diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index a4a88d0..3ff6f25 100644
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -520,6 +520,17 @@
   let Documentation = [AvailabilityDocs];
 }
 
+def ExternalSourceSymbol : InheritableAttr {
+  let Spellings = [GNU<"external_source_symbol">,
+                   CXX11<"clang", "external_source_symbol">];
+  let Args = [StringArgument<"language", 1>,
+              StringArgument<"definedIn", 1>,
+              BoolArgument<"generatedDeclaration", 1>];
+  let HasCustomParsing = 1;
+//  let Subjects = SubjectList<[Named]>;
+  let Documentation = [ExternalSourceSymbolDocs];
+}
+
 def Blocks : InheritableAttr {
   let Spellings = [GNU<"blocks">];
   let Args = [EnumArgument<"Type", "BlockType", ["byref"], ["ByRef"]>];
diff --git a/include/clang/Basic/AttrDocs.td b/include/clang/Basic/AttrDocs.td
index ccf4778..0c8b57a 100644
--- a/include/clang/Basic/AttrDocs.td
+++ b/include/clang/Basic/AttrDocs.td
@@ -960,6 +960,63 @@
   }];
 }
 
+def ExternalSourceSymbolDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``external_source_symbol`` attribute specifies that a declaration originates
+from an external source and describes the nature of that source.
+
+The fact that Clang is capable of recognizing declarations that were defined
+externally can be used to provide better tooling support for mixed-language
+projects or projects that rely on auto-generated code. For instance, an IDE that
+uses Clang and that supports mixed-language projects can use this attribute to
+provide a correct 'jump-to-definition' feature. For a concrete example,
+consider a protocol that's defined in a Swift file:
+
+.. code-block:: swift
+
+  @objc public protocol SwiftProtocol {
+    func method()
+  }
+
+This protocol can be used from Objective-C code by including a header file that
+was generated by the Swift compiler. The declarations in that header can use
+the ``external_source_symbol`` attribute to make Clang aware of the fact
+that ``SwiftProtocol`` actually originates from a Swift module:
+
+.. code-block:: objc
+
+  __attribute__((external_source_symbol(language=Swift,defined_in="module")))
+  @protocol SwiftProtocol
+  @required
+  - (void) method;
+  @end
+
+Consequently, when 'jump-to-definition' is performed at a location that
+references ``SwiftProtocol``, the IDE can jump to the original definition in
+the Swift source file rather than jumping to the Objective-C declaration in the
+auto-generated header file.
+
+The ``external_source_symbol`` attribute is a comma-separated list that includes
+clauses that describe the origin and the nature of the particular declaration.
+Those clauses can be:
+
+language=\ *string-literal*
+  The name of the source language in which this declaration was defined.
+
+defined_in=\ *string-literal*
+  The name of the source container in which the declaration was defined. The
+  exact definition of source container is language-specific, e.g. Swift's
+  source containers are modules, so ``defined_in`` should specify the Swift
+  module name.
+
+generated_declaration
+  This declaration was automatically generated by some tool.
+
+The clauses can be specified in any order. The clauses that are listed above are
+all optional, but the attribute has to have at least one clause.
+  }];
+}
 
 def RequireConstantInitDocs : Documentation {
   let Category = DocCatVariable;
diff --git a/include/clang/Basic/DiagnosticCommonKinds.td b/include/clang/Basic/DiagnosticCommonKinds.td
index aeaa824..fac6f38 100644
--- a/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/include/clang/Basic/DiagnosticCommonKinds.td
@@ -45,7 +45,9 @@
   "must end with ':'">;
 def err_expected_string_literal : Error<"expected string literal "
   "%select{in %1|for diagnostic message in static_assert|"
-          "for optional message in 'availability' attribute}0">;
+          "for optional message in 'availability' attribute|"
+          "for %select{language|source container}1 name in "
+          "'external_source_symbol' attribute}0">;
 def err_invalid_string_udl : Error<
   "string literal with user-defined suffix cannot be used here">;
 def err_invalid_character_udl : Error<
diff --git a/include/clang/Basic/DiagnosticParseKinds.td b/include/clang/Basic/DiagnosticParseKinds.td
index 76e776c..e3575b8 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -859,6 +859,12 @@
 def err_availability_query_repeated_star : Error<
   "'*' query has already been specified">;
 
+// External source symbol attribute
+def err_external_source_symbol_expected_keyword : Error<
+  "expected 'language', 'defined_in', or 'generated_declaration'">;
+def err_external_source_symbol_duplicate_clause : Error<
+  "duplicate %0 clause in an 'external_source_symbol' attribute">;
+
 // Type safety attributes
 def err_type_safety_unknown_flag : Error<
   "invalid comparison flag %0; use 'layout_compatible' or 'must_be_null'">;
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index c28465a..700e844 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2659,7 +2659,8 @@
   "|functions, methods, enums, and classes"
   "|structs, classes, variables, functions, and inline namespaces"
   "|variables, functions, methods, types, enumerations, enumerators, labels, and non-static data members"
-  "|classes and enumerations}1">,
+  "|classes and enumerations"
+  "|named declarations}1">,
   InGroup<IgnoredAttributes>;
 def err_attribute_wrong_decl_type : Error<warn_attribute_wrong_decl_type.Text>;
 def warn_type_attribute_wrong_type : Warning<
diff --git a/include/clang/Parse/Parser.h b/include/clang/Parse/Parser.h
index 5fae263..2e93bec 100644
--- a/include/clang/Parse/Parser.h
+++ b/include/clang/Parse/Parser.h
@@ -142,6 +142,10 @@
   /// \brief Identifier for "replacement".
   IdentifierInfo *Ident_replacement;
 
+  /// Identifiers used by the 'external_source_symbol' attribute.
+  IdentifierInfo *Ident_language, *Ident_defined_in,
+      *Ident_generated_declaration;
+
   /// C++0x contextual keywords.
   mutable IdentifierInfo *Ident_final;
   mutable IdentifierInfo *Ident_GNU_final;
@@ -2177,6 +2181,12 @@
                              Declarator *D);
   IdentifierLoc *ParseIdentifierLoc();
 
+  unsigned
+  ParseClangAttributeArgs(IdentifierInfo *AttrName, SourceLocation AttrNameLoc,
+                          ParsedAttributes &Attrs, SourceLocation *EndLoc,
+                          IdentifierInfo *ScopeName, SourceLocation ScopeLoc,
+                          AttributeList::Syntax Syntax);
+
   void MaybeParseCXX11Attributes(Declarator &D) {
     if (getLangOpts().CPlusPlus11 && isCXX11AttributeSpecifier()) {
       ParsedAttributesWithRange attrs(AttrFactory);
@@ -2266,6 +2276,14 @@
   Optional<AvailabilitySpec> ParseAvailabilitySpec();
   ExprResult ParseAvailabilityCheckExpr(SourceLocation StartLoc);
 
+  void ParseExternalSourceSymbolAttribute(IdentifierInfo &ExternalSourceSymbol,
+                                          SourceLocation Loc,
+                                          ParsedAttributes &Attrs,
+                                          SourceLocation *EndLoc,
+                                          IdentifierInfo *ScopeName,
+                                          SourceLocation ScopeLoc,
+                                          AttributeList::Syntax Syntax);
+
   void ParseObjCBridgeRelatedAttribute(IdentifierInfo &ObjCBridgeRelated,
                                        SourceLocation ObjCBridgeRelatedLoc,
                                        ParsedAttributes &attrs,
diff --git a/include/clang/Sema/AttributeList.h b/include/clang/Sema/AttributeList.h
index e74bf6a..7c16780 100644
--- a/include/clang/Sema/AttributeList.h
+++ b/include/clang/Sema/AttributeList.h
@@ -927,6 +927,7 @@
   ExpectedStructClassVariableFunctionOrInlineNamespace,
   ExpectedForMaybeUnused,
   ExpectedEnumOrClass,
+  ExpectedNamedDecl,
 };
 
 }  // end namespace clang
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index b89419d..423225f 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -388,6 +388,10 @@
     ParseAvailabilityAttribute(*AttrName, AttrNameLoc, Attrs, EndLoc, ScopeName,
                                ScopeLoc, Syntax);
     return;
+  } else if (AttrKind == AttributeList::AT_ExternalSourceSymbol) {
+    ParseExternalSourceSymbolAttribute(*AttrName, AttrNameLoc, Attrs, EndLoc,
+                                       ScopeName, ScopeLoc, Syntax);
+    return;
   } else if (AttrKind == AttributeList::AT_ObjCBridgeRelated) {
     ParseObjCBridgeRelatedAttribute(*AttrName, AttrNameLoc, Attrs, EndLoc,
                                     ScopeName, ScopeLoc, Syntax);
@@ -425,6 +429,25 @@
                            ScopeLoc, Syntax);
 }
 
+unsigned Parser::ParseClangAttributeArgs(
+    IdentifierInfo *AttrName, SourceLocation AttrNameLoc,
+    ParsedAttributes &Attrs, SourceLocation *EndLoc, IdentifierInfo *ScopeName,
+    SourceLocation ScopeLoc, AttributeList::Syntax Syntax) {
+  assert(Tok.is(tok::l_paren) && "Attribute arg list not starting with '('");
+
+  AttributeList::Kind AttrKind =
+      AttributeList::getKind(AttrName, ScopeName, Syntax);
+
+  if (AttrKind == AttributeList::AT_ExternalSourceSymbol) {
+    ParseExternalSourceSymbolAttribute(*AttrName, AttrNameLoc, Attrs, EndLoc,
+                                       ScopeName, ScopeLoc, Syntax);
+    return Attrs.getList() ? Attrs.getList()->getNumArgs() : 0;
+  }
+
+  return ParseAttributeArgsCommon(AttrName, AttrNameLoc, Attrs, EndLoc,
+                                  ScopeName, ScopeLoc, Syntax);
+}
+
 bool Parser::ParseMicrosoftDeclSpecArgs(IdentifierInfo *AttrName,
                                         SourceLocation AttrNameLoc,
                                         ParsedAttributes &Attrs) {
@@ -1115,6 +1138,119 @@
                Syntax, StrictLoc, ReplacementExpr.get());
 }
 
+/// \brief Parse the contents of the "external_source_symbol" attribute.
+///
+/// external-source-symbol-attribute:
+///   'external_source_symbol' '(' keyword-arg-list ')'
+///
+/// keyword-arg-list:
+///   keyword-arg
+///   keyword-arg ',' keyword-arg-list
+///
+/// keyword-arg:
+///   'language' '=' <string>
+///   'defined_in' '=' <string>
+///   'generated_declaration'
+void Parser::ParseExternalSourceSymbolAttribute(
+    IdentifierInfo &ExternalSourceSymbol, SourceLocation Loc,
+    ParsedAttributes &Attrs, SourceLocation *EndLoc, IdentifierInfo *ScopeName,
+    SourceLocation ScopeLoc, AttributeList::Syntax Syntax) {
+  // Opening '('.
+  BalancedDelimiterTracker T(*this, tok::l_paren);
+  if (T.expectAndConsume())
+    return;
+
+  // Initialize the pointers for the keyword identifiers when required.
+  if (!Ident_language) {
+    Ident_language = PP.getIdentifierInfo("language");
+    Ident_defined_in = PP.getIdentifierInfo("defined_in");
+    Ident_generated_declaration = PP.getIdentifierInfo("generated_declaration");
+  }
+
+  ExprResult Language;
+  bool HasLanguage = false;
+  ExprResult DefinedInExpr;
+  bool HasDefinedIn = false;
+  IdentifierLoc *GeneratedDeclaration = nullptr;
+
+  // Parse the language/defined_in/generated_declaration keywords
+  do {
+    if (Tok.isNot(tok::identifier)) {
+      Diag(Tok, diag::err_external_source_symbol_expected_keyword);
+      SkipUntil(tok::r_paren, StopAtSemi);
+      return;
+    }
+
+    SourceLocation KeywordLoc = Tok.getLocation();
+    IdentifierInfo *Keyword = Tok.getIdentifierInfo();
+    if (Keyword == Ident_generated_declaration) {
+      if (GeneratedDeclaration) {
+        Diag(Tok, diag::err_external_source_symbol_duplicate_clause) << Keyword;
+        SkipUntil(tok::r_paren, StopAtSemi);
+        return;
+      }
+      GeneratedDeclaration = ParseIdentifierLoc();
+      continue;
+    }
+
+    if (Keyword != Ident_language && Keyword != Ident_defined_in) {
+      Diag(Tok, diag::err_external_source_symbol_expected_keyword);
+      SkipUntil(tok::r_paren, StopAtSemi);
+      return;
+    }
+
+    ConsumeToken();
+    if (ExpectAndConsume(tok::equal, diag::err_expected_after,
+                         Keyword->getName())) {
+      SkipUntil(tok::r_paren, StopAtSemi);
+      return;
+    }
+
+    bool HadLanguage = HasLanguage, HadDefinedIn = HasDefinedIn;
+    if (Keyword == Ident_language)
+      HasLanguage = true;
+    else
+      HasDefinedIn = true;
+
+    if (Tok.isNot(tok::string_literal)) {
+      Diag(Tok, diag::err_expected_string_literal)
+          << /*Source='external_source_symbol attribute'*/ 3
+          << /*language | source container*/ (Keyword != Ident_language);
+      SkipUntil(tok::comma, tok::r_paren, StopAtSemi | StopBeforeMatch);
+      continue;
+    }
+    if (Keyword == Ident_language) {
+      if (HadLanguage) {
+        Diag(KeywordLoc, diag::err_external_source_symbol_duplicate_clause)
+            << Keyword;
+        ParseStringLiteralExpression();
+        continue;
+      }
+      Language = ParseStringLiteralExpression();
+    } else {
+      assert(Keyword == Ident_defined_in && "Invalid clause keyword!");
+      if (HadDefinedIn) {
+        Diag(KeywordLoc, diag::err_external_source_symbol_duplicate_clause)
+            << Keyword;
+        ParseStringLiteralExpression();
+        continue;
+      }
+      DefinedInExpr = ParseStringLiteralExpression();
+    }
+  } while (TryConsumeToken(tok::comma));
+
+  // Closing ')'.
+  if (T.consumeClose())
+    return;
+  if (EndLoc)
+    *EndLoc = T.getCloseLocation();
+
+  ArgsUnion Args[] = {Language.get(), DefinedInExpr.get(),
+                      GeneratedDeclaration};
+  Attrs.addNew(&ExternalSourceSymbol, SourceRange(Loc, T.getCloseLocation()),
+               ScopeName, ScopeLoc, Args, llvm::array_lengthof(Args), Syntax);
+}
+
 /// \brief Parse the contents of the "objc_bridge_related" attribute.
 /// objc_bridge_related '(' related_class ',' opt-class_method ',' opt-instance_method ')'
 /// related_class:
diff --git a/lib/Parse/ParseDeclCXX.cpp b/lib/Parse/ParseDeclCXX.cpp
index d2165d8..1758578 100644
--- a/lib/Parse/ParseDeclCXX.cpp
+++ b/lib/Parse/ParseDeclCXX.cpp
@@ -3823,36 +3823,44 @@
     return false;
   }
 
-  if (ScopeName && ScopeName->getName() == "gnu")
+  if (ScopeName && ScopeName->getName() == "gnu") {
     // GNU-scoped attributes have some special cases to handle GNU-specific
     // behaviors.
     ParseGNUAttributeArgs(AttrName, AttrNameLoc, Attrs, EndLoc, ScopeName,
                           ScopeLoc, AttributeList::AS_CXX11, nullptr);
-  else {
-    unsigned NumArgs =
+    return true;
+  }
+
+  unsigned NumArgs;
+  // Some Clang-scoped attributes have some special parsing behavior.
+  if (ScopeName && ScopeName->getName() == "clang")
+    NumArgs =
+        ParseClangAttributeArgs(AttrName, AttrNameLoc, Attrs, EndLoc, ScopeName,
+                                ScopeLoc, AttributeList::AS_CXX11);
+  else
+    NumArgs =
         ParseAttributeArgsCommon(AttrName, AttrNameLoc, Attrs, EndLoc,
                                  ScopeName, ScopeLoc, AttributeList::AS_CXX11);
-    
-    const AttributeList *Attr = Attrs.getList();
-    if (Attr && IsBuiltInOrStandardCXX11Attribute(AttrName, ScopeName)) {
-      // If the attribute is a standard or built-in attribute and we are
-      // parsing an argument list, we need to determine whether this attribute
-      // was allowed to have an argument list (such as [[deprecated]]), and how
-      // many arguments were parsed (so we can diagnose on [[deprecated()]]).
-      if (Attr->getMaxArgs() && !NumArgs) {
-        // The attribute was allowed to have arguments, but none were provided
-        // even though the attribute parsed successfully. This is an error.
-        Diag(LParenLoc, diag::err_attribute_requires_arguments) << AttrName;
-        Attr->setInvalid(true);
-      } else if (!Attr->getMaxArgs()) {
-        // The attribute parsed successfully, but was not allowed to have any
-        // arguments. It doesn't matter whether any were provided -- the
-        // presence of the argument list (even if empty) is diagnosed.
-        Diag(LParenLoc, diag::err_cxx11_attribute_forbids_arguments)
-            << AttrName
-            << FixItHint::CreateRemoval(SourceRange(LParenLoc, *EndLoc));
-        Attr->setInvalid(true);
-      }
+
+  const AttributeList *Attr = Attrs.getList();
+  if (Attr && IsBuiltInOrStandardCXX11Attribute(AttrName, ScopeName)) {
+    // If the attribute is a standard or built-in attribute and we are
+    // parsing an argument list, we need to determine whether this attribute
+    // was allowed to have an argument list (such as [[deprecated]]), and how
+    // many arguments were parsed (so we can diagnose on [[deprecated()]]).
+    if (Attr->getMaxArgs() && !NumArgs) {
+      // The attribute was allowed to have arguments, but none were provided
+      // even though the attribute parsed successfully. This is an error.
+      Diag(LParenLoc, diag::err_attribute_requires_arguments) << AttrName;
+      Attr->setInvalid(true);
+    } else if (!Attr->getMaxArgs()) {
+      // The attribute parsed successfully, but was not allowed to have any
+      // arguments. It doesn't matter whether any were provided -- the
+      // presence of the argument list (even if empty) is diagnosed.
+      Diag(LParenLoc, diag::err_cxx11_attribute_forbids_arguments)
+          << AttrName
+          << FixItHint::CreateRemoval(SourceRange(LParenLoc, *EndLoc));
+      Attr->setInvalid(true);
     }
   }
   return true;
diff --git a/lib/Parse/Parser.cpp b/lib/Parse/Parser.cpp
index e1a99fd..d9c383a 100644
--- a/lib/Parse/Parser.cpp
+++ b/lib/Parse/Parser.cpp
@@ -501,6 +501,8 @@
   Ident_strict = nullptr;
   Ident_replacement = nullptr;
 
+  Ident_language = Ident_defined_in = Ident_generated_declaration = nullptr;
+
   Ident__except = nullptr;
 
   Ident__exception_code = Ident__exception_info = nullptr;
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index fba9aea..e25a11c 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -2438,6 +2438,32 @@
   }
 }
 
+static void handleExternalSourceSymbolAttr(Sema &S, Decl *D,
+                                           const AttributeList &Attr) {
+  if (!checkAttributeAtLeastNumArgs(S, Attr, 1))
+    return;
+  assert(checkAttributeAtMostNumArgs(S, Attr, 3) &&
+         "Invalid number of arguments in an external_source_symbol attribute");
+
+  if (!isa<NamedDecl>(D)) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+        << Attr.getName() << ExpectedNamedDecl;
+    return;
+  }
+
+  StringRef Language;
+  if (const auto *SE = dyn_cast_or_null<StringLiteral>(Attr.getArgAsExpr(0)))
+    Language = SE->getString();
+  StringRef DefinedIn;
+  if (const auto *SE = dyn_cast_or_null<StringLiteral>(Attr.getArgAsExpr(1)))
+    DefinedIn = SE->getString();
+  bool IsGeneratedDeclaration = Attr.getArgAsIdent(2) != nullptr;
+
+  D->addAttr(::new (S.Context) ExternalSourceSymbolAttr(
+      Attr.getRange(), S.Context, Language, DefinedIn, IsGeneratedDeclaration,
+      Attr.getAttributeSpellingListIndex()));
+}
+
 template <class T>
 static T *mergeVisibilityAttr(Sema &S, Decl *D, SourceRange range,
                               typename T::VisibilityType value,
@@ -6271,6 +6297,9 @@
   case AttributeList::AT_ExtVectorType:
     handleExtVectorTypeAttr(S, scope, D, Attr);
     break;
+  case AttributeList::AT_ExternalSourceSymbol:
+    handleExternalSourceSymbolAttr(S, D, Attr);
+    break;
   case AttributeList::AT_MinSize:
     handleMinSizeAttr(S, D, Attr);
     break;
diff --git a/test/Misc/ast-dump-attr.cpp b/test/Misc/ast-dump-attr.cpp
index e0575cb..f18fbac 100644
--- a/test/Misc/ast-dump-attr.cpp
+++ b/test/Misc/ast-dump-attr.cpp
@@ -154,3 +154,28 @@
 struct __attribute__((objc_bridge_related(NSParagraphStyle,,))) TestBridgedRef;
 // CHECK: CXXRecordDecl{{.*}} struct TestBridgedRef
 // CHECK-NEXT: ObjCBridgeRelatedAttr{{.*}} NSParagraphStyle
+
+void TestExternalSourceSymbolAttr1()
+__attribute__((external_source_symbol(language="Swift", defined_in="module", generated_declaration)));
+// CHECK: FunctionDecl{{.*}} TestExternalSourceSymbolAttr1
+// CHECK-NEXT: ExternalSourceSymbolAttr{{.*}} "Swift" "module" GeneratedDeclaration
+
+void TestExternalSourceSymbolAttr2()
+__attribute__((external_source_symbol(defined_in="module", language="Swift")));
+// CHECK: FunctionDecl{{.*}} TestExternalSourceSymbolAttr2
+// CHECK-NEXT: ExternalSourceSymbolAttr{{.*}} "Swift" "module"{{$}}
+
+void TestExternalSourceSymbolAttr3()
+__attribute__((external_source_symbol(generated_declaration, language="Objective-C++", defined_in="module")));
+// CHECK: FunctionDecl{{.*}} TestExternalSourceSymbolAttr3
+// CHECK-NEXT: ExternalSourceSymbolAttr{{.*}} "Objective-C++" "module" GeneratedDeclaration
+
+void TestExternalSourceSymbolAttr4()
+__attribute__((external_source_symbol(defined_in="Some external file.cs", generated_declaration, language="C Sharp")));
+// CHECK: FunctionDecl{{.*}} TestExternalSourceSymbolAttr4
+// CHECK-NEXT: ExternalSourceSymbolAttr{{.*}} "C Sharp" "Some external file.cs" GeneratedDeclaration
+
+void TestExternalSourceSymbolAttr5()
+__attribute__((external_source_symbol(generated_declaration, defined_in="module", language="Swift")));
+// CHECK: FunctionDecl{{.*}} TestExternalSourceSymbolAttr5
+// CHECK-NEXT: ExternalSourceSymbolAttr{{.*}} "Swift" "module" GeneratedDeclaration
diff --git a/test/Parser/attr-external-source-symbol-cxx11.cpp b/test/Parser/attr-external-source-symbol-cxx11.cpp
new file mode 100644
index 0000000..3457c6a
--- /dev/null
+++ b/test/Parser/attr-external-source-symbol-cxx11.cpp
@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+// expected-no-diagnostics
+
+[[clang::external_source_symbol(language="Swift", defined_in="module")]]
+void function() { }
diff --git a/test/Parser/attr-external-source-symbol.m b/test/Parser/attr-external-source-symbol.m
new file mode 100644
index 0000000..772fde0
--- /dev/null
+++ b/test/Parser/attr-external-source-symbol.m
@@ -0,0 +1,84 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+void function() __attribute__((external_source_symbol(language="Swift", defined_in="module", generated_declaration)));
+
+__attribute__((external_source_symbol(language="Swift", defined_in="module")))
+@interface I
+
+- (void)method __attribute__((external_source_symbol(defined_in= "module")));
+
+@end
+
+enum E {
+  CaseA __attribute__((external_source_symbol(generated_declaration))),
+  CaseB __attribute__((external_source_symbol(generated_declaration, language="Swift")))
+} __attribute__((external_source_symbol(language = "Swift")));
+
+void f2()
+__attribute__((external_source_symbol())); // expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
+void f3()
+__attribute__((external_source_symbol(invalid))); // expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
+void f4()
+__attribute__((external_source_symbol(language))); // expected-error {{expected '=' after language}}
+void f5()
+__attribute__((external_source_symbol(language=))); // expected-error {{expected string literal for language name in 'external_source_symbol' attribute}}
+void f6()
+__attribute__((external_source_symbol(defined_in=20))); // expected-error {{expected string literal for source container name in 'external_source_symbol' attribute}}
+
+void f7()
+__attribute__((external_source_symbol(generated_declaration, generated_declaration))); // expected-error {{duplicate 'generated_declaration' clause in an 'external_source_symbol' attribute}}
+void f8()
+__attribute__((external_source_symbol(language="Swift", language="Swift"))); // expected-error {{duplicate 'language' clause in an 'external_source_symbol' attribute}}
+void f9()
+__attribute__((external_source_symbol(defined_in="module", language="Swift", defined_in="foo"))); // expected-error {{duplicate 'defined_in' clause in an 'external_source_symbol' attribute}}
+
+void f10()
+__attribute__((external_source_symbol(generated_declaration, language="Swift", defined_in="foo", generated_declaration, generated_declaration, language="Swift"))); // expected-error {{duplicate 'generated_declaration' clause in an 'external_source_symbol' attribute}}
+
+void f11()
+__attribute__((external_source_symbol(language="Objective-C++", defined_in="Some file with spaces")));
+
+void f12()
+__attribute__((external_source_symbol(language="C Sharp", defined_in="file:////Hello world with spaces. cs")));
+
+void f13()
+__attribute__((external_source_symbol(language=Swift))); // expected-error {{expected string literal for language name in 'external_source_symbol' attribute}}
+
+void f14()
+__attribute__((external_source_symbol(=))); // expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
+
+void f15()
+__attribute__((external_source_symbol(="Swift"))); // expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
+
+void f16()
+__attribute__((external_source_symbol("Swift", "module", generated_declaration))); // expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
+
+void f17()
+__attribute__((external_source_symbol(language="Swift", "generated_declaration"))); // expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
+
+void f18()
+__attribute__((external_source_symbol(language= =))); // expected-error {{expected string literal for language name in 'external_source_symbol' attribute}}
+
+void f19()
+__attribute__((external_source_symbol(defined_in="module" language="swift"))); // expected-error {{expected ')'}} expected-note {{to match this '('}}
+
+void f20()
+__attribute__((external_source_symbol(defined_in="module" language="swift" generated_declaration))); // expected-error {{expected ')'}} expected-note {{to match this '('}}
+
+void f21()
+__attribute__((external_source_symbol(defined_in= language="swift"))); // expected-error {{expected string literal for source container name in 'external_source_symbol' attribute}}
+
+void f22()
+__attribute__((external_source_symbol)); // expected-error {{'external_source_symbol' attribute takes at least 1 argument}}
+
+void f23()
+__attribute__((external_source_symbol(defined_in=, language="swift" generated_declaration))); // expected-error {{expected string literal for source container name in 'external_source_symbol' attribute}} expected-error{{expected ')'}} expected-note{{to match this '('}}
+
+void f24()
+__attribute__((external_source_symbol(language = generated_declaration))); // expected-error {{expected string literal for language name in 'external_source_symbol' attribute}}
+
+void f25()
+__attribute__((external_source_symbol(defined_in=123, defined_in="module"))); // expected-error {{expected string literal for source container name in 'external_source_symbol'}} expected-error {{duplicate 'defined_in' clause in an 'external_source_symbol' attribute}}
+
+void f26()
+__attribute__((external_source_symbol(language=Swift, language="Swift", error))); // expected-error {{expected string literal for language name in 'external_source_symbol'}} expected-error {{duplicate 'language' clause in an 'external_source_symbol' attribute}} expected-error {{expected 'language', 'defined_in', or 'generated_declaration'}}
diff --git a/test/Sema/attr-external-source-symbol.c b/test/Sema/attr-external-source-symbol.c
new file mode 100644
index 0000000..af6e6bc
--- /dev/null
+++ b/test/Sema/attr-external-source-symbol.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -fsyntax-only -fblocks -verify %s
+
+void threeClauses() __attribute__((external_source_symbol(language="Swift", defined_in="module", generated_declaration)));
+
+void twoClauses() __attribute__((external_source_symbol(language="Swift", defined_in="module")));
+
+void fourClauses() __attribute__((external_source_symbol(language="Swift", defined_in="module", generated_declaration, generated_declaration))); // expected-error {{duplicate 'generated_declaration' clause in an 'external_source_symbol' attribute}}
+
+void oneClause() __attribute__((external_source_symbol(generated_declaration)));
+
+void noArguments()
+__attribute__((external_source_symbol)); // expected-error {{'external_source_symbol' attribute takes at least 1 argument}}
+
+void namedDeclsOnly() {
+  int (^block)(void) = ^ (void)
+    __attribute__((external_source_symbol(language="Swift"))) { // expected-warning {{'external_source_symbol' attribute only applies to named declarations}}
+      return 1;
+  };
+}