tests/test-issue1877.t

logtoprocess: drop support for ui.log() call with invalid msg arguments (BC)

Before, the logtoprocess extension put a formatted message into $MSG1, and
its arguments to $MSG2... If the specified arguments couldn't be formatted
because of a caller bug, an unformatted message was passed in to $MSG1
instead of exploding. This behavior doesn't make sense.

Since I'm planning to formalize the ui.log() interface such that we'll no
longer have to extend the ui class, I want to remove any features not
conforming to the ui.log() API. So this patch removes the support for
ill-formed arguments, and $MSG{n} (where n > 1) parameters which seems
useless as long as the message can be formatted. The $MSG1 variable isn't
renamed for the maximum compatibility.

In future patches, a formatted msg will be passed to a processlogger object,
instead of overriding the ui.log() function.

.. bc::

   The logtoprocess extension no longer supports invalid ``ui.log()``
   arguments. A log message is always formatted and passed in to the
   ``$MSG1`` environment variable.

https://bz.mercurial-scm.org/1877

  $ hg init a
  $ cd a
  $ echo a > a
  $ hg add a
  $ hg ci -m 'a'
  $ echo b > a
  $ hg ci -m'b'
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg book main
  $ hg book
   * main                      0:cb9a9f314b8b
  $ echo c > c
  $ hg add c
  $ hg ci -m'c'
  created new head
  $ hg book
   * main                      2:d36c0562f908
  $ hg heads
  changeset:   2:d36c0562f908
  bookmark:    main
  tag:         tip
  parent:      0:cb9a9f314b8b
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     c
  
  changeset:   1:1e6c11564562
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b
  
  $ hg up 1e6c11564562
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (leaving bookmark main)
  $ hg merge main
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg book
     main                      2:d36c0562f908
  $ hg ci -m'merge'
  $ hg book
     main                      2:d36c0562f908

  $ cd ..