tests/test-convert-bzr-ghosts.t

revset: introduce new operator "##" to concatenate strings/symbols at runtime

Before this patch, there is no way to concatenate strings at runtime.

For example, to search for the issue ID "1234" in descriptions against
all of "issue 1234", "issue:1234", issue1234" and "bug(1234)"
patterns, the revset below should be written fully from scratch for
each issue ID.

    grep(r"\bissue[ :]?1234\b|\bbug\(1234\)")

This patch introduces new infix operator "##" to concatenate
strings/symbols at runtime. Operator symbol "##" comes from the same
one of C pre-processor. This concatenation allows parametrizing a part
of strings in revset queries.

In the case of example above, the definition of the revset alias using
operator "##" below can search issue ID "1234" in complicated patterns
by "issue(1234)" simply:

    issue($1) = grep(r"\bissue[ :]?" ## $1 ## r"\b|\bbug\(" ## $1 ## r"\)")

"##" operator does:

  - concatenate not only strings but also symbols into the string

    Exact distinction between strings and symbols seems not to be
    convenience, because it is tiresome for users (and
    "revset.getstring" treats both similarly)

    For example of revset alias "issue()", "issue(1234)" is easier
    than "issue('1234')".

  - have higher priority than any other prefix, infix and postfix
    operators (like as "##" of C pre-processor)

    This patch (re-)assigns the priority 20 to "##", and 21 to "(",
    because priority 19 is already assigned to "-" as prefix "negate".

  $ . "$TESTDIR/bzr-definitions"
  $ cat > ghostcreator.py <<EOF
  > import sys
  > from bzrlib import workingtree
  > wt = workingtree.WorkingTree.open('.')
  > 
  > message, ghostrev = sys.argv[1:]
  > wt.set_parent_ids(wt.get_parent_ids() + [ghostrev])
  > wt.commit(message)
  > EOF

ghost revisions

  $ mkdir test-ghost-revisions
  $ cd test-ghost-revisions
  $ bzr init -q source
  $ cd source
  $ echo content > somefile
  $ bzr add -q somefile
  $ bzr commit -q -m 'Initial layout setup'
  $ echo morecontent >> somefile
  $ python ../../ghostcreator.py 'Commit with ghost revision' ghostrev
  $ cd ..
  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial layout setup
  0 Commit with ghost revision
  $ glog -R source-hg
  o  1@source "Commit with ghost revision" files: somefile
  |
  o  0@source "Initial layout setup" files: somefile
  

  $ cd ..