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Merge pull request swiftlang#70677 from DougGregor/se-0413-typed-throws
Enable SE-0413 "Typed Throws" by default
2 parents fea6ff6 + cde18d1 commit baaa8f3

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‎CHANGELOG.md

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> **Note**\
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> This is in reverse chronological order, so newer entries are added to the top.
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## Swift 5.11
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* [SE-0413][]:
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Functions can now specify the type of error that they throw as part of the
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function signature. For example:
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```swift
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func parseRecord(from string: String) throws(ParseError) -> Record { ... }
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```
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A call to `parseRecord(from:)` will either return a `Record` instance or throw
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an error of type `ParseError`. For example, a `do..catch` block will infer
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the `error` variable as being of type `ParseError`:
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```swift
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do {
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let record = try parseRecord(from: myString)
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} catch {
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// error has type ParseError
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}
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```
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Typed throws generalizes over throwing and non-throwing functions. A function
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that is specified as `throws` (without an explicitly-specified error type) is
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equivalent to one that specifies `throws(any Error)`, whereas a non-throwing
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is equivalent to one that specifies `throws(Never)`. Calls to functions that
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are `throws(Never)` are non-throwing.
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Typed throws can also be used in generic functions to propagate error types
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from parameters, in a manner that is more precise than `rethrows`. For
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example, the `Sequence.map` operation can propagate the thrown error type from
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its closure parameter, indicating that it only throws errors of the same type
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as that closure does:
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```swift
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extension Sequence {
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func map<T, E>(_ body: (Element) throws(E) -> T) throws(E) -> [T] { ... }
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}
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```
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When given a non-throwing closure as a parameter, `map` will not throw.
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* [#70065][]:
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With the implementation of [SE-0110][], a closure parameter syntax consisting
@@ -9861,6 +9904,7 @@ using the `.dynamicType` member to retrieve the type of an expression should mig
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[SE-0394]: https://github.com/apple/swift-evolution/blob/main/proposals/0394-swiftpm-expression-macros.md
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[SE-0397]: https://github.com/apple/swift-evolution/blob/main/proposals/0397-freestanding-declaration-macros.md
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[SE-0407]: https://github.com/apple/swift-evolution/blob/main/proposals/0407-member-macro-conformances.md
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[SE-0413]: https://github.com/apple/swift-evolution/blob/main/proposals/0413-typed-throws.md
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[#64927]: <https://github.com/apple/swift/issues/64927>
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[#42697]: <https://github.com/apple/swift/issues/42697>
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[#42728]: <https://github.com/apple/swift/issues/42728>

‎include/swift/AST/DiagnosticsSema.def

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@@ -5238,9 +5238,6 @@ WARNING(no_throw_in_try,none,
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WARNING(no_throw_in_do_with_catch,none,
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"'catch' block is unreachable because no errors are thrown in 'do' block", ())
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ERROR(experimental_typed_throws,none,
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"typed throws is an experimental feature", ())
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ERROR(thrown_type_not_error,none,
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"thrown type %0 does not conform to the 'Error' protocol", (Type))
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‎include/swift/Basic/Features.def

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@@ -116,6 +116,7 @@ LANGUAGE_FEATURE(ParameterPacks, 393, "Value and type parameter packs", true)
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SUPPRESSIBLE_LANGUAGE_FEATURE(LexicalLifetimes, 0, "@_eagerMove/@_noEagerMove/@_lexicalLifetimes annotations", true)
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LANGUAGE_FEATURE(FreestandingMacros, 397, "freestanding declaration macros", true)
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SUPPRESSIBLE_LANGUAGE_FEATURE(RetroactiveAttribute, 364, "@retroactive", true)
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LANGUAGE_FEATURE(TypedThrows, 413, "Typed throws", true)
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UPCOMING_FEATURE(ConciseMagicFile, 274, 6)
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UPCOMING_FEATURE(ForwardTrailingClosures, 286, 6)
@@ -249,9 +250,6 @@ EXPERIMENTAL_FEATURE(Embedded, true)
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/// Enables noncopyable generics
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EXPERIMENTAL_FEATURE(NoncopyableGenerics, false)
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/// Enables typed throws.
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EXPERIMENTAL_FEATURE(TypedThrows, true)
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/// Allow destructuring stored `let` bindings in structs.
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EXPERIMENTAL_FEATURE(StructLetDestructuring, true)
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‎lib/ASTGen/Sources/ASTGen/SourceFile.swift

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@@ -52,7 +52,6 @@ extension Parser.ExperimentalFeatures {
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}
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}
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mapFeature(.ThenStatements, to: .thenStatements)
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mapFeature(.TypedThrows, to: .typedThrows)
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mapFeature(.DoExpressions, to: .doExpressions)
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mapFeature(.NonescapableTypes, to: .nonescapableTypes)
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mapFeature(.TransferringArgsAndResults, to: .transferringArgsAndResults)

‎lib/Sema/ConstraintSystem.cpp

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@@ -374,7 +374,7 @@ void ConstraintSystem::recordPotentialThrowSite(
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ASTContext &ctx = getASTContext();
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// Only record potential throw sites when typed throws is enabled.
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if (!ctx.LangOpts.hasFeature(Feature::TypedThrows))
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if (!ctx.LangOpts.hasFeature(Feature::FullTypedThrows))
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return;
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380380
// Catch node location is determined by the source location.
@@ -432,6 +432,9 @@ Type ConstraintSystem::getCaughtErrorType(CatchNode catchNode) {
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return getClosureType(closure)->getEffectiveThrownErrorTypeOrNever();
433433
}
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435+
if (!ctx.LangOpts.hasFeature(Feature::FullTypedThrows))
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return ctx.getErrorExistentialType();
437+
435438
// Handle inference of caught error types.
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437440
// Collect all of the potential throw sites for this catch node.

‎lib/Sema/TypeCheckEffects.cpp

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@@ -663,8 +663,7 @@ static Expr *removeErasureToExistentialError(Expr *expr) {
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return expr;
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665665
ASTContext &ctx = type->getASTContext();
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if (!ctx.LangOpts.hasFeature(Feature::FullTypedThrows) ||
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!ctx.LangOpts.hasFeature(Feature::TypedThrows))
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if (!ctx.LangOpts.hasFeature(Feature::FullTypedThrows))
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return expr;
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// Look for an outer erasure expression.

‎lib/Sema/TypeCheckPattern.cpp

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} else if (auto MTT = diagTy->getAs<AnyMetatypeType>()) {
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if (MTT->getInstanceType()->isAnyObject())
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shouldRequireType = true;
1242-
} else if (diagTy->isStructurallyUninhabited()) {
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} else if (diagTy->isStructurallyUninhabited() &&
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!(options.contains(TypeResolutionFlags::SilenceNeverWarnings) &&
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type->isNever())) {
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shouldRequireType = true;
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diag = isOptional ? diag::type_inferred_to_undesirable_type
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: diag::type_inferred_to_uninhabited_type;
@@ -1428,11 +1430,15 @@ Pattern *TypeChecker::coercePatternToType(
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if (type->hasError()) {
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return nullptr;
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}
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diags
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.diagnose(IP->getLoc(), diag::downcast_to_unrelated, type,
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IP->getCastType())
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.highlight(IP->getLoc())
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.highlight(IP->getCastTypeRepr()->getSourceRange());
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if (!(options.contains(TypeResolutionFlags::SilenceNeverWarnings) &&
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type->isNever())) {
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diags
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.diagnose(IP->getLoc(), diag::downcast_to_unrelated, type,
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IP->getCastType())
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.highlight(IP->getLoc())
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.highlight(IP->getCastTypeRepr()->getSourceRange());
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}
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IP->setCastKind(CheckedCastKind::ValueCast);
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break;

‎lib/Sema/TypeCheckStmt.cpp

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@@ -1468,6 +1468,7 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
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}
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void checkCaseLabelItemPattern(CaseStmt *caseBlock, CaseLabelItem &labelItem,
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CaseParentKind parentKind,
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bool &limitExhaustivityChecks,
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Type subjectType) {
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Pattern *pattern = labelItem.getPattern();
@@ -1484,6 +1485,9 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
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if (subjectType) {
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auto contextualPattern = ContextualPattern::forRawPattern(pattern, DC);
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TypeResolutionOptions patternOptions(TypeResolverContext::InExpression);
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if (parentKind == CaseParentKind::DoCatch)
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patternOptions |= TypeResolutionFlags::SilenceNeverWarnings;
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auto coercedPattern = TypeChecker::coercePatternToType(
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contextualPattern, subjectType, patternOptions);
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if (coercedPattern)
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for (auto &labelItem : caseLabelItemArray) {
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// Resolve the pattern in our case label if it has not been resolved and
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// check that our var decls follow invariants.
1587-
checkCaseLabelItemPattern(caseBlock, labelItem, limitExhaustivityChecks,
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subjectType);
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checkCaseLabelItemPattern(caseBlock, labelItem, parentKind,
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limitExhaustivityChecks, subjectType);
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// Check the guard expression, if present.
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if (auto *guard = labelItem.getGuardExpr()) {

‎lib/Sema/TypeCheckType.cpp

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Type thrownTy;
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if (auto thrownTypeRepr = repr->getThrownTypeRepr()) {
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ASTContext &ctx = getASTContext();
3723-
if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
3724-
diagnoseInvalid(
3725-
thrownTypeRepr, thrownTypeRepr->getLoc(), diag::experimental_typed_throws);
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}
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auto thrownTypeOptions = options.withoutContext();
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thrownTy = resolveType(thrownTypeRepr, thrownTypeOptions);
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if (thrownTy->hasError()) {
@@ -5694,10 +5689,6 @@ Type ExplicitCaughtTypeRequest::evaluate(
56945689
}
56955690

56965691
// We have an explicit thrown error type, so resolve it.
5697-
if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
5698-
ctx.Diags.diagnose(thrownTypeRepr->getLoc(), diag::experimental_typed_throws);
5699-
}
5700-
57015692
auto options = TypeResolutionOptions(TypeResolverContext::None);
57025693
if (func->preconcurrency())
57035694
options |= TypeResolutionFlags::Preconcurrency;
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57135704
if (auto closure = catchNode.dyn_cast<ClosureExpr *>()) {
57145705
// Explicit thrown error type.
57155706
if (auto thrownTypeRepr = closure->getExplicitThrownTypeRepr()) {
5716-
if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
5717-
ctx.Diags.diagnose(thrownTypeRepr->getLoc(),
5718-
diag::experimental_typed_throws);
5719-
}
5720-
57215707
return TypeResolution::resolveContextualType(
57225708
thrownTypeRepr, closure,
57235709
TypeResolutionOptions(TypeResolverContext::None),
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57395725
// A do..catch block with no explicit 'throws' annotation will infer
57405726
// the thrown error type.
57415727
if (doCatch->getThrowsLoc().isInvalid()) {
5742-
// Prior to typed throws, the do..catch always throws 'any Error'.
5743-
if (!ctx.LangOpts.hasFeature(Feature::TypedThrows))
5744-
return ctx.getErrorExistentialType();
5745-
57465728
return Type();
57475729
}
57485730

5749-
if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
5750-
ctx.Diags.diagnose(doCatch->getThrowsLoc(), diag::experimental_typed_throws);
5751-
return ctx.getErrorExistentialType();
5752-
}
5753-
57545731
auto typeRepr = doCatch->getCaughtTypeRepr();
57555732

57565733
// If there is no explicitly-specified thrown error type, it's 'any Error'.

‎lib/Sema/TypeCheckType.h

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8383
/// Whether this is a resolution based on a pack reference.
8484
FromPackReference = 1 << 12,
85+
86+
/// Whether to suppress warnings about conversions from and bindings of type
87+
/// Never
88+
SilenceNeverWarnings = 1 << 13,
8589
};
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8791
/// Type resolution contexts that require special handling.

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