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[Diagnostics] Suppress unused expression warning if result is discard… #65445

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Merged
merged 1 commit into from
May 2, 2023
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[Diagnostics] Suppress unused expression warning if result is discard… #65445

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4 changes: 4 additions & 0 deletions include/swift/AST/Types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2459,6 +2459,10 @@ class TupleType final : public TypeBase, public llvm::FoldingSetNode,

bool containsPackExpansionType() const;

/// Check whether this tuple consists of a single unlabeled element
/// of \c PackExpansionType.
bool isSingleUnlabeledPackExpansion() const;

private:
TupleType(ArrayRef<TupleTypeElt> elements, const ASTContext *CanCtx,
RecursiveTypeProperties properties)
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8 changes: 8 additions & 0 deletions lib/AST/ParameterPack.cpp
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Expand Up @@ -134,6 +134,14 @@ bool CanTupleType::containsPackExpansionTypeImpl(CanTupleType tuple) {
return false;
}

bool TupleType::isSingleUnlabeledPackExpansion() const {
if (getNumElements() != 1)
return false;

const auto &elt = getElement(0);
return !elt.hasName() && elt.getType()->is<PackExpansionType>();
}

bool AnyFunctionType::containsPackExpansionType(ArrayRef<Param> params) {
for (auto param : params) {
if (param.getPlainType()->is<PackExpansionType>())
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10 changes: 10 additions & 0 deletions lib/Sema/TypeCheckStmt.cpp
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Expand Up @@ -1749,6 +1749,16 @@ Stmt *PreCheckReturnStmtRequest::evaluate(Evaluator &evaluator, ReturnStmt *RS,
}

static bool isDiscardableType(Type type) {
// If type is `(_: repeat ...)`, it can be discardable.
if (auto *tuple = type->getAs<TupleType>()) {
if (tuple->isSingleUnlabeledPackExpansion()) {
type = tuple->getElementType(0);
}
}

if (auto *expansion = type->getAs<PackExpansionType>())
return isDiscardableType(expansion->getPatternType());

return (type->hasError() ||
type->isUninhabited() ||
type->lookThroughAllOptionalTypes()->isVoid());
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11 changes: 11 additions & 0 deletions test/Constraints/pack-expansion-expressions.swift
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Expand Up @@ -397,3 +397,14 @@ do {
_ = Defaulted(t: "b", 0) // Ok
_ = Defaulted(t: "c", 1.0, u: "d", 0) // Ok
}

// rdar://108064941 - unused result diagnostic is unaware of Void packs
func test_no_unused_result_warning(arr: inout [Any]) {
func test1<each T>(_ value: (repeat each T)) {
repeat arr.append(each value.element) // no warning
}

func test2<each T>(_ value: repeat each T) {
((repeat arr.append(each value))) // no warning
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Is there any reason to do this with a tuple instead of just writing the underlying pack expansion expression? I'm wondering if we should still diagnose this for tuples

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I did it that way because users don't actually know that this is a tuple, syntactically it's just parens which seems reasonable to make consistent with non-variadic cases.

}
}