How do I get mercurial to show the diff during `hg com`?

Question

Is there a way to configure hg com so that in the commit message file that pops up in the external editor, instead of just showing which files were changed (in the HG: lines) it actually shows the full diff? I'd rather view the output and compose my commit message simultaneously from the comfort of my text editor as opposed to doing hg diff on the command line separately beforehand.

Answer 1

As of 2016, it's possible to do this with the committemplate configuration option. Adding the following to an hgrc file will include the diff in the editor window inline as you type your commit message.

[committemplate]
changeset = {desc}\n\n
    HG: {extramsg}
    HG: user: {author}\n{ifeq(p2rev, "-1", "",
   "HG: branch merge\n")
   }HG: branch '{branch}'\n{if(currentbookmark,
   "HG: bookmark '{currentbookmark}'\n")  }{subrepos %
   "HG: subrepo {subrepo}\n"              }
   {splitlines(diff()) % 'HG: {line}\n'}

See hg help hgrc and search for committemplate for more information.

Answer 2

Mercurial doesn't have that as a built-in feature, but it's easy to simulate in your editor (as launched by commit).

Here's an example using VIM: https://www.mercurial-scm.org/wiki/DiffsInCommitMessageInVIM

The hgeditor script https://www.mercurial-scm.org/hg/hg-stable/raw-file/tip/hgeditor provides further examples.

The basic jist is:

1. at editor launch run hg diff redirecting to a temp file
2. have your editor load both the commit message file and the diff