[PROPOSAL] Add pre-registry

sanic/app.py

@@ -67,6 +67,7 @@
     URLBuildError,
 )
 from sanic.handlers import ErrorHandler
+from sanic.helpers import Default, _default
 from sanic.http import Stage
 from sanic.log import LOGGING_CONFIG_DEFAULTS, Colors, error_logger, logger
 from sanic.mixins.listeners import ListenerEvent
@@ -536,6 +537,30 @@ def blueprint(
             blueprint.strict_slashes = self.strict_slashes
         blueprint.register(self, options)
 
+    def _register_lazy_blueprints(self):
+        registry = {**Blueprint.__pre_registry__}
+        if _default in Blueprint.__pre_registry__:
+            if len(Sanic._app_registry) > 1:
+                raise SanicException(
+                    "Ambiguous Blueprint pre-registration detected. When "
+                    "there are multiple Sanic application instances, all "
+                    "pre-registrations must use an application name."
+                )
+
+            if self.name in registry and _default in registry:
+                registry[_default].extend(registry.pop(self.name))
+
+            registry = {
+                self.name if k is _default else k: v
+                for k, v in registry.items()
+            }
+
+        for name, registrants in registry.items():
+            for reg_info in registrants:
+                blueprint = reg_info.pop("bp")
+                if name == self.name and blueprint.name not in self.blueprints:
+                    self.blueprint(blueprint, **reg_info)
+
     def url_for(self, view_name: str, **kwargs):
         """Build a URL based on a view name and the values provided.
 
@@ -1677,6 +1702,32 @@ def get_app(
                 return cls(name)
             raise SanicException(f'Sanic app name "{name}" not found.')
 
+    @classmethod
+    def lazy(
+        cls,
+        app_name: Union[str, Default] = _default,
+        *,
+        name: str = None,
+        url_prefix: Optional[str] = None,
+        host: Optional[Union[List[str], str]] = None,
+        version: Optional[Union[int, str, float]] = None,
+        strict_slashes: Optional[bool] = None,
+        version_prefix: str = "/v",
+    ) -> Blueprint:
+        if not name:
+            flat = [1 for x in Blueprint.__pre_registry__.values() for _ in x]
+            name = f"bp{len(flat)}"
+        bp = Blueprint(
+            name=name,
+            url_prefix=url_prefix,
+            host=host,
+            version=version,
+            strict_slashes=strict_slashes,
+            version_prefix=version_prefix,
+        )
+        bp.pre_register(app_name)
+        return bp
+
     # -------------------------------------------------------------------- #
     # Lifecycle
     # -------------------------------------------------------------------- #
@@ -1697,6 +1748,7 @@ def signalize(self):
 
     async def _startup(self):
         self._future_registry.clear()
+        self._register_lazy_blueprints()
         self.signalize()
         self.finalize()
         ErrorHandler.finalize(

sanic/blueprints.py

@@ -107,6 +107,7 @@ class Blueprint(BaseSanic):
         "version_prefix",
         "websocket_routes",
     )
+    __pre_registry__: Dict[Union[str, Default], Any] = defaultdict(list)
 
     def __init__(
         self,
@@ -461,3 +462,30 @@ def register_futures(
     ):
         for app in apps:
             app._future_registry.update(set((bp, item) for item in futures))
+
+    def pre_register(
+        self,
+        name: Union[str, Default],
+        url_prefix: Optional[str] = None,
+        host: Optional[Union[List[str], str]] = None,
+        version: Optional[Union[int, str, float]] = None,
+        strict_slashes: Optional[bool] = None,
+        version_prefix: Union[str, Default] = _default,
+    ) -> None:
+        if not hasattr(self.ctx, "_prereg"):
+            self.ctx._prereg = []
+        self.ctx._prereg.append(name)
+        self.__class__.__pre_registry__[name].append(
+            {
+                k: v
+                for k, v in {
+                    "bp": self,
+                    "url_prefix": url_prefix,
+                    "host": host,
+                    "version": version,
+                    "strict_slashes": strict_slashes,
+                    "version_prefix": version_prefix,
+                }.items()
+                if v is not None and v is not _default
+            }
+        )

sanic/cli/app.py

@@ -10,7 +10,9 @@
 
 from sanic.app import Sanic
 from sanic.application.logo import get_logo
+from sanic.blueprints import Blueprint
 from sanic.cli.arguments import Group
+from sanic.helpers import _default
 from sanic.log import error_logger
 from sanic.simple import create_simple_server
 
@@ -20,6 +22,7 @@ class SanicArgumentParser(ArgumentParser):
 
 
 class SanicCLI:
+    DEFAULT_APP_NAME = "SANIC"
     DESCRIPTION = indent(
         f"""
 {get_logo(True)}
@@ -131,7 +134,17 @@ def _get_app(self):
 
                 app_type_name = type(app).__name__
 
-                if not isinstance(app, Sanic):
+                if isinstance(app, Blueprint):
+                    bp = app
+                    name = (
+                        bp.ctx._prereg[0]
+                        if hasattr(bp.ctx, "_prereg")
+                        else _default
+                    )
+                    if name is _default:
+                        name = self.DEFAULT_APP_NAME
+                    app = Sanic(name)
+                elif not isinstance(app, Sanic):
                     raise ValueError(
                         f"Module is not a Sanic app, it is a {app_type_name}\n"
                         f"  Perhaps you meant {self.args.module}.app?"