Enable SE-0413 "Typed Throws" by default

CHANGELOG.md

@@ -3,6 +3,49 @@
 > **Note**\
 > This is in reverse chronological order, so newer entries are added to the top.
 
+## Swift 5.11
+
+* [SE-0413][]:
+
+  Functions can now specify the type of error that they throw as part of the
+  function signature. For example:
+
+  ```swift
+  func parseRecord(from string: String) throws(ParseError) -> Record { ... }
+  ```
+
+  A call to `parseRecord(from:)` will either return a `Record` instance or throw
+  an error of type `ParseError`. For example, a `do..catch` block will infer
+  the `error` variable as being of type `ParseError`:
+
+  ```swift
+  do {
+    let record = try parseRecord(from: myString)
+  } catch {
+    // error has type ParseError
+  }
+  ```
+
+  Typed throws generalizes over throwing and non-throwing functions. A function
+  that is specified as `throws` (without an explicitly-specified error type) is
+  equivalent to one that specifies `throws(any Error)`, whereas a non-throwing
+  is equivalent to one that specifies `throws(Never)`. Calls to functions that
+  are `throws(Never)` are non-throwing.
+
+  Typed throws can also be used in generic functions to propagate error types
+  from parameters, in a manner that is more precise than `rethrows`. For
+  example, the `Sequence.map` operation can propagate the thrown error type from
+  its closure parameter, indicating that it only throws errors of the same type
+  as that closure does:
+
+  ```swift
+  extension Sequence {
+    func map<T, E>(_ body: (Element) throws(E) -> T) throws(E) -> [T] { ... }
+  }
+  ```
+
+  When given a non-throwing closure as a parameter, `map` will not throw.
+
 * [#70065][]:
 
   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
 [SE-0394]: https://github.com/apple/swift-evolution/blob/main/proposals/0394-swiftpm-expression-macros.md
 [SE-0397]: https://github.com/apple/swift-evolution/blob/main/proposals/0397-freestanding-declaration-macros.md
 [SE-0407]: https://github.com/apple/swift-evolution/blob/main/proposals/0407-member-macro-conformances.md
+[SE-0413]: https://github.com/apple/swift-evolution/blob/main/proposals/0413-typed-throws.md
 [#64927]: <https://github.com/apple/swift/issues/64927>
 [#42697]: <https://github.com/apple/swift/issues/42697>
 [#42728]: <https://github.com/apple/swift/issues/42728>

include/swift/AST/DiagnosticsSema.def

@@ -5231,9 +5231,6 @@ WARNING(no_throw_in_try,none,
 WARNING(no_throw_in_do_with_catch,none,
         "'catch' block is unreachable because no errors are thrown in 'do' block", ())
 
-ERROR(experimental_typed_throws,none,
-      "typed throws is an experimental feature", ())
-
 ERROR(thrown_type_not_error,none,
       "thrown type %0 does not conform to the 'Error' protocol", (Type))
 

include/swift/Basic/Features.def

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

lib/ASTGen/Sources/ASTGen/SourceFile.swift

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

lib/Sema/ConstraintSystem.cpp

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

lib/Sema/TypeCheckEffects.cpp

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

lib/Sema/TypeCheckPattern.cpp

@@ -1239,7 +1239,9 @@ Pattern *TypeChecker::coercePatternToType(
     } else if (auto MTT = diagTy->getAs<AnyMetatypeType>()) {
       if (MTT->getInstanceType()->isAnyObject())
         shouldRequireType = true;
-    } else if (diagTy->isStructurallyUninhabited()) {
+    } else if (diagTy->isStructurallyUninhabited() &&
+               !(options.contains(TypeResolutionFlags::SilenceNeverWarnings) &&
+                 type->isNever())) {
       shouldRequireType = true;
       diag = isOptional ? diag::type_inferred_to_undesirable_type
                         : diag::type_inferred_to_uninhabited_type;
@@ -1428,11 +1430,15 @@ Pattern *TypeChecker::coercePatternToType(
       if (type->hasError()) {
         return nullptr;
       }
-      diags
-          .diagnose(IP->getLoc(), diag::downcast_to_unrelated, type,
-                    IP->getCastType())
-          .highlight(IP->getLoc())
-          .highlight(IP->getCastTypeRepr()->getSourceRange());
+
+      if (!(options.contains(TypeResolutionFlags::SilenceNeverWarnings) &&
+            type->isNever())) {
+        diags
+            .diagnose(IP->getLoc(), diag::downcast_to_unrelated, type,
+                      IP->getCastType())
+            .highlight(IP->getLoc())
+            .highlight(IP->getCastTypeRepr()->getSourceRange());
+      }
 
       IP->setCastKind(CheckedCastKind::ValueCast);
       break;

lib/Sema/TypeCheckStmt.cpp

@@ -1468,6 +1468,7 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
   }
 
   void checkCaseLabelItemPattern(CaseStmt *caseBlock, CaseLabelItem &labelItem,
+                                 CaseParentKind parentKind,
                                  bool &limitExhaustivityChecks,
                                  Type subjectType) {
     Pattern *pattern = labelItem.getPattern();
@@ -1484,6 +1485,9 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
     if (subjectType) {
       auto contextualPattern = ContextualPattern::forRawPattern(pattern, DC);
       TypeResolutionOptions patternOptions(TypeResolverContext::InExpression);
+      if (parentKind == CaseParentKind::DoCatch)
+        patternOptions |= TypeResolutionFlags::SilenceNeverWarnings;
+
       auto coercedPattern = TypeChecker::coercePatternToType(
           contextualPattern, subjectType, patternOptions);
       if (coercedPattern)
@@ -1584,8 +1588,8 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
       for (auto &labelItem : caseLabelItemArray) {
         // Resolve the pattern in our case label if it has not been resolved and
         // check that our var decls follow invariants.
-        checkCaseLabelItemPattern(caseBlock, labelItem, limitExhaustivityChecks,
-                                  subjectType);
+        checkCaseLabelItemPattern(caseBlock, labelItem, parentKind,
+                                  limitExhaustivityChecks, subjectType);
 
         // Check the guard expression, if present.
         if (auto *guard = labelItem.getGuardExpr()) {

lib/Sema/TypeCheckType.cpp

@@ -3715,11 +3715,6 @@ NeverNullType TypeResolver::resolveASTFunctionType(
   Type thrownTy;
   if (auto thrownTypeRepr = repr->getThrownTypeRepr()) {
     ASTContext &ctx = getASTContext();
-    if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
-      diagnoseInvalid(
-          thrownTypeRepr, thrownTypeRepr->getLoc(), diag::experimental_typed_throws);
-    }
-
     auto thrownTypeOptions = options.withoutContext();
     thrownTy = resolveType(thrownTypeRepr, thrownTypeOptions);
     if (thrownTy->hasError()) {
@@ -5691,10 +5686,6 @@ Type ExplicitCaughtTypeRequest::evaluate(
     }
 
     // We have an explicit thrown error type, so resolve it.
-    if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
-      ctx.Diags.diagnose(thrownTypeRepr->getLoc(), diag::experimental_typed_throws);
-    }
-
     auto options = TypeResolutionOptions(TypeResolverContext::None);
     if (func->preconcurrency())
       options |= TypeResolutionFlags::Preconcurrency;
@@ -5710,11 +5701,6 @@ Type ExplicitCaughtTypeRequest::evaluate(
   if (auto closure = catchNode.dyn_cast<ClosureExpr *>()) {
     // Explicit thrown error type.
     if (auto thrownTypeRepr = closure->getExplicitThrownTypeRepr()) {
-      if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
-        ctx.Diags.diagnose(thrownTypeRepr->getLoc(),
-                           diag::experimental_typed_throws);
-      }
-
       return TypeResolution::resolveContextualType(
                thrownTypeRepr, closure,
                TypeResolutionOptions(TypeResolverContext::None),
@@ -5736,18 +5722,9 @@ Type ExplicitCaughtTypeRequest::evaluate(
     // A do..catch block with no explicit 'throws' annotation will infer
     // the thrown error type.
     if (doCatch->getThrowsLoc().isInvalid()) {
-      // Prior to typed throws, the do..catch always throws 'any Error'.
-      if (!ctx.LangOpts.hasFeature(Feature::TypedThrows))
-        return ctx.getErrorExistentialType();
-
       return Type();
     }
 
-    if (!ctx.LangOpts.hasFeature(Feature::TypedThrows)) {
-      ctx.Diags.diagnose(doCatch->getThrowsLoc(), diag::experimental_typed_throws);
-      return ctx.getErrorExistentialType();
-    }
-
     auto typeRepr = doCatch->getCaughtTypeRepr();
 
     // If there is no explicitly-specified thrown error type, it's 'any Error'.

lib/Sema/TypeCheckType.h

@@ -82,6 +82,10 @@ enum class TypeResolutionFlags : uint16_t {
 
   /// Whether this is a resolution based on a pack reference.
   FromPackReference = 1 << 12,
+
+  /// Whether to suppress warnings about conversions from and bindings of type
+  /// Never
+  SilenceNeverWarnings = 1 << 13,
 };
 
 /// Type resolution contexts that require special handling.

test/Concurrency/typed_throws.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -enable-experimental-feature TypedThrows
+// RUN: %target-typecheck-verify-swift
 
 // REQUIRES: concurrency
 

test/Generics/typed_throws.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -debug-generic-signatures -enable-experimental-feature TypedThrows 2>&1 | %FileCheck %s
+// RUN: %target-typecheck-verify-swift -debug-generic-signatures 2>&1 | %FileCheck %s
 
 protocol P1 {
   associatedtype A

test/IDE/complete_exception.swift

@@ -42,7 +42,7 @@
 // RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -code-completion -source-filename %s -code-completion-token=INSIDE_CATCH_ERR_DOT1 | %FileCheck %s -check-prefix=ERROR_DOT
 // RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -code-completion -source-filename %s -code-completion-token=INSIDE_CATCH_ERR_DOT2 | %FileCheck %s -check-prefix=ERROR_DOT
 // RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -code-completion -source-filename %s -code-completion-token=INSIDE_CATCH_ERR_DOT3 | %FileCheck %s -check-prefix=NSERROR_DOT
-// RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -code-completion -source-filename %s -code-completion-token=INSIDE_CATCH_ERR_DOT4 | %FileCheck %s -check-prefix=INT_DOT
+// RUNFIXME: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -code-completion -source-filename %s -code-completion-token=INSIDE_CATCH_ERR_DOT4 | %FileCheck %s -check-prefix=INT_DOT
 
 // RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -code-completion -source-filename %s -code-completion-token=TOP_LEVEL_INSIDE_CATCH1 > %t.top_level_inside_catch1
 // RUN: %FileCheck %s -check-prefix=STMT < %t.top_level_inside_catch1
@@ -71,10 +71,10 @@ func getNSError() -> NSError { return NSError(domain: "", code: 1, userInfo: [:]
 func test001() {
   do {} catch #^CATCH1^#
 
-// CATCH1-DAG:  Decl[Enum]/CurrModule/TypeRelation[Convertible]:              Error4[#Error4#]; name=Error4{{$}}
-// CATCH1-DAG:  Decl[Class]/CurrModule/TypeRelation[Convertible]:             Error3[#Error3#]; name=Error3{{$}}
-// CATCH1-DAG:  Decl[Class]/CurrModule/TypeRelation[Convertible]:             Error2[#Error2#]; name=Error2{{$}}
-// CATCH1-DAG:  Decl[Class]/CurrModule/TypeRelation[Convertible]:             Error1[#Error1#]; name=Error1{{$}}
+// CATCH1-DAG:  Decl[Enum]/CurrModule:              Error4[#Error4#]; name=Error4{{$}}
+// CATCH1-DAG:  Decl[Class]/CurrModule:             Error3[#Error3#]; name=Error3{{$}}
+// CATCH1-DAG:  Decl[Class]/CurrModule:             Error2[#Error2#]; name=Error2{{$}}
+// CATCH1-DAG:  Decl[Class]/CurrModule:             Error1[#Error1#]; name=Error1{{$}}
 // CATCH1-DAG:  Keyword[let]/None:                  let{{; name=.+$}}
 // CATCH1-DAG:  Decl[Class]/CurrModule:             NoneError1[#NoneError1#]; name=NoneError1{{$}}
 // CATCH1-DAG:  Decl[Class]/OtherModule[Foundation]/IsSystem: NSError[#NSError#]{{; name=.+$}}
@@ -147,14 +147,14 @@ func test006() {
   } catch {
     #^INSIDE_CATCH1^#
   }
-// IMPLICIT_ERROR: Decl[LocalVar]/Local:  error[#any Error#]; name=error
+// IMPLICIT_ERROR: Decl[LocalVar]/Local:  error[#Never#]; name=error
 }
 func test007() {
   do {
   } catch let e {
     #^INSIDE_CATCH2^#
   }
-// EXPLICIT_ERROR_E: Decl[LocalVar]/Local: e[#any Error#]; name=e
+// EXPLICIT_ERROR_E: Decl[LocalVar]/Local: e[#Never#]; name=e
 }
 func test008() {
   do {
@@ -170,7 +170,7 @@ func test009() {
   }
 
 // FIXME: we're getting parentheses around the type when it's unnamed...
-// EXPLICIT_ERROR_PAYLOAD_I: Decl[LocalVar]/Local: i[#(Int32)#]; name=i
+// EXPLICIT_ERROR_PAYLOAD_I: Decl[LocalVar]/Local: i[#<<error type>>#]; name=i
 }
 func test010() {
   do {
@@ -195,7 +195,7 @@ func test012() {
     error.#^INSIDE_CATCH_ERR_DOT1^#
   }
 }
-// ERROR_DOT: Keyword[self]/CurrNominal: self[#any Error#]; name=self
+// ERROR_DOT: Keyword[self]/CurrNominal: self[#Never#]; name=self
 func test013() {
   do {
   } catch let e {

test/IRGen/typed_throws.swift

@@ -1,8 +1,8 @@
-// RUN: %target-swift-frontend -primary-file %s -emit-ir -enable-experimental-feature TypedThrows -disable-availability-checking -runtime-compatibility-version none -target %module-target-future | %FileCheck %s --check-prefix=CHECK-MANGLE
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -disable-availability-checking -runtime-compatibility-version none -target %module-target-future | %FileCheck %s --check-prefix=CHECK-MANGLE
 
-// RUN: %target-swift-frontend -primary-file %s -emit-ir -enable-experimental-feature TypedThrows -disable-availability-checking -runtime-compatibility-version 5.8 -disable-concrete-type-metadata-mangled-name-accessors | %FileCheck %s --check-prefix=CHECK-NOMANGLE
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -disable-availability-checking -runtime-compatibility-version 5.8 -disable-concrete-type-metadata-mangled-name-accessors | %FileCheck %s --check-prefix=CHECK-NOMANGLE
 
-// RUN: %target-swift-frontend -primary-file %s -emit-ir -enable-experimental-feature TypedThrows  | %FileCheck %s --check-prefix=CHECK
+// RUN: %target-swift-frontend -primary-file %s -emit-ir  | %FileCheck %s --check-prefix=CHECK
 
 // XFAIL: CPU=arm64e
 // REQUIRES: PTRSIZE=64

test/IRGen/typed_throws_exec.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-build-swift -module-name=test -enable-experimental-feature TypedThrows %s -o %t/a.out
+// RUN: %target-build-swift -module-name=test %s -o %t/a.out
 // RUN: %target-codesign %t/a.out
 // RUN: %target-run %t/a.out | %FileCheck %s
 // REQUIRES: executable_test

test/IRGen/typed_throws_thunks.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -primary-file %s -emit-irgen -enable-experimental-feature TypedThrows -disable-availability-checking -runtime-compatibility-version none -target %module-target-future -enable-library-evolution | %FileCheck %s --check-prefix=CHECK
+// RUN: %target-swift-frontend -primary-file %s -emit-irgen -disable-availability-checking -runtime-compatibility-version none -target %module-target-future -enable-library-evolution | %FileCheck %s --check-prefix=CHECK
 
 // REQUIRES: PTRSIZE=64
 // UNSUPPORTED: CPU=arm64e

test/ModuleInterface/typed_throws.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s -module-name Test -enable-experimental-feature TypedThrows
-// RUN: %target-swift-typecheck-module-from-interface(%t.swiftinterface) -module-name Test -enable-experimental-feature TypedThrows
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s -module-name Test
+// RUN: %target-swift-typecheck-module-from-interface(%t.swiftinterface) -module-name Test
 // RUN: %FileCheck %s < %t.swiftinterface
 
 public enum MyError: Error {

test/Parse/errors.swift

@@ -19,12 +19,14 @@ func one() {
   do {
 
   } catch { // expected-warning {{'catch' block is unreachable because no errors are thrown in 'do' block}}
-    let error2 = error
+    let error2 = error // expected-warning{{constant 'error2' inferred to have type 'Never', which is an enum with no cases}}
+    // expected-note@-1{{add an explicit type annotation to silence this warning}}
   }
 
   do {
   } catch where true { // expected-warning {{'catch' block is unreachable because no errors are thrown in 'do' block}}
-    let error2 = error
+    let error2 = error // expected-warning{{constant 'error2' inferred to have type 'Never', which is an enum with no cases}}
+    // expected-note@-1{{add an explicit type annotation to silence this warning}}
   } catch {
   }
 

test/Parse/typed_throws.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -swift-version 5 -module-name test -enable-experimental-feature TypedThrows
+// RUN: %target-typecheck-verify-swift -swift-version 5 -module-name test
 
 // Parsing support for typed throws.
 

test/Runtime/demangleToMetadata.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-build-swift -Xfrontend -disable-availability-checking -parse-stdlib -enable-experimental-feature TypedThrows %s -module-name main -o %t/a.out
+// RUN: %target-build-swift -Xfrontend -disable-availability-checking -parse-stdlib %s -module-name main -o %t/a.out
 // RUN: %target-codesign %t/a.out
 // RUN: %target-run %t/a.out
 // REQUIRES: executable_test

test/SILGen/typed_throws.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-emit-silgen %s -enable-experimental-feature TypedThrows | %FileCheck %s
+// RUN: %target-swift-emit-silgen %s | %FileCheck %s
 
 enum MyError: Error {
   case fail

test/SILGen/typed_throws_generic.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-emit-silgen %s -enable-experimental-feature TypedThrows -enable-experimental-feature FullTypedThrows | %FileCheck %s
+// RUN: %target-swift-emit-silgen %s -enable-experimental-feature FullTypedThrows | %FileCheck %s
 
 public func genericThrow<E>(e: E) throws(E) {
   throw e