From 8368872ccd439dc5089ba0626eb5d691085c4a6d Mon Sep 17 00:00:00 2001
From: Josh Michael Karamuth <michael@confuzeus.com>
Date: Wed, 26 Oct 2022 14:22:00 +0400
Subject: [PATCH] Fix subdomain inheritance for nested blueprints.

Fixes #4834
---
 CHANGES.rst              |  2 ++
 src/flask/blueprints.py  |  9 +++++++++
 tests/test_blueprints.py | 21 +++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/CHANGES.rst b/CHANGES.rst
index 6c3ff32c..5bb26d22 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -9,6 +9,8 @@ Version 2.2.3
 
 Unreleased
 
+- Fix subdomain inheritance for nested blueprints. :issue:`4834`
+
 
 Version 2.2.2
 -------------
diff --git a/src/flask/blueprints.py b/src/flask/blueprints.py
index 104f8acf..10c218d5 100644
--- a/src/flask/blueprints.py
+++ b/src/flask/blueprints.py
@@ -453,6 +453,15 @@ class Blueprint(Scaffold):
         for blueprint, bp_options in self._blueprints:
             bp_options = bp_options.copy()
             bp_url_prefix = bp_options.get("url_prefix")
+            bp_subdomain = bp_options.get("subdomain")
+
+            if bp_subdomain is None:
+                bp_subdomain = blueprint.subdomain
+
+            if state.subdomain is not None and bp_subdomain is None:
+                bp_options["subdomain"] = state.subdomain
+            elif bp_subdomain is not None:
+                bp_options["subdomain"] = bp_subdomain
 
             if bp_url_prefix is None:
                 bp_url_prefix = blueprint.url_prefix
diff --git a/tests/test_blueprints.py b/tests/test_blueprints.py
index 1bf130f5..2081ff23 100644
--- a/tests/test_blueprints.py
+++ b/tests/test_blueprints.py
@@ -950,6 +950,27 @@ def test_nesting_url_prefixes(
     assert response.status_code == 200
 
 
+def test_nesting_subdomains(app, client) -> None:
+    subdomain = "api"
+    parent = flask.Blueprint("parent", __name__)
+    child = flask.Blueprint("child", __name__)
+
+    @child.route("/child/")
+    def index():
+        return "child"
+
+    parent.register_blueprint(child)
+    app.register_blueprint(parent, subdomain=subdomain)
+
+    client.allow_subdomain_redirects = True
+
+    domain_name = "domain.tld"
+    app.config["SERVER_NAME"] = domain_name
+    response = client.get("/child/", base_url="http://api." + domain_name)
+
+    assert response.status_code == 200
+
+
 def test_unique_blueprint_names(app, client) -> None:
     bp = flask.Blueprint("bp", __name__)
     bp2 = flask.Blueprint("bp", __name__)