[cxx-interop] Implements CxxMutableSpan, created from an UnsafeMutableBufferPointer

include/swift/AST/KnownProtocols.def

@@ -136,6 +136,7 @@ PROTOCOL(CxxSequence)
 PROTOCOL(CxxUniqueSet)
 PROTOCOL(CxxVector)
 PROTOCOL(CxxSpan)
+PROTOCOL(CxxMutableSpan)
 PROTOCOL(UnsafeCxxInputIterator)
 PROTOCOL(UnsafeCxxMutableInputIterator)
 PROTOCOL(UnsafeCxxRandomAccessIterator)

lib/AST/ASTContext.cpp

@@ -1406,6 +1406,7 @@ ProtocolDecl *ASTContext::getProtocol(KnownProtocolKind kind) const {
   case KnownProtocolKind::CxxUniqueSet:
   case KnownProtocolKind::CxxVector:
   case KnownProtocolKind::CxxSpan:
+  case KnownProtocolKind::CxxMutableSpan:
   case KnownProtocolKind::UnsafeCxxInputIterator:
   case KnownProtocolKind::UnsafeCxxMutableInputIterator:
   case KnownProtocolKind::UnsafeCxxRandomAccessIterator:

lib/ClangImporter/ClangDerivedConformances.cpp

@@ -1164,23 +1164,22 @@ void swift::conformToCxxSpanIfNeeded(ClangImporter::Implementation &impl,
   if (!elementType || !sizeType)
     return;
 
-  auto constPointerTypeDecl =
-      lookupNestedClangTypeDecl(clangDecl, "const_pointer");
+  auto pointerTypeDecl = lookupNestedClangTypeDecl(clangDecl, "pointer");
   auto countTypeDecl = lookupNestedClangTypeDecl(clangDecl, "size_type");
 
-  if (!constPointerTypeDecl || !countTypeDecl)
+  if (!pointerTypeDecl || !countTypeDecl)
     return;
 
-  // create fake variable for constPointer (constructor arg 1)
-  auto constPointerType = clangCtx.getTypeDeclType(constPointerTypeDecl);
-  auto fakeConstPointerVarDecl = clang::VarDecl::Create(
+  // create fake variable for pointer (constructor arg 1)
+  clang::QualType pointerType = clangCtx.getTypeDeclType(pointerTypeDecl);
+  auto fakePointerVarDecl = clang::VarDecl::Create(
       clangCtx, /*DC*/ clangCtx.getTranslationUnitDecl(),
       clang::SourceLocation(), clang::SourceLocation(), /*Id*/ nullptr,
-      constPointerType, clangCtx.getTrivialTypeSourceInfo(constPointerType),
+      pointerType, clangCtx.getTrivialTypeSourceInfo(pointerType),
       clang::StorageClass::SC_None);
 
-  auto fakeConstPointer = new (clangCtx) clang::DeclRefExpr(
-      clangCtx, fakeConstPointerVarDecl, false, constPointerType,
+  auto fakePointer = new (clangCtx) clang::DeclRefExpr(
+      clangCtx, fakePointerVarDecl, false, pointerType,
       clang::ExprValueKind::VK_LValue, clang::SourceLocation());
 
   // create fake variable for count (constructor arg 2)
@@ -1197,8 +1196,7 @@ void swift::conformToCxxSpanIfNeeded(ClangImporter::Implementation &impl,
 
   // Use clangSema.BuildCxxTypeConstructExpr to create a CXXTypeConstructExpr,
   // passing constPointer and count
-  SmallVector<clang::Expr *, 2> constructExprArgs = {fakeConstPointer,
-                                                     fakeCount};
+  SmallVector<clang::Expr *, 2> constructExprArgs = {fakePointer, fakeCount};
 
   auto clangDeclTyInfo = clangCtx.getTrivialTypeSourceInfo(
       clang::QualType(clangDecl->getTypeForDecl(), 0));
@@ -1226,5 +1224,10 @@ void swift::conformToCxxSpanIfNeeded(ClangImporter::Implementation &impl,
                                elementType->getUnderlyingType());
   impl.addSynthesizedTypealias(decl, ctx.getIdentifier("Size"),
                                sizeType->getUnderlyingType());
-  impl.addSynthesizedProtocolAttrs(decl, {KnownProtocolKind::CxxSpan});
+
+  if (pointerType->getPointeeType().isConstQualified()) {
+    impl.addSynthesizedProtocolAttrs(decl, {KnownProtocolKind::CxxSpan});
+  } else {
+    impl.addSynthesizedProtocolAttrs(decl, {KnownProtocolKind::CxxMutableSpan});
+  }
 }

lib/IRGen/GenMeta.cpp

@@ -6878,6 +6878,7 @@ SpecialProtocol irgen::getSpecialProtocolID(ProtocolDecl *P) {
   case KnownProtocolKind::CxxUniqueSet:
   case KnownProtocolKind::CxxVector:
   case KnownProtocolKind::CxxSpan:
+  case KnownProtocolKind::CxxMutableSpan:
   case KnownProtocolKind::UnsafeCxxInputIterator:
   case KnownProtocolKind::UnsafeCxxMutableInputIterator:
   case KnownProtocolKind::UnsafeCxxRandomAccessIterator:

stdlib/public/Cxx/CxxSpan.swift

@@ -29,4 +29,29 @@ extension CxxSpan {
                   "UnsafeBufferPointer should not point to nil")
     self.init(unsafeBufferPointer.baseAddress!, Size(unsafeBufferPointer.count))
   }
+
+  @inlinable
+  public init(_ unsafeMutableBufferPointer: UnsafeMutableBufferPointer<Element>) {
+    precondition(unsafeMutableBufferPointer.baseAddress != nil, 
+                  "UnsafeMutableBufferPointer should not point to nil")
+    self.init(unsafeMutableBufferPointer.baseAddress!, Size(unsafeMutableBufferPointer.count))
+  }
+}
+
+public protocol CxxMutableSpan<Element> {
+  associatedtype Element
+  associatedtype Size: BinaryInteger
+
+  init()
+  init(_ unsafeMutablePointer : UnsafeMutablePointer<Element>, _ count: Size)
+}
+
+extension CxxMutableSpan {
+  /// Creates a C++ span from a Swift UnsafeMutableBufferPointer
+  @inlinable
+  public init(_ unsafeMutableBufferPointer: UnsafeMutableBufferPointer<Element>) {
+    precondition(unsafeMutableBufferPointer.baseAddress != nil, 
+                  "UnsafeMutableBufferPointer should not point to nil")
+    self.init(unsafeMutableBufferPointer.baseAddress!, Size(unsafeMutableBufferPointer.count))
+  }
 }

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

@@ -5,24 +5,51 @@
 #include <string>
 #include <span>
 
-using Span = std::span<const int>;
-using SpanOfString = std::span<const std::string>;
+using ConstSpan = std::span<const int>;
+using Span = std::span<int>;
+using ConstSpanOfString = std::span<const std::string>;
+using SpanOfString = std::span<std::string>;
 
 static int iarray[]{1, 2, 3};
 static std::string sarray[]{"", "ab", "abc"};
+static ConstSpan icspan = {iarray};
 static Span ispan = {iarray};
+static ConstSpanOfString scspan = {sarray};
 static SpanOfString sspan = {sarray};
 
 struct SpanBox {
-  std::span<const int> ispan;
-  std::span<const std::string> sspan;
+  ConstSpan icspan;
+  Span ispan;
+  ConstSpanOfString scspan;
+  SpanOfString sspan;
 };
 
-inline Span initSpan() { 
+class CppApi {
+public:
+  ConstSpan getConstSpan();
+  Span getSpan();
+};
+
+ConstSpan CppApi::getConstSpan() {
+  ConstSpan sp{new int[2], 2};
+  return sp;
+}
+
+Span CppApi::getSpan() {
+  Span sp{new int[2], 2};
+  return sp;
+}
+
+inline ConstSpan initConstSpan() {
   const int a[]{1, 2, 3};
+  return ConstSpan(a);
+}
+
+inline Span initSpan() {
+  int a[]{1, 2, 3};
   return Span(a);
 }
 
-inline struct SpanBox getStructSpanBox() { return {iarray, sarray}; }
+inline struct SpanBox getStructSpanBox() { return {iarray, iarray, sarray, sarray}; }
 
 #endif // TEST_INTEROP_CXX_STDLIB_INPUTS_STD_SPAN_H