E1009: fix_it

E1009 fix_it — a near-miss the parser knows the correction for.

A compile-time error of soma check, the checker of the Soma programming language (soma explain E1009).

The rule

E1009 covers near-misses for which the parser knows the exact correction, and the message states it. Here a require has no else Tag: Soma needs the tag because it becomes the error kind the caller sees when the condition is false. Add else and a tag name, for example require amount <= current else InsufficientFunds.

A program that triggers it

cell Wallet {
    memory {
        balances: Map<String, Int> [persistent]
    }
    on withdraw(owner: String, amount: Int) {
        let current = balances.get(owner) ?? 0
        require amount <= current
        balances.set(owner, current - amount)
        return current - amount
    }
}

What soma check prints:

$ soma check wrong.cell
error: `require` needs `else Tag` — `require len(rows) < 500 else Full` (the tag is the error kind a caller sees)
  --> wrong.cell:8:9
  |
8 |         balances.set(owner, current - amount)
  |         ^
  = code: E1009

The fix

On line 7, require amount <= current becomes require amount <= current else InsufficientFunds.

--- wrong.cell
+++ right.cell
@@ -5,5 +5,5 @@
     on withdraw(owner: String, amount: Int) {
         let current = balances.get(owner) ?? 0
-        require amount <= current
+        require amount <= current else InsufficientFunds
         balances.set(owner, current - amount)
         return current - amount

With the fix, soma check accepts the program:

$ soma check right.cell
✓ All checks passed.