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[ASTPrinter] Print the desugared constraint type following the any keyword. #59041

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Merged
merged 2 commits into from
May 24, 2022
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[ASTPrinter] Print the desugared constraint type following the any keyword. #59041

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e9c14cd
[ASTPrinter] Print the desugared constraint type following the 'any'
hborla May 24, 2022
38dfb99
[ASTPrinter] Put desugaring constraints for existential types behind a
hborla May 24, 2022
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3 changes: 3 additions & 0 deletions include/swift/AST/PrintOptions.h
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Expand Up @@ -285,6 +285,9 @@ struct PrintOptions {
/// types.
bool PrintExplicitAny = false;

/// Whether to desugar the constraint for an existential type.
bool DesugarExistentialConstraint = false;

/// Whether to skip keywords with a prefix of underscore such as __consuming.
bool SkipUnderscoredKeywords = false;

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12 changes: 11 additions & 1 deletion lib/AST/ASTPrinter.cpp
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Expand Up @@ -156,6 +156,7 @@ PrintOptions PrintOptions::printSwiftInterfaceFile(ModuleDecl *ModuleToPrint,
result.AlwaysTryPrintParameterLabels = true;
result.PrintSPIs = printSPIs;
result.PrintExplicitAny = true;
result.DesugarExistentialConstraint = true;

// We should print __consuming, __owned, etc for the module interface file.
result.SkipUnderscoredKeywords = false;
Expand Down Expand Up @@ -6211,7 +6212,16 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
if (Options.PrintExplicitAny)
Printer << "any ";

visit(T->getConstraintType());
// FIXME: The desugared type is used here only to support
// existential types with protocol typealiases in Swift
// interfaces. Verifying that the underlying type of a
// protocol typealias is a constriant type is fundamentally
// circular, so the desugared type should be written in source.
if (Options.DesugarExistentialConstraint) {
visit(T->getConstraintType()->getDesugaredType());
} else {
visit(T->getConstraintType());
}
}

void visitLValueType(LValueType *T) {
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8 changes: 8 additions & 0 deletions test/ModuleInterface/existential-any.swift
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Expand Up @@ -38,3 +38,11 @@ public struct S {
// CHECK: public var q: any main.Q
public var q: any Q
}


public protocol ProtocolTypealias {
typealias A = P
}

// CHECK: public func dependentExistential<T>(value: (T) -> any main.P) where T : main.ProtocolTypealias
public func dependentExistential<T: ProtocolTypealias>(value: (T) -> T.A) {}
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My only hesitation here is that we might want to think about whether this interferes with the ability of -preserve-types-as-written to help library owners work around naming ambiguities. There are already places where library owners can't control the type names that are written into the interface, though, so maybe it's not much of a regression to lack control for this kind of signature.

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I think -preserve-types-as-written will skip this code path entirely, right? It should print the TypeRepr if available (which will print T.A without any) and not look at the Type at all.

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In any case, this isn't a long term fix; either we need to figure out how to make any with protocol typealiases work (seems unlikely), or eventually ban them in source.