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Mercurial: how to amend the last commit? (4)

I'm looking for a counter-part of git commit --amend in Mercurial, i.e. a way to modify the commit which my working copy is linked to. The requirements for this amend-procedure are:

  • if possible, it should not require any extensions. It must not require non-default extensions, i.e. extensions which do not come with an official Mercurial installation.

  • if the commit to amend is one head of my current branch, no new head should be created. If the commit is not head, a new head may be created.

  • the procedure should be safe in a way that if for whatever reasons the amending fails, I want to have the same working copy and repository state restored as before the amending. With other words, if the amending itself can fail, there should be a fail-safe procedure to restore the working copy and repository state. I'm referring to "failures" which lie in the nature of the amend-procedure (like e.g. conflicts), not to file-system-related problems (like access restrictions, not being able to lock a file for writing, ...)

Update (1):

  • the procedure must be automatable, so it can be performed by a GUI client without any user interaction required.

Update (2):

  • files in the working directory must not be touched (there may be file system locks on certain modified files). This especially means, that a possible approach may at no point require a clean working directory.

GUI equivalent for hg commit --amend:

This also works from TortoiseHG's GUI (I'm using v2.5):

Swich to the 'Commit' view or, in the workbench view, select the 'working directory' entry. The 'Commit' button has an option named 'Amend current revision' (click the button's drop-down arrow to find it).

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Caveat emptor:

This extra option will only be enabled if the mercurial version is at least 2.2.0, and if the current revision is not public, is not a patch and has no children. [...]

Clicking the button will call 'commit --amend' to 'amend' the revision.

More info about this on the THG dev channel


Assuming that you have not yet propagated your changes, here is what you can do.

  • Add to your .hgrc:

    [extensions]
    mq =
    
  • In your repository:

    hg qimport -r0:tip
    hg qpop -a
    

    Of course you need not start with revision zero or pop all patches, for the last just one pop (hg qpop) suffices (see below).

  • remove the last entry in the .hg/patches/series file, or the patches you do not like. Reordering is possible too.

  • hg qpush -a; hg qfinish -a
  • remove the .diff files (unapplied patches) still in .hg/patches (should be one in your case).

If you don't want to take back all of your patch, you can edit it by using hg qimport -r0:tip (or similar), then edit stuff and use hg qrefresh to merge the changes into the topmost patch on your stack. Read hg help qrefresh.

By editing .hg/patches/series, you can even remove several patches, or reorder some. If your last revision is 99, you may just use hg qimport -r98:tip; hg qpop; [edit series file]; hg qpush -a; hg qfinish -a.

Of course, this procedure is highly discouraged and risky. Make a backup of everything before you do this!

As a sidenote, I've done it zillions of times on private-only repositories.


Recent versions of Mercurial include the evolve extension which provides the hg amend command. This allows amending a commit without losing the pre-amend history in your version control.

hg amend [OPTION]... [FILE]...

aliases: refresh

combine a changeset with updates and replace it with a new one

Commits a new changeset incorporating both the changes to the given files
and all the changes from the current parent changeset into the repository.

See 'hg commit' for details about committing changes.

If you don't specify -m, the parent's message will be reused.

Behind the scenes, Mercurial first commits the update as a regular child
of the current parent. Then it creates a new commit on the parent's
parents with the updated contents. Then it changes the working copy parent
to this new combined changeset. Finally, the old changeset and its update
are hidden from 'hg log' (unless you use --hidden with log).

See https://www.mercurial-scm.org/doc/evolution/user-guide.html#example-3-amend-a-changeset-with-evolve for a complete description of the evolve extension.


With the release of Mercurial 2.2, you can use the --amend option with hg commit to update the last commit with the current working directory

From the command line reference:

The --amend flag can be used to amend the parent of the working directory with a new commit that contains the changes in the parent in addition to those currently reported by hg status, if there are any. The old commit is stored in a backup bundle in .hg/strip-backup (see hg help bundle and hg help unbundle on how to restore it).

Message, user and date are taken from the amended commit unless specified. When a message isn't specified on the command line, the editor will open with the message of the amended commit.

The great thing is that this mechanism is "safe", because it relies on the relatively new "Phases" feature to prevent updates that would change history that's already been made available outside of the local repository.





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