mercurial/registrar.py

registrar: replace "cmdtype" with an intent-based mechanism (API)

Commands perform varied actions and repositories vary in their
capabilities.

Historically, the .hg/requires file has been used to lock out clients
lacking a requirement. But this is a very heavy-handed approach and
is typically reserved for cases where the on-disk storage format
changes and we want to prevent incompatible clients from operating on
a repo.

Outside of the .hg/requires file, we tend to deal with things like
optional, extension-provided features via checking at call sites.
We'll either have checks in core or extensions will monkeypatch
functions in core disabling incompatible features, enabling new
features, etc.

Things are somewhat tolerable today. But once we introduce alternate
storage backends with varying support for repository features and
vastly different modes of behavior, the current model will quickly
grow unwieldy. For example, the implementation of the "simple store"
required a lot of hacks to deal with stripping and verify because
various parts of core assume things are implemented a certain way.
Partial clone will require new ways of modeling file data retrieval,
because we can no longer assume that all file data is already local.
In this new world, some commands might not make any sense for certain
types of repositories.

What we need is a mechanism to affect the construction of repository
(and eventually peer) instances so the requirements/capabilities
needed for the current operation can be taken into account. "Current
operation" can almost certainly be defined by a command. So it makes
sense for commands to declare their intended actions.

This commit introduces the "intents" concept on the command registrar.
"intents" captures a set of strings that declare actions that are
anticipated to be taken, requirements the repository must possess, etc.
These intents will be passed into hg.repo(), which will pass them into
localrepository, where they can be used to influence the object being
created. Some use cases for this include:

* For read-only intents, constructing a repository object that doesn't
  expose methods that can mutate the repository. Its VFS instances
  don't even allow opening a file with write access.
* For read-only intents, constructing a repository object without
  cache invalidation logic. If the repo never changes during its lifetime,
  nothing ever needs to be invalidated and we don't need to do expensive
  things like verify the changelog's hidden revisions state is accurate
  every time we access repo.changelog.
* We can automatically hide commands from `hg help` when the current
  repository doesn't provide that command. For example, an alternate
  storage backend may not support `hg commit`, so we can hide that
  command or anything else that would perform local commits.

We already kind of had an "intents" mechanism on the registrar in the
form of "cmdtype." However, it was never used. And it was limited to
a single value. We really need something that supports multiple
intents. And because intents may be defined by extensions and at this
point are advisory, I think it is best to define them in a set rather
than as separate arguments/attributes on the command.

Differential Revision: https://phab.mercurial-scm.org/D3376

# registrar.py - utilities to register function for specific purpose
#
#  Copyright FUJIWARA Katsunori <[e-mail]> and others
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

from . import (
    configitems,
    error,
    pycompat,
    util,
)

# unlike the other registered items, config options are neither functions or
# classes. Registering the option is just small function call.
#
# We still add the official API to the registrar module for consistency with
# the other items extensions want might to register.
configitem = configitems.getitemregister

class _funcregistrarbase(object):
    """Base of decorator to register a function for specific purpose

    This decorator stores decorated functions into own dict 'table'.

    The least derived class can be defined by overriding 'formatdoc',
    for example::

        class keyword(_funcregistrarbase):
            _docformat = ":%s: %s"

    This should be used as below:

        keyword = registrar.keyword()

        @keyword('bar')
        def barfunc(*args, **kwargs):
            '''Explanation of bar keyword ....
            '''
            pass

    In this case:

    - 'barfunc' is stored as 'bar' in '_table' of an instance 'keyword' above
    - 'barfunc.__doc__' becomes ":bar: Explanation of bar keyword"
    """
    def __init__(self, table=None):
        if table is None:
            self._table = {}
        else:
            self._table = table

    def __call__(self, decl, *args, **kwargs):
        return lambda func: self._doregister(func, decl, *args, **kwargs)

    def _doregister(self, func, decl, *args, **kwargs):
        name = self._getname(decl)

        if name in self._table:
            msg = 'duplicate registration for name: "%s"' % name
            raise error.ProgrammingError(msg)

        if func.__doc__ and not util.safehasattr(func, '_origdoc'):
            doc = pycompat.sysbytes(func.__doc__).strip()
            func._origdoc = doc
            func.__doc__ = pycompat.sysstr(self._formatdoc(decl, doc))

        self._table[name] = func
        self._extrasetup(name, func, *args, **kwargs)

        return func

    def _parsefuncdecl(self, decl):
        """Parse function declaration and return the name of function in it
        """
        i = decl.find('(')
        if i >= 0:
            return decl[:i]
        else:
            return decl

    def _getname(self, decl):
        """Return the name of the registered function from decl

        Derived class should override this, if it allows more
        descriptive 'decl' string than just a name.
        """
        return decl

    _docformat = None

    def _formatdoc(self, decl, doc):
        """Return formatted document of the registered function for help

        'doc' is '__doc__.strip()' of the registered function.
        """
        return self._docformat % (decl, doc)

    def _extrasetup(self, name, func):
        """Execute exra setup for registered function, if needed
        """

class command(_funcregistrarbase):
    """Decorator to register a command function to table

    This class receives a command table as its argument. The table should
    be a dict.

    The created object can be used as a decorator for adding commands to
    that command table. This accepts multiple arguments to define a command.

    The first argument is the command name (as bytes).

    The `options` keyword argument is an iterable of tuples defining command
    arguments. See ``mercurial.fancyopts.fancyopts()`` for the format of each
    tuple.

    The `synopsis` argument defines a short, one line summary of how to use the
    command. This shows up in the help output.

    There are three arguments that control what repository (if any) is found
    and passed to the decorated function: `norepo`, `optionalrepo`, and
    `inferrepo`.

    The `norepo` argument defines whether the command does not require a
    local repository. Most commands operate against a repository, thus the
    default is False. When True, no repository will be passed.

    The `optionalrepo` argument defines whether the command optionally requires
    a local repository. If no repository can be found, None will be passed
    to the decorated function.

    The `inferrepo` argument defines whether to try to find a repository from
    the command line arguments. If True, arguments will be examined for
    potential repository locations. See ``findrepo()``. If a repository is
    found, it will be used and passed to the decorated function.

    The `intents` argument defines a set of intended actions or capabilities
    the command is taking. These intents can be used to affect the construction
    of the repository object passed to the command. For example, commands
    declaring that they are read-only could receive a repository that doesn't
    have any methods allowing repository mutation. Other intents could be used
    to prevent the command from running if the requested intent could not be
    fulfilled.

    The following intents are defined:

    readonly
       The command is read-only

    The signature of the decorated function looks like this:
        def cmd(ui[, repo] [, <args>] [, <options>])

      `repo` is required if `norepo` is False.
      `<args>` are positional args (or `*args`) arguments, of non-option
      arguments from the command line.
      `<options>` are keyword arguments (or `**options`) of option arguments
      from the command line.

    See the WritingExtensions and MercurialApi documentation for more exhaustive
    descriptions and examples.
    """

    def _doregister(self, func, name, options=(), synopsis=None,
                    norepo=False, optionalrepo=False, inferrepo=False,
                    intents=None):

        func.norepo = norepo
        func.optionalrepo = optionalrepo
        func.inferrepo = inferrepo
        func.intents = intents or set()
        if synopsis:
            self._table[name] = func, list(options), synopsis
        else:
            self._table[name] = func, list(options)
        return func

INTENT_READONLY = b'readonly'

class revsetpredicate(_funcregistrarbase):
    """Decorator to register revset predicate

    Usage::

        revsetpredicate = registrar.revsetpredicate()

        @revsetpredicate('mypredicate(arg1, arg2[, arg3])')
        def mypredicatefunc(repo, subset, x):
            '''Explanation of this revset predicate ....
            '''
            pass

    The first string argument is used also in online help.

    Optional argument 'safe' indicates whether a predicate is safe for
    DoS attack (False by default).

    Optional argument 'takeorder' indicates whether a predicate function
    takes ordering policy as the last argument.

    Optional argument 'weight' indicates the estimated run-time cost, useful
    for static optimization, default is 1. Higher weight means more expensive.
    Usually, revsets that are fast and return only one revision has a weight of
    0.5 (ex. a symbol); revsets with O(changelog) complexity and read only the
    changelog have weight 10 (ex. author); revsets reading manifest deltas have
    weight 30 (ex. adds); revset reading manifest contents have weight 100
    (ex. contains). Note: those values are flexible. If the revset has a
    same big-O time complexity as 'contains', but with a smaller constant, it
    might have a weight of 90.

    'revsetpredicate' instance in example above can be used to
    decorate multiple functions.

    Decorated functions are registered automatically at loading
    extension, if an instance named as 'revsetpredicate' is used for
    decorating in extension.

    Otherwise, explicit 'revset.loadpredicate()' is needed.
    """
    _getname = _funcregistrarbase._parsefuncdecl
    _docformat = "``%s``\n    %s"

    def _extrasetup(self, name, func, safe=False, takeorder=False, weight=1):
        func._safe = safe
        func._takeorder = takeorder
        func._weight = weight

class filesetpredicate(_funcregistrarbase):
    """Decorator to register fileset predicate

    Usage::

        filesetpredicate = registrar.filesetpredicate()

        @filesetpredicate('mypredicate()')
        def mypredicatefunc(mctx, x):
            '''Explanation of this fileset predicate ....
            '''
            pass

    The first string argument is used also in online help.

    Optional argument 'callstatus' indicates whether a predicate
     implies 'matchctx.status()' at runtime or not (False, by
     default).

    Optional argument 'callexisting' indicates whether a predicate
    implies 'matchctx.existing()' at runtime or not (False, by
    default).

    'filesetpredicate' instance in example above can be used to
    decorate multiple functions.

    Decorated functions are registered automatically at loading
    extension, if an instance named as 'filesetpredicate' is used for
    decorating in extension.

    Otherwise, explicit 'fileset.loadpredicate()' is needed.
    """
    _getname = _funcregistrarbase._parsefuncdecl
    _docformat = "``%s``\n    %s"

    def _extrasetup(self, name, func, callstatus=False, callexisting=False):
        func._callstatus = callstatus
        func._callexisting = callexisting

class _templateregistrarbase(_funcregistrarbase):
    """Base of decorator to register functions as template specific one
    """
    _docformat = ":%s: %s"

class templatekeyword(_templateregistrarbase):
    """Decorator to register template keyword

    Usage::

        templatekeyword = registrar.templatekeyword()

        # new API (since Mercurial 4.6)
        @templatekeyword('mykeyword', requires={'repo', 'ctx'})
        def mykeywordfunc(context, mapping):
            '''Explanation of this template keyword ....
            '''
            pass

        # old API
        @templatekeyword('mykeyword')
        def mykeywordfunc(repo, ctx, templ, cache, revcache, **args):
            '''Explanation of this template keyword ....
            '''
            pass

    The first string argument is used also in online help.

    Optional argument 'requires' should be a collection of resource names
    which the template keyword depends on. This also serves as a flag to
    switch to the new API. If 'requires' is unspecified, all template
    keywords and resources are expanded to the function arguments.

    'templatekeyword' instance in example above can be used to
    decorate multiple functions.

    Decorated functions are registered automatically at loading
    extension, if an instance named as 'templatekeyword' is used for
    decorating in extension.

    Otherwise, explicit 'templatekw.loadkeyword()' is needed.
    """

    def _extrasetup(self, name, func, requires=None):
        func._requires = requires

class templatefilter(_templateregistrarbase):
    """Decorator to register template filer

    Usage::

        templatefilter = registrar.templatefilter()

        @templatefilter('myfilter', intype=bytes)
        def myfilterfunc(text):
            '''Explanation of this template filter ....
            '''
            pass

    The first string argument is used also in online help.

    Optional argument 'intype' defines the type of the input argument,
    which should be (bytes, int, templateutil.date, or None for any.)

    'templatefilter' instance in example above can be used to
    decorate multiple functions.

    Decorated functions are registered automatically at loading
    extension, if an instance named as 'templatefilter' is used for
    decorating in extension.

    Otherwise, explicit 'templatefilters.loadkeyword()' is needed.
    """

    def _extrasetup(self, name, func, intype=None):
        func._intype = intype

class templatefunc(_templateregistrarbase):
    """Decorator to register template function

    Usage::

        templatefunc = registrar.templatefunc()

        @templatefunc('myfunc(arg1, arg2[, arg3])', argspec='arg1 arg2 arg3')
        def myfuncfunc(context, mapping, args):
            '''Explanation of this template function ....
            '''
            pass

    The first string argument is used also in online help.

    If optional 'argspec' is defined, the function will receive 'args' as
    a dict of named arguments. Otherwise 'args' is a list of positional
    arguments.

    'templatefunc' instance in example above can be used to
    decorate multiple functions.

    Decorated functions are registered automatically at loading
    extension, if an instance named as 'templatefunc' is used for
    decorating in extension.

    Otherwise, explicit 'templatefuncs.loadfunction()' is needed.
    """
    _getname = _funcregistrarbase._parsefuncdecl

    def _extrasetup(self, name, func, argspec=None):
        func._argspec = argspec

class internalmerge(_funcregistrarbase):
    """Decorator to register in-process merge tool

    Usage::

        internalmerge = registrar.internalmerge()

        @internalmerge('mymerge', internalmerge.mergeonly,
                       onfailure=None, precheck=None):
        def mymergefunc(repo, mynode, orig, fcd, fco, fca,
                        toolconf, files, labels=None):
            '''Explanation of this internal merge tool ....
            '''
            return 1, False # means "conflicted", "no deletion needed"

    The first string argument is used to compose actual merge tool name,
    ":name" and "internal:name" (the latter is historical one).

    The second argument is one of merge types below:

    ========== ======== ======== =========
    merge type precheck premerge fullmerge
    ========== ======== ======== =========
    nomerge     x        x        x
    mergeonly   o        x        o
    fullmerge   o        o        o
    ========== ======== ======== =========

    Optional argument 'onfailure' is the format of warning message
    to be used at failure of merging (target filename is specified
    at formatting). Or, None or so, if warning message should be
    suppressed.

    Optional argument 'precheck' is the function to be used
    before actual invocation of internal merge tool itself.
    It takes as same arguments as internal merge tool does, other than
    'files' and 'labels'. If it returns false value, merging is aborted
    immediately (and file is marked as "unresolved").

    'internalmerge' instance in example above can be used to
    decorate multiple functions.

    Decorated functions are registered automatically at loading
    extension, if an instance named as 'internalmerge' is used for
    decorating in extension.

    Otherwise, explicit 'filemerge.loadinternalmerge()' is needed.
    """
    _docformat = "``:%s``\n    %s"

    # merge type definitions:
    nomerge = None
    mergeonly = 'mergeonly'  # just the full merge, no premerge
    fullmerge = 'fullmerge'  # both premerge and merge

    def _extrasetup(self, name, func, mergetype,
                    onfailure=None, precheck=None):
        func.mergetype = mergetype
        func.onfailure = onfailure
        func.precheck = precheck