Fixed #23092: Squashing handles external dependencies

from django.core.management.base import BaseCommand, CommandError

from django.utils import six

from django.conf import settings

from django.db import connections, DEFAULT_DB_ALIAS, migrations

from django.db.migrations.loader import AmbiguityError

from django.db.migrations.executor import MigrationExecutor

from django.db.migrations.writer import MigrationWriter

from django.db.migrations.optimizer import MigrationOptimizer

from django.db.migrations.migration import SwappableTuple

class Command(BaseCommand):

                if answer != "y":

                    return

        # Load the operations from all those migrations and concat together

        # Load the operations from all those migrations and concat together,

        # along with collecting external dependencies and detecting

        # double-squashing

        operations = []

        dependencies = set()

        for smigration in migrations_to_squash:

            if smigration.replaces:

                raise CommandError("You cannot squash squashed migrations! Please transition it to a normal migration first: https://docs.djangoproject.com/en/1.7/topics/migrations/#squashing-migrations")

            operations.extend(smigration.operations)

            for dependency in smigration.dependencies:

                if isinstance(dependency, SwappableTuple):

                    if settings.AUTH_USER_MODEL == dependency.setting:

                        dependencies.add(("__setting__", "AUTH_USER_MODEL"))

                    else:

                        dependencies.add(dependency)

                elif dependency[0] != smigration.app_label:

                    dependencies.add(dependency)

        if self.verbosity > 0:

            self.stdout.write(self.style.MIGRATE_HEADING("Optimizing..."))

        # Make a new migration with those operations

        subclass = type("Migration", (migrations.Migration, ), {

            "dependencies": [],

            "dependencies": dependencies,

            "operations": new_operations,

            "replaces": replaces,

        })

        return project_state

class SwappableTuple(tuple):

    """

    Subclass of tuple so Django can tell this was originally a swappable

    dependency when it reads the migration file.

    """

    def __new__(cls, value, setting):

        self = tuple.__new__(cls, value)

        self.setting = setting

        return self

def swappable_dependency(value):

    """

    Turns a setting value into a dependency.

    """

    return (value.split(".", 1)[0], "__first__")

    return SwappableTuple((value.split(".", 1)[0], "__first__"), value)