E0013: unmatched_await

E0013 unmatched_await — an await names a signal nothing sends.

A compile-time error of soma check, the checker of the Soma programming language (soma explain E0013).

The rule

Inside an interior block, sibling cells are wired by name: an await x(…) in one cell's face must match a signal x(…) that a sibling declares. soma check reports an await that no sibling emits (here order_paid, while Checkout only emits order_placed), since it would never be delivered. Await the signal a sibling actually declares, or add that signal to the sibling that should send it.

A program that triggers it

cell Shop {
    interior {
        cell Checkout {
            face {
                signal order_placed(order_id: String, total: Int)
            }
            on order_placed(order_id: String, total: Int) {
                return order_id
            }
        }
        cell Fulfillment {
            face {
                await order_paid(order_id: String, total: Int)
            }
            memory {
                queue: List<String> [persistent]
            }
            on order_placed(order_id: String, total: Int) {
                queue.push(order_id)
            }
        }
    }
}

What soma check prints:

$ soma check wrong.cell
warning: cell 'Fulfillment' declares await 'order_paid' but has no handler for it (will it be delivered via bus?)
  --> wrong.cell:13:17
   |
13 |                 await order_paid(order_id: String, total: Int)
   |                 ^
error: unmatched await: cell 'Fulfillment' awaits signal 'order_paid' but no sibling emits it
  --> wrong.cell:13:17
   |
13 |                 await order_paid(order_id: String, total: Int)
   |                 ^
  = code: E0013
✗ 1 error(s), 1 warning(s).

The fix field of soma check --json: unmatched await: cell 'Fulfillment' awaits signal 'order_paid' but no sibling emits it

The fix

On line 13, await order_paid(order_id: String, total: Int) becomes await order_placed(order_id: String, total: Int).

--- wrong.cell
+++ right.cell
@@ -11,5 +11,5 @@
         cell Fulfillment {
             face {
-                await order_paid(order_id: String, total: Int)
+                await order_placed(order_id: String, total: Int)
             }
             memory {

With the fix, soma check accepts the program:

$ soma check right.cell
✓ All checks passed.