[cxx-interop] Don't add incomplete records to lookup table.

Author: zoecarver

lib/ClangImporter/SwiftLookupTable.cpp

@@ -1869,6 +1869,30 @@ void importer::addEntryToLookupTable(SwiftLookupTable &table,
   if (shouldSuppressDeclImport(named))
     return;
 
+  // Leave incomplete struct/enum/union types out of the table; Swift only
+  // handles pointers to them.
+  // FIXME: At some point we probably want to be importing incomplete types,
+  // so that pointers to different incomplete types themselves have distinct
+  // types. At that time it will be necessary to make the decision of whether
+  // or not to import an incomplete type declaration based on whether it's
+  // actually the struct backing a CF type:
+  //
+  //    typedef struct CGColor *CGColorRef;
+  //
+  // The best way to do this is probably to change CFDatabase.def to include
+  // struct names when relevant, not just pointer names. That way we can check
+  // both CFDatabase.def and the objc_bridge attribute and cover all our bases.
+  if (auto *tagDecl = dyn_cast<clang::TagDecl>(named)) {
+    // We add entries for ClassTemplateSpecializations that don't have
+    // definition. It's possible that the decl will be instantiated by
+    // SwiftDeclConverter later on. We cannot force instantiating
+    // ClassTemplateSPecializations here because we're currently writing the
+    // AST, so we cannot modify it.
+    if (!isa<clang::ClassTemplateSpecializationDecl>(named) &&
+        !tagDecl->getDefinition()) {
+      return;
+    }
+  }
   // If we have a name to import as, add this entry to the table.
   auto currentVersion =
       ImportNameVersion::fromOptions(nameImporter.getLangOpts());

test/Interop/Cxx/class/invalid-class-errors.swift

@@ -9,8 +9,6 @@ module Test {
 }
 
 //--- Inputs/test.h
-struct X;
-
 struct A {
         A(const A&) = delete;
 };
@@ -23,9 +21,6 @@ struct __attribute__((swift_attr("import_unsafe"))) B {
 
 import Test
 
-// CHECK: note: record 'X' is not defined (incomplete)
-public func test(x: X) { }
-
 // CHECK: note: record 'A' is not automatically importable: does not have a copy constructor or destructor. Refer to the C++ Interop User Manual to classify this type.
 public func test(x: A) { }
 // CHECK: note: record 'B' is not automatically importable: does not have a copy constructor or destructor. Refer to the C++ Interop User Manual to classify this type.