Merge pull request #65643 from kavon/5.9-noncopyable-metatypes

[5.9🍒] Prevent noncopyable metatypes from being converted to `Any`

Author: kavon

lib/AST/Module.cpp

@@ -1768,10 +1768,18 @@ static ProtocolConformanceRef getBuiltinFunctionTypeConformance(
 /// appropriate.
 static ProtocolConformanceRef getBuiltinMetaTypeTypeConformance(
     Type type, const AnyMetatypeType *metatypeType, ProtocolDecl *protocol) {
-  // All metatypes are Sendable and Copyable
-  if (protocol->isSpecificProtocol(KnownProtocolKind::Sendable) ||
-      protocol->isSpecificProtocol(KnownProtocolKind::Copyable)) {
-    ASTContext &ctx = protocol->getASTContext();
+  ASTContext &ctx = protocol->getASTContext();
+
+  // Only metatypes of Copyable types are Copyable.
+  if (protocol->isSpecificProtocol(KnownProtocolKind::Copyable) &&
+      !metatypeType->getInstanceType()->isPureMoveOnly()) {
+    return ProtocolConformanceRef(
+        ctx.getBuiltinConformance(type, protocol, GenericSignature(), { },
+                                  BuiltinConformanceKind::Synthesized));
+  }
+
+  // All metatypes are Sendable
+  if (protocol->isSpecificProtocol(KnownProtocolKind::Sendable)) {
     return ProtocolConformanceRef(
         ctx.getBuiltinConformance(type, protocol, GenericSignature(), { },
                                   BuiltinConformanceKind::Synthesized));

lib/Sema/CSSimplify.cpp

@@ -3831,8 +3831,8 @@ ConstraintSystem::matchExistentialTypes(Type type1, Type type2,
     return getTypeMatchAmbiguous();
   }
 
-  // move-only types cannot match with any existential types.
-  if (type1->isPureMoveOnly()) {
+  // move-only types (and their metatypes) cannot match with existential types.
+  if (type1->getMetatypeInstanceType()->isPureMoveOnly()) {
     // tailor error message
     if (shouldAttemptFixes()) {
       auto *fix = MustBeCopyable::create(*this, type1,

lib/Sema/TypeCheckConstraints.cpp

@@ -1652,12 +1652,12 @@ TypeChecker::typeCheckCheckedCast(Type fromType, Type toType,
   }
 
   // Since move-only types currently cannot conform to protocols, nor be a class
-  // type, the subtyping hierarchy is a bit bizarre as of now:
+  // type, the subtyping hierarchy looks a bit like this:
   //
-  //              noncopyable
-  //           structs and enums
-  //                   |
-  //       +--------- Any
+  //                  ~Copyable
+  //                    /  \
+  //                   /    \
+  //       +--------- Any    noncopyable structs/enums
   //       |           |
   //   AnyObject    protocol
   //       |       existentials
@@ -1669,7 +1669,9 @@ TypeChecker::typeCheckCheckedCast(Type fromType, Type toType,
   //
   //
   // Thus, right now, a move-only type is only a subtype of itself.
-  if (fromType->isPureMoveOnly() || toType->isPureMoveOnly())
+  // We also want to prevent conversions of a move-only type's metatype.
+  if (fromType->getMetatypeInstanceType()->isPureMoveOnly()
+      || toType->getMetatypeInstanceType()->isPureMoveOnly())
     return CheckedCastKind::Unresolved;
 
   // Check for a bridging conversion.

test/Constraints/moveonly_constraints.swift

@@ -148,6 +148,11 @@ func checkCasting(_ b: any Box, _ mo: borrowing MO, _ a: Any) {
   let _: MO = dup.get()
   let _: MO = dup.val
 
+  let _: Any = MO.self // expected-error {{move-only type 'MO.Type' cannot be used with generics yet}}
+  let _: AnyObject = MO.self // expected-error {{move-only type 'MO.Type' cannot be used with generics yet}}
+  let _ = MO.self as Any // expected-error {{move-only type 'MO.Type' cannot be used with generics yet}}
+  let _ = MO.self is Any // expected-warning {{cast from 'MO.Type' to unrelated type 'Any' always fails}}
+
   let _: Sendable = (MO(), MO()) // expected-error {{move-only type '(MO, MO)' cannot be used with generics yet}}
   let _: Sendable = MO() // expected-error {{move-only type 'MO' cannot be used with generics yet}}
   let _: _Copyable = mo // expected-error {{'_Copyable' is unavailable}}
@@ -266,3 +271,14 @@ struct GenerousGuy: Gives { // expected-error {{type 'GenerousGuy' does not conf
   typealias Ty = MO // expected-note {{possibly intended match 'GenerousGuy.Ty' (aka 'MO') does not conform to '_Copyable'}}
   func give() -> Ty {}
 }
+
+func doBadMetatypeStuff<T>(_ t: T) {
+  let y = t as! Any.Type
+  if let MO_MetaType = y as? MO.Type { // expected-warning {{cast from 'any Any.Type' to unrelated type 'MO.Type' always fails}}
+    let x = MO_MetaType.init()
+    let _ = x
+  }
+}
+func tryToDoBadMetatypeStuff() {
+  doBadMetatypeStuff(MO.self) // expected-error {{move-only type 'MO.Type' cannot be used with generics yet}}
+}