Revert "[ConstraintSystem] C++ Interop: Binding a string literal to std.string shouldn't increase the score"

This reverts commit cd9c37c

This is causing build failures for some projects. We need more time to investigate. Reverting this temporarily in the meantime.

rdar://158439395

Author: egorzhdan

include/swift/AST/KnownIdentifiers.def

@@ -35,7 +35,6 @@ IDENTIFIER(Any)
 IDENTIFIER(ArrayLiteralElement)
 IDENTIFIER(asLocalActor)
 IDENTIFIER(atIndexedSubscript)
-IDENTIFIER(basic_string)
 IDENTIFIER_(bridgeToObjectiveC)
 IDENTIFIER(buildArray)
 IDENTIFIER(buildBlock)

include/swift/AST/Types.h

@@ -1110,9 +1110,6 @@ class alignas(1 << TypeAlignInBits) TypeBase
   /// Check if this is a ObjCBool type from the Objective-C module.
   bool isObjCBool();
 
-  /// Check if this is a std.string type from C++.
-  bool isCxxString();
-
   /// Check if this is the type Unicode.Scalar from the Swift standard library.
   bool isUnicodeScalar();
 

lib/AST/Type.cpp

@@ -43,7 +43,6 @@
 #include "swift/AST/Types.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/Compiler.h"
-#include "clang/AST/DeclCXX.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -1303,21 +1302,6 @@ bool TypeBase::isObjCBool() {
   return module->getName().is("ObjectiveC") && NTD->getName().is("ObjCBool");
 }
 
-bool TypeBase::isCxxString() {
-  auto *nominal = getAnyNominal();
-  if (!nominal)
-    return false;
-
-  auto *clangDecl =
-      dyn_cast_or_null<clang::CXXRecordDecl>(nominal->getClangDecl());
-  if (!clangDecl)
-    return false;
-
-  auto &ctx = nominal->getASTContext();
-  return clangDecl->isInStdNamespace() && clangDecl->getIdentifier() &&
-         ctx.Id_basic_string.is(clangDecl->getName());
-}
-
 bool TypeBase::isUnicodeScalar() {
   if (!is<StructType>())
     return false;

lib/Sema/ConstraintSystem.cpp

@@ -257,28 +257,11 @@ void ConstraintSystem::assignFixedType(TypeVariableType *typeVar, Type type,
 
       // If the protocol has a default type, check it.
       if (auto defaultType = TypeChecker::getDefaultType(literalProtocol, DC)) {
-        auto isDefaultType = [&literalProtocol, &defaultType](Type type) {
-          // Treat `std.string` as a default type just like we do
-          // Swift standard library `String`. This helps to disambiguate
-          // operator overloads that use `std.string` vs. a custom C++
-          // type that conforms to `ExpressibleByStringLiteral` as well.
-          //
-          // This doesn't clash with String because inference won't attempt
-          // C++ types unless we discover them from a constraint and the
-          // optimizer and old hacks always prefer the actual default type.
-          if (literalProtocol->getKnownProtocolKind() ==
-                  KnownProtocolKind::ExpressibleByStringLiteral &&
-              type->isCxxString()) {
-            return true;
-          }
-
-          // Check whether the nominal types match. This makes sure that we
-          // properly handle Array vs. Array<T>.
-          return defaultType->getAnyNominal() == type->getAnyNominal();
-        };
-
-        if (!isDefaultType(type))
+        // Check whether the nominal types match. This makes sure that we
+        // properly handle Array vs. Array<T>.
+        if (defaultType->getAnyNominal() != type->getAnyNominal()) {
           increaseScore(SK_NonDefaultLiteral, locator);
+        }
       }
 
       break;

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

@@ -6,15 +6,3 @@ struct HasMethodThatReturnsString {
 };
 
 inline std::string takesStringWithDefaultArg(std::string s = "abc") { return s; }
-
-struct StringBox {
-  std::string value;
-
-  friend bool operator==(const StringBox &lhs, const std::string &rhs) {
-    return lhs.value == rhs;
-  }
-
-  friend bool operator==(const std::string &lhs, const StringBox &rhs) {
-    return rhs == lhs;
-  }
-};