prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Update I1022 to only suggest sub if all values can be in the sub
  ### CloudFormation Lint Version
  
  0.64.1
  
  ### What operating system are you using?
  
  All
  
  ### Describe the bug
  
  Original feedback provided by @iann0036.  Translated to an issue for tracking.
  
  ```yaml
  Fn::Join:
    - ""
    - - Fn::Select:
         - 0
         - Fn::Split:
            - "/"
            - !Ref MySubnet1CIDR
      - !Ref MySubnetsCIDRSize
  ```
  
  ```
  I1022: Prefer using Fn::Sub over Fn::Join with an empty delimiter
  ```
  
  ### Expected behavior
  
  Currently the way to make this comply would be
  
  ```yaml
  Fn::Sub:
      - ${CIDR}${MySubnetsCIDRSize}
      - CIDR:
          Fn::Select:
            - 0
            - Fn::Split:
              - "/"
              - !Ref MySubnet1CIDR
  ```
  
  which may not be as optimal 
  
  ### Reproduction template
  
  ```yaml
  Fn::Join:
      - ""
      - - Fn::Select:
          - 0
          - Fn::Split:
            - "/"
            - !Ref MySubnet1CIDR
        - !Ref MySubnetsCIDRSize
   ````
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `src/cfnlint/rules/functions/SubNotJoin.py`
  Content:
  ```
  1 """
  2 Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
  3 SPDX-License-Identifier: MIT-0
  4 """
  5 from cfnlint.rules import CloudFormationLintRule, RuleMatch
  6 
  7 
  8 class SubNotJoin(CloudFormationLintRule):
  9     """Check if Join is being used with no join characters"""
  10     id = 'I1022'
  11     shortdesc = 'Use Sub instead of Join'
  12     description = 'Prefer a sub instead of Join when using a join delimiter that is empty'
  13     source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html'
  14     tags = ['functions', 'sub', 'join']
  15 
  16     def match(self, cfn):
  17         matches = []
  18 
  19         join_objs = cfn.search_deep_keys('Fn::Join')
  20 
  21         for join_obj in join_objs:
  22             if isinstance(join_obj[-1], list):
  23                 join_operator = join_obj[-1][0]
  24                 if isinstance(join_operator, str):
  25                     if join_operator == '':
  26                         matches.append(RuleMatch(
  27                             join_obj[0:-1], 'Prefer using Fn::Sub over Fn::Join with an empty delimiter'))
  28         return matches
  29
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/src/cfnlint/rules/functions/SubNotJoin.py b/src/cfnlint/rules/functions/SubNotJoin.py
  --- a/src/cfnlint/rules/functions/SubNotJoin.py
  +++ b/src/cfnlint/rules/functions/SubNotJoin.py
  @@ -7,12 +7,34 @@
   
   class SubNotJoin(CloudFormationLintRule):
       """Check if Join is being used with no join characters"""
  +
       id = 'I1022'
       shortdesc = 'Use Sub instead of Join'
  -    description = 'Prefer a sub instead of Join when using a join delimiter that is empty'
  +    description = (
  +        'Prefer a sub instead of Join when using a join delimiter that is empty'
  +    )
       source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html'
       tags = ['functions', 'sub', 'join']
   
  +    def _check_element(self, element):
  +        if isinstance(element, dict):
  +            if len(element) == 1:
  +                for key, value in element.items():
  +                    if key in ['Fn::Sub']:
  +                        if not isinstance(value, str):
  +                            return False
  +                    elif key not in ['Ref', 'Fn::GetAtt']:
  +                        return False
  +
  +        return True
  +
  +    def _check_elements(self, elements):
  +        for element in elements:
  +            if not self._check_element(element):
  +                return False
  +
  +        return True
  +
       def match(self, cfn):
           matches = []
   
  @@ -21,8 +43,15 @@
           for join_obj in join_objs:
               if isinstance(join_obj[-1], list):
                   join_operator = join_obj[-1][0]
  +                join_elements = join_obj[-1][1]
                   if isinstance(join_operator, str):
                       if join_operator == '':
  -                        matches.append(RuleMatch(
  -                            join_obj[0:-1], 'Prefer using Fn::Sub over Fn::Join with an empty delimiter'))
  +                        if isinstance(join_elements, list):
  +                            if self._check_elements(join_elements):
  +                                matches.append(
  +                                    RuleMatch(
  +                                        join_obj[0:-1],
  +                                        'Prefer using Fn::Sub over Fn::Join with an empty delimiter',
  +                                    )
  +                                )
           return matches
  
verification_info: {"golden_diff": "diff --git a/src/cfnlint/rules/functions/SubNotJoin.py b/src/cfnlint/rules/functions/SubNotJoin.py\n--- a/src/cfnlint/rules/functions/SubNotJoin.py\n+++ b/src/cfnlint/rules/functions/SubNotJoin.py\n@@ -7,12 +7,34 @@\n \n class SubNotJoin(CloudFormationLintRule):\n     \"\"\"Check if Join is being used with no join characters\"\"\"\n+\n     id = 'I1022'\n     shortdesc = 'Use Sub instead of Join'\n-    description = 'Prefer a sub instead of Join when using a join delimiter that is empty'\n+    description = (\n+        'Prefer a sub instead of Join when using a join delimiter that is empty'\n+    )\n     source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html'\n     tags = ['functions', 'sub', 'join']\n \n+    def _check_element(self, element):\n+        if isinstance(element, dict):\n+            if len(element) == 1:\n+                for key, value in element.items():\n+                    if key in ['Fn::Sub']:\n+                        if not isinstance(value, str):\n+                            return False\n+                    elif key not in ['Ref', 'Fn::GetAtt']:\n+                        return False\n+\n+        return True\n+\n+    def _check_elements(self, elements):\n+        for element in elements:\n+            if not self._check_element(element):\n+                return False\n+\n+        return True\n+\n     def match(self, cfn):\n         matches = []\n \n@@ -21,8 +43,15 @@\n         for join_obj in join_objs:\n             if isinstance(join_obj[-1], list):\n                 join_operator = join_obj[-1][0]\n+                join_elements = join_obj[-1][1]\n                 if isinstance(join_operator, str):\n                     if join_operator == '':\n-                        matches.append(RuleMatch(\n-                            join_obj[0:-1], 'Prefer using Fn::Sub over Fn::Join with an empty delimiter'))\n+                        if isinstance(join_elements, list):\n+                            if self._check_elements(join_elements):\n+                                matches.append(\n+                                    RuleMatch(\n+                                        join_obj[0:-1],\n+                                        'Prefer using Fn::Sub over Fn::Join with an empty delimiter',\n+                                    )\n+                                )\n         return matches\n", "issue": "Update I1022 to only suggest sub if all values can be in the sub\n### CloudFormation Lint Version\n\n0.64.1\n\n### What operating system are you using?\n\nAll\n\n### Describe the bug\n\nOriginal feedback provided by @iann0036.  Translated to an issue for tracking.\r\n\r\n```yaml\r\nFn::Join:\r\n  - \"\"\r\n  - - Fn::Select:\r\n       - 0\r\n       - Fn::Split:\r\n          - \"/\"\r\n          - !Ref MySubnet1CIDR\r\n    - !Ref MySubnetsCIDRSize\r\n```\r\n\r\n```\r\nI1022: Prefer using Fn::Sub over Fn::Join with an empty delimiter\r\n```\n\n### Expected behavior\n\nCurrently the way to make this comply would be\r\n\r\n```yaml\r\nFn::Sub:\r\n    - ${CIDR}${MySubnetsCIDRSize}\r\n    - CIDR:\r\n        Fn::Select:\r\n          - 0\r\n          - Fn::Split:\r\n            - \"/\"\r\n            - !Ref MySubnet1CIDR\r\n```\r\n\r\nwhich may not be as optimal \n\n### Reproduction template\n\n```yaml\r\nFn::Join:\r\n    - \"\"\r\n    - - Fn::Select:\r\n        - 0\r\n        - Fn::Split:\r\n          - \"/\"\r\n          - !Ref MySubnet1CIDR\r\n      - !Ref MySubnetsCIDRSize\r\n ````\n", "before_files": [{"content": "\"\"\"\nCopyright Amazon.com, Inc. or its affiliates. All Rights Reserved.\nSPDX-License-Identifier: MIT-0\n\"\"\"\nfrom cfnlint.rules import CloudFormationLintRule, RuleMatch\n\n\nclass SubNotJoin(CloudFormationLintRule):\n    \"\"\"Check if Join is being used with no join characters\"\"\"\n    id = 'I1022'\n    shortdesc = 'Use Sub instead of Join'\n    description = 'Prefer a sub instead of Join when using a join delimiter that is empty'\n    source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html'\n    tags = ['functions', 'sub', 'join']\n\n    def match(self, cfn):\n        matches = []\n\n        join_objs = cfn.search_deep_keys('Fn::Join')\n\n        for join_obj in join_objs:\n            if isinstance(join_obj[-1], list):\n                join_operator = join_obj[-1][0]\n                if isinstance(join_operator, str):\n                    if join_operator == '':\n                        matches.append(RuleMatch(\n                            join_obj[0:-1], 'Prefer using Fn::Sub over Fn::Join with an empty delimiter'))\n        return matches\n", "path": "src/cfnlint/rules/functions/SubNotJoin.py"}], "after_files": [{"content": "\"\"\"\nCopyright Amazon.com, Inc. or its affiliates. All Rights Reserved.\nSPDX-License-Identifier: MIT-0\n\"\"\"\nfrom cfnlint.rules import CloudFormationLintRule, RuleMatch\n\n\nclass SubNotJoin(CloudFormationLintRule):\n    \"\"\"Check if Join is being used with no join characters\"\"\"\n\n    id = 'I1022'\n    shortdesc = 'Use Sub instead of Join'\n    description = (\n        'Prefer a sub instead of Join when using a join delimiter that is empty'\n    )\n    source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html'\n    tags = ['functions', 'sub', 'join']\n\n    def _check_element(self, element):\n        if isinstance(element, dict):\n            if len(element) == 1:\n                for key, value in element.items():\n                    if key in ['Fn::Sub']:\n                        if not isinstance(value, str):\n                            return False\n                    elif key not in ['Ref', 'Fn::GetAtt']:\n                        return False\n\n        return True\n\n    def _check_elements(self, elements):\n        for element in elements:\n            if not self._check_element(element):\n                return False\n\n        return True\n\n    def match(self, cfn):\n        matches = []\n\n        join_objs = cfn.search_deep_keys('Fn::Join')\n\n        for join_obj in join_objs:\n            if isinstance(join_obj[-1], list):\n                join_operator = join_obj[-1][0]\n                join_elements = join_obj[-1][1]\n                if isinstance(join_operator, str):\n                    if join_operator == '':\n                        if isinstance(join_elements, list):\n                            if self._check_elements(join_elements):\n                                matches.append(\n                                    RuleMatch(\n                                        join_obj[0:-1],\n                                        'Prefer using Fn::Sub over Fn::Join with an empty delimiter',\n                                    )\n                                )\n        return matches\n", "path": "src/cfnlint/rules/functions/SubNotJoin.py"}]}