4 files changed, 39 insertions, 0 deletions
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index f73907a7c4..d898447ab5 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -3652,6 +3652,9 @@ bool Parser::isTypeSpecifierQualifier() {
   case tok::kw_volatile:
   case tok::kw_restrict:
 
+    // Debugger support.
+  case tok::kw___unknown_anytype:
+
     // typedef-name
   case tok::annot_typename:
     return true;
@@ -3751,6 +3754,9 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
     // Modules
   case tok::kw___module_private__:
 
+    // Debugger support
+  case tok::kw___unknown_anytype:
+
     // type-specifiers
   case tok::kw_short:
   case tok::kw_long:
diff --git a/lib/Parse/ParseTentative.cpp b/lib/Parse/ParseTentative.cpp
index 40c4eee199..b26181f08e 100644
--- a/lib/Parse/ParseTentative.cpp
+++ b/lib/Parse/ParseTentative.cpp
@@ -837,6 +837,7 @@ Parser::isExpressionOrTypeSpecifierSimple(tok::TokenKind Kind) {
   case tok::kw___vector:
   case tok::kw___pixel:
   case tok::kw__Atomic:
+  case tok::kw___unknown_anytype:
     return TPResult::False();
 
   default:
@@ -1056,6 +1057,9 @@ Parser::isCXXDeclarationSpecifier(Parser::TPResult BracedCastResult,
 
     // Modules
   case tok::kw___module_private__:
+
+    // Debugger support
+  case tok::kw___unknown_anytype:
       
     // type-specifier:
     //   simple-type-specifier
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index bf4abfcb74..58c212b62f 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -11850,6 +11850,22 @@ ExprResult Sema::forceUnknownAnyToType(Expr *E, QualType ToType) {
   return RebuildUnknownAnyExpr(*this, ToType).Visit(E);
 }
 
+QualType Sema::checkUnknownAnyArg(Expr *&arg) {
+  // Filter out placeholders.
+  ExprResult argR = CheckPlaceholderExpr(arg);
+  if (argR.isInvalid()) return QualType();
+  arg = argR.take();
+
+  // If the argument is an explicit cast, use that exact type as the
+  // effective parameter type.
+  if (ExplicitCastExpr *castArg = dyn_cast<ExplicitCastExpr>(arg)) {
+    return castArg->getTypeAsWritten();
+  }
+
+  // Otherwise, try to pass by value.
+  return arg->getType().getUnqualifiedType();
+}
+
 static ExprResult diagnoseUnknownAnyExpr(Sema &S, Expr *E) {
   Expr *orig = E;
   unsigned diagID = diag::err_uncasted_use_of_unknown_any;
diff --git a/lib/Sema/SemaExprObjC.cpp b/lib/Sema/SemaExprObjC.cpp
index e43b6bff55..b0f9958bb5 100644
--- a/lib/Sema/SemaExprObjC.cpp
+++ b/lib/Sema/SemaExprObjC.cpp
@@ -1196,6 +1196,19 @@ bool Sema::CheckMessageArgumentTypes(QualType ReceiverType,
         !param->hasAttr<CFConsumedAttr>())
       argExpr = stripARCUnbridgedCast(argExpr);
 
+    // If the parameter is __unknown_anytype, infer its type
+    // from the argument.
+    if (param->getType() == Context.UnknownAnyTy) {
+      QualType paramType = checkUnknownAnyArg(argExpr);
+      if (paramType.isNull()) {
+        IsError = true;
+        continue;
+      }
+
+      // Update the parameter type in-place.
+      param->setType(paramType);
+    }
+
     if (RequireCompleteType(argExpr->getSourceRange().getBegin(),
                             param->getType(),
                             diag::err_call_incomplete_argument, argExpr))