Enforce that FileUnit + LoadedFile have trivial destructors

We already do this for other ASTContext-allocated types (see
Decl.cpp). This will prevent the sort of mistakes in the previous two
commits.

Note that if any particular subclass of FileUnit wants to have its
destructor run, it can opt into that manually using
ASTContext::addDestructorCleanup. SourceFile and BuiltinUnit both do
this. But we generally don't /want/ to do this if we can avoid it
because it adds to compiler teardown time.

Author: jrose-apple

include/swift/AST/Module.h

@@ -644,7 +644,10 @@ static inline unsigned alignOfFileUnit();
 /// FileUnit is an abstract base class; its subclasses represent different
 /// sorts of containers that can each provide a set of decls, e.g. a source
 /// file. A module can contain several file-units.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnon-virtual-dtor"
 class FileUnit : public DeclContext {
+#pragma clang diagnostic pop
   virtual void anchor();
 
   // FIXME: Stick this in a PointerIntPair.
@@ -655,8 +658,6 @@ class FileUnit : public DeclContext {
     : DeclContext(DeclContextKind::FileUnit, &M), Kind(kind) {
   }
 
-  virtual ~FileUnit() = default;
-
 public:
   FileUnitKind getKind() const {
     return Kind;
@@ -891,13 +892,7 @@ class FileUnit : public DeclContext {
   // Make placement new and vanilla new/delete illegal for FileUnits.
   void *operator new(size_t Bytes) throw() = delete;
   void *operator new(size_t Bytes, void *Mem) throw() = delete;
-
-protected:
-  // Unfortunately we can't remove this altogether because the virtual
-  // destructor requires it to be accessible.
-  void operator delete(void *Data) throw() {
-    llvm_unreachable("Don't use operator delete on a SourceFile");
-  }
+  void operator delete(void *Data) throw() = delete;
 
 public:
   // Only allow allocation of FileUnits using the allocator in ASTContext
@@ -1380,9 +1375,11 @@ class BuiltinUnit final : public FileUnit {
 };
 
 /// Represents an externally-loaded file of some kind.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnon-virtual-dtor"
 class LoadedFile : public FileUnit {
+#pragma clang diagnostic pop
 protected:
-  ~LoadedFile() = default;
   LoadedFile(FileUnitKind Kind, ModuleDecl &M) noexcept
     : FileUnit(Kind, M) {
     assert(classof(this) && "invalid kind");

include/swift/ClangImporter/ClangModule.h

@@ -39,8 +39,6 @@ class ClangModuleUnit final : public LoadedFile {
   /// The metadata of the underlying Clang module.
   clang::ExternalASTSource::ASTSourceDescriptor ASTSourceDescriptor;
 
-  ~ClangModuleUnit() = default;
-
 public:
   /// True if the given Module contains an imported Clang module unit.
   static bool hasClangModule(ModuleDecl *M);

include/swift/Serialization/SerializedModuleLoader.h

@@ -253,8 +253,6 @@ class SerializedASTFile final : public LoadedFile {
 
   bool IsSIB;
 
-  ~SerializedASTFile() = default;
-
   SerializedASTFile(ModuleDecl &M, ModuleFile &file, bool isSIB = false)
     : LoadedFile(FileUnitKind::SerializedAST, M), File(file), IsSIB(isSIB) {}
 

lib/AST/Module.cpp

@@ -55,6 +55,11 @@
 
 using namespace swift;
 
+static_assert(IsTriviallyDestructible<FileUnit>::value,
+              "FileUnits are BumpPtrAllocated; the d'tor may not be called");
+static_assert(IsTriviallyDestructible<LoadedFile>::value,
+              "LoadedFiles are BumpPtrAllocated; the d'tor may not be called");
+
 //===----------------------------------------------------------------------===//
 // Builtin Module Name lookup
 //===----------------------------------------------------------------------===//

lib/ClangImporter/ClangImporter.cpp

@@ -3176,6 +3176,9 @@ void ClangImporter::verifyAllModules() {
 // ClangModule Implementation
 //===----------------------------------------------------------------------===//
 
+static_assert(IsTriviallyDestructible<ClangModuleUnit>::value,
+              "ClangModuleUnits are BumpPtrAllocated; the d'tor is not called");
+
 ClangModuleUnit::ClangModuleUnit(ModuleDecl &M,
                                  ClangImporter::Implementation &owner,
                                  const clang::Module *clangModule)

lib/ClangImporter/DWARFImporter.cpp

@@ -20,7 +20,6 @@ void DWARFImporterDelegate::anchor() {}
 /// Represents a Clang module that was "imported" from debug info. Since all the
 /// loading of types is done on demand, this class is effectively empty.
 class DWARFModuleUnit final : public LoadedFile {
-  ~DWARFModuleUnit() = default;
   ClangImporter::Implementation &Owner;
 
 public:
@@ -96,6 +95,9 @@ class DWARFModuleUnit final : public LoadedFile {
   }
 };
 
+static_assert(IsTriviallyDestructible<DWARFModuleUnit>::value,
+              "DWARFModuleUnits are BumpPtrAllocated; the d'tor is not called");
+
 ModuleDecl *ClangImporter::Implementation::loadModuleDWARF(
     SourceLoc importLoc, ArrayRef<std::pair<Identifier, SourceLoc>> path) {
   // There's no importing from debug info if no importer is installed.

lib/Serialization/ModuleFile.cpp

@@ -38,6 +38,9 @@ using namespace swift::serialization;
 using namespace llvm::support;
 using llvm::Expected;
 
+static_assert(IsTriviallyDestructible<SerializedASTFile>::value,
+              "SerializedASTFiles are BumpPtrAllocated; d'tors are not called");
+
 static bool checkModuleSignature(llvm::BitstreamCursor &cursor,
                                  ArrayRef<unsigned char> signature) {
   for (unsigned char byte : signature)