Merge pull request #60537 from DougGregor/preconcurrency-typealias

[Concurrency] Apply `@preconcurrency` to typealiases at the point of use

Author: DougGregor

lib/Sema/TypeCheckDecl.cpp

@@ -1826,6 +1826,8 @@ UnderlyingTypeRequest::evaluate(Evaluator &evaluator,
   TypeResolutionOptions options((typeAlias->getGenericParams()
                                      ? TypeResolverContext::GenericTypeAliasDecl
                                      : TypeResolverContext::TypeAliasDecl));
+  if (typeAlias->preconcurrency())
+    options |= TypeResolutionFlags::Preconcurrency;
 
   // This can happen when code completion is attempted inside
   // of typealias underlying type e.g. `typealias F = () -> Int#^TOK^#`
@@ -2091,8 +2093,11 @@ ResultTypeRequest::evaluate(Evaluator &evaluator, ValueDecl *decl) const {
             : ErrorType::get(ctx));
   }
 
-  const auto options =
+  auto options =
       TypeResolutionOptions(TypeResolverContext::FunctionResult);
+  if (decl->preconcurrency())
+    options |= TypeResolutionFlags::Preconcurrency;
+
   auto *const dc = decl->getInnermostDeclContext();
   return TypeResolution::forInterface(dc, options,
                                       /*unboundTyOpener*/ nullptr,
@@ -2193,6 +2198,13 @@ static Type validateParameterType(ParamDecl *decl) {
     options = TypeResolutionOptions(TypeResolverContext::EnumElementDecl);
   }
 
+  // Set the "preconcurrency" flag if this is a parameter of a preconcurrency
+  // declaration.
+  if (auto decl = dc->getAsDecl()) {
+    if (decl->preconcurrency())
+      options |= TypeResolutionFlags::Preconcurrency;
+  }
+
   // If the element is a variadic parameter, resolve the parameter type as if
   // it were in non-parameter position, since we want functions to be
   // @escaping in this case.

lib/Sema/TypeCheckType.cpp

@@ -286,6 +286,37 @@ static Type getIdentityOpaqueTypeArchetypeType(
   return OpaqueTypeArchetypeType::get(opaqueDecl, interfaceType, subs);
 }
 
+/// Adjust the underlying type of a typealias within the given context to
+/// account for @preconcurrency.
+static Type adjustTypeAliasTypeInContext(
+    Type type, TypeAliasDecl *aliasDecl, DeclContext *fromDC,
+    TypeResolutionOptions options) {
+  // If we are in a @preconcurrency declaration, don't adjust the types of
+  // type aliases.
+  if (options.contains(TypeResolutionFlags::Preconcurrency))
+    return type;
+
+  // If the type alias itself isn't marked with @preconcurrency, don't
+  // adjust the type.
+  if (!aliasDecl->preconcurrency())
+    return type;
+
+  // Only adjust the type within a strict concurrency context, so we don't
+  // change the types as seen by code that hasn't adopted concurrency.
+  if (contextRequiresStrictConcurrencyChecking(
+          fromDC,
+          [](const AbstractClosureExpr *closure) {
+            return closure->getType();
+          },
+          [](const ClosureExpr *closure) {
+            return closure->isIsolatedByPreconcurrency();
+          }))
+    return type;
+
+  return type->stripConcurrency(
+      /*recurse=*/true, /*dropGlobalActor=*/true);
+}
+
 Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
                                           DeclContext *foundDC,
                                           bool isSpecialized) const {
@@ -307,6 +338,13 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
     return genericParam->getDeclaredInterfaceType();
   }
 
+  /// Call this function before returning the underlying type of a typealias,
+  /// to adjust its type for concurrency.
+  auto adjustAliasType = [&](Type type) -> Type {
+    return adjustTypeAliasTypeInContext(
+        type, cast<TypeAliasDecl>(typeDecl), fromDC, options);
+  };
+
   if (!isSpecialized) {
     // If we are referring to a type within its own context, and we have either
     // a generic type with no generic arguments or a non-generic type, use the
@@ -342,9 +380,9 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
               if (ugAliasDecl == aliasDecl) {
                 if (getStage() == TypeResolutionStage::Structural &&
                     aliasDecl->getUnderlyingTypeRepr() != nullptr) {
-                  return aliasDecl->getStructuralType();
+                  return adjustAliasType(aliasDecl->getStructuralType());
                 }
-                return aliasDecl->getDeclaredInterfaceType();
+                return adjustAliasType(aliasDecl->getDeclaredInterfaceType());
               }
 
               extendedType = unboundGeneric->getParent();
@@ -356,9 +394,9 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
             if (aliasType->getDecl() == aliasDecl) {
               if (getStage() == TypeResolutionStage::Structural &&
                   aliasDecl->getUnderlyingTypeRepr() != nullptr) {
-                return aliasDecl->getStructuralType();
+                return adjustAliasType(aliasDecl->getStructuralType());
               }
-              return aliasDecl->getDeclaredInterfaceType();
+              return adjustAliasType(aliasDecl->getDeclaredInterfaceType());
             }
             extendedType = aliasType->getParent();
             continue;
@@ -381,9 +419,9 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
       // Otherwise, return the appropriate type.
       if (getStage() == TypeResolutionStage::Structural &&
           aliasDecl->getUnderlyingTypeRepr() != nullptr) {
-        return aliasDecl->getStructuralType();
+        return adjustAliasType(aliasDecl->getStructuralType());
       }
-      return aliasDecl->getDeclaredInterfaceType();
+      return adjustAliasType(aliasDecl->getDeclaredInterfaceType());
     }
 
     // When a nominal type used outside its context, return the unbound
@@ -1591,6 +1629,13 @@ static Type resolveNestedIdentTypeComponent(TypeResolution resolution,
                                         AssociatedTypeDecl *inferredAssocType) {
     bool hasUnboundOpener = !!resolution.getUnboundTypeOpener();
 
+    // Type aliases might require adjustment due to @preconcurrency.
+    if (auto aliasDecl = dyn_cast<TypeAliasDecl>(member)) {
+      memberType = adjustTypeAliasTypeInContext(
+          memberType, aliasDecl, resolution.getDeclContext(),
+          resolution.getOptions());
+    }
+
     if (options.contains(TypeResolutionFlags::SilenceErrors)) {
       if (TypeChecker::isUnsupportedMemberTypeAccess(parentTy, member,
                                                      hasUnboundOpener)
@@ -4493,6 +4538,7 @@ class ExistentialTypeVisitor
       }
     } else if (auto *alias = dyn_cast_or_null<TypeAliasDecl>(comp->getBoundDecl())) {
       auto type = Type(alias->getDeclaredInterfaceType()->getDesugaredType());
+
       // If this is a type alias to a constraint type, the type
       // alias name must be prefixed with 'any' to be used as an
       // existential type.

lib/Sema/TypeCheckType.h

@@ -67,6 +67,9 @@ enum class TypeResolutionFlags : uint16_t {
   /// Needed to enforce that \c any P<some Q> does not resolve to a
   /// parameterized existential with an opaque type constraint.
   DisallowOpaqueTypes = 1 << 9,
+
+  /// We are in a `@preconcurrency` declaration.
+  Preconcurrency = 1 << 10,
 };
 
 /// Type resolution contexts that require special handling.

test/Concurrency/preconcurrency_typealias.swift

@@ -0,0 +1,48 @@
+// RUN: %target-swift-frontend -typecheck -verify %s
+// REQUIRES: concurrency
+
+@preconcurrency @MainActor func f() { }
+// expected-note@-1 2{{calls to global function 'f()' from outside of its actor context are implicitly asynchronous}}
+
+@preconcurrency typealias FN = @Sendable () -> Void
+
+struct Outer {
+  @preconcurrency typealias FN = @Sendable () -> Void
+}
+
+@preconcurrency func preconcurrencyFunc(callback: FN) {}
+
+func test() {
+  var _: Outer.FN = {
+    f()
+  }
+
+  var _: FN = {
+    f()
+    print("Hello")
+  }
+
+  var mutableVariable = 0
+  preconcurrencyFunc {
+    mutableVariable += 1 // no sendable warning
+  }
+  mutableVariable += 1
+}
+
+@available(SwiftStdlib 5.1, *)
+func testAsync() async {
+  var _: Outer.FN = {
+    f() // expected-error{{call to main actor-isolated global function 'f()' in a synchronous nonisolated context}}
+  }
+
+  var _: FN = {
+    f() // expected-error{{call to main actor-isolated global function 'f()' in a synchronous nonisolated context}}
+    print("Hello")
+  }
+
+  var mutableVariable = 0
+  preconcurrencyFunc {
+    mutableVariable += 1 // expected-warning{{mutation of captured var 'mutableVariable' in concurrently-executing code; this is an error in Swift 6}}
+  }
+  mutableVariable += 1
+}