fix: Recover from MIR field projections on slices#22758
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Fixes #22757
MIR diagnostic borrow checking can encounter a
Fieldprojection whose base place has an array or slice type.PlaceTy::field_typreviously treated that as an invariant violation and panicked with:
text can't project out of [T] A
Fieldprojection contains a field index but no array or slice element index, so it cannot produce a meaningful element-field type. This change treats array and slice bases as failed MIR type recovery and propagates an error type. Other unexpected base types retain the existing invariant check.The regression test exercises the production
PlaceTy::projection_typath with a slice base and aFieldprojection. Before the fix it panics withcan't project out of [bool]; afterward it returns the error type.Tests:
text cargo test -p hir-ty All 998
hir-tytests pass.