tests/test-check-commit.t

internals: document CBOR utilization

I spoke with some people at Mozilla about CBOR and they advised me
that we should be careful about the subset of CBOR we use in order
to mitigate security, performance, and compatibility concerns.

This commit establishes a document that attempts to formalize our
use of CBOR.

Its main limitations are on what types are allowed. It explicitly
enumerates which types are supported. Notable missing features
include:

* Indefinite-length arrays and maps
* Text strings (bytes all the way)
* Floats
* Date/time types
* Big integers
* Use of indefinite-length byte strings for map keys, values in
  containers.

If we have a need for any of these, we can have a discussion about
them when the time comes.

Differential Revision: https://phab.mercurial-scm.org/D4412

#require test-repo

Enable obsolescence to avoid the warning issue when obsmarker are found

  $ . "$TESTDIR/helpers-testrepo.sh"

Go back in the hg repo

  $ cd $TESTDIR/..

  $ REVSET='not public() and ::. and not desc("# no-check-commit")'

  $ mkdir "$TESTTMP/p"
  $ REVS=`testrepohg log -r "$REVSET" -T.`
  $ if [ -n "$REVS" ] ; then
  >   testrepohg export --git -o "$TESTTMP/p/%n-%h" -r "$REVSET"
  >   for f in `ls "$TESTTMP/p"`; do
  >      contrib/check-commit < "$TESTTMP/p/$f" > "$TESTTMP/check-commit.out"
  >      if [ $? -ne 0 ]; then
  >          node="${f##*-}"
  >          echo "Revision $node does not comply with rules"
  >          echo '------------------------------------------------------'
  >          cat ${TESTTMP}/check-commit.out
  >          echo
  >     fi
  >   done
  > fi