[GCU] Handling non-compliant leaf-list with string values (#2174)

#### What I did
Fixes #2170

Converting xpath to path:
- There is only 1 case where the path is referring to the list itself. Example:
```
path="/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
xpath="/sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list",
```
- There is no other case as we the list is just a single string, and we cannot refer to individual elements in string in ConfigDb.

Converting path to xpath, there are 2 cases:
- Xpath is pointing to leaf-list as a whole, return path of whole list
```
xpath="/sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list",
path="/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
```
- Xpath is pointing to an element of the leaf-list, return path of whole list as well since it is not possible to point to specific element -- here we are pointing to the element `egress_lossy_profile`
```
xpath="/sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list[.='egress_lossy_profile']",
path="/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
```

#### How I did it
Only a single change if the xpath is pointing to a specific element, just return whole list token from ConfigDb format.

Please note this solution is future proof, if ConfigDb changes how a list is saved as a string or json list, we don't care.

#### How to verify it
unit-test

#### Previous command output (if the output of a command-line utility has changed)

#### New command output (if the output of a command-line utility has changed)

Author: ghooo

generic_config_updater/gu_common.py

@@ -750,6 +750,19 @@ def _get_path_tokens_from_leaf(self, model, token_index, xpath_tokens, config):
             # leaf_list_name = match.group(1)
             leaf_list_value = match.group(1)
             list_config = config[leaf_list_name]
+            # Workaround for those fields who is defined as leaf-list in YANG model but have string value in config DB
+            # No need to lookup the item index in ConfigDb since the list is represented as a string, return path to string immediately
+            # Example:
+            #   xpath: /sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list[.='egress_lossy_profile']
+            #   path: /BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list
+            if isinstance(list_config, str):
+                return [leaf_list_name]
+
+            if not isinstance(list_config, list):
+                raise ValueError(f"list_config is expected to be of type list or string. Found {type(list_config)}.\n  " + \
+                                 f"model: {model}\n  token_index: {token_index}\n  " + \
+                                 f"xpath_tokens: {xpath_tokens}\n  config: {config}")
+
             list_idx = list_config.index(leaf_list_value)
             return [leaf_list_name, list_idx]
 

tests/generic_config_updater/files/config_db_with_profile_list.json

@@ -0,0 +1,42 @@
+{
+    "BUFFER_POOL": {
+        "egress_lossless_pool": {
+           "mode": "static",
+           "size": "33004032",
+           "xoff": "196608",
+           "type": "egress"
+        },
+        "egress_lossy_pool": {
+            "size": "12766208",
+            "type": "egress",
+            "mode": "dynamic"
+        }
+    },
+    "BUFFER_PROFILE": {
+        "egress_lossless_profile": {
+            "pool":"egress_lossless_pool",
+            "size":"1518",
+            "dynamic_th":"3"
+        },
+        "egress_lossy_profile": {
+            "pool":"egress_lossy_pool",
+            "size":"1518",
+            "dynamic_th":"3"
+        }
+    },
+    "BUFFER_PORT_EGRESS_PROFILE_LIST": {
+        "Ethernet9": {
+            "profile_list": "egress_lossless_profile,egress_lossy_profile"
+        }
+    },
+    "PORT": {
+        "Ethernet9": {
+            "alias": "Eth3/2",
+            "lanes": "74",
+            "description": "",
+            "speed": "11100",
+            "tpid": "0x8100",
+            "admin_status": "up"
+        }
+    }
+}

tests/generic_config_updater/gu_common_test.py

@@ -779,6 +779,19 @@ def test_find_ref_paths__does_not_remove_tables_without_yang(self):
         # Assert
         self.assertEqual(expected_config, config)
 
+    def test_find_ref_paths__ref_path_is_leaflist_in_yang_but_string_in_config_db__path_to_string_returned(self):
+        # Arrange
+        path = "/BUFFER_PROFILE/egress_lossless_profile"
+        expected = [
+            "/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
+        ]
+
+        # Act
+        actual = self.path_addressing.find_ref_paths(path, Files.CONFIG_DB_WITH_PROFILE_LIST)
+
+        # Assert
+        self.assertEqual(expected, actual)
+
     def test_convert_path_to_xpath(self):
         def check(path, xpath, config=None):
             if not config:
@@ -839,6 +852,9 @@ def check(path, xpath, config=None):
         check(path="/LLDP/GLOBAL/mode",
               xpath="/sonic-lldp:sonic-lldp/LLDP/GLOBAL/mode",
               config=Files.CONFIG_DB_WITH_LLDP)
+        check(path="/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
+              xpath="/sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list",
+              config=Files.CONFIG_DB_WITH_PROFILE_LIST)
 
     def test_convert_xpath_to_path(self):
         def check(xpath, path, config=None):
@@ -914,6 +930,12 @@ def check(xpath, path, config=None):
         check(xpath="/sonic-lldp:sonic-lldp/LLDP/GLOBAL/mode",
               path="/LLDP/GLOBAL/mode",
               config=Files.CONFIG_DB_WITH_LLDP)
+        check(xpath="/sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list",
+              path="/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
+              config=Files.CONFIG_DB_WITH_PROFILE_LIST)
+        check(xpath="/sonic-buffer-port-egress-profile-list:sonic-buffer-port-egress-profile-list/BUFFER_PORT_EGRESS_PROFILE_LIST/BUFFER_PORT_EGRESS_PROFILE_LIST_LIST[port='Ethernet9']/profile_list[.='egress_lossy_profile']",
+              path="/BUFFER_PORT_EGRESS_PROFILE_LIST/Ethernet9/profile_list",
+              config=Files.CONFIG_DB_WITH_PROFILE_LIST)
 
     def test_has_path(self):
         def check(config, path, expected):