Filter PhantomData fields in CoerceShared borrowck field matching#156785
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ikow wants to merge 2 commits into
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Filter PhantomData fields in CoerceShared borrowck field matching#156785ikow wants to merge 2 commits into
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The `add_generic_reborrow_constraint` function matches source and dest struct fields by name when establishing borrow constraints for CoerceShared. However, it uses `all_fields()` which includes PhantomData fields, while the coherence check (`coerce_shared_info`) filters them out via `collect_struct_data_fields`. This mismatch means PhantomData fields with different names between source and dest are silently skipped, potentially dropping lifetime constraints. Fix: filter out PhantomData fields before matching, consistent with the coherence check. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
The
add_generic_reborrow_constraintfunction incompiler/rustc_borrowck/src/type_check/mod.rsmatches source and dest struct fields by name when establishing borrow constraints forCoerceShared. However, it usesall_fields()which includesPhantomDatafields, while the coherence check (coerce_shared_info) filters them out viacollect_struct_data_fields.This mismatch means
PhantomDatafields with different names between source and dest structs are silently skipped viacontinue(line 2524), potentially dropping lifetime constraints that should be established.Fix
Filter out
PhantomDatafields before matching, consistent with the coherence check's use ofcollect_struct_data_fields.Test plan
tests/ui/reborrow/coerce_shared_phantom_field_names.rs— a run-pass test withCoerceSharedsource/dest structs that have differently-namedPhantomDatafields (_markervs_lifetime)Tracking issue: #145612 (reborrow feature)