Issue #1137: A narrowed in-place Block? arm binding lowers wrong

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ready · opened 2026-11-01 · updated 2026-11-01 · 0 comments

Found by the r3c move of type_rules (#125), docs/briefs/r3c-type-rules-direct.md.report.md; the case is on branch wip/r3c-type-rules-chunk2.

An arm that binds an optional part (Block?) of a mut place and narrows it, to change it in place, lowers to Rust that does not compile (the binding is a moved value, not a &mut into the place). 3a3089b0 fixed the narrowed mut option for a parameter; this case is the binding inside an arm.

To build:

• a probe of a few lines in tests/compiler/ from the wip’s case
• lower the narrowed binding as a place in the arm (as_mut), as 3a3089b0 does for a parameter

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