Wednesday, March 17, 2010

DPM: Darcs Patch Manager

I’ve just released the initial version of DPM on Hackage! The Darcs Patch Manager (DPM for short) is a tool that simplifies working with the revision control system darcs. It is most effective when used in an environment where developers do not push their patches directly to the main repository but where patches undergo a reviewing process before they are actually applied. Here is a short story that illustrates how would use the DPM in such sitations.

Suppose that Dave Developer implements a very cool feature. After polishing his patch, Dave uses darcs send to send the patch:

  $ darcs send host:MAIN_REPO
  Tue Mar 16 16:55:09 CET 2010  Dave Developer <dave@example.com>

    * very cool feature
  Shall I send this patch? (1/1)  [ynWsfvplxdaqjk], or ? for help: y
  Successfully sent patch bundle to: patches@example.com

After the patch has been sent to the address patches@example.com, DPM comes into play. For this example, we assume that mail devivery for patches@example.com is handled by some mailfilter program such as maildrop (http://www.courier-mta.org/maildrop/) or procmail (http://www.procmail.org/). The task of the mailfilter program is the add all patches sent to patches@example.com to the DPM database. This is achieved with the DPM command add:

  $ dpm add –help
  add: Put the given patch bundles under DPM’s control (use ‘-’ to read from stdin).
  Usage: add FILE…

  Command options:

  Global options:
    -r DIR  –repo-dir=DIR                  directory of the darcs repository
    -s DIR  –storage-dir=DIR               directory for storing DPM data
    -v      –verbose                       be verbose
            –debug                         output debug messages
            –batch                         run in batch mode
            –no-colors                     do not use colors when printing text
            –user=USER                     current user
            –from=EMAIL_ADDRESS            from address for emails
            –review-address=EMAIL_ADDRESS  email address for sending reviews
    -h, -?  –help                          display this help message

Now suppose that Dave’s patch is in the DPM database. A reviewer, call him Richard Reviewer, uses the DPM command list to see what patches are available in this database:

  $ dpm list –help
  list: List the patches matching the given query.

  Query ::= Query ‘ + ‘ Query  — logical OR
          | Query ‘ ‘   Query  — logical AND
          | ‘^’ Query          — logical NOT
          | ‘{‘ Query ‘}’      — grouping
          | ‘:’ Special
          | String

  Special is one of "undecided", "rejected", "obsolete", "applied",
  "reviewed", "open", or "closed", and String is an arbitrary sequence
  of non-whitespace characters not starting with ‘^’, ‘{‘, ‘}’, ‘+’, or ‘:’.

  If no query is given, DPM lists all open patch groups.

  Usage: list QUERY …

  Command options:

  Global options:
    -r DIR  –repo-dir=DIR                  directory of the darcs repository
    -s DIR  –storage-dir=DIR               directory for storing DPM data
    -v      –verbose                       be verbose
            –debug                         output debug messages
            –batch                         run in batch mode
            –no-colors                     do not use colors when printing text
            –user=USER                     current user
            –from=EMAIL_ADDRESS            from address for emails
            –review-address=EMAIL_ADDRESS  email address for sending reviews
    -h, -?  –help                          display this help message

In our example, the output of the list command might look as follows:

  $ dpm -r MAIN_REPO -s DPM_DB list
    very cool feature [State: OPEN]
      7861 Tue Mar 16 17:20:45  2010 Dave Devloper <dave@example.com>
           State: UNDECIDED, Reviewed: no
           added
    some other patch [State: OPEN]
      7631 Tue Mar 16 13:15:20  2010 Eric E. <eric@example.com>
           State: REJECTED, Reviewed: yes
           added
    …

(The -r option specifies a directory containing the DPM database. Initially, you simply create an empty directory. The -s option specifies the path to the darcs repository in question.)

DPM groups all patches with the same name inside a patch group. Patch groups allow keeping track of multiple revisions of the same patch. In the example, the patch group of name very cool feature has only a single member, which is the patch Dave just created. The patch is identified by a unique suffix of its hash (7861 in the example). The output of the list command further tells us that no reviewer decided yet what to do with the patch (its in state UNDECIDED).

At this point, Richard Reviewer reviews Dave’s patch. During the review, he detects a minor bug so he rejects the patch:

  $ dpm -r MAIN_REPO -s DPM_DB review 7861
    Reviewing patch 7861
    Starting editor on DPM_DB/reviews/2010-03-16_7861_swehr_24166.dpatch
      <inspect patch in editor>
    Mark patch 7861 as reviewed? [Y/n] y
    Patch 7861 is in state UNDECIDED, reject this patch? [y/N] y
    Enter a comment: one minor bug
    Marked patch 7861 as reviewed
    Moved patch 7861 to REJECTED state
    Send review to Dave Developer <dave@example.com>? [Y/n] y
    Mail sent successfully.

Now Dave Developer receives an email stating that has patch has been rejected. The email also contains the full review so that Dave sees why the patch has been rejected. Thus, Dave starts fixing the bug, does an amend-record of the patch, and finally sends the patch again. (Alternatively, he could also create a new patch with exactly the same name as the original patch.)

  $ darcs send MAIN_REPO
  Tue Mar 16 16:55:09 CET 2010  Dave Developer <dave@example.com>
    * very cool feature
  Shall I send this patch? (1/1)  [ynWsfvplxdaqjk], or ? for help: y
  Successfully sent patch bundle to: patches@example.com

Once the email is received, the improved patch is added to the DPM database. The output of the list command now looks like this:

  $ dpm -r MAIN_REPO -s DPM_DB list
    very cool feature [State: OPEN]
      2481 Tue Mar 16 17:50:23  2010 Dave Devloper <dave@example.com>
           State: UNDECIDED, Reviewed: no
           added
      7861 Tue Mar 16 17:20:45  2010 Dave Devloper <dave@example.com>

           State: REJECTED, Reviewed: yes
           marked as rejected: one minor bug
    some other patch [State: OPEN]
      7631 Tue Mar 16 13:15:20  2010 Eric E. <eric@example.com>
           State: REJECTED, Reviewed: yes
           added
    …

The patch 2481 is the improved revision of the original patch 7861. It is in the same group as the original patch because both patches have the same name. Richard Reviewer reviews the improved patch and has no complains anymore:

  $ dpm -r MAIN_REPO -s DPM_DB review 2481
    Reviewing patch 2481
    Starting editor on DPM_DB/reviews/2010-03-16_2481_swehr_876102.dpatch
      <inspect patch in editor>
    Mark patch 2481 as reviewed? [Y/n] y
    Patch 2481 is in state UNDECIDED, reject this patch? [y/N] n
    Enter a comment: ok
    Marked patch 2481 as reviewed
    Send review to Dave Developer <dave@example.com>? [y/N] n

At this point, Richard Reviewer applies the patch with the very cool feature:

  $ dpm apply 2481
    About to apply patch 2481
    Entering DPM’s dumb (aka interactive) apply command.
    Future will hopefully bring more intelligence.

    Instructions:
    =============
    – Press ‘n’ until you reach
      Tue Mar 16 17:50:23  2010 Dave Devloper <dave@example.com>

        * very cool feature
      (Hash: 20100316162041-c71f4-871aedab8f4dd3bd042b9188f1496011c7dd2481)
    – Press ‘y’ once
    – Press ‘d’

    Tue Mar 16 17:50:23  2010 Dave Devloper <dave@example.com>
      * very cool feature
    Shall I apply this patch? (1/1)  [ynWsfvplxdaqjk], or ? for help: y
    Finished applying…
    Patch 2481 applied successfully
    Send notification to author Dave Developer <dave@example.com> of patch 2481? [Y/n] y
    Mail sent successfully.

Applying a patch closes the corresponding patch group. Per default, the list command doesn’t display closed patch groups, but we can force it to do so with the :closed query:

  $ dpm list :closed
    very cool feature [State: CLOSED]
      2481 Tue Mar 16 17:50:23  2010 Dave Devloper <dave@example.com>

           State: APPLIED, Reviewed: yes
           marked as applied: -
      7861 Tue Mar 16 17:20:45  2010 Dave Devloper <dave@example.com>
           State: REJECTED, Reviewed: yes
           marked as rejected: one minor bug
      …

Author: Stefan Wehr

1 comment:

Eric Kow said...

Hi Stefan, You may want to consider getting your blog (or maybe just a Darcs part) to Planet Darcs - http://planet.darcs.net/

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