Issue #1138: A drain / for mut element match handed to a mut parameter gives partially moved

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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.

Matching an element of a for mut loop (or of a drain) and handing the matched value, or a part of it, to a mut parameter lowers to Rust that rustc refuses with use of partially moved value. 5a18a962 made a part handed to a mut parameter lent; the match on the element still moves.

To build:

• a probe of a few lines in tests/compiler/ from the wip’s case
• lower the match on a for mut / drained element by reference where the arm hands it on as mut

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