Ensure the "orm" plugin is used unconditionally for bundles

This also introduces that the "orm" plugin may be used
when the plugin_subject is None.

Fixed regression where the :paramref:`.Bundle.single_entity` flag would
take effect for a :class:`.Bundle` even though it were not set.
Additionally, this flag is legacy as it only makes sense for the
:class:`_orm.Query` object and not 2.0 style execution.  a deprecation
warning is emitted when used with new-style execution.

Fixes: #5702
Change-Id: If9f43365b9d966cb398890aeba2efa555658a7e5

4 files changed, 45 insertions, 12 deletions

diff --git a/lib/sqlalchemy/orm/context.py b/lib/sqlalchemy/orm/context.py
index 12759f018..cd654ed3d 100644
--- a/lib/sqlalchemy/orm/context.py
+++ b/lib/sqlalchemy/orm/context.py
@@ -242,7 +242,8 @@ class ORMCompileState(CompileState):
         except KeyError:
             assert False, "statement had 'orm' plugin but no plugin_subject"
         else:
-            bind_arguments["mapper"] = plugin_subject.mapper
+            if plugin_subject:
+                bind_arguments["mapper"] = plugin_subject.mapper
 
         if load_options._autoflush:
             session._autoflush()
@@ -342,10 +343,10 @@ class ORMFromStatementCompileState(ORMCompileState):
         self._polymorphic_adapters = {}
         self._no_yield_pers = set()
 
-        _QueryEntity.to_compile_state(self, statement_container._raw_columns)
-
         self.compile_options = statement_container._compile_options
 
+        _QueryEntity.to_compile_state(self, statement_container._raw_columns)
+
         self.current_path = statement_container._compile_options._current_path
 
         if toplevel and statement_container._with_options:
@@ -494,10 +495,10 @@ class ORMSelectCompileState(ORMCompileState, SelectState):
             )
             self._setup_with_polymorphics()
 
-        _QueryEntity.to_compile_state(self, select_statement._raw_columns)
-
         self.compile_options = select_statement._compile_options
 
+        _QueryEntity.to_compile_state(self, select_statement._raw_columns)
+
         # determine label style.   we can make different decisions here.
         # at the moment, trying to see if we can always use DISAMBIGUATE_ONLY
         # rather than LABEL_STYLE_NONE, and if we can use disambiguate style
@@ -2365,6 +2366,14 @@ class _BundleEntity(_QueryEntity):
                     )
 
         self.supports_single_entity = self.bundle.single_entity
+        if (
+            self.supports_single_entity
+            and not compile_state.compile_options._use_legacy_query_style
+        ):
+            util.warn_deprecated_20(
+                "The Bundle.single_entity flag has no effect when "
+                "using 2.0 style execution."
+            )
 
     @property
     def mapper(self):
diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 1d4709726..7f7bab682 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -2730,7 +2730,14 @@ class SelectInLoader(PostLoader, util.MemoizedSlots):
         q = sql.lambda_stmt(
             lambda: sql.select(
                 orm_util.Bundle("pk", *pk_cols), effective_entity
-            ).apply_labels(),
+            )
+            .apply_labels()
+            ._set_propagate_attrs(
+                {
+                    "compile_state_plugin": "orm",
+                    "plugin_subject": effective_entity,
+                }
+            ),
             lambda_cache=self._query_cache,
             global_track_bound_values=False,
             track_on=(self, effective_entity) + tuple(pk_cols),
diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index 7d1650a1a..4502d5b89 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -1361,11 +1361,26 @@ class Bundle(ORMColumnsClauseRole, SupportsCloneAnnotations, InspectionAttr):
         # ensure existing entity_namespace remains
         annotations = {"bundle": self, "entity_namespace": self}
         annotations.update(self._annotations)
-        return expression.ClauseList(
-            _literal_as_text_role=roles.ColumnsClauseRole,
-            group=False,
-            *[e._annotations.get("bundle", e) for e in self.exprs]
-        )._annotate(annotations)
+
+        plugin_subject = self.exprs[0]._propagate_attrs.get(
+            "plugin_subject", self.entity
+        )
+        return (
+            expression.ClauseList(
+                _literal_as_text_role=roles.ColumnsClauseRole,
+                group=False,
+                *[e._annotations.get("bundle", e) for e in self.exprs]
+            )
+            ._annotate(annotations)
+            ._set_propagate_attrs(
+                # the Bundle *must* use the orm plugin no matter what.  the
+                # subject can be None but it's much better if it's not.
+                {
+                    "compile_state_plugin": "orm",
+                    "plugin_subject": plugin_subject,
+                }
+            )
+        )
 
     @property
     def clauses(self):
diff --git a/lib/sqlalchemy/sql/traversals.py b/lib/sqlalchemy/sql/traversals.py
index a24d010cd..2887813ad 100644
--- a/lib/sqlalchemy/sql/traversals.py
+++ b/lib/sqlalchemy/sql/traversals.py
@@ -176,7 +176,9 @@ class HasCacheKey(object):
                             obj["compile_state_plugin"],
                             obj["plugin_subject"]._gen_cache_key(
                                 anon_map, bindparams
-                            ),
+                            )
+                            if obj["plugin_subject"]
+                            else None,
                         )
                     elif meth is InternalTraversal.dp_annotations_key:
                         # obj is here is the _annotations dict.   however, we