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fix: propagate stack underflow error in continuation instead of masking with undefined #34

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TheUncharted merged 1 commit into from
Mar 13, 2026
+4 −2
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fix: propagate stack underflow error in continuation instead of masking with undefined #34

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6 changes: 4 additions & 2 deletions crates/zapcode-core/src/vm/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -421,8 +421,10 @@ impl Vm {
return Ok(false);
}

// The callback just returned — collect its result from the stack
let callback_result = self.pop().unwrap_or(Value::Undefined);
// The callback just returned — collect its result from the stack.
// The compiler always emits PushUndefined+Return for implicit returns,
// so an empty stack here indicates a VM bug.
let callback_result = self.pop()?;

// Unwrap internal promise values: async callbacks return
// {__promise__: true, status: "resolved", value: X} or {status: "rejected", ...}.
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