Issue #1159: lower: a lambda with both return null and return (x, x) lowers to a tuple where an Option is wanted

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ready · opened 2026-11-02 · updated 2026-11-02 · 0 comments

Found by the grammar_run move (M2, #125), 2026-11-02.

A lambda whose body holds both return null and return (x, x) lowers to Rust that rustc refuses: “expected Option, found tuple”. The non-null return is not wrapped in Some(...) when the lambda’s result is optional.

To build:

• Every non-null return in a lambda whose result is T? lowers wrapped as Some(...).
• A test in tests/compiler/ (a lambda passed to .filter_map with return null and return (x, x)) with its .stdout.

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