fix when conandata.yml is empty and scm_to_conandata (#8215)

conans/client/cmd/export.py

@@ -287,6 +287,7 @@ def _replace_scm_data_in_recipe(package_layout, scm_data, scm_to_conandata):
         conandata_yml = {}
         if os.path.exists(conandata_path):
             conandata_yml = yaml.safe_load(load(conandata_path))
+            conandata_yml = conandata_yml or {}  # In case the conandata is a blank file
             if '.conan' in conandata_yml:
                 raise ConanException("Field '.conan' inside '{}' file is reserved to "
                                      "Conan usage.".format(DATA_YML))

conans/test/functional/scm/test_scm_to_conandata.py

@@ -138,6 +138,31 @@ class Recipe(ConanFile):
         self.assertIn("ERROR: Field '.conan' inside 'conandata.yml' file is"
                       " reserved to Conan usage.", t.out)
 
+    @pytest.mark.tool_git
+    def test_empty_conandata(self):
+        # https://github.com/conan-io/conan/issues/8209
+        conanfile = textwrap.dedent("""
+            from conans import ConanFile
+
+            class Recipe(ConanFile):
+                scm = {"type": "git", "url": "auto", "revision": "auto"}
+            """)
+        t = TestClient()
+        commit = t.init_git_repo({'conanfile.py': conanfile,
+                                  'conandata.yml': ""})
+        t.run_command('git remote add origin https://myrepo.com.git')
+        t.run("config set general.scm_to_conandata=1")
+        t.run("export . name/version@")
+
+        # Check exported files
+        package_layout = t.cache.package_layout(self.ref)
+        exported_conanfile = load(package_layout.conanfile())
+        self.assertEqual(exported_conanfile, conanfile)
+        exported_conandata = load(os.path.join(package_layout.export(), DATA_YML))
+        conan_data = yaml.safe_load(exported_conandata)
+        self.assertDictEqual(conan_data['.conan']['scm'],
+                             {"type": "git", "url": 'https://myrepo.com.git', "revision": commit})
+
 
 class ParseSCMFromConanDataTestCase(unittest.TestCase):
     loader = ConanFileLoader(runner=None, output=TestBufferConanOutput(),