Merge pull request #64295 from jckarter/noncopyable-hide-field-types

Don't let reflection handle noncopyable types yet.

Author: jckarter

lib/IRGen/GenReflection.cpp

@@ -264,6 +264,54 @@ getTypeRefByFunction(IRGenModule &IGM,
           ? genericEnv->mapTypeIntoContext(t)->getCanonicalType()
           : t;
 
+        // If a type is noncopyable, lie about the resolved type unless the
+        // runtime is sufficiently aware of noncopyable types.
+        if (substT->isPureMoveOnly()) {
+          // Darwin-based platforms have ABI stability, and we want binaries
+          // that use noncopyable types nongenerically today to be forward
+          // compatible with a future OS runtime that supports noncopyable
+          // generics. On other platforms, a new Swift compiler and runtime
+          // require recompilation anyway, so this dance is unnecessary, and
+          // for now, we can unconditionally lie.
+          bool useForwardCompatibility =
+            IGM.Context.LangOpts.Target.isOSDarwin();
+          
+          llvm::Instruction *br = nullptr;
+          llvm::BasicBlock *supportedBB = nullptr;
+          if (useForwardCompatibility) {
+            auto runtimeSupportsNoncopyableTypesSymbol
+              = IGM.Module.getOrInsertGlobal("swift_runtimeSupportsNoncopyableTypes",
+                                             IGM.Int8Ty);
+            cast<llvm::GlobalVariable>(runtimeSupportsNoncopyableTypesSymbol)
+              ->setLinkage(llvm::GlobalValue::ExternalWeakLinkage);
+              
+            auto runtimeSupportsNoncopyableTypes
+              = IGF.Builder.CreateIsNotNull(runtimeSupportsNoncopyableTypesSymbol,
+                                            "supports.noncopyable");
+            supportedBB = IGF.createBasicBlock("does.support.noncopyable");
+            auto unsupportedBB = IGF.createBasicBlock("does.not.support.noncopyable");
+            br = IGF.Builder.CreateCondBr(runtimeSupportsNoncopyableTypes,
+                                     supportedBB,
+                                     unsupportedBB);
+                                     
+            IGF.Builder.emitBlock(unsupportedBB);
+          }
+          
+          // If the runtime does not yet support noncopyable types, lie that the
+          // field is an empty tuple, so the runtime doesn't try to do anything
+          // with the actual value.
+          auto phonyRet = IGF.emitTypeMetadataRef(IGM.Context.TheEmptyTupleType);
+          IGF.Builder.CreateRet(phonyRet);
+
+          if (!useForwardCompatibility) {
+            goto done_building_function;
+          }
+          
+          // Emit the type metadata normally otherwise.
+          IGF.Builder.SetInsertPoint(br);
+          IGF.Builder.emitBlock(supportedBB);
+        }
+
         bindFromGenericRequirementsBuffer(
             IGF, requirements,
             Address(bindingsBufPtr, IGM.Int8Ty, IGM.getPointerAlignment()),
@@ -276,6 +324,7 @@ getTypeRefByFunction(IRGenModule &IGM,
         auto ret = IGF.emitTypeMetadataRef(substT);
         IGF.Builder.CreateRet(ret);
       }
+    done_building_function:
       // Form the mangled name with its relative reference.
       auto S = B.beginStruct();
       S.setPacked(true);
@@ -315,6 +364,21 @@ getTypeRefImpl(IRGenModule &IGM,
   case MangledTypeRefRole::FlatUnique:
     useFlatUnique = true;
     break;
+    
+  case MangledTypeRefRole::FieldMetadata:
+    // We want to keep fields of noncopyable type from being exposed to
+    // in-process runtime reflection libraries in older Swift runtimes, since
+    // they more than likely assume they can copy field values, and the language
+    // support for noncopyable types as dynamic or generic types isn't yet
+    // implemented as of the writing of this comment. If the type is
+    // noncopyable, use a function to emit the type ref which will look for a
+    // signal from future runtimes whether they support noncopyable types before
+    // exposing their metadata to them.
+    if (type->isPureMoveOnly()) {
+      IGM.IRGen.noteUseOfTypeMetadata(type);
+      return getTypeRefByFunction(IGM, sig, type);
+    }
+    LLVM_FALLTHROUGH;
 
   case MangledTypeRefRole::DefaultAssociatedTypeWitness:
   case MangledTypeRefRole::Metadata:
@@ -724,14 +788,14 @@ class FieldTypeMetadataBuilder : public ReflectionMetadataBuilder {
       if (type->isForeignReferenceType()) {
         auto opaqueType = type->getASTContext().getOpaquePointerType();
         // The standard library's Mirror demangles metadata from field
-        // descriptors, so use MangledTypeRefRole::Metadata to ensure
+        // descriptors, so use MangledTypeRefRole::FieldMetadata to ensure
         // runtime metadata is available.
-        addTypeRef(opaqueType, genericSig, MangledTypeRefRole::Metadata);
+        addTypeRef(opaqueType, genericSig, MangledTypeRefRole::FieldMetadata);
       } else {
         // The standard library's Mirror demangles metadata from field
-        // descriptors, so use MangledTypeRefRole::Metadata to ensure
+        // descriptors, so use MangledTypeRefRole::FieldMetadata to ensure
         // runtime metadata is available.
-        addTypeRef(type, genericSig, MangledTypeRefRole::Metadata);
+        addTypeRef(type, genericSig, MangledTypeRefRole::FieldMetadata);
       }
     }
 

lib/IRGen/IRGenMangler.cpp

@@ -300,6 +300,7 @@ mangleSymbolNameForSymbolicMangling(const SymbolicMangling &mangling,
     prefix = "default assoc type ";
     break;
 
+  case MangledTypeRefRole::FieldMetadata:
   case MangledTypeRefRole::Metadata:
   case MangledTypeRefRole::Reflection:
     prefix = "symbolic ";

lib/IRGen/IRGenModule.h

@@ -575,6 +575,10 @@ class TypeEntityReference {
 
 /// Describes the role of a mangled type reference string.
 enum class MangledTypeRefRole {
+  /// The mangled type reference is used for field metadata, which is used
+  /// by both in-process and out-of-process reflection, so still requires
+  /// referenced types' metadata to be fully emitted.
+  FieldMetadata,
   /// The mangled type reference is used for normal metadata.
   Metadata,
   /// The mangled type reference is used for reflection metadata.

lib/IRGen/MetadataRequest.cpp

@@ -377,6 +377,7 @@ llvm::Constant *IRGenModule::getAddrOfStringForTypeRef(
 
   case MangledTypeRefRole::Metadata:
   case MangledTypeRefRole::Reflection:
+  case MangledTypeRefRole::FieldMetadata:
     break;
   }
 

stdlib/public/runtime/Metadata.cpp

@@ -75,6 +75,19 @@ extern "C" void _objc_setClassCopyFixupHandler(void (* _Nonnull newFixupHandler)
 using namespace swift;
 using namespace metadataimpl;
 
+#if defined(__APPLE__)
+// Binaries using noncopyable types check the address of the symbol
+// `swift_runtimeSupportsNoncopyableTypes` before exposing any noncopyable
+// type metadata through in-process reflection, to prevent existing code
+// that expects all types to be copyable from crashing or causing bad behavior
+// by copying noncopyable types. The runtime does not yet support noncopyable
+// types, so we explicitly define this symbol to be zero for now. Binaries
+// weak-import this symbol so they will resolve it to a zero address on older
+// runtimes as well.
+__asm__("  .globl _swift_runtimeSupportsNoncopyableTypes\n");
+__asm__(".set _swift_runtimeSupportsNoncopyableTypes, 0\n");
+#endif
+
 // GenericParamDescriptor is a single byte, so while it's difficult to
 // imagine needing even a quarter this many generic params, there's very
 // little harm in doing it.

test/Interpreter/moveonly_field_in_class_reflection.swift

@@ -0,0 +1,44 @@
+// RUN: %target-run-simple-swift(-Xfrontend -enable-experimental-move-only)
+// REQUIRES: executable_test
+
+// Verify that iterating through the fields of an object whose class has
+// a move-only field does not trap from trying to reflect and copy those
+// move-only fields.
+
+@_moveOnly
+public struct MO {
+    var x: Int8 = 0
+    var y: Int8 = 0
+    var z: Int8 = 0
+
+    deinit { print("destroyed MO") }
+}
+
+public class MOHaver {
+    var s: String = "hello"
+    var mo: MO = MO()
+    var b: Int8 = 42
+    var c: Any.Type = MOHaver.self
+}
+
+// CHECK-LABEL: doing nongeneric
+print("doing nongeneric")
+do {
+    let k = MOHaver()
+
+    let mirror = Mirror(reflecting: k)
+    // CHECK-NEXT: s: hello
+    // Whether this actually prints the value of `k.mo` or not is irrelevant
+    // to the test; we care that attempting to reflect the field does not trap
+    // copying a noncopyable field.
+    // CHECK-NEXT: mo:
+    // CHECK-NEXT: b: 42
+    // CHECK-NEXT: c: {{.*}}.MOHaver
+    for c in mirror.children {
+        print("\(c.label!): \(c.value)")
+    }
+    // CHECK-NEXT: destroyed MO
+}
+// CHECK-NEXT: done with nongeneric
+print("done with nongeneric")
+