[interop][SwiftToCxx] add a Swift stdlib overlay header

lib/PrintAsClang/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(datafiles
     _SwiftCxxInteroperability.h
+    _SwiftStdlibCxxOverlay.h
 )
 
 set(SWIFTLIB_DIR

lib/PrintAsClang/ClangSyntaxPrinter.cpp

@@ -333,3 +333,24 @@ void ClangSyntaxPrinter::printPrimaryCxxTypeName(
   // FIXME: Print class qualifiers for nested class references.
   printBaseName(type);
 }
+
+void ClangSyntaxPrinter::printIncludeForShimHeader(StringRef headerName) {
+  os << "// Look for the C++ interop support header relative to clang's "
+        "resource dir:\n";
+  os << "//  "
+        "'<toolchain>/usr/lib/clang/<version>/include/../../../swift/"
+        "swiftToCxx'.\n";
+  os << "#if __has_include(<../../../swift/swiftToCxx/" << headerName << ">)\n";
+  os << "#include <../../../swift/swiftToCxx/" << headerName << ">\n";
+  os << "#elif __has_include(<../../../../lib/swift/swiftToCxx/" << headerName
+     << ">)\n";
+  os << "//  "
+        "'<toolchain>/usr/local/lib/clang/<version>/include/../../../../lib/"
+        "swift/swiftToCxx'.\n";
+  os << "#include <../../../../lib/swift/swiftToCxx/" << headerName << ">\n";
+  os << "// Alternatively, allow user to find the header using additional "
+        "include path into '<toolchain>/lib/swift'.\n";
+  os << "#elif __has_include(<swiftToCxx/" << headerName << ">)\n";
+  os << "#include <swiftToCxx/" << headerName << ">\n";
+  os << "#endif\n";
+}

lib/PrintAsClang/ClangSyntaxPrinter.h

@@ -184,6 +184,9 @@ class ClangSyntaxPrinter {
   void printPrimaryCxxTypeName(const NominalTypeDecl *type,
                                const ModuleDecl *moduleContext);
 
+  // Print the #include sequence for the specified C++ interop shim header.
+  void printIncludeForShimHeader(StringRef headerName);
+
 protected:
   raw_ostream &os;
 };

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -759,6 +759,11 @@ EmittedClangHeaderDependencyInfo swift::printModuleContentsAsCxx(
                       OutputLanguageMode::Cxx);
   writer.write();
   info.dependsOnStandardLibrary = writer.isStdlibRequired();
+  if (M.isStdlibModule()) {
+    // Embed an overlay for the standard library.
+    ClangSyntaxPrinter(moduleOS).printIncludeForShimHeader(
+        "_SwiftStdlibCxxOverlay.h");
+  }
 
   os << "#ifndef SWIFT_PRINTED_CORE\n";
   os << "#define SWIFT_PRINTED_CORE\n";

lib/PrintAsClang/PrintAsClang.cpp

@@ -12,6 +12,7 @@
 
 #include "swift/PrintAsClang/PrintAsClang.h"
 
+#include "ClangSyntaxPrinter.h"
 #include "ModuleContentsWriter.h"
 #include "SwiftToClangInteropContext.h"
 
@@ -107,17 +108,8 @@ static void writePrologue(raw_ostream &out, ASTContext &ctx,
         out << "#include <stdlib.h>\n";
         out << "#include <new>\n";
         out << "#include <type_traits>\n";
-        out << "// Look for the C++ interop support header relative to clang's resource dir:\n";
-        out << "//  '<toolchain>/usr/lib/clang/<version>/include/../../../swift/swiftToCxx'.\n";
-        out << "#if __has_include(<../../../swift/swiftToCxx/_SwiftCxxInteroperability.h>)\n";
-        out << "#include <../../../swift/swiftToCxx/_SwiftCxxInteroperability.h>\n";
-        out << "#elif __has_include(<../../../../lib/swift/swiftToCxx/_SwiftCxxInteroperability.h>)\n";
-        out << "//  '<toolchain>/usr/local/lib/clang/<version>/include/../../../../lib/swift/swiftToCxx'.\n";
-        out << "#include <../../../../lib/swift/swiftToCxx/_SwiftCxxInteroperability.h>\n";
-        out << "// Alternatively, allow user to find the header using additional include path into '<toolchain>/lib/swift'.\n";
-        out << "#elif __has_include(<swiftToCxx/_SwiftCxxInteroperability.h>)\n";
-        out << "#include <swiftToCxx/_SwiftCxxInteroperability.h>\n";
-        out << "#endif\n";
+        ClangSyntaxPrinter(out).printIncludeForShimHeader(
+            "_SwiftCxxInteroperability.h");
       },
       [&] {
         out << "#include <stdint.h>\n"

lib/PrintAsClang/_SwiftStdlibCxxOverlay.h

@@ -0,0 +1,72 @@
+//===--- _SwiftStlibCxxOverlay.h - Additions for Stdlib ---------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __cplusplus
+#error "no C++"
+#endif
+
+static_assert(sizeof(_impl::_impl_String) >= 0,
+              "included outside of stdlib bindings");
+
+namespace cxxOverlay {
+
+class IterationEndSentinel;
+
+/// Abstract Swift collection iterator.
+template <class Collection, class T> class CollectionIterator {
+public:
+  using Index =
+      decltype(reinterpret_cast<Collection *>(0x123)->getStartIndex());
+
+  inline CollectionIterator(const Collection &collection)
+      : collection(collection) {
+    index = collection.getStartIndex();
+    endIndex = collection.getEndIndex();
+    // FIXME: Begin read access.
+  }
+
+  inline ~CollectionIterator() {
+    // FIXME: End read access.
+  }
+
+  inline T operator*() const { return collection[index]; }
+  inline void operator++() {
+    ++index;
+    // FIXME: assert(index <= endIndex); // No need to go past the end.
+  }
+
+  inline bool operator!=(const IterationEndSentinel &) const {
+    return index != endIndex;
+  }
+
+private:
+  Index index, endIndex;
+  const Collection &collection;
+};
+
+class IterationEndSentinel {};
+
+template <class T> using ArrayIterator = CollectionIterator<Array<T>, T>;
+
+} // namespace cxxOverlay
+
+// FIXME: This should apply to more than the Array type.
+template <class T>
+inline cxxOverlay::ArrayIterator<T> begin(const Array<T> &array
+                                          [[clang::lifetimebound]]) {
+  return cxxOverlay::ArrayIterator<T>(array);
+}
+
+template <class T>
+inline cxxOverlay::IterationEndSentinel end(const Array<T> &) {
+  return {};
+}

test/Interop/SwiftToCxx/stdlib/array/array-execution.cpp

@@ -37,6 +37,12 @@ int main() {
   {
     Array<int> val = UseArray::createArray(2);
     UseArray::printArray(UseArray::passthroughArray(val));
+    int count = 2;
+    for (int x: val) {
+      assert(x == 2);
+      --count;
+    }
+    assert(count == 0);
   }
 // CHECK: [2, 2]
   {

test/Interop/SwiftToCxx/stdlib/swift-stdlib-in-cxx.swift

@@ -69,4 +69,14 @@
 // CHECK-NEXT:  #endif
 // CHECK-NEXT: private:
 
+// CHECK: #if __has_include(<../../../swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>)
+// CHECK-NEXT: #include <../../../swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>
+// CHECK-NEXT: #elif __has_include(<../../../../lib/swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>)
+// CHECK-NEXT: //  '<toolchain>/usr/local/lib/clang/<version>/include/../../../../lib/swift/swiftToCxx'.
+// CHECK-NEXT: #include <../../../../lib/swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>
+// CHECK-NEXT: // Alternatively, allow user to find the header using additional include path into '<toolchain>/lib/swift'.
+// CHECK-NEXT: #elif __has_include(<swiftToCxx/_SwiftStdlibCxxOverlay.h>)
+// CHECK-NEXT: #include <swiftToCxx/_SwiftStdlibCxxOverlay.h>
+// CHECK-NEXT: #endif
+
 // CHECK: } // namespace Swift