Question

Both hg revert and hg backout revert changes made by a former revision. What is the difference between the two?

Answer 1

Given the history of changesets:

A --- B --- C --- D --- E
          [bad]        (*)

hg revert -r B: Stay at current revision, but update the working directory
as of revision B. It has the effect of a patch that revokes the changes
of C, D and E.

hg backout -r C: Update the working directory so that it contains the merge
of revision C’s parent (B) and the current revision, preserving the changes
made in between the two revisions (working dir still contains changes of
revision D and E). This has the effect of a patch applied on E,
undoing the changes of only C.

You may want to edit some files if not all of C was bad. Remember to do
a hg commit in any case:

A --- B --- C --- D --- E --- F
          [bad]              (*)