[cxx-interop] Make automatic conformances work with the bridging header

For C++ types that are defined in the bridging header, or are `#include`-d from the bridging header, we did not generate the automatic conformances to `CxxSequence`, `CxxRandomAccessCollection` protocols.

To check whether we should try to conform a C++ type to those protocols, the compiler checks for the presence of `requires cplusplus` in the module declaration in a modulemap file. This check is there to prevent us from accidentally pulling in `Cxx`/`CxxStdlib` modules when a client is importing a C library.

This change makes sure those conformances are generated.

rdar://121927459

Author: egorzhdan

lib/ClangImporter/ImportDecl.cpp

@@ -2808,7 +2808,7 @@ namespace {
       // If this module is declared as a C++ module, try to synthesize
       // conformances to Swift protocols from the Cxx module.
       auto clangModule = Impl.getClangOwningModule(result->getClangNode());
-      if (clangModule && requiresCPlusPlus(clangModule)) {
+      if (!clangModule || requiresCPlusPlus(clangModule)) {
         if (auto nominalDecl = dyn_cast<NominalTypeDecl>(result)) {
           conformToCxxIteratorIfNeeded(Impl, nominalDecl, decl);
           conformToCxxSequenceIfNeeded(Impl, nominalDecl, decl);

test/Interop/Cxx/stdlib/Inputs/std-vector.h

@@ -17,4 +17,9 @@ class VectorSubclass: public Vector {
 public:
 };
 
+class VectorOfStringSubclass : public std::vector<std::string> {
+public:
+  using std::vector<std::string>::vector;
+};
+
 #endif // TEST_INTEROP_CXX_STDLIB_INPUTS_STD_VECTOR_H

test/Interop/Cxx/stdlib/use-std-vector.swift

@@ -1,12 +1,21 @@
 // RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop)
 // RUN: %target-run-simple-swift(-I %S/Inputs -cxx-interoperability-mode=upcoming-swift)
+
+// Also test this with a bridging header instead of the StdVector module.
+// RUN: %empty-directory(%t2)
+// RUN: cp %S/Inputs/std-vector.h %t2/std-vector-bridging-header.h
+// RUN: %target-run-simple-swift(-D BRIDGING_HEADER -import-objc-header %t2/std-vector-bridging-header.h -Xfrontend -enable-experimental-cxx-interop)
+// RUN: %target-run-simple-swift(-D BRIDGING_HEADER -import-objc-header %t2/std-vector-bridging-header.h -cxx-interoperability-mode=upcoming-swift)
+
 // FIXME: also run in C++20 mode when conformance works properly on UBI platform (rdar://109366764):
 // %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop -Xcc -std=gnu++20)
 //
 // REQUIRES: executable_test
 
 import StdlibUnittest
+#if !BRIDGING_HEADER
 import StdVector
+#endif
 import CxxStdlib
 
 var StdVectorTestSuite = TestSuite("StdVector")
@@ -132,4 +141,16 @@ StdVectorTestSuite.test("VectorOfInt subclass for loop") {
     expectEqual(count, 2)
 }
 
+StdVectorTestSuite.test("VectorOfString subclass for loop") {
+    var v = VectorOfStringSubclass()
+    v.push_back(std.string("abc"))
+
+    var count: CInt = 0
+    for e in v {
+        expectEqual(std.string("abc"), e)
+        count += 1
+    }
+    expectEqual(count, 1)
+}
+
 runAllTests()