Build out new declarative systems; deprecate mapper()

The ORM Declarative system is now unified into the ORM itself, with new
import spaces under ``sqlalchemy.orm`` and new kinds of mappings.  Support
for decorator-based mappings without using a base class, support for
classical style-mapper() calls that have access to the declarative class
registry for relationships, and full integration of Declarative with 3rd
party class attribute systems like ``dataclasses`` and ``attrs`` is now
supported.

Fixes: #5508
Change-Id: I130b2b6edff6450bfe8a3e6baa099ff04b5471ff

2 files changed, 13 insertions, 9 deletions

diff --git a/lib/sqlalchemy/util/__init__.py b/lib/sqlalchemy/util/__init__.py
index 1d92084cc..5fdcdf654 100644
--- a/lib/sqlalchemy/util/__init__.py
+++ b/lib/sqlalchemy/util/__init__.py
@@ -101,6 +101,7 @@ from .deprecations import deprecated_20_cls  # noqa
 from .deprecations import deprecated_cls  # noqa
 from .deprecations import deprecated_params  # noqa
 from .deprecations import inject_docstring_text  # noqa
+from .deprecations import moved_20  # noqa
 from .deprecations import SQLALCHEMY_WARN_20  # noqa
 from .deprecations import warn_deprecated  # noqa
 from .deprecations import warn_deprecated_20  # noqa
diff --git a/lib/sqlalchemy/util/deprecations.py b/lib/sqlalchemy/util/deprecations.py
index 0a79344c5..eae4be768 100644
--- a/lib/sqlalchemy/util/deprecations.py
+++ b/lib/sqlalchemy/util/deprecations.py
@@ -27,10 +27,12 @@ if os.getenv("SQLALCHEMY_WARN_20", "false").lower() in ("true", "yes", "1"):
 
 
 def _warn_with_version(msg, version, type_, stacklevel):
-    if type_ is exc.RemovedIn20Warning and not SQLALCHEMY_WARN_20:
+    is_20 = issubclass(type_, exc.RemovedIn20Warning)
+
+    if is_20 and not SQLALCHEMY_WARN_20:
         return
 
-    if type_ is exc.RemovedIn20Warning:
+    if is_20:
         msg += " (Background on SQLAlchemy 2.0 at: http://sqlalche.me/e/b8d9)"
 
     warn = type_(msg)
@@ -150,6 +152,12 @@ def deprecated(
     return decorate
 
 
+def moved_20(message, **kw):
+    return deprecated(
+        "2.0", message=message, warning=exc.MovedIn20Warning, **kw
+    )
+
+
 def deprecated_20(api_name, alternative=None, **kw):
     message = (
         "The %s function/method is considered legacy as of the "
@@ -325,19 +333,14 @@ def _decorate_with_warning(
             " (Background on SQLAlchemy 2.0 at: "
             ":ref:`migration_20_toplevel`)"
         )
-        warning_only = (
-            " (Background on SQLAlchemy 2.0 at: http://sqlalche.me/e/b8d9)"
-        )
     else:
-        doc_only = warning_only = ""
+        doc_only = ""
 
     @decorator
     def warned(fn, *args, **kwargs):
         skip_warning = kwargs.pop("_sa_skip_warning", False)
         if not skip_warning:
-            _warn_with_version(
-                message + warning_only, version, wtype, stacklevel=3
-            )
+            _warn_with_version(message, version, wtype, stacklevel=3)
         return fn(*args, **kwargs)
 
     doc = func.__doc__ is not None and func.__doc__ or ""