mercurial/help/templates.txt

revlog: optimize _chunkraw when startrev==endrev

In many cases, _chunkraw() is called with startrev==endrev. When
this is true, we can avoid an extra index lookup and some other
minor operations.

On the mozilla-unified repo, `hg perfrevlogchunks -c` says this
has the following impact:

! read w/ reused fd
! wall 0.371846 comb 0.370000 user 0.350000 sys 0.020000 (best of 27)
! wall 0.337930 comb 0.330000 user 0.300000 sys 0.030000 (best of 30)

! read batch w/ reused fd
! wall 0.014952 comb 0.020000 user 0.000000 sys 0.020000 (best of 197)
! wall 0.014866 comb 0.010000 user 0.000000 sys 0.010000 (best of 196)

So, we've gone from ~25x slower than batch to ~22.5x slower.

At this point, there's probably not much else we can do except
implement an optimized function in the index itself, including in C.

Mercurial allows you to customize output of commands through
templates. You can either pass in a template or select an existing
template-style from the command line, via the --template option.

You can customize output for any "log-like" command: log,
outgoing, incoming, tip, parents, and heads.

Some built-in styles are packaged with Mercurial. These can be listed
with :hg:`log --template list`. Example usage::

    $ hg log -r1.0::1.1 --template changelog

A template is a piece of text, with markup to invoke variable
expansion::

    $ hg log -r1 --template "{node}\n"
    b56ce7b07c52de7d5fd79fb89701ea538af65746

Strings in curly braces are called keywords. The availability of
keywords depends on the exact context of the templater. These
keywords are usually available for templating a log-like command:

.. keywordsmarker

The "date" keyword does not produce human-readable output. If you
want to use a date in your output, you can use a filter to process
it. Filters are functions which return a string based on the input
variable. Be sure to use the stringify filter first when you're
applying a string-input filter to a list-like input variable.
You can also use a chain of filters to get the desired output::

   $ hg tip --template "{date|isodate}\n"
   2008-08-21 18:22 +0000

List of filters:

.. filtersmarker

Note that a filter is nothing more than a function call, i.e.
``expr|filter`` is equivalent to ``filter(expr)``.

In addition to filters, there are some basic built-in functions:

.. functionsmarker

We provide a limited set of infix arithmetic operations on integers::

  + for addition
  - for subtraction
  * for multiplication
  / for floor division (division rounded to integer nearest -infinity)

Division fulfils the law x = x / y + mod(x, y).

Also, for any expression that returns a list, there is a list operator::

    expr % "{template}"

As seen in the above example, ``{template}`` is interpreted as a template.
To prevent it from being interpreted, you can use an escape character ``\{``
or a raw string prefix, ``r'...'``.

New keywords and functions can be defined in the ``templatealias`` section of
a Mercurial configuration file::

  <alias> = <definition>

Arguments of the form `a1`, `a2`, etc. are substituted from the alias into
the definition.

For example,

::

  [templatealias]
  r = rev
  rn = "{r}:{node|short}"
  leftpad(s, w) = pad(s, w, ' ', True)

defines two symbol aliases, ``r`` and ``rn``, and a function alias
``leftpad()``.

It's also possible to specify complete template strings, using the
``templates`` section. The syntax used is the general template string syntax.

For example,

::

  [templates]
  nodedate = "{node|short}: {date(date, "%Y-%m-%d")}\n"

defines a template, ``nodedate``, which can be called like::

  $ hg log -r . -Tnodedate

Some sample command line templates:

- Format lists, e.g. files::

   $ hg log -r 0 --template "files:\n{files % '  {file}\n'}"

- Join the list of files with a ", "::

   $ hg log -r 0 --template "files: {join(files, ', ')}\n"

- Join the list of files ending with ".py" with a ", "::

   $ hg log -r 0 --template "pythonfiles: {join(files('**.py'), ', ')}\n"

- Separate non-empty arguments by a " "::

   $ hg log -r 0 --template "{separate(' ', node, bookmarks, tags}\n"

- Modify each line of a commit description::

   $ hg log --template "{splitlines(desc) % '**** {line}\n'}"

- Format date::

   $ hg log -r 0 --template "{date(date, '%Y')}\n"

- Display date in UTC::

   $ hg log -r 0 --template "{localdate(date, 'UTC')|date}\n"

- Output the description set to a fill-width of 30::

   $ hg log -r 0 --template "{fill(desc, 30)}"

- Use a conditional to test for the default branch::

   $ hg log -r 0 --template "{ifeq(branch, 'default', 'on the main branch',
   'on branch {branch}')}\n"

- Append a newline if not empty::

   $ hg tip --template "{if(author, '{author}\n')}"

- Label the output for use with the color extension::

   $ hg log -r 0 --template "{label('changeset.{phase}', node|short)}\n"

- Invert the firstline filter, i.e. everything but the first line::

   $ hg log -r 0 --template "{sub(r'^.*\n?\n?', '', desc)}\n"

- Display the contents of the 'extra' field, one per line::

   $ hg log -r 0 --template "{join(extras, '\n')}\n"

- Mark the active bookmark with '*'::

   $ hg log --template "{bookmarks % '{bookmark}{ifeq(bookmark, active, '*')} '}\n"

- Find the previous release candidate tag, the distance and changes since the tag::

   $ hg log -r . --template "{latesttag('re:^.*-rc$') % '{tag}, {changes}, {distance}'}\n"

- Mark the working copy parent with '@'::

   $ hg log --template "{ifcontains(rev, revset('.'), '@')}\n"

- Show details of parent revisions::

   $ hg log --template "{revset('parents(%d)', rev) % '{desc|firstline}\n'}"

- Show only commit descriptions that start with "template"::

   $ hg log --template "{startswith('template', firstline(desc))}\n"

- Print the first word of each line of a commit message::

   $ hg log --template "{word(0, desc)}\n"