Initial implementation of a @_cdecl attribute to export top-level functions to C

include/swift/AST/Attr.def

@@ -245,6 +245,10 @@ SIMPLE_DECL_ATTR(warn_unqualified_access, WarnUnqualifiedAccess,
 SIMPLE_DECL_ATTR(_show_in_interface, ShowInInterface,
                  OnProtocol | UserInaccessible, 62)
 
+DECL_ATTR(_cdecl, CDecl,
+          OnFunc | LongAttribute | UserInaccessible, 63)
+
+
 #undef TYPE_ATTR
 #undef DECL_ATTR_ALIAS
 #undef SIMPLE_DECL_ATTR

include/swift/AST/Attr.h

@@ -516,6 +516,24 @@ class SILGenNameAttr : public DeclAttribute {
   }
 };
 
+/// Defines the @_cdecl attribute.
+class CDeclAttr : public DeclAttribute {
+public:
+  CDeclAttr(StringRef Name, SourceLoc AtLoc, SourceRange Range, bool Implicit)
+    : DeclAttribute(DAK_CDecl, AtLoc, Range, Implicit),
+      Name(Name) {}
+
+  CDeclAttr(StringRef Name, bool Implicit)
+    : CDeclAttr(Name, SourceLoc(), SourceRange(), /*Implicit=*/true) {}
+
+  /// The symbol name.
+  const StringRef Name;
+
+  static bool classof(const DeclAttribute *DA) {
+    return DA->getKind() == DAK_CDecl;
+  }
+};
+
 /// Defines the @_semantics attribute.
 class SemanticsAttr : public DeclAttribute {
 public:

include/swift/AST/DiagnosticsSema.def

@@ -836,6 +836,14 @@ ERROR(no_objc_tagged_pointer_not_class_protocol,none,
 ERROR(swift_native_objc_runtime_base_not_on_root_class,none,
       "@_swift_native_objc_runtime_base_not_on_root_class can only be applied "
       "to root classes", ())
+
+ERROR(cdecl_not_at_top_level,none,
+      "@_cdecl can only be applied to global functions", ())
+ERROR(cdecl_empty_name,none,
+      "@_cdecl symbol name cannot be empty", ())
+ERROR(cdecl_throws,none,
+      "raising errors from @_cdecl functions is not supported", ())
+
 ERROR(attr_methods_only,none,
       "only methods can be declared %0", (DeclAttribute))
 ERROR(access_control_in_protocol,none,
@@ -2487,7 +2495,7 @@ ERROR(objc_enum_case_multi,none,
       "'@objc' enum case declaration defines multiple enum cases with the same Objective-C name", ())
 
 // If you change this, also change enum ObjCReason
-#define OBJC_ATTR_SELECT "select{marked dynamic|marked @objc|marked @IBOutlet|marked @NSManaged|a member of an @objc protocol|implicitly @objc|an @objc override}"
+#define OBJC_ATTR_SELECT "select{marked @_cdecl|marked dynamic|marked @objc|marked @IBOutlet|marked @NSManaged|a member of an @objc protocol|implicitly @objc|an @objc override}"
 
 ERROR(objc_invalid_on_var,none,
       "property cannot be %" OBJC_ATTR_SELECT "0 "

include/swift/Serialization/ModuleFormat.h

@@ -43,7 +43,7 @@ const unsigned char MODULE_DOC_SIGNATURE[] = { 0xE2, 0x9C, 0xA8, 0x07 };
 
 /// Serialized module format major version number.
 ///
-/// Always 0 for Swift 1.0.
+/// Always 0 for Swift 1.x and 2.x.
 const uint16_t VERSION_MAJOR = 0;
 
 /// Serialized module format minor version number.
@@ -53,7 +53,8 @@ const uint16_t VERSION_MAJOR = 0;
 /// in source control, you should also update the comment to briefly
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
-const uint16_t VERSION_MINOR = 239; // multiple results for SILFunctionType
+/// describe what change you made.
+const uint16_t VERSION_MINOR = 240; // Last change: @_cdecl
 
 using DeclID = PointerEmbeddedInt<unsigned, 31>;
 using DeclIDField = BCFixed<31>;
@@ -1223,6 +1224,13 @@ namespace decls_block {
     BCFixed<1>, // implicit flag
     BCBlob      // _silgen_name
   >;
+
+  using CDeclDeclAttrLayout = BCRecordLayout<
+    CDecl_DECL_ATTR,
+    BCFixed<1>, // implicit flag
+    BCBlob      // _silgen_name
+  >;
+
 
   using AlignmentDeclAttrLayout = BCRecordLayout<
     Alignment_DECL_ATTR,

lib/AST/ASTContext.cpp

@@ -1908,7 +1908,10 @@ void AbstractFunctionDecl::setForeignErrorConvention(
 
 Optional<ForeignErrorConvention>
 AbstractFunctionDecl::getForeignErrorConvention() const {
-  if (!isObjC() || !isBodyThrowing()) return None;
+  if (!isObjC() && !getAttrs().hasAttribute<CDeclAttr>())
+    return None;
+  if (!isBodyThrowing())
+    return None;
   auto &conventionsMap = getASTContext().Impl.ForeignErrorConventions;
   auto it = conventionsMap.find(this);
   if (it == conventionsMap.end()) return None;

lib/AST/ASTVerifier.cpp

@@ -2200,8 +2200,9 @@ struct ASTNodeBase {};
         abort();
       }
 
-      if (AFD->getForeignErrorConvention() && !AFD->isObjC()) {
-        Out << "foreign error convention on non-@objc function\n";
+      if (AFD->getForeignErrorConvention()
+          && !AFD->isObjC() && !AFD->getAttrs().hasAttribute<CDeclAttr>()) {
+        Out << "foreign error convention on non-@objc, non-@_cdecl function\n";
         AFD->dump(Out);
         abort();
       }

lib/AST/Attr.cpp

@@ -372,6 +372,11 @@ bool DeclAttribute::printImpl(ASTPrinter &Printer, const PrintOptions &Options)
     if (cast<AutoClosureAttr>(this)->isEscaping())
       Printer << "(escaping)";
     break;
+
+  case DAK_CDecl:
+    Printer << "@_cdecl(\"" << cast<CDeclAttr>(this)->Name << "\")";
+    break;
+
   case DAK_ObjC: {
     Printer.printAttrName("@objc");
     llvm::SmallString<32> scratch;
@@ -487,6 +492,8 @@ StringRef DeclAttribute::getAttrName() const {
     return "_silgen_name";
   case DAK_Alignment:
     return "_alignment";
+  case DAK_CDecl:
+    return "_cdecl";
   case DAK_SwiftNativeObjCRuntimeBase:
     return "_swift_native_objc_runtime_base";
   case DAK_Semantics:

lib/IRGen/Linking.cpp

@@ -232,7 +232,7 @@ void LinkEntity::mangle(raw_ostream &buffer) const {
 
   //   entity ::= declaration                     // other declaration
   case Kind::Function:
-    // As a special case, functions can have external asm names.
+    // As a special case, functions can have manually mangled names.
     if (auto AsmA = getDecl()->getAttrs().getAttribute<SILGenNameAttr>()) {
       mangler.append(AsmA->Name);
       return mangler.finalize(buffer);

lib/Parse/ParseDecl.cpp

@@ -565,6 +565,7 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
     break;
   }
 
+  case DAK_CDecl:
   case DAK_SILGenName: {
     if (!consumeIf(tok::l_paren)) {
       diagnose(Loc, diag::attr_expected_lparen, AttrName,
@@ -601,9 +602,16 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
       diagnose(Loc, diag::attr_only_at_non_local_scope, AttrName);
     }
 
-    if (!DiscardAttribute)
-      Attributes.add(new (Context) SILGenNameAttr(AsmName.getValue(), AtLoc,
+    if (!DiscardAttribute) {
+      if (DK == DAK_SILGenName)
+        Attributes.add(new (Context) SILGenNameAttr(AsmName.getValue(), AtLoc,
+                                                AttrRange, /*Implicit=*/false));
+      else if (DK == DAK_CDecl)
+        Attributes.add(new (Context) CDeclAttr(AsmName.getValue(), AtLoc,
                                                AttrRange, /*Implicit=*/false));
+      else
+        llvm_unreachable("out of sync with switch");
+    }
 
     break;
   }