Unknown exception while processing rule WS1004: expected string or bytes-like object

[t2b]

The cfn-lint rule WS1004 raises an exception if the property LogGroupName of an AWS::Logs::LogGroup is a Sub function with a variable map.

Expected Behavior

The rule WS1004 should analyze LogGroupName properties without errors and match correct configured LogGroups to the lambda functions.

Current Behavior

Rule WS1004 raises an exception:
TypeError: expected string or bytes-like object

Steps to Reproduce (for bugs)

template.yml

Transform: AWS::Serverless-2016-10-31

Resources:
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      Runtime: python3.8
      Handler: index.handler
      MemorySize: 128
      Timeout: 3
      Tracing: Active

  CodePipelineNotificationLogGroup:
    Type: AWS::Logs::LogGroup
    UpdateReplacePolicy: Delete
    DeletionPolicy: Delete
    Properties:
      LogGroupName: !Sub
        - "/aws/lambda/${FunctionName}"
        - FunctionName: !Ref MyFunction
      RetentionInDays: 400

cfn-lint -a cfn_lint_serverless.rules -t template.yml

Environment

• cfn-lint==0.49.2
• cfn-lint-serverless==0.1.8

paste logs here

E0002 Unknown exception while processing rule WS1004: expected string or bytes-like object
template.yml:1:1

[nmoutschen]

Hi @t2b !

Thanks for reporting this. I can confirm the bug and will push out a fix soon in version 0.1.9.

I'm also adding two new test cases to catch this:

Ref in a Sub:

AWSTemplateFormatVersion: "2010-09-09"
Transform: "AWS::Serverless-2016-10-31"

Resources:
  Function:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: .
      Runtime: python3.8
      Handler: main.handler
      Tracing: Active

  LogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub
        - "/aws/lambda/${Fn}"
        - Fn: !Ref Function

      RetentionInDays: 7

Hard coded value in a Sub:

AWSTemplateFormatVersion: "2010-09-09"
Transform: "AWS::Serverless-2016-10-31"

Resources:
  Function:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: my-function-name
      CodeUri: .
      Runtime: python3.8
      Handler: main.handler
      Tracing: Active

  LogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub
        - "/aws/lambda/${Fn}"
        - Fn: my-function-name

      RetentionInDays: 7

[nmoutschen]

And there we go: version 0.1.9 is out with the bug fix. 😄 Thanks again for reporting the issue!