Better error messages for `Unexpected type` errors

[shaobo-he-aws]

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Bug Category

Schemas and Validation

Describe the bug

If we replace the Policy 2 of the TinyTodo example like this,

// Policy 2: A User can see a List if they are either a reader or editor
permit (
    principal,
    action == Action::"GetList",
    resource
)
when { 3 < resource.readers || principal in resource.editors };

We get error messages,

Unexpected type. Expected {"type":"Long"} but saw {"type":"Entity","name":"Team"}

Expected behavior

This error message could be more readable like Expected type 'Long' but saw entity type 'Team'

Reproduction steps

1. Replace Policy 2
2. Run cedar validate --schema tinytodo.cedarschema.json --policies policies.cedar

Code Snippet

// Put your code below this line.

Log output

// Put your output below this line

Additional configuration

No response

Operating System

No response

Additional information and screenshots

No response

[khieta]

More generally, we may want to revisit the decision to print types using the JSON format in error messages

[john-h-kastner-aws]

If we accepts the RFC for a non-json format, then I'm in favor of printing in that format. Until then I think it makes the most sense to print in the format that types appear as in the schema.

[khieta]

Was just looking at EvaluationError::TypeError and noticed that we print a short form of the error there (e.g., "type error: expected (entity of type any_entity_type), got long"). I think the short form makes more sense there, since users don't have to write a schema for evaluation and thus may not be familiar with the JSON schema syntax.

So: whenever we update the validation error messages to use a non-JSON syntax for printing types, we should update the printing for EvaluationError::TypeError too for consistency.

[cdisselkoen]

Noting that the non-JSON syntax for schemas (and thus types) is shipping soon, so we should revisit the discussion above

[john-h-kastner-aws]

@aaronjeline do we already have a function to print types in their natural Cedar schema format? Could be an easy issue to knock out if we do