Fixed #30446 -- Resolved Value.output_field for stdlib types.

This required implementing a limited form of dynamic dispatch to combine
expressions with numerical output. Refs #26355 should eventually provide
a better interface for that.

django/db/models/expressions.py

@@ -1,7 +1,9 @@
 import copy
 import datetime
+import functools
 import inspect
 from decimal import Decimal
+from uuid import UUID
 
 from django.core.exceptions import EmptyResultSet, FieldError
 from django.db import NotSupportedError, connection
@@ -56,12 +58,7 @@ class Combinable:
     def _combine(self, other, connector, reversed):
         if not hasattr(other, 'resolve_expression'):
             # everything must be resolvable to an expression
-            output_field = (
-                fields.DurationField()
-                if isinstance(other, datetime.timedelta) else
-                None
-            )
-            other = Value(other, output_field=output_field)
+            other = Value(other)
 
         if reversed:
             return CombinedExpression(other, connector, self)
@@ -422,6 +419,25 @@ class Expression(BaseExpression, Combinable):
     pass
 
 
+_connector_combinators = {
+    connector: [
+        (fields.IntegerField, fields.DecimalField, fields.DecimalField),
+        (fields.DecimalField, fields.IntegerField, fields.DecimalField),
+        (fields.IntegerField, fields.FloatField, fields.FloatField),
+        (fields.FloatField, fields.IntegerField, fields.FloatField),
+    ]
+    for connector in (Combinable.ADD, Combinable.SUB, Combinable.MUL, Combinable.DIV)
+}
+
+
+@functools.lru_cache(maxsize=128)
+def _resolve_combined_type(connector, lhs_type, rhs_type):
+    combinators = _connector_combinators.get(connector, ())
+    for combinator_lhs_type, combinator_rhs_type, combined_type in combinators:
+        if issubclass(lhs_type, combinator_lhs_type) and issubclass(rhs_type, combinator_rhs_type):
+            return combined_type
+
+
 class CombinedExpression(SQLiteNumericMixin, Expression):
 
     def __init__(self, lhs, connector, rhs, output_field=None):
@@ -442,6 +458,19 @@ class CombinedExpression(SQLiteNumericMixin, Expression):
     def set_source_expressions(self, exprs):
         self.lhs, self.rhs = exprs
 
+    def _resolve_output_field(self):
+        try:
+            return super()._resolve_output_field()
+        except FieldError:
+            combined_type = _resolve_combined_type(
+                self.connector,
+                type(self.lhs.output_field),
+                type(self.rhs.output_field),
+            )
+            if combined_type is None:
+                raise
+            return combined_type()
+
     def as_sql(self, compiler, connection):
         expressions = []
         expression_params = []
@@ -721,6 +750,30 @@ class Value(Expression):
     def get_group_by_cols(self, alias=None):
         return []
 
+    def _resolve_output_field(self):
+        if isinstance(self.value, str):
+            return fields.CharField()
+        if isinstance(self.value, bool):
+            return fields.BooleanField()
+        if isinstance(self.value, int):
+            return fields.IntegerField()
+        if isinstance(self.value, float):
+            return fields.FloatField()
+        if isinstance(self.value, datetime.datetime):
+            return fields.DateTimeField()
+        if isinstance(self.value, datetime.date):
+            return fields.DateField()
+        if isinstance(self.value, datetime.time):
+            return fields.TimeField()
+        if isinstance(self.value, datetime.timedelta):
+            return fields.DurationField()
+        if isinstance(self.value, Decimal):
+            return fields.DecimalField()
+        if isinstance(self.value, bytes):
+            return fields.BinaryField()
+        if isinstance(self.value, UUID):
+            return fields.UUIDField()
+
 
 class RawSQL(Expression):
     def __init__(self, sql, params, output_field=None):
@@ -1177,7 +1230,6 @@ class OrderBy(BaseExpression):
             copy.expression = Case(
                 When(self.expression, then=True),
                 default=False,
-                output_field=fields.BooleanField(),
             )
             return copy.as_sql(compiler, connection)
         return self.as_sql(compiler, connection)