E0050: unknown_checker_predicate

E0050 unknown_checker_predicate — a checker rule names a predicate nothing implements.

A compile-time error of soma check, the checker of the Soma programming language (soma explain E0050).

The rule

A require in a cell checker rule must name one of the structural predicates: all_persistent, all_encrypted, all_consistent, has_memory, has_face, has_signals, has_auth. An unknown predicate would make the rule hold for every cell (or fail every cell under !), so the checker would enforce nothing. Fix the predicate name; the message suggests the closest one.

A program that triggers it

cell checker durable_storage {
    face {
        promise "every cell keeps its data across restarts"
    }
    rules {
        check {
            require all_persisted else NotPersistent
        }
    }
}

cell Accounts {
    face {
        signal open(owner: String) -> String
    }
    memory {
        owners: Map<String, String> [persistent]
    }
    on open(owner: String) {
        owners.set(owner, "open")
        return owner
    }
}

What soma check prints:

$ soma check wrong.cell
error: checker 'durable_storage' requires 'all_persisted' (did you mean 'all_persistent'?), which nothing implements — the rule would hold for every cell (and fail every cell under `!`). The predicates are: all_persistent, all_encrypted, all_consistent, has_memory, has_face, has_signals, has_auth
  --> wrong.cell:7:21
  |
7 |             require all_persisted else NotPersistent
  |                     ^
  = code: E0050
✗ 1 error(s), 0 warning(s).

The fix field of soma check --json: the rule would hold for every cell (and fail every cell under `!`). The predicates are: all_persistent, all_encrypted, all_consistent, has_memory, has_face, has_signals, has_auth

The fix

On line 7, require all_persisted else NotPersistent becomes require all_persistent else NotPersistent.

--- wrong.cell
+++ right.cell
@@ -5,5 +5,5 @@
     rules {
         check {
-            require all_persisted else NotPersistent
+            require all_persistent else NotPersistent
         }
     }

With the fix, soma check accepts the program:

$ soma check right.cell
✓ All checks passed.