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Document the relationship of AddCanonicalWitnessesBlock to IdentifiedFacetType #6461

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Merged
jonmeow merged 1 commit into from
Dec 4, 2025
+9 −3
Merged

Document the relationship of AddCanonicalWitnessesBlock to IdentifiedFacetType #6461

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4 changes: 4 additions & 0 deletions toolchain/sem_ir/facet_type_info.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -267,6 +267,10 @@ auto AddCanonicalWitnessesBlock(File& sem_ir,
CARBON_FATAL("Unhandled inst: {0}", inst);
}
}
// This matches the sort order of IdentifiedFacetType::required_interfaces,
// which is the order of the witnesses returned from impl lookup, and is
// canonical order in which the witnesses must appear for a given facet type
// so that ImplWitnessAccess can find the appropriate witness.
llvm::sort(sortable, [](auto& lhs, auto& rhs) {
return ImplsLess(lhs.first, rhs.first);
});
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8 changes: 5 additions & 3 deletions toolchain/sem_ir/facet_type_info.h
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Expand Up @@ -213,9 +213,11 @@ inline auto CarbonHashValue(const FacetTypeInfo& value, uint64_t seed)
return static_cast<HashCode>(hasher);
}

// Given an array of witnesses, sorts them to match the FacetTypeInfo ordering
// and returns the resulting block ID. This assumes witnesses have already been
// deduplicated, because it's mainly for imports.
// Given an array of witnesses, sorts them to match the ordering of the specific
// interfaces in the IdentifiedFacetType that produced the witness set, which is
// the canonical witness order, and returns the resulting block ID. This assumes
// witnesses have already been deduplicated, and do not contain errors, because
// it's mainly for imports.
auto AddCanonicalWitnessesBlock(File& sem_ir,
llvm::SmallVector<InstId>& witnesses)
-> InstBlockId;
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