[cxx-interop] Import const T& parameters as T.

lib/ClangImporter/ImportType.cpp

@@ -1967,15 +1967,17 @@ ParameterList *ClangImporter::Implementation::importFunctionParameterList(
           cast<clang::TemplateTypeParmType>(paramTy->getPointeeType());
       swiftParamTy =
           findGenericTypeInGenericDecls(templateParamType, genericParams);
-      isInOut = true;
+      if (!paramTy->getPointeeType().isConstQualified())
+        isInOut = true;
     } else if (auto *templateParamType =
                    dyn_cast<clang::TemplateTypeParmType>(paramTy)) {
       swiftParamTy =
           findGenericTypeInGenericDecls(templateParamType, genericParams);
     } else {
       if (auto refType = dyn_cast<clang::ReferenceType>(paramTy)) {
         paramTy = refType->getPointeeType();
-        isInOut = true;
+        if (!paramTy.isConstQualified())
+          isInOut = true;
       }
       auto importedType = importType(paramTy, importKind, allowNSUIntegerAsInt,
                                      Bridgeability::Full, OptionalityOfParam);

lib/SIL/IR/SILFunctionType.cpp

@@ -1323,6 +1323,14 @@ static bool isClangTypeMoreIndirectThanSubstType(TypeConverter &TC,
 
     return true;
   }
+
+  // Pass C++ const reference types indirectly. Right now there's no way to
+  // express immutable borrowed params, so we have to have this hack.
+  // Eventually, we should just express these correctly: rdar://89647503
+  if (clangTy->isReferenceType() &&
+      clangTy->getPointeeType().isConstQualified())
+    return true;
+
   return false;
 }
 

test/Interop/Cxx/ergonomics/implicit-computed-properties-module-interface.swift

@@ -211,7 +211,7 @@
 // CHECK-NEXT:    init()
 // CHECK-NEXT:    init(value: Int32)
 // CHECK-NEXT:    mutating func getXMutating() -> UnsafePointer<Int32>
-// CHECK-NEXT:    mutating func setXMutating(_ v: inout Int32)
+// CHECK-NEXT:    mutating func setXMutating(_ v: Int32)
 // CHECK-NEXT:    var value: Int32
 // CHECK-NEXT: }
 

test/Interop/Cxx/reference/Inputs/reference.cpp

@@ -16,3 +16,7 @@ void setConstStaticIntRvalueRef(const int &&i) { staticInt = i; }
 
 auto getFuncRef() -> int (&)() { return getStaticInt; }
 auto getFuncRvalueRef() -> int (&&)() { return getStaticInt; }
+
+void takeConstRef(const int &value) {
+  staticInt = value;
+}

test/Interop/Cxx/reference/Inputs/reference.h

@@ -20,4 +20,6 @@ auto getFuncRvalueRef() -> int (&&)();
 // crashing when we have an "_Atomic" type or a reference to one.
 void dontImportAtomicRef(_Atomic(int)&) { }
 
+void takeConstRef(const int &);
+
 #endif // TEST_INTEROP_CXX_REFERENCE_INPUTS_REFERENCE_H

test/Interop/Cxx/reference/reference-irgen.swift

@@ -39,8 +39,8 @@ public func setCxxRef() {
 // CHECK: call void @{{_Z15setStaticIntRefRi|"\?setStaticIntRef@@YAXAEAH@Z"}}(i32* %{{.*}})
 
 public func setCxxConstRef() {
-  var val: CInt = 21
-  setConstStaticIntRef(&val)
+  let val: CInt = 21
+  setConstStaticIntRef(val)
 }
 
 // CHECK: define {{(protected |dllexport )?}}swiftcc void @"$s4main14setCxxConstRefyyF"()
@@ -55,8 +55,8 @@ public func setCxxRvalueRef() {
 // CHECK: call void @{{_Z21setStaticIntRvalueRefOi|"\?setStaticIntRvalueRef@@YAX\$\$QEAH@Z"}}(i32* %{{.*}})
 
 public func setCxxConstRvalueRef() {
-  var val: CInt = 21
-  setConstStaticIntRvalueRef(&val)
+  let val: CInt = 21
+  setConstStaticIntRvalueRef(val)
 }
 
 // CHECK: define {{(protected |dllexport )?}}swiftcc void @"$s4main20setCxxConstRvalueRefyyF"()

test/Interop/Cxx/reference/reference-module-interface.swift

@@ -8,8 +8,8 @@
 // CHECK: func setStaticInt(_: Int32)
 // CHECK: func setStaticIntRef(_: inout Int32)
 // CHECK: func setStaticIntRvalueRef(_: inout Int32)
-// CHECK: func setConstStaticIntRef(_: inout Int32)
-// CHECK: func setConstStaticIntRvalueRef(_: inout Int32)
+// CHECK: func setConstStaticIntRef(_: Int32)
+// CHECK: func setConstStaticIntRvalueRef(_: Int32)
 // CHECK: func getFuncRef() -> @convention(c) () -> Int32
 // CHECK: func getFuncRvalueRef() -> @convention(c) () -> Int32
 

test/Interop/Cxx/reference/reference-silgen.swift

@@ -44,13 +44,13 @@ func setCxxRef() {
 // CHECK: apply [[REF]](%{{[0-9]+}}) : $@convention(c) (@inout Int32) -> ()
 
 func setCxxConstRef() {
-  var val: CInt = 21
-  setConstStaticIntRef(&val)
+  let val: CInt = 21
+  setConstStaticIntRef(val)
 }
 
 // CHECK: sil hidden @$s4main14setCxxConstRefyyF : $@convention(thin) () -> ()
-// CHECK: [[REF:%.*]] = function_ref @{{_Z20setConstStaticIntRefRKi|\?setConstStaticIntRef@@YAXAEBH@Z}} : $@convention(c) (@inout Int32) -> ()
-// CHECK: apply [[REF]](%{{[0-9]+}}) : $@convention(c) (@inout Int32) -> ()
+// CHECK: [[REF:%.*]] = function_ref @{{_Z20setConstStaticIntRefRKi|\?setConstStaticIntRef@@YAXAEBH@Z}} : $@convention(c) (@in Int32) -> ()
+// CHECK: apply [[REF]](%{{[0-9]+}}) : $@convention(c) (@in Int32) -> ()
 
 func setCxxRvalueRef() {
   var val: CInt = 21
@@ -62,10 +62,10 @@ func setCxxRvalueRef() {
 // CHECK: apply [[REF]](%{{[0-9]+}}) : $@convention(c) (@inout Int32) -> ()
 
 func setCxxConstRvalueRef() {
-  var val: CInt = 21
-  setConstStaticIntRvalueRef(&val)
+  let val: CInt = 21
+  setConstStaticIntRvalueRef(val)
 }
 
 // CHECK: sil hidden @$s4main20setCxxConstRvalueRefyyF : $@convention(thin) () -> ()
-// CHECK: [[REF:%.*]] = function_ref @{{_Z26setConstStaticIntRvalueRefOKi|\?setConstStaticIntRvalueRef@@YAX\$\$QEBH@Z}} : $@convention(c) (@inout Int32) -> ()
-// CHECK: apply [[REF]](%{{[0-9]+}}) : $@convention(c) (@inout Int32) -> ()
+// CHECK: [[REF:%.*]] = function_ref @{{_Z26setConstStaticIntRvalueRefOKi|\?setConstStaticIntRvalueRef@@YAX\$\$QEBH@Z}} : $@convention(c) (@in Int32) -> ()
+// CHECK: apply [[REF]](%{{[0-9]+}}) : $@convention(c) (@in Int32) -> ()

test/Interop/Cxx/reference/reference.swift

@@ -46,8 +46,8 @@ ReferenceTestSuite.test("pass-lvalue-reference") {
 
 ReferenceTestSuite.test("pass-const-lvalue-reference") {
   expectNotEqual(22, getStaticInt())
-  var val: CInt = 22
-  setConstStaticIntRef(&val)
+  let val: CInt = 22
+  setConstStaticIntRef(val)
   expectEqual(22, getStaticInt())
 }
 
@@ -60,8 +60,8 @@ ReferenceTestSuite.test("pass-rvalue-reference") {
 
 ReferenceTestSuite.test("pass-const-rvalue-reference") {
   expectNotEqual(53, getStaticInt())
-  var val: CInt = 53
-  setConstStaticIntRvalueRef(&val)
+  let val: CInt = 53
+  setConstStaticIntRvalueRef(val)
   expectEqual(53, getStaticInt())
 }
 
@@ -81,4 +81,10 @@ ReferenceTestSuite.test("func-rvalue-reference") {
   expectEqual(61, cxxF())
 }
 
+ReferenceTestSuite.test("pod-struct-const-lvalue-reference") {
+  expectNotEqual(getStaticInt(), 78)
+  takeConstRef(78)
+  expectEqual(getStaticInt(), 78)
+}
+
 runAllTests()

test/Interop/Cxx/templates/Inputs/dependent-types.h

@@ -51,7 +51,10 @@ template<class T, class U>
 M<T> multipleDependentArgs(M<T> a, M<U> b) { return {a.value}; }
 
 template<class T>
-M<T> refToDependent(const T &a) { return {a}; }
+M<T> refToDependent(T &a) { return {a}; }
+
+template<class T>
+M<T> constRefToDependent(const T &a) { return {a}; }
 
 // TODO: We can't import this template rdar://89028943
 template<class T>

test/Interop/Cxx/templates/dependent-types-module-interface.swift

@@ -8,4 +8,4 @@
 // CHECK: func multipleDependentArgs<T, U>(_ a: Any, _ b: Any, T: T.Type, U: U.Type) -> Any
 // CHECK: func refToDependent<T>(_ a: inout T) -> Any
 // CHECK: func dependentRef<T>(_ a: inout Any, T: T.Type) -> Any
-// CHECK: func dependentRefAndRefInferred<T>(_ a: inout Any, _ b: inout T) -> Any
+// CHECK: func dependentRefAndRefInferred<T>(_ a: Any, _ b: inout T) -> Any

test/Interop/Cxx/templates/dependent-types.swift

@@ -53,6 +53,11 @@ DependentTypesTestSuite.test("Takes inout argument and returns dependent type.")
   expectEqual(m.getValue(), 42)
 }
 
+DependentTypesTestSuite.test("Takes const ref and returns dependent type.") {
+  let m = constRefToDependent(42) as! M<Int>
+  expectEqual(m.getValue(), 42)
+}
+
 
 // We still have some problems calling methods on Windows: SR-13129 and rdar://88391102
 #if !os(Windows)

test/Interop/Cxx/templates/function-template-module-interface.swift

@@ -15,7 +15,7 @@
 // CHECK: }
 
 // CHECK: func lvalueReference<T>(_ ref: inout T)
-// CHECK: func constLvalueReference<T>(_: inout T)
+// CHECK: func constLvalueReference<T>(_: T)
 // CHECK: func forwardingReference<T>(_: inout T)
 // CHECK: func PointerTemplateParameter<T>(_: UnsafeMutablePointer<T>)
 

test/Interop/Cxx/templates/member-templates-module-interface.swift

@@ -8,7 +8,7 @@
 // CHECK:   mutating func passThroughConst<T>(_ val: T) -> T
 // CHECK:   func passThroughOnConst<T>(_ val: T) -> T
 // CHECK:   func passThroughConstOnConst<T>(_ val: T) -> T
-// CHECK:   mutating func doNothingConstRef<T>(_ val: inout T)
+// CHECK:   mutating func doNothingConstRef<T>(_ val: T)
 // CHECK:   mutating func make42Ref<T>(_ val: inout T)
 // CHECK: }
 

test/Interop/Cxx/templates/member-templates-silgen.swift

@@ -16,8 +16,8 @@ import MemberTemplates
 // CHECK: [[ADD_ALL:%.*]] = function_ref @_ZN18HasMemberTemplates6addAllIiiEEiiT_T0_ : $@convention(cxx_method) (Int32, Int32, Int32, @inout HasMemberTemplates) -> Int32
 // CHECK: apply [[ADD_ALL]]({{.*}}) : $@convention(cxx_method) (Int32, Int32, Int32, @inout HasMemberTemplates) -> Int32
 
-// CHECK: [[DO_NOTHING:%.*]] = function_ref @_ZN18HasMemberTemplates17doNothingConstRefIiEEvRKT_ : $@convention(cxx_method) (@inout Int32, @inout HasMemberTemplates) -> ()
-// CHECK: apply [[DO_NOTHING]]({{.*}}) : $@convention(cxx_method) (@inout Int32, @inout HasMemberTemplates) -> ()
+// CHECK: [[DO_NOTHING:%.*]] = function_ref @_ZN18HasMemberTemplates17doNothingConstRefIiEEvRKT_ : $@convention(cxx_method) (@in Int32, @inout HasMemberTemplates) -> ()
+// CHECK: apply [[DO_NOTHING]]({{.*}}) : $@convention(cxx_method) (@in Int32, @inout HasMemberTemplates) -> ()
 
 // CHECK-LABEL: end sil function '$s4main9basicTestyyF'
 func basicTest() {
@@ -26,7 +26,7 @@ func basicTest() {
   obj.addSameTypeParams(i, i)
   obj.addMixedTypeParams(i, i)
   obj.addAll(i, i, i)
-  obj.doNothingConstRef(&i)
+  obj.doNothingConstRef(i)
 }
 
 // CHECK-LABEL: sil [clang HasMemberTemplates.addSameTypeParams] @_ZN18HasMemberTemplates17addSameTypeParamsIiEET_S1_S1_ : $@convention(cxx_method) (Int32, Int32, @inout HasMemberTemplates) -> Int32
@@ -35,7 +35,7 @@ func basicTest() {
 
 // CHECK-LABEL: sil [clang HasMemberTemplates.addAll] @_ZN18HasMemberTemplates6addAllIiiEEiiT_T0_ : $@convention(cxx_method) (Int32, Int32, Int32, @inout HasMemberTemplates) -> Int32
 
-// CHECK-LABEL: sil [clang HasMemberTemplates.doNothingConstRef] @_ZN18HasMemberTemplates17doNothingConstRefIiEEvRKT_ : $@convention(cxx_method) (@inout Int32, @inout HasMemberTemplates) -> ()
+// CHECK-LABEL: sil [clang HasMemberTemplates.doNothingConstRef] @_ZN18HasMemberTemplates17doNothingConstRefIiEEvRKT_ : $@convention(cxx_method) (@in Int32, @inout HasMemberTemplates) -> ()
 
 // CHECK-LABEL: sil hidden @$s4main12testSetValueyyF : $@convention(thin) () -> ()