[ASTGen] Generate from 'MissingTypeSyntax'

Just emit ErrorTypeRepr

Author: rintaro

include/swift/AST/ASTBridging.h

@@ -2510,6 +2510,10 @@ BridgedDictionaryTypeRepr BridgedDictionaryTypeRepr_createParsed(
     BridgedTypeRepr keyType, BridgedSourceLoc cColonloc,
     BridgedTypeRepr valueType, BridgedSourceLoc cRSquareLoc);
 
+SWIFT_NAME("BridgedErrorTypeRepr.create(_:range:)")
+BridgedErrorTypeRepr BridgedErrorTypeRepr_create(BridgedASTContext cContext,
+                                                 BridgedSourceRange cRange);
+
 SWIFT_NAME("BridgedFunctionTypeRepr.createParsed(_:argsType:asyncLoc:throwsLoc:"
            "thrownType:arrowLoc:resultType:)")
 BridgedFunctionTypeRepr BridgedFunctionTypeRepr_createParsed(

include/swift/AST/Decl.h

@@ -7459,6 +7459,8 @@ class SubscriptDecl : public GenericContext, public AbstractStorageDecl {
   /// operation.
   Type getElementInterfaceType() const;
 
+  std::optional<Type> getCachedElementInterfaceType() const;
+
   TypeRepr *getElementTypeRepr() const { return ElementTy.getTypeRepr(); }
   SourceRange getElementTypeSourceRange() const {
     return ElementTy.getSourceRange();

lib/AST/ASTDumper.cpp

@@ -2563,6 +2563,8 @@ namespace {
       printCommon(SD, "subscript_decl", label);
       printStorageImpl(SD);
       printAttributes(SD);
+      printTypeOrTypeRepr(SD->getCachedElementInterfaceType(),
+                          SD->getElementTypeRepr(), Label::always("element"));
       printAccessors(SD);
       printFoot();
     }

lib/AST/Bridging/TypeReprBridging.cpp

@@ -95,6 +95,11 @@ BridgedDictionaryTypeRepr BridgedDictionaryTypeRepr_createParsed(
                          SourceRange{lSquareLoc, rSquareLoc});
 }
 
+BridgedErrorTypeRepr BridgedErrorTypeRepr_create(BridgedASTContext cContext,
+                                                 BridgedSourceRange cRange) {
+  return ErrorTypeRepr::create(cContext.unbridged(), cRange.unbridged());
+}
+
 BridgedInverseTypeRepr
 BridgedInverseTypeRepr_createParsed(BridgedASTContext cContext,
                                     BridgedSourceLoc cTildeLoc,

lib/AST/Decl.cpp

@@ -9343,6 +9343,11 @@ Type SubscriptDecl::getElementInterfaceType() const {
   return ErrorType::get(ctx);
 }
 
+std::optional<Type> SubscriptDecl::getCachedElementInterfaceType() const {
+  auto mutableThis = const_cast<SubscriptDecl *>(this);
+  return ResultTypeRequest{mutableThis}.getCachedResult();
+}
+
 ObjCSubscriptKind SubscriptDecl::getObjCSubscriptKind() const {
   // If the index type is an integral type, we have an indexed
   // subscript.

lib/ASTGen/Sources/ASTGen/Types.swift

@@ -44,8 +44,8 @@ extension ASTGenVisitor {
       return self.generate(memberType: node).asTypeRepr
     case .metatypeType(let node):
       return self.generate(metatypeType: node)
-    case .missingType:
-      fatalError("unimplemented")
+    case .missingType(let node):
+      return self.generate(missingType: node)
     case .namedOpaqueReturnType(let node):
       return self.generate(namedOpaqueReturnType: node).asTypeRepr
     case .optionalType(let node):
@@ -164,6 +164,13 @@ extension ASTGenVisitor {
     }
   }
 
+  func generate(missingType node: MissingTypeSyntax) -> BridgedTypeRepr {
+    return BridgedErrorTypeRepr.create(
+      self.ctx,
+      range: self.generateSourceRange(node)
+    ).asTypeRepr
+  }
+
   func generate(
     implicitlyUnwrappedOptionalType node: ImplicitlyUnwrappedOptionalTypeSyntax
   ) -> BridgedImplicitlyUnwrappedOptionalTypeRepr {

test/ASTGen/diagnostics.swift

@@ -28,3 +28,8 @@ func dummy() {}
 
 @_silgen_name("whatever", extra)  // expected-error@:27 {{unexpected arguments in '_silgen_name' attribute}}
 func _whatever()
+
+struct S {
+    subscript(x: Int) { _ = 1 } // expected-error@:23 {{expected '->' and return type in subscript}}
+                                // expected-note@-1:23 {{insert '->' and return type}}
+}