[ASTGen] Generate @_typeEraser attribute

Author: rintaro

include/swift/AST/ASTBridging.h

@@ -1375,6 +1375,11 @@ BridgedTransposeAttr BridgedTransposeAttr_createParsed(
     BridgedDeclNameRef cOriginalName, BridgedDeclNameLoc cOriginalNameLoc,
     BridgedArrayRef cParams);
 
+SWIFT_NAME("BridgedTypeEraserAttr.createParsed(_:atLoc:range:typeExpr:)")
+BridgedTypeEraserAttr BridgedTypeEraserAttr_createParsed(
+    BridgedASTContext cContext, BridgedSourceLoc cAtLoc,
+    BridgedSourceRange cRange, BridgedTypeExpr cTypeExpr);
+
 SWIFT_NAME(
     "BridgedUnavailableFromAsyncAttr.createParsed(_:atLoc:range:message:)")
 BridgedUnavailableFromAsyncAttr BridgedUnavailableFromAsyncAttr_createParsed(

lib/AST/Bridging/DeclAttributeBridging.cpp

@@ -867,6 +867,15 @@ BridgedTransposeAttr BridgedTransposeAttr_createParsed(
       params);
 }
 
+BridgedTypeEraserAttr BridgedTypeEraserAttr_createParsed(
+    BridgedASTContext cContext, BridgedSourceLoc cAtLoc,
+    BridgedSourceRange cRange, BridgedTypeExpr cTypeExpr
+
+) {
+  return TypeEraserAttr::create(cContext.unbridged(), cAtLoc.unbridged(),
+                                cRange.unbridged(), cTypeExpr.unbridged());
+}
+
 BridgedUnavailableFromAsyncAttr BridgedUnavailableFromAsyncAttr_createParsed(
     BridgedASTContext cContext, BridgedSourceLoc cAtLoc,
     BridgedSourceRange cRange, BridgedStringRef cMessage) {

lib/ASTGen/Sources/ASTGen/DeclAttrs.swift

@@ -190,7 +190,7 @@ extension ASTGenVisitor {
       case .transpose:
         return handle(self.generateTransposeAttr(attribute: node)?.asDeclAttribute)
       case .typeEraser:
-        fatalError("unimplemented")
+        return handle(self.generateTypeEraserAttr(attribute: node)?.asDeclAttribute)
       case .unavailableFromAsync:
         return handle(self.generateUnavailableFromAsyncAttr(attribute: node)?.asDeclAttribute)
       case .reasync:
@@ -2124,6 +2124,33 @@ extension ASTGenVisitor {
     )
   }
 
+  /// E.g.:
+  ///   ```
+  ///   @_typeEraser(MyProtocol)
+  ///   ```
+  func generateTypeEraserAttr(attribute node: AttributeSyntax) -> BridgedTypeEraserAttr? {
+    // FIXME: Should be normal LabeledExprListSyntax arguments.
+    // FIXME: Error handling
+    let type: BridgedTypeRepr? = self.generateSingleAttrOption(attribute: node, { token in
+      let nameLoc = self.generateIdentifierAndSourceLoc(token)
+      return BridgedUnqualifiedIdentTypeRepr.createParsed(
+        self.ctx,
+        loc: nameLoc.sourceLoc,
+        name: nameLoc.identifier
+      ).asTypeRepr
+    })
+    guard let type else {
+      return nil
+    }
+
+    return .createParsed(
+      self.ctx,
+      atLoc: self.generateSourceLoc(node.atSign),
+      range: self.generateAttrSourceRange(node),
+      typeExpr: .createParsed(self.ctx, type: type)
+    )
+  }
+
   /// E.g.:
   ///   ```
   ///   @_unavailableFromAsync

test/ASTGen/attrs.swift

@@ -259,3 +259,8 @@ struct LayoutOuter {
 @rethrows protocol RethrowingProtocol {
   func source() throws
 }
+
+@_typeEraser(AnyEraser) protocol EraserProto {}
+struct AnyEraser: EraserProto {
+  init<T: EraserProto>(erasing: T) {}
+}