docs/user-guide.rst
author Pierre-Yves David <pierre-yves.david@octobus.net>
Sun, 17 Sep 2017 19:59:25 +0200
changeset 2939 7759d040d48d
parent 2931 83d2c9637e89
child 4615 8406d9b06130
permissions -rw-r--r--
topic: provide more information when behind count cannot be computed The behind count has been confusing for various user and the associated error message is even worth. We try to clarify it to see if that helps.
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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.. Copyright © 2014 Greg Ward <greg@gerg.ca>
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------------------
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Evolve: User Guide
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------------------
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.. contents::
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Life without ``evolve``
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-----------------------
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Before we dive into learning about ``evolve``, let's look into some
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features of core Mercurial that interact with ``evolve``. ``commit``
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affects ``evolve``, and ``evolve`` modifies how ``commit --amend``
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works.
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Example 1: Commit a new changeset
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=================================
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To create a new changeset, simply run ``hg commit`` as usual.
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``evolve`` does not change the behaviour of ``commit`` at all.
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However, it's important to understand that new changesets are in the
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*draft* phase by default: they are mutable. This means that they can
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be modified by Mercurial's existing history-editing commands
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(``rebase``, ``histedit``, etc.), and also by the ``evolve``
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extension. Specifically, ``evolve`` adds a number of commands that can
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be used to modify history: ``amend``, ``uncommit``, ``prune``,
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``fold``, and ``evolve``. ::
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  $ hg commit -m 'implement feature X'
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  $ hg phase -r .
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  1: draft
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Generally speaking, changesets remain in *draft* phase until they are
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pushed to another repository, at which point they enter the *public*
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phase. (Strictly speaking, changesets only become public when they are
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pushed to a *publishing* repository. But all repositories are publishing
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by default; you have to explicitly configure repositories to be
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*non-publishing*. Non-publishing repositories are an advanced topic
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which we'll see when we get to `sharing mutable history`_.)
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.. _`sharing mutable history`: sharing.html
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Example 2: Amend a changeset (traditional)
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==========================================
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Imagine you've just committed a new changeset, and then you discover a
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mistake. Maybe you forgot to run the tests and a failure slipped in.
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You want to modify history so that you push one perfect changeset,
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rather than one flawed changeset followed by an "oops" commit. (Or
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perhaps you made a typo in the commit message—this is really feature
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*Y*, not feature X. You can't fix that with a followup commit.)
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This is actually trivial with plain vanilla Mercurial since 2.2: fix
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your mistake and run ::
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  $ hg commit --amend -m 'implement feature Y'
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to create a new, amended changeset. The drawback of doing this with
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vanilla Mercurial is that your original, flawed, changeset is removed
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from the repository. This is *unsafe* history editing. It's probably
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not too serious if all you did was fix a syntax error, but for deeper
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changes there can be more serious consequences to unsafe history editing.
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.. figure:: figures/figure-ug01.svg
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   Figure 1: unsafe history modification with core Mercurial (not
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   using ``evolve``): the original revision 1 is destroyed.
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(Incidentally, Mercurial's traditional history modification mechanism
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isn't *really* unsafe: any changeset(s) removed from the repository
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are kept in a backup directory, so you can manually restore them later
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if you change your mind. However, this mechanism is very awkward and
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inconvenient compared to the features provided by ``evolve`` and
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changeset obsolescence.)
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Life with ``evolve`` (basic usage)
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----------------------------------
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Once you enable the ``evolve`` extension, a number of features are
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available to you. First, we're going to explore several examples of
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painless, trouble-free history modification.
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Example 3: Amend a changeset (with ``evolve``)
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==============================================
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Outwardly, amending a changeset with ``evolve`` can look exactly the
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same as it does with core Mercurial (example 2)::
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  $ hg commit --amend -m 'implement feature Y'
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Alternately, you can use the new ``amend`` command added by
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``evolve``::
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  $ hg amend -m 'implement feature Y'
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(``hg amend`` is nearly synonymous with ``hg commit --amend``. The
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difference is that ``hg amend`` reuses the existing commit message by
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default, whereas ``hg commit --amend`` runs your editor if you don't
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pass ``-m`` or ``-l``.)
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Under the hood, though, things are quite different. Mercurial has
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simply marked the old changeset as *obsolete*, replacing it with a new
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one. We'll explore what this means in detail later, after working
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through a few more examples.
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Example 4: Prune an unwanted changeset
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======================================
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Sometimes you make a change, and then decide it was such a bad idea
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that you don't want anyone to know about it. Or maybe it was a
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debugging hack that you needed to keep around for a while, but do not
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intend to ever push publicly. ::
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  $ echo 'debug hack' >> file1.c
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  $ hg commit -m 'debug hack'
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In either case, ``hg prune`` is the answer. ``prune`` simply marks
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changesets obsolete without creating any new changesets to replace
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them::
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  $ hg prune .
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  1 changesets pruned
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  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
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  working directory now at 934359450037
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Outwardly, it appears that your “debug hack” commit never happened;
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we're right back where we started::
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  $ hg parents --template '{rev}:{node|short}  {desc|firstline}\n'
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  3:934359450037  implement feature Y
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In reality, though, the “debug hack” is still there, obsolete and hidden.
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Example 5: Uncommit changes to certain files
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============================================
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Occasionally you commit more than you intended: perhaps you made
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unrelated changes to different files, and thus intend to commit
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different files separately. ::
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  $ echo 'relevant' >> file1.c
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  $ echo 'irrelevant' >> file2.c
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If you forget to specify filenames on the ``commit`` command line,
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Mercurial commits all those changes together::
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  $ hg commit -m 'fix bug 234'          # oops: too many files
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Luckily, this mistake is easy to fix with ``uncommit``::
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  $ hg uncommit file2.c
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  $ hg status
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  M file2.c
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Let's verify that the replacement changeset looks right (i.e.,
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modifies only ``file1.c``)::
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  $ hg parents --template '{rev}:{node|short}  {desc|firstline}\n{files}\n'
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  6:c8defeecf7a4  fix bug 234
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  file1.c
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As before, the original flawed changeset is still there, but obsolete
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and hidden. It won't be exchanged with other repositories by ``push``,
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``pull``, or ``clone``.
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Example 6: Fold multiple changesets together into one
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=====================================================
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If you're making extensive changes to fragile source code, you might
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commit more frequently than normal so that you can fallback on a
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known good state if one step goes badly. ::
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  $ echo step1 >> file1.c
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  $ hg commit -m 'step 1'               # revision 7
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  $ echo step2 >> file1.c
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  $ hg commit -m 'step 2'               # revision 8
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  $ echo step3 >> file2.c
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  $ hg commit -m 'step 3'               # revision 9
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At the end of such a sequence, you often end up with a series of small
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changesets that are tedious to review individually. It might make more
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sense to combine them into a single changeset using the ``fold``
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command.
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To make sure we pass the right revisions to ``fold``, let's review the
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changesets we just created, from revision 7::
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  $ hg log --template '{rev}:{node|short}  {desc|firstline}\n' -r 7::
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  7:05e61aab8294  step 1
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  8:be6d5bc8e4cc  step 2
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  9:35f432d9f7c1  step 3
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and fold them::
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  $ hg fold -m 'fix bug 64' -r 7:: --exact
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  3 changesets folded
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  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
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This time, Mercurial marks three changesets obsolete, replacing them
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all with a single *successor*.
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(You might be familiar with this operation under other names, like
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*squash* or *collapse*.)
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Changeset obsolescence under the hood
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-------------------------------------
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So far, everything has gone just fine: we haven't run into merge
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conflicts or other trouble. Before we start exploring advanced usage
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that can run into trouble, let's step back and see what happens when
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Mercurial marks changesets obsolete. That will make it much easier to
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understand the more advanced use cases we'll see later.
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When you have the ``evolve`` extension enabled, all history
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modification uses the same underlying mechanism: the original
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changesets are marked *obsolete* and replaced by zero or more
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*successors*. The obsolete changesets are the *predecessors* of their
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successors. This applies equally to built-in commands (``commit
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--amend``), commands added by ``evolve`` (``amend``, ``prune``,
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``uncommit``, ``fold``), and commands provided by other extensions
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(``rebase``, ``histedit``).
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Another way of looking at it is that obsolescence is second-order
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version control, i.e. the history of your history. We'll cover this in
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more detail (and mathematical precision) in the `concepts`_ guide.
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.. _`concepts`: concepts.html
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Under the hood: Amend a changeset
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=================================
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Consider Example 2, amending a changeset with ``evolve``. We saw above
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that you can do this using the exact same command-line syntax as core
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Mercurial, namely ``hg commit --amend``. But the implementation is
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quite different, as Figure 2 shows.
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.. figure:: figures/figure-ug02.svg
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   Figure 2: safe history modification using ``evolve``: the original
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   revision 1 is preserved as an obsolete changeset. (The "temporary
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   amend commit", marked with T, is an implementation detail stemming
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   from limitations in Mercurial's current merge machinery. Future
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   versions of Mercurial will not create them.)
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In this case, the obsolete changesets are also *hidden*. That is the
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usual end state for obsolete changesets. However, many scenarios result
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in obsolete changesets that are still visible, which indicates your
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history modification work is not yet done. We'll see examples of that
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later, when we cover advanced usage.
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Understanding revision numbers and hidden changesets
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====================================================
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As the name implies, hidden changesets are normally not visible. If
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you run ``hg log`` on the repository from Figure 2, Mercurial will
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show revisions 0 and 3, but not 1 and 2. That's something you don't
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see with plain vanilla Mercurial—normally, revision *N* is always
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followed by revision *N* + 1.
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This is just the visible manifestation of hidden changesets. If
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revision 0 is followed by revision 3, that means there are two hidden
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changesets, 1 and 2, in between.
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To see those hidden changesets, use the ``--hidden`` option::
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  $ hg --hidden log --graph --template '{rev}:{node|short}  {desc|firstline}\n'
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  @  3:934359450037  implement feature Y
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  |
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  | x  2:6c5f78d5d467  temporary amend commit for fe0ecd3bd2a4
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  | |
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  | x  1:fe0ecd3bd2a4  implement feature Y
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  |/
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  o  0:08c4b6f4efc8  init
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Note that changeset IDs are still the permanent, immutable identifier
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for changesets. Revision numbers are, as ever, a handy shorthand that
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work in your local repository, but cannot be used across repositories.
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They also have the useful property of showing when there are hidden
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changesets lurking under the covers, which is why this document uses
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revision numbers.
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Under the hood: Prune an unwanted changeset
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===========================================
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``prune`` (example 4 above) is the simplest history modification
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command provided by ``evolve``. All it does is mark the specified
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changeset(s) obsolete, with no successor/precursor relationships
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involved. (If the working directory parent was one of the obsoleted
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changesets, ``prune`` updates back to a suitable ancestor.)
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.. figure:: figures/figure-ug03.svg
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   Figure 3: pruning a changeset marks it obsolete with no successors.
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Under the hood: Uncommit changes to certain files
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=================================================
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In one sense, ``uncommit`` is a simplified version of ``amend``. Like
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``amend``, it obsoletes one changeset and leaves it with a single
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successor. In another sense, ``uncommit`` is the inverse of ``amend``:
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``amend`` takes any uncommitted changes in the working dir and “adds”
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them to the working directory's parent changeset. (In reality, of
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course, it creates a successor changeset, marking the original
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obsolete.) In contrast, ``uncommit`` takes some changes in the working
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directory's parent and moves them to the working dir, creating a new
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successor changeset in the process. Figure 4 illustrates.
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.. figure:: figures/figure-ug04.svg
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   Figure 4: uncommit moves some of the changes from the working
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   directory parent into the working dir, preserving the remaining
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   changes as a new successor changeset. (N.B. revision 4 is not shown
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   here because it was marked obsolete in the previous example.)
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Under the hood: Fold multiple changesets together into one
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==========================================================
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The last basic example is folding multiple changesets into one, which
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marks multiple changesets obsolete, replacing them all with a single
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successor.
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.. figure:: figures/figure-ug05.svg
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   Figure 5: fold combines multiple changesets into a single
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   successor, marking the original (folded) changesets obsolete.
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Obsolete is not hidden
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======================
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1269
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So far, every obsolete changeset we have seen is also hidden. However,
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these are *not* the same thing—that's why they have different names.
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It's entirely possible to have obsolete changesets that are not
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hidden. We'll see examples of that soon, when we create *unstable*
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changesets.
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Note that all hidden changesets are obsolete: hidden is a subset of
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obsolete. This is explained in more depth in the `concepts`_ section.
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.. _`concepts`: concepts.html
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Life with ``evolve`` (advanced usage)
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-------------------------------------
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Now that you've got a solid understanding of how ``evolve`` works in
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concert with changeset obsolescence, let's explore some more advanced
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scenarios. All of these scenarios will involve *unstable* changesets,
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which is an unavoidable consequence of obsolescence. What really sets
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``evolve`` apart from other history modification mechanisms is the
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fact that it recognizes troubles like unstable changesets and provides
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a consistent way for you to get back to a stable repository.
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(Incidentally, there are two other types of troubles that changesets
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can get into with ``evolve``: they may be *divergent* or
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*bumped*. Both of those states are more likely to occur when
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`sharing mutable history`_, so we won't cover them in this user guide.)
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.. _`sharing mutable history`: sharing.html
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Example 7: Amend an older changeset
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===================================
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Sometimes you don't notice a mistake until after you have committed
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new changesets on top of the changeset with the mistake. ::
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  $ hg commit -m 'fix bug 17'         # rev 11 (mistake here)
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  $ hg commit -m 'cleanup'            # rev 12
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  $ hg commit -m 'feature 23'         # rev 13
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Traditionally, your only option is to commit an "oops" changeset that
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fixes your mistake. That works, of course, but it makes you look bad:
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you made a mistake, and the record of that mistake is recorded in
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history for all eternity. (If the mistake was in the commit message,
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too bad: you cannot fix it.)
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More subtly, there now exist changesets that are *worse* than what
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came before—the code no longer builds, the tests don't pass, or
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similar. Anyone reviewing these patches will waste time on the error
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in the earlier patch, and then the correction later on.
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You can avoid all this by amending the bad changeset and *evolving*
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subsequent history. Here's how it works, assuming you have just
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committed revision 13 and noticed the mistake in revision 11::
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  $ hg update 11
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  [...fix mistake...]
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  $ hg amend
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At this point, revision 11 is *obsolete* and revisions 12 and 13—the
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descendants of 11—are in a funny state: they are *unstable*.
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.. figure:: figures/figure-ug06.svg
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   Figure 6: amending a changeset with descendants means the amended
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   changeset is obsolete but remains visible; its non-obsolete
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   descendants are *unstable*. The temporary amend commit, revision
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   14, is hidden because it has no non-obsolete descendants.
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All non-obsolete descendants of an obsolete changeset are considered
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unstable. An interesting consequence of this is that revision 11 is
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still visible, even though it is obsolete. Obsolete changesets with
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non-obsolete descendants are not hidden.
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The fix is to *evolve* history::
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  $ hg evolve --all
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This is a separate step, not automatically part of ``hg amend``,
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because there might be conflicts. If your amended changeset modifies a
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file that one of its descendants also modified, Mercurial has to fire
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up your merge tool to resolve the conflict. More importantly, you have
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to switch from "writing code" to "resolving conflicts". That can be an
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expensive context switch, so Mercurial lets you decide when to do it.
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The end state, after ``evolve`` finishes, is that the original
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revisions (11-13) are obsolete and hidden. Their successor revisions
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(15-17) replace them.
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.. figure:: figures/figure-ug07.svg
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   Figure 7: evolve your repository (``hg evolve --all``) to take care
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   of instability. Unstable changesets become obsolete, and are
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   replaced by successors just like the amended changeset was.
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Example 8: Prune an older changeset
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===================================
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Let's say you've just committed the following changesets::
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  $ hg commit -m 'useful work'       # rev 18
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  $ hg commit -m 'debug hack'        # rev 19
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  $ hg commit -m 'more work'         # rev 20
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You want to drop revision 19, but keep 18 and 20. No problem::
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  $ hg prune 19
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  1 changesets pruned
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  1 new unstable changesets
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As above, this leaves your repository in a funny intermediate state:
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revision 20 is the non-obsolete descendant of obsolete revision 19.
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That is, revision 20 is unstable.
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.. figure:: figures/figure-ug08.svg
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   Figure 8: ``hg prune`` marks a changeset obsolete without creating
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   a successor. Just like with ``hg amend``, non-obsolete descendants
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   of the pruned changeset are now unstable.
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As before, the solution to unstable changesets is to evolve your
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repository::
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  $ hg evolve --all
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This rebases revision 20 on top of 18 as the new revision 21, leaving
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19 and 20 obsolete and hidden:
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.. figure:: figures/figure-ug09.svg
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   Figure 9: once again, ``hg evolve --all`` takes care of instability.
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Example 9: Uncommit files from an older changeset (discard changes)
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=======================================================================
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As in example 5, let's say you accidentally commit some unrelated
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changes together. Unlike example 5, you don't notice your mistake
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   473
immediately, but commit a new changeset on top of the bad one. ::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   474
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   475
  $ echo 'this fixes bug 53' >> file1.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   476
  $ echo 'debug hack' >> file2.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   477
  $ hg commit -m 'fix bug 53'                     # rev 22 (oops)
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   478
  $ echo 'and this handles bug 67' >> file1.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   479
  $ hg commit -m 'fix bug 67'                     # rev 23 (fine)
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   480
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   481
As with ``amend``, you need to travel back in time and repair revision
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   482
22, leaving your changes to ``file2.c`` back in the working
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   483
directory::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   484
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   485
  $ hg update 22
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   486
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   487
  $ hg uncommit file2.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   488
  1 new unstable changesets
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   489
  $ hg status
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   490
  M file2.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   491
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   492
Now your repository has unstable changesets, so you need to evolve it.
2931
83d2c9637e89 user-guide: edit pass
Ryan McElroy <rmcelroy@fb.com>
parents: 1270
diff changeset
   493
However, ``hg evolve`` requires a clean working directory to resolve merge
978
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   494
conflicts, so you need to decide what to do with ``file2.c``.
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   495
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   496
In this case, the change to ``file2.c`` was a temporary debugging
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   497
hack, so we can discard it and immediately evolve the instability away::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   498
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   499
  $ hg revert file2.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   500
  $ hg evolve --all
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   501
  move:[23] fix bug 67
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   502
  atop:[24] fix bug 53
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   503
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   504
Figure 10 illustrates the whole process.
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   505
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   506
.. figure:: figures/figure-ug10.svg
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   507
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   508
   Figure 10: ``hg uncommit`` of a changeset with descendants results
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   509
   in instability *and* a dirty working directory, both of which must
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   510
   be dealt with.
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   511
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   512
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   513
Example 10: Uncommit files to an older changeset (keep changes)
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   514
===================================================================
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   515
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   516
This is very similar to example 9. The difference that this time, our
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   517
change to ``file2.c`` is valuable enough to commit, making things a
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   518
bit more complicated. The setup is nearly identical::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   519
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   520
  $ echo 'fix a bug' >> file1.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   521
  $ echo 'useful but unrelated' >> file2.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   522
  $ hg commit -u dan -d '11 0' -m 'fix a bug'     # rev 26 (oops)
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   523
  $ echo 'new feature' >> file1.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   524
  $ hg commit -u dan -d '12 0' -m 'new feature'   # rev 27 (fine)
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   525
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   526
As before, we update back to the flawed changeset (this time,
2931
83d2c9637e89 user-guide: edit pass
Ryan McElroy <rmcelroy@fb.com>
parents: 1270
diff changeset
   527
revision 26) and use ``uncommit``, leaving uncommitted changes to
978
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   528
``file2.c`` in the working dir::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   529
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   530
  $ hg update -q 26
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   531
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
2931
83d2c9637e89 user-guide: edit pass
Ryan McElroy <rmcelroy@fb.com>
parents: 1270
diff changeset
   532
  $ hg uncommit -q file2.c  # obsoletes rev 26, creates rev 28
978
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   533
  1 new unstable changesets
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   534
  $ hg status
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   535
  M file2.c
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   536
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   537
This time, let's save that useful change before evolving::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   538
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   539
  $ hg commit -m 'useful tweak'                   # rev 29
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   540
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   541
Figure 11 shows the story so far: ``uncommit`` obsoleted revision 26
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   542
and created revision 28, the successor of 26. Then we committed
2931
83d2c9637e89 user-guide: edit pass
Ryan McElroy <rmcelroy@fb.com>
parents: 1270
diff changeset
   543
revision 29, a child of 28. We still have to deal with the revision 27,
83d2c9637e89 user-guide: edit pass
Ryan McElroy <rmcelroy@fb.com>
parents: 1270
diff changeset
   544
which is an unstable changeset.
978
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   545
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   546
.. figure:: figures/figure-ug11.svg
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   547
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   548
   Figure 11: Uncommitting a file and then committing that change
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   549
   separately will soon result in a two-headed repository.
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   550
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   551
This is where things get tricky. As usual when a repository has
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   552
unstable changesets, we want to evolve it::
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   553
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   554
  $ hg evolve --all
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   555
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   556
The problem is that ``hg evolve`` rebases revision 27 onto revision
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   557
28, creating 30 (the successor of 27). This is entirely logical: 27
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   558
was the child of 26, and 26's successor is 28. So of course 27's
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   559
successor (30) should be the child of 26's successor (28).
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   560
Unfortunately, that leaves us with a two-headed repository:
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   561
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   562
.. figure:: figures/figure-ug12.svg
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   563
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   564
   Figure 12: ``evolve`` takes care of unstable changesets; it does
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   565
   not solve all the world's problems.
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   566
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   567
As usual when faced with a two-headed repository, you can either merge
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   568
or rebase. It's up to you.
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   569
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   570
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   571
Example 11: Recover an obsolete changeset
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   572
=========================================
8328337d23b2 docs: add new user guide
Greg Ward <greg@gerg.ca>
parents:
diff changeset
   573
1270
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   574
Sometimes you might obsolete a changeset, and then change your mind. You'll
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   575
probably start looking for an “unobsolete” command to restore a changeset
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   576
to normal state. For complicated implementation reasons, that command
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   577
doesn't exist. (If you have already pushed an obsolescence marker to
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   578
another repo, then Mercurial would need a way to revoke that remote
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   579
obsolesence marker. That's a hard problem.)
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   580
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   581
Instead, ``evolve`` provides a ``touch`` command to resurrect an
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   582
obsolete changeset. An unexpected quirk: you almost certainly need to
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   583
use ``--hidden``, since obsolete changesets tend to be hidden, and you
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   584
can't reference a hidden changeset otherwise. Typical usage thus looks
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   585
like ::
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   586
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   587
  $ hg --hidden touch REV
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   588
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   589
This creates a new, normal changeset which is the same as ``REV``—except
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   590
with a different changeset ID. The new changeset will have the same parent
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   591
as ``REV``, and will be a successor of ``REV``.
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   592
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   593
The current implementation of ``hg touch`` is not ideal, and is likely to
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   594
change in the future. Consider the history in Figure 12, where revision 27
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   595
is obsolete and the child of 26, also obsolete. If we ``hg touch 27``, that
2931
83d2c9637e89 user-guide: edit pass
Ryan McElroy <rmcelroy@fb.com>
parents: 1270
diff changeset
   596
creates a new revision which is a non-obsolete child of 26—i.e., it is an
1270
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   597
unstable. It's also *divergent*, another type of trouble that we'll learn
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   598
about in the `next section`_.
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   599
0683e3030316 docs: cover 'touch' command
Greg Ward <greg@gerg.ca>
parents: 1269
diff changeset
   600
.. _`next section`: sharing.html