Internal transform failure on bad Condition syntax

[jlhood]

Description:

Customer pinged me that deployment was failing with "FAILED - Transform AWS::Serverless-2016-10-31 failed with: Internal transform failure."

The issue was a syntax error in their template, but SAM should handle that case more gracefully and provide a helpful error message.

The syntax error was in the use of Condition support on SAM resources. Sample template that reproduces the issue:

"Conditions":
  "MyCondition":
    "Fn::Equals":
      - true
      - true

"Resources":
 "MyFunction":
    "Type": "AWS::Serverless::Function"
    "Condition":
      "Ref": "MyCondition"  # bad template syntax: don't need to Ref the condition name
    "Properties":
      ...
      "Events":
        "PostApi":
          "Type": "Api"
          "Properties":
            "Method": "POST"
            "Path": "/foo"

Steps to reproduce the issue:

1. Try to deploy the sample template using SAM.

Observed result:
ChangeSet fails with “FAILED - Transform AWS::Serverless-2016-10-31 failed with: Internal transform failure.”

Expected result:
ChangeSet fails with more helpful error message from SAM translator.

[keetonian]

Fix for this issue:

1. Validate that the Condition (if it exists) is a string: https://github.com/awslabs/serverless-application-model/blob/develop/samtranslator/sdk/resource.py#L27

• Note: If something other than a string is used as a Condition on a resource, CFN throws an error: An error occurred (ValidationError) when calling the CreateChangeSet operation: Template format error: Every Condition member must be a string.

1. Add error case test: https://github.com/awslabs/serverless-application-model/blob/develop/tests/translator/test_translator.py#L444