panic: interface conversion: interface {} is map[interface {}]interface {}, not string

[TheDeveloper]

Issue

When validating a template that contains a 'AWS::Serverless::Function' with a Policies property I get the following error:

2017/08/16 15:08:57 0.1.0
panic: interface conversion: interface {} is map[interface {}]interface {}, not string

goroutine 1 [running]:
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources.safeProcessStringArray(0x196b820, 0xc420236cf0, 0x167733c, 0x8, 0xc4204c9048)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources/safe-processing.go:46 +0x15f
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources.(*functionTemplate).Scaffold(0xc4201380b0, 0x196b860, 0xc4202a8f20, 0x0, 0x0, 0xe, 0x168b7c4, 0x26, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources/aws-serverless-function.go:146 +0x3bf
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources.(*awsServerlessFunction).Scaffold(0x19bcdc0, 0x196b860, 0xc4202a8f20, 0x0, 0x0, 0x26, 0x0, 0x0, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources/aws-serverless-function.go:80 +0x6a
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources.(*awsServerlessFunction).ClassConstructor(0x19bcdc0, 0x196b860, 0xc4202a8f20, 0x0, 0x0, 0x0, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/resources/aws-serverless-function.go:61 +0x55
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation.postProcess(0x196e4e0, 0xc420448a00, 0x196e4e0, 0xc420448a00, 0x0, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/post-process.go:46 +0x533
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation.Parse(0xc420312000, 0xc4e, 0x1e00, 0xc4e, 0x1e00, 0x0, 0x0, 0xc42000c050, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/goformation.go:72 +0x407
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation.read(0x1966360, 0xc42000c050, 0xc42000c050, 0x0, 0x0, 0x0, 0x1, 0x1)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/goformation.go:40 +0x105
github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation.Open(0xc4202ab02e, 0xd, 0xc4202ab02e, 0xd, 0x13, 0x0, 0x0, 0xc4202dcf90)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/awslabs/goformation/goformation.go:29 +0x27e
main.validate(0xc42041b040)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/validate.go:13 +0x7a
github.com/awslabs/aws-sam-local/vendor/github.com/codegangsta/cli.HandleAction(0x1587e60, 0x169a720, 0xc42041b040, 0xc42006ea00, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/codegangsta/cli/app.go:487 +0x7c
github.com/awslabs/aws-sam-local/vendor/github.com/codegangsta/cli.Command.Run(0x1677894, 0x8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x16971ee, 0xa7, 0x0, ...)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/codegangsta/cli/command.go:207 +0xb72
github.com/awslabs/aws-sam-local/vendor/github.com/codegangsta/cli.(*App).Run(0xc420338820, 0xc42000e240, 0x3, 0x3, 0x0, 0x0)
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/vendor/github.com/codegangsta/cli/app.go:250 +0x7d0
main.main()
	/home/ubuntu/repo/src/github.com/awslabs/aws-sam-local/main.go:302 +0x1be1

Reproduce

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Resources:
  FunctionName:
      Type: 'AWS::Serverless::Function'
      Properties:
        Handler: index.handler
        Runtime: nodejs6.10
        Policies:
          - Effect: Allow
            Action:
              - 'dynamodb:*'
            Resource: '*'

Remove the policies property and sam validate succeeds.

Looks related to #35

[PaulMaddox]

We're rewriting some of the library we use for CloudFormation/SAM parsing (github.com/awslabs/goformation) to make it more resilient against issues like this.

I can confirm this bug is fixed in the 0.1.0 branch of goformation, however we've got a bit more work to do before we can start using it in SAM Local. Shouldn't be much longer.

[sanathkr]

Fixed in v0.2.0