ hg ci -Ama
  adding a

  $ hg an a
  0: a

  $ hg --config ui.strict=False an a
  0: a

  $ echo "[ui]" >> $HGRCPATH
  $ echo "strict=True" >> $HGRCPATH

  $ hg an a
  hg: unknown command 'an'
  Mercurial Distributed SCM
  
  basic commands:
  
   add           add the specified files on the next commit
   annotate      show changeset information by line for each file
   clone         make a copy of an existing repository
   commit        commit the specified files or all outstanding changes
   diff          diff repository (or selected files)
   export        dump the header and diffs for one or more changesets
   forget        forget the specified files on the next commit
   init          create a new repository in the given directory
   log           show revision history of entire repository or files
   merge         merge another revision into working directory
   pull          pull changes from the specified source
   push          push changes to the specified destination
   remove        remove the specified files on the next commit
   serve         start stand-alone webserver
   status        show changed files in the working directory
   summary       summarize working directory state
   update        update working directory (or switch revisions)
  
  (use 'hg help' for the full list of commands or 'hg -v' for details)
  [255]
  $ hg annotate a
  0: a

should succeed - up is an alias, not an abbreviation

  $ hg up
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved