Fix remotes not loaded for conan alias command (#8704)

* Fix remotes not loaded for alias command

* Add test

conans/client/conan_api.py

@@ -1166,6 +1166,8 @@ def get_path(self, reference, package_id=None, path=None, remote_name=None):
 
     @api_method
     def export_alias(self, reference, target_reference):
+        self.app.load_remotes()
+
         ref = ConanFileReference.loads(reference)
         target_ref = ConanFileReference.loads(target_reference)
 

conans/test/integration/command/alias_test.py

@@ -398,6 +398,19 @@ def test_repeated_alias(self):
         client.run("alias Hello/0.X@lasote/channel Hello/0.2@lasote/channel")
         client.run("alias Hello/0.X@lasote/channel Hello/0.3@lasote/channel")
 
+    def test_existing_python_requires(self):
+        # https://github.com/conan-io/conan/issues/8702
+        client = TestClient()
+        client.save({"conanfile.py": GenConanfile()})
+        client.run("create . test-python-requires/0.1@user/testing")
+        client.save({"conanfile.py": """from conans import ConanFile
+class Pkg(ConanFile):
+    python_requires = 'test-python-requires/0.1@user/testing'"""})
+        client.run("create . Pkg/0.1@user/testing")
+        client.run("alias Pkg/0.1@user/testing Pkg/0.2@user/testing", assert_error=True)
+        self.assertIn("ERROR: Reference 'Pkg/0.1@user/testing' is already a package",
+                      client.out)
+
     def test_basic(self):
         test_server = TestServer()
         servers = {"default": test_server}