Fix Conan Source folders.root issue

- Fixed issue in local.py where source() method did not account for
  self.folders.root (when specified)

- Added
test/integration/command/source_test.py::SourceTest::test_local_source_layout_root

Close #18376

Author: timviola-cmi

conan/api/subapi/local.py

@@ -82,7 +82,9 @@ def source(self, path, name=None, version=None, user=None, channel=None, remotes
             with conanfile_exception_formatter(conanfile, "layout"):
                 conanfile.layout()
 
-        folder = conanfile.recipe_folder
+        folder = conanfile.recipe_folder if conanfile.folders.root is None else \
+            os.path.normpath(os.path.join(conanfile.recipe_folder, conanfile.folders.root))
+
         conanfile.folders.set_base_source(folder)
         conanfile.folders.set_base_export_sources(folder)
         conanfile.folders.set_base_recipe_metadata(os.path.join(folder, "metadata"))

test/integration/command/source_test.py

@@ -142,6 +142,30 @@ def source(self):
         self.assertIn("conanfile.py: Running source!", client.out)
         self.assertEqual("Hello World", client.load("file1.txt"))
 
+    def test_local_source_layout_root(self):
+        # Ensure that if a root folder is specified Conan source method
+        # uses it. This is especially important when running with
+        # no_copy_source where both the build()  and source() methods
+        # need to reference source_folder (so the value must be the
+        # same in both methods)
+        conanfile = textwrap.dedent('''
+            from conan import ConanFile
+
+            class ConanLib(ConanFile):
+                
+                def layout(self):
+                    self.folders.root = "root_folder"
+
+                def source(self):
+                    self.output.info(f"Source Folder: {self.source_folder}")
+        ''')
+        # First, failing source()
+        client = TestClient(light=True)
+        client.save({CONANFILE: conanfile})
+
+        client.run("source .")
+        self.assertTrue(client.out.strip().endswith("spaces\\root_folder"))
+
     def test_retrieve_exports_sources(self):
         # For Conan 2.0 if we install a package from a remote and we want to upload to other
         # remote we need to download the sources, as we consider revisions immutable, let's