E0016: custom_checker_failed

E0016 custom_checker_failed — a cell checker rule failed.

A compile-time error of soma check, the checker of the Soma programming language (soma explain E0016).

The rule

A cell checker holds project rules that soma check runs against every other cell; a require <predicate> else Tag that is false for a cell is reported with the checker name, the cell and the tag. Here has_auth holds only for a cell whose face declares a given auth (or given token). Fix the cell so the predicate holds — or change the rule if it is wrong.

A program that triggers it

cell checker every_api_authenticated {
    face {
        promise "every cell with signals takes an auth token"
    }
    rules {
        check {
            require has_auth else MissingAuth
        }
    }
}

cell OrdersApi {
    face {
        signal cancel(order_id: String) -> String
    }
    on cancel(order_id: String) {
        return "cancelled {order_id}"
    }
}

What soma check prints:

$ soma check wrong.cell
error: checker 'every_api_authenticated' failed: cell 'OrdersApi' failed check 'MissingAuth' (every cell with signals takes an auth token)
  --> wrong.cell:7:21
  |
7 |             require has_auth else MissingAuth
  |                     ^
  = code: E0016
✗ 1 error(s), 0 warning(s).

The fix field of soma check --json: checker 'every_api_authenticated' failed: cell 'OrdersApi' failed check 'MissingAuth' (every cell with signals takes an auth token)

The fix

1 line is added after line 13.

--- wrong.cell
+++ right.cell
@@ -12,4 +12,5 @@
 cell OrdersApi {
     face {
+        given auth: String
         signal cancel(order_id: String) -> String
     }

With the fix, soma check accepts the program:

$ soma check right.cell
✓ All checks passed.