[Strict memory safety] Nested types are safe/unsafe independent of their enclosing type

When determining whether a nested type is safe, don't consider whether
its enclosing type is safe. They're independent.

(cherry picked from commit 8ec52c8)

Author: DougGregor

lib/AST/ASTContext.cpp

@@ -4190,6 +4190,55 @@ void UnboundGenericType::Profile(llvm::FoldingSetNodeID &ID,
   ID.AddPointer(Parent.getPointer());
 }
 
+/// The safety of a parent type does not have an impact on a nested type within
+/// it. This produces the recursive properties of a given type that should
+/// be propagated to a nested type, which won't include any "IsUnsafe" bit
+/// determined based on the declaration itself.
+static RecursiveTypeProperties getRecursivePropertiesAsParent(Type type) {
+  if (!type)
+    return RecursiveTypeProperties();
+
+  // We only need to do anything interesting at all for unsafe types.
+  auto properties = type->getRecursiveProperties();
+  if (!properties.isUnsafe())
+    return properties;
+
+  if (auto nominal = type->getAnyNominal()) {
+    // If the nominal wasn't itself unsafe, then we got the unsafety from
+    // something else (e.g., a generic argument), so it won't change.
+    if (nominal->getExplicitSafety() != ExplicitSafety::Unsafe)
+      return properties;
+  }
+
+  // Drop the "unsafe" bit. We have to recompute it without considering the
+  // enclosing nominal type.
+  properties = RecursiveTypeProperties(
+      properties.getBits() & ~static_cast<unsigned>(RecursiveTypeProperties::IsUnsafe));
+
+  // Check generic arguments of parent types.
+  while (type) {
+    // Merge from the generic arguments.
+    if (auto boundGeneric = type->getAs<BoundGenericType>()) {
+      for (auto genericArg : boundGeneric->getGenericArgs())
+        properties |= genericArg->getRecursiveProperties();
+    }
+
+    if (auto nominalOrBound = type->getAs<NominalOrBoundGenericNominalType>()) {
+      type = nominalOrBound->getParent();
+      continue;
+    }
+
+    if (auto unbound = type->getAs<UnboundGenericType>()) {
+      type = unbound->getParent();
+      continue;
+    }
+
+    break;
+  };
+
+  return properties;
+}
+
 UnboundGenericType *UnboundGenericType::
 get(GenericTypeDecl *TheDecl, Type Parent, const ASTContext &C) {
   llvm::FoldingSetNodeID ID;
@@ -4198,7 +4247,7 @@ get(GenericTypeDecl *TheDecl, Type Parent, const ASTContext &C) {
   RecursiveTypeProperties properties;
   if (TheDecl->getExplicitSafety() == ExplicitSafety::Unsafe)
     properties |= RecursiveTypeProperties::IsUnsafe;
-  if (Parent) properties |= Parent->getRecursiveProperties();
+  properties |= getRecursivePropertiesAsParent(Parent);
 
   auto arena = getArena(properties);
 
@@ -4252,7 +4301,7 @@ BoundGenericType *BoundGenericType::get(NominalTypeDecl *TheDecl,
   RecursiveTypeProperties properties;
   if (TheDecl->getExplicitSafety() == ExplicitSafety::Unsafe)
     properties |= RecursiveTypeProperties::IsUnsafe;
-  if (Parent) properties |= Parent->getRecursiveProperties();
+  properties |= getRecursivePropertiesAsParent(Parent);
   for (Type Arg : GenericArgs) {
     properties |= Arg->getRecursiveProperties();
   }
@@ -4335,7 +4384,7 @@ EnumType *EnumType::get(EnumDecl *D, Type Parent, const ASTContext &C) {
   RecursiveTypeProperties properties;
   if (D->getExplicitSafety() == ExplicitSafety::Unsafe)
     properties |= RecursiveTypeProperties::IsUnsafe;
-  if (Parent) properties |= Parent->getRecursiveProperties();
+  properties |= getRecursivePropertiesAsParent(Parent);
   auto arena = getArena(properties);
 
   auto *&known = C.getImpl().getArena(arena).EnumTypes[{D, Parent}];
@@ -4353,7 +4402,7 @@ StructType *StructType::get(StructDecl *D, Type Parent, const ASTContext &C) {
   RecursiveTypeProperties properties;
   if (D->getExplicitSafety() == ExplicitSafety::Unsafe)
     properties |= RecursiveTypeProperties::IsUnsafe;
-  if (Parent) properties |= Parent->getRecursiveProperties();
+  properties |= getRecursivePropertiesAsParent(Parent);
   auto arena = getArena(properties);
 
   auto *&known = C.getImpl().getArena(arena).StructTypes[{D, Parent}];
@@ -4371,7 +4420,7 @@ ClassType *ClassType::get(ClassDecl *D, Type Parent, const ASTContext &C) {
   RecursiveTypeProperties properties;
   if (D->getExplicitSafety() == ExplicitSafety::Unsafe)
     properties |= RecursiveTypeProperties::IsUnsafe;
-  if (Parent) properties |= Parent->getRecursiveProperties();
+  properties |= getRecursivePropertiesAsParent(Parent);
   auto arena = getArena(properties);
 
   auto *&known = C.getImpl().getArena(arena).ClassTypes[{D, Parent}];
@@ -5538,7 +5587,7 @@ ProtocolType *ProtocolType::get(ProtocolDecl *D, Type Parent,
   RecursiveTypeProperties properties;
   if (D->getExplicitSafety() == ExplicitSafety::Unsafe)
     properties |= RecursiveTypeProperties::IsUnsafe;
-  if (Parent) properties |= Parent->getRecursiveProperties();
+  properties |= getRecursivePropertiesAsParent(Parent);
   auto arena = getArena(properties);
 
   auto *&known = C.getImpl().getArena(arena).ProtocolTypes[{D, Parent}];

lib/Sema/TypeCheckUnsafe.cpp

@@ -330,7 +330,12 @@ bool swift::enumerateUnsafeUses(ArrayRef<ProtocolConformanceRef> conformances,
 bool swift::enumerateUnsafeUses(SubstitutionMap subs,
                                 SourceLoc loc,
                                 llvm::function_ref<bool(UnsafeUse)> fn) {
-  // FIXME: Check replacement types?
+  // Replacement types.
+  for (auto replacementType : subs.getReplacementTypes()) {
+    if (replacementType->isUnsafe() &&
+        fn(UnsafeUse::forReferenceToUnsafe(nullptr, false, replacementType, loc)))
+      return true;
+  }
 
   // Check conformances.
   if (enumerateUnsafeUses(subs.getConformances(), loc, fn))
@@ -379,24 +384,69 @@ void swift::diagnoseUnsafeType(ASTContext &ctx, SourceLoc loc, Type type,
     return;
 
   // Look for a specific @unsafe nominal type along the way.
-  auto findSpecificUnsafeType = [](Type type) {
+  class Walker : public TypeWalker {
+  public:
     Type specificType;
-    (void)type.findIf([&specificType](Type type) {
+
+    Action walkToTypePre(Type type) override {
+      if (specificType)
+        return Action::Stop;
+
+      // If this refers to a nominal type that is @unsafe, store that.
       if (auto typeDecl = type->getAnyNominal()) {
         if (typeDecl->getExplicitSafety() == ExplicitSafety::Unsafe) {
           specificType = type;
-          return false;
+          return Action::Stop;
         }
       }
 
-      return false;
-    });
-    return specificType;
+      // Do not recurse into nominal types, because we do not want to visit
+      // their "parent" types.
+      if (isa<NominalOrBoundGenericNominalType>(type.getPointer()) ||
+          isa<UnboundGenericType>(type.getPointer())) {
+        // Recurse into the generic arguments. This operation is recursive,
+        // because we also need to see the generic arguments of parent types.
+        walkGenericArguments(type);
+
+        return Action::SkipNode;
+      }
+
+      return Action::Continue;
+    }
+
+  private:
+    /// Recursively walk the generic arguments of this type and its parent
+    /// types.
+    void walkGenericArguments(Type type) {
+      if (!type)
+        return;
+
+      // Walk the generic arguments.
+      if (auto boundGeneric = type->getAs<BoundGenericType>()) {
+        for (auto genericArg : boundGeneric->getGenericArgs())
+          genericArg.walk(*this);
+      }
+
+      if (auto nominalOrBound = type->getAs<NominalOrBoundGenericNominalType>())
+        return walkGenericArguments(nominalOrBound->getParent());
+
+      if (auto unbound = type->getAs<UnboundGenericType>())
+        return walkGenericArguments(unbound->getParent());
+    }
   };
 
-  Type specificType = findSpecificUnsafeType(type);
-  if (!specificType)
-    specificType = findSpecificUnsafeType(type->getCanonicalType());
+  // Look for a canonical unsafe type.
+  Walker walker;
+  type->getCanonicalType().walk(walker);
+  Type specificType = walker.specificType;
+
+  // Look for an unsafe type in the non-canonical type, which is a better answer
+  // if we can find it.
+  walker.specificType = Type();
+  type.walk(walker);
+  if (specificType && walker.specificType &&
+      specificType->isEqual(walker.specificType))
+    specificType = walker.specificType;
 
   diagnose(specificType ? specificType : type);
 }

test/Unsafe/safe.swift

@@ -277,6 +277,15 @@ struct UnsafeContainingUnspecified {
   typealias A = Int
 
   func getA() -> A { 0 }
+
+  @safe
+  struct Y {
+    var value: Int
+  }
+
+  func f() {
+    _ = Y(value: 5)
+  }
 }