comparison mercurial/wireproto.py @ 35981:ef683a0fd21f

wireproto: define and use types for wire protocol commands

Wire protocol commands have historically been declared as
2-tuples in wireproto.commands. There are some additional features I'd
like to implement that require going beyond 2-tuples. But because
the 2-tuple API (both destructuring assignment and direct assignment
into the dict) is used throughout the code base and in 3rd party
extensions, we can't do a trivial type change.

This commit creates a new "commandentry" type to represent declared
wire protocol commands. It implements __getitem__ and __iter__ so
it can quack like a 2-tuple. The @wireprotocommand decorator now
creates "commandentry" instances.

We also create a "commanddict" type to represent the dictionary of
declared wire protocol commands. It inherits from "dict" but provides
a custom __setitem__ to coerce passed 2-tuples to "commandentry"
instances. wireproto.commands is now an instance of this type.

Various callers in core rely on the new functionality. And tests
pass. So I'm reasonably confident things will "just work" in 3rd
party extensions as well.

Differential Revision: https://phab.mercurial-scm.org/D1998

35980:b4976912a6ef

                          hint=_('usable compression engines: %s') %
                          ', '.sorted(validnames))

    return compengines

# list of commands
commands = {}

def wireprotocommand(name, args=''):
    """Decorator to declare a wire protocol command.

    ``name`` is the name of the wire protocol command being provided.

    ``args`` is a space-delimited list of named arguments that the command
    accepts. ``*`` is a special value that says to accept all arguments.
    """
    def register(func):
        commands[name] = (func, args)
        return func
    return register

@wireprotocommand('batch', 'cmds *')
def batch(repo, proto, cmds, others):

35981:ef683a0fd21f

                          hint=_('usable compression engines: %s') %
                          ', '.sorted(validnames))

    return compengines

class commandentry(object):
    """Represents a declared wire protocol command."""
    def __init__(self, func, args=''):
        self.func = func
        self.args = args

    def _merge(self, func, args):
        """Merge this instance with an incoming 2-tuple.

        This is called when a caller using the old 2-tuple API attempts
        to replace an instance. The incoming values are merged with
        data not captured by the 2-tuple and a new instance containing
        the union of the two objects is returned.
        """
        return commandentry(func, args)

    # Old code treats instances as 2-tuples. So expose that interface.
    def __iter__(self):
        yield self.func
        yield self.args

    def __getitem__(self, i):
        if i == 0:
            return self.func
        elif i == 1:
            return self.args
        else:
            raise IndexError('can only access elements 0 and 1')

class commanddict(dict):
    """Container for registered wire protocol commands.

    It behaves like a dict. But __setitem__ is overwritten to allow silent
    coercion of values from 2-tuples for API compatibility.
    """
    def __setitem__(self, k, v):
        if isinstance(v, commandentry):
            pass
        # Cast 2-tuples to commandentry instances.
        elif isinstance(v, tuple):
            if len(v) != 2:
                raise ValueError('command tuples must have exactly 2 elements')

            # It is common for extensions to wrap wire protocol commands via
            # e.g. ``wireproto.commands[x] = (newfn, args)``. Because callers
            # doing this aren't aware of the new API that uses objects to store
            # command entries, we automatically merge old state with new.
            if k in self:
                v = self[k]._merge(v[0], v[1])
            else:
                v = commandentry(v[0], v[1])
        else:
            raise ValueError('command entries must be commandentry instances '
                             'or 2-tuples')

        return super(commanddict, self).__setitem__(k, v)

commands = commanddict()

def wireprotocommand(name, args=''):
    """Decorator to declare a wire protocol command.

    ``name`` is the name of the wire protocol command being provided.

    ``args`` is a space-delimited list of named arguments that the command
    accepts. ``*`` is a special value that says to accept all arguments.
    """
    def register(func):
        commands[name] = commandentry(func, args)
        return func
    return register

@wireprotocommand('batch', 'cmds *')
def batch(repo, proto, cmds, others):