mercurial/registrar.py

pager: use less as a fallback on Unix

This seems reasonable choice per discussion, and the default-default of Git.
See also the inline-comment for why.

https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-April/097042.html

# 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 (
    error,
    pycompat,
    util,
)

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
        """
        pass

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.

    '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):
        func._safe = safe
        func._takeorder = takeorder

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()

        @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.

    '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.
    """

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

    Usage::

        templatefilter = registrar.templatefilter()

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

    The first string argument is used also in online help.

    '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.
    """

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 'templater.loadfunction()' is needed.
    """
    _getname = _funcregistrarbase._parsefuncdecl

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