From e042024b28fcef43606557554714352781fc1d13 Mon Sep 17 00:00:00 2001
From: Nick Pope <nick@nickpope.me.uk>
Date: Wed, 7 Jun 2023 12:34:35 +0100
Subject: [PATCH] Allowed custom formatting of lazy() objects.

This allows for formatting of lazy objects which have a custom formatter
defined by overriding the default implementation from `object`.
---
 django/utils/functional.py           |  3 +++
 tests/utils_tests/test_functional.py | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/django/utils/functional.py b/django/utils/functional.py
index 0bc641cb21f..25003204f81 100644
--- a/django/utils/functional.py
+++ b/django/utils/functional.py
@@ -151,6 +151,9 @@ def lazy(func, *resultclasses):
         def __hash__(self):
             return hash(self.__cast())
 
+        def __format__(self, format_spec):
+            return format(self.__cast(), format_spec)
+
         # Explicitly wrap methods which are required for certain operations on
         # int/str objects to function correctly.
 
diff --git a/tests/utils_tests/test_functional.py b/tests/utils_tests/test_functional.py
index c8b8fe5a3f6..fa23debb4de 100644
--- a/tests/utils_tests/test_functional.py
+++ b/tests/utils_tests/test_functional.py
@@ -246,6 +246,17 @@ class FunctionalTests(SimpleTestCase):
         self.assertEqual(lazy_a() * 5, "aaaaa")
         self.assertEqual(lazy_a() * lazy_5(), "aaaaa")
 
+    def test_lazy_format(self):
+        class QuotedString(str):
+            def __format__(self, format_spec):
+                value = super().__format__(format_spec)
+                return f"“{value}”"
+
+        lazy_f = lazy(lambda: QuotedString("Hello!"), QuotedString)
+        self.assertEqual(format(lazy_f(), ""), "“Hello!”")
+        f = lazy_f()
+        self.assertEqual(f"I said, {f}", "I said, “Hello!”")
+
     def test_lazy_equality(self):
         """
         == and != work correctly for Promises.