Prevent noncopyable metatypes from being converted to Any

These metatypes are a gateway to more incorrect
uses of these noncopyable values because we don't
yet have the corresponding runtime support yet.
The other use cases of using metatypes of
noncopyable types in generics is not high enough to
warrant people using them yet.

resolves rdar://106452518

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

@@ -3806,8 +3806,8 @@ 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

@@ -1629,12 +1629,12 @@ 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
@@ -1646,7 +1646,9 @@ 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.

stdlib/public/Concurrency/PartialAsyncTask.swift

@@ -142,9 +142,9 @@ public struct ExecutorJob: Sendable {
     /// and it appearing as 0 for _different_ jobs may lead to misunderstanding it as
     /// being "the same 0 id job", we specifically print 0 (id not set) as nil.
     if (id > 0) {
-      return "\(Self.self)(id: \(id))"
+      return "ExecutorJob(id: \(id))"
     } else {
-      return "\(Self.self)(id: nil)"
+      return "ExecutorJob(id: nil)"
     }
   }
 }

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}}
+}