How do I customize the 'commit message file' generated by `hg commit`?

Question

When I run hg commit, Mercurial generates a file for my commit message that looks like this :

HG: Enter commit message.  Lines beginning with 'HG:' are removed.
HG: Leave message empty to abort commit.
HG: --
HG: user: Henri Wiechers <[email protected]>
HG: branch 'default'
HG: added a.txt

Is there a way to customize this file? I'd like to include if the working copy has any unknown files.

Answer 1

It's possible to specify this in the [committemplate] config section (see hg help config.committemplate):

 "committemplate"
----------------

"changeset"
    String: configuration in this section is used as the template to
    customize the text shown in the editor when committing.

In addition to pre-defined template keywords, commit log specific one
below can be used for customization:

"extramsg"
    String: Extra message (typically 'Leave message empty to abort
    commit.'). This may be changed by some commands or extensions.

For example, the template configuration below shows as same text as one
shown by default:

  [committemplate]
  changeset = {desc}\n\n
      HG: Enter commit message.  Lines beginning with 'HG:' are removed.
      HG: {extramsg}
      HG: --
      HG: user: {author}\n{ifeq(p2rev, "-1", "",
     "HG: branch merge\n")
     }HG: branch '{branch}'\n{if(activebookmark,
     "HG: bookmark '{activebookmark}'\n")   }{subrepos %
     "HG: subrepo {subrepo}\n"              }{file_adds %
     "HG: added {file}\n"                   }{file_mods %
     "HG: changed {file}\n"                 }{file_dels %
     "HG: removed {file}\n"                 }{if(files, "",
     "HG: no files changed\n")}

"diff()"
    String: show the diff (see 'hg help templates' for detail)

Answer 2

There's no official way to do it w/o modifying mercurial itself (not terribly intimidating, it's very clean Python), but here's a way to do it by tweaking the editor setting the [ui] section of your ~/.hgrc:

editor = hg status --unknown >! /tmp/unknown_list ; /usr/bin/vim -c "r /tmp/unknown_list"

That is, of course vim on Linux specific, but the same could be done for any decent editor on any OS.