[Strict memory safety] Diagnose unsafe types in the superclass of a class

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -8162,6 +8162,10 @@ NOTE(decl_storage_mark_safe,none,
       "add '@safe' if this type encapsulates the unsafe storage in "
       "a safe interface", ())
 
+GROUPED_WARNING(unsafe_superclass,Unsafe,none,
+     "%kindbase0 has superclass involving unsafe type %1", 
+     (const ValueDecl *, Type))
+
 GROUPED_WARNING(conformance_involves_unsafe,Unsafe,none,
      "conformance of %0 to %kind1 involves unsafe code; use '@unsafe' to "
      "indicate that the conformance is not memory-safe",

lib/Sema/TypeCheckUnsafe.cpp

@@ -392,6 +392,27 @@ void swift::checkUnsafeStorage(NominalTypeDecl *nominal) {
     break;
   }
 
+  // Check whether the superclass is unsafe. If so, the only thing one can
+  // do is mark the class unsafe.
+  ASTContext &ctx = nominal->getASTContext();
+  if (auto classDecl = dyn_cast<ClassDecl>(nominal)) {
+    if (Type superclassType = classDecl->getSuperclass()) {
+      superclassType = classDecl->mapTypeIntoContext(superclassType);
+      bool diagnosed = false;
+      diagnoseUnsafeType(ctx, classDecl->getLoc(), superclassType, [&](Type type) {
+        if (diagnosed)
+          return;
+
+        classDecl->diagnose(diag::unsafe_superclass, classDecl, type)
+          .fixItInsert(classDecl->getAttributeInsertionLoc(false), "@unsafe ");
+        diagnosed = true;
+      });
+
+      if (diagnosed)
+        return;
+    }
+  }
+
   // Visitor that finds unsafe storage.
   class UnsafeStorageVisitor: public StorageVisitor {
     ASTContext &ctx;
@@ -421,7 +442,6 @@ void swift::checkUnsafeStorage(NominalTypeDecl *nominal) {
   };
 
   // Look for any unsafe storage in this nominal type.
-  ASTContext &ctx = nominal->getASTContext();
   SmallVector<UnsafeUse, 4> unsafeUses;
   UnsafeStorageVisitor(ctx, unsafeUses).visit(nominal, nominal->getDeclContext());
 

test/Unsafe/unsafe.swift

@@ -120,7 +120,7 @@ class ExclusivityChecking {
   func f() { }
 };
 
-// TODO: diagnose the need for @unsafe when there's an unsafe superclass.
+// expected-warning@+1{{class 'UnsafeSub' has superclass involving unsafe type 'UnsafeSuper' [Unsafe]}}{{1-1=@unsafe }}
 class UnsafeSub: UnsafeSuper { }
 
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