[ASDAlexander77]

Problem

This program crashed with a stack dump under every memory model (gc, rc, none, own):

class W {
    constructor(private f: (v: number) => void) {}
    run() { this.f(1); }
}
function main() {
    let seen = 0;
    const w = new W((v) => { seen += 1; });
    w.run();
    print(seen);
}

The arrow (v) => ... has no parameter types, so it stays generic until the cast to the constructor parameter's type instantiates it. verifyFunctionCastRules did that through instantiateSpecializedFunction, but it kept only the LogicalResult. When the arrow captures something, the result is a new value: the closure bound over the captured variables. The cast carried on with the bare function, so the constructor stored a function whose captures were a null pointer.

The same arrow worked as an argument to an ordinary call, where the delayed instantiation already uses the returned value. It also worked with typed parameters, or when it captured nothing.

Fix

verifyFunctionCastRules now takes value and valueType by reference. It finishes the cast with the returned closure, the same way instantiateGenericsForBinaryOp already did, and refreshes valueType after instantiation.

Results

• gc, rc, none: the program prints 1.
• -mm=own: the program now gets the same "captured by a closure that escapes" diagnostic that the explicitly typed form already got.
• New test 00capture_in_new_untyped_arrow.ts covers a parameter property, a stored field, a value-returning arrow and a non-capturing control. It runs as gc compile and JIT, and as rc and none through the corpus.
• Full ctest -C Release: 100% passed, 0 failed out of 6026.

🤖 Generated with Claude Code