[Variadic Generics] Add a contextual each keyword for pack element references in pack expansion patterns.
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…he 'each' keyword.
…pack element generic signature.
… Bind constraints, vend potential bindings through PotentialBindings::infer. This allows for bidirectional binding inference from the pack type to the element type and vice versa.
…cation for PackElementExpr.
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…ns followed by an unlabeled element until pack type variables are resolved.
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@swift-ci please smoke test |
xedin
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Dec 21, 2022
| : public StoredPointerElement<GenericEnvironment> { | ||
| public: | ||
| OpenedPackElement(GenericEnvironment *env) | ||
| : StoredPointerElement(PathElementKind::OpenedPackElement, env) {} |
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Should we assert that env is never null in here?
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| auto *loc = constraint->getLocator(); | ||
| auto openedElement = | ||
| loc->getLastElementAs<LocatorPathElt::OpenedPackElement>(); |
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Probably castLastElementTo is better here
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This change parses a contextual
eachkeyword in expressions asPackElementExpr, and changesPackExpansionExprto represent pack element bindings asPackElementExpr. The corresponding SwiftSyntax PR is swiftlang/swift-syntax#1146.In addition to clarifying for the programmer which expressions in a pack expansion are expanded, making pack elements explicit in the AST has a number of implementation benefits:
...is a pack expansion or a postfix operator call.PackElementOfconstraint.PotentialBindingsinfrastructure, and type information can flow bidirectionally (from the pack type to the element type and vice versa).