Vim and Mercurial
Nowadays there is a number of plugins for interaction with mercurial. Here is the description of the VCSCommand plugin, you may find other on the page with OtherTools list.
Vim, VCSCommand and Mercurial
Bob Hiestand has developed a vim plugin useful for manipulating files controlled by CVS, SVN and SVK within VIM, including committing changes and performing diffs using the vimdiff system. It was later extended to support other VCS software, including Mercurial (since version 1.99.31 posted on 21 July 2009).
After installing the plugin, you may use it to add, remove, commit, annotate, view older versions, changes (as a diff or in a vimdiff split) of files; update directory state and view log.