7 files changed, 98 insertions, 2 deletions

diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index d7db7186b3e..28695b9b696 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -527,6 +527,17 @@ def Availability : InheritableAttr {
   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/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 7c7f6d355cc..9a9c82b7d6d 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -960,6 +960,63 @@ When one method overrides another, the overriding method can be more widely avai
   }];
 }
 
+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/clang/include/clang/Basic/DiagnosticCommonKinds.td b/clang/include/clang/Basic/DiagnosticCommonKinds.td
index af0612a829e..b8293f08c52 100644
--- a/clang/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/clang/include/clang/Basic/DiagnosticCommonKinds.td
@@ -45,7 +45,9 @@ def err_expected_colon_after_setter_name : Error<
   "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/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index 2f34bf1faca..b486e62c350 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -859,6 +859,12 @@ def err_availability_query_repeated_platform: Error<
 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/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index a2269a1026d..86a445ba4ab 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2754,7 +2754,8 @@ def warn_attribute_wrong_decl_type : Warning<
   "|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/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index bf032992dfe..70381e507e4 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -142,6 +142,10 @@ class Parser : public CodeCompletionHandler {
   /// \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;
@@ -2197,6 +2201,12 @@ private:
                              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);
@@ -2286,6 +2296,14 @@ private:
   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/clang/include/clang/Sema/AttributeList.h b/clang/include/clang/Sema/AttributeList.h
index e74bf6a7cc8..7c1678086c2 100644
--- a/clang/include/clang/Sema/AttributeList.h
+++ b/clang/include/clang/Sema/AttributeList.h
@@ -927,6 +927,7 @@ enum AttributeDeclKind {
   ExpectedStructClassVariableFunctionOrInlineNamespace,
   ExpectedForMaybeUnused,
   ExpectedEnumOrClass,
+  ExpectedNamedDecl,
 };
 
 }  // end namespace clang