Complete deprecation of from_self()

For most from_self() tests, move them into
test/orm/test_deprecated.py and replace the existing
test with one that uses aliased() plus a subquery.
This then revealed a few more issues.

Related items:

* Added slice() method to GenerativeSelect, to match that
  of orm.Query and to make possible migration of one of the
  from_self() tests.  moved the utility functions used for this
  from orm/util into sql/util.

* repairs a caching issue related to subqueryload
  where information being derived from the cached path info
  was mixing up with query information based on the per-query
  state, specifically an AliasedClass that is per query.

* for the above issue, it seemed like path_registry maybe
  had to change so that it represents AliasedClass objects
  as their cache key rather than on identity, but it wasn't
  needed.  still seems like it would be more correct.

* enhances the error message raised by coercions for a case
  such as when an AliasedClass holds onto a select() object
  and not a subquery(); will name the original and resolved
  object for clarity  (although how is AliasedClass able to
  accept a Select() object in the first place?)

* Added _set_propagate_attrs() to Query so that again if
  it's passed to AliasedClass, it doesn't raise an error
  during coercion, but again maybe that should also be
  rejected up front

Fixes: #5368
Change-Id: I5912aa611d899acc87a75eb5ee9f95990592f210

1 files changed, 72 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index b3ead718a..264976cc8 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -12,7 +12,9 @@
 from collections import deque
 from itertools import chain
 
+from . import coercions
 from . import operators
+from . import roles
 from . import visitors
 from .annotation import _deep_annotate  # noqa
 from .annotation import _deep_deannotate  # noqa
@@ -980,3 +982,73 @@ class ColumnAdapter(ClauseAdapter):
     def __setstate__(self, state):
         self.__dict__.update(state)
         self.columns = util.WeakPopulateDict(self._locate_col)
+
+
+def _offset_or_limit_clause(element, name=None, type_=None):
+    """Convert the given value to an "offset or limit" clause.
+
+    This handles incoming integers and converts to an expression; if
+    an expression is already given, it is passed through.
+
+    """
+    return coercions.expect(
+        roles.LimitOffsetRole, element, name=name, type_=type_
+    )
+
+
+def _offset_or_limit_clause_asint_if_possible(clause):
+    """Return the offset or limit clause as a simple integer if possible,
+    else return the clause.
+
+    """
+    if clause is None:
+        return None
+    if hasattr(clause, "_limit_offset_value"):
+        value = clause._limit_offset_value
+        return util.asint(value)
+    else:
+        return clause
+
+
+def _make_slice(limit_clause, offset_clause, start, stop):
+    """Compute LIMIT/OFFSET in terms of slice start/end
+    """
+
+    # for calculated limit/offset, try to do the addition of
+    # values to offset in Python, however if a SQL clause is present
+    # then the addition has to be on the SQL side.
+    if start is not None and stop is not None:
+        offset_clause = _offset_or_limit_clause_asint_if_possible(
+            offset_clause
+        )
+        if offset_clause is None:
+            offset_clause = 0
+
+        if start != 0:
+            offset_clause = offset_clause + start
+
+        if offset_clause == 0:
+            offset_clause = None
+        else:
+            offset_clause = _offset_or_limit_clause(offset_clause)
+
+        limit_clause = _offset_or_limit_clause(stop - start)
+
+    elif start is None and stop is not None:
+        limit_clause = _offset_or_limit_clause(stop)
+    elif start is not None and stop is None:
+        offset_clause = _offset_or_limit_clause_asint_if_possible(
+            offset_clause
+        )
+        if offset_clause is None:
+            offset_clause = 0
+
+        if start != 0:
+            offset_clause = offset_clause + start
+
+        if offset_clause == 0:
+            offset_clause = None
+        else:
+            offset_clause = _offset_or_limit_clause(offset_clause)
+
+    return limit_clause, offset_clause