Implicitly look through UncheckedOptional<T> when it's the

base of a member access or subscript.

Swift SVN r12345

lib/Sema/CSApply.cpp

@@ -305,6 +305,17 @@ namespace {
     Expr *coerceViaUserConversion(Expr *expr, Type toType,
                                   ConstraintLocatorBuilder locator);
 
+    /// \brief Coerce an expression of (possibly unchecked) optional
+    /// type to have a different (possibly unchecked) optional type.
+    Expr *coerceOptionalToOptional(Expr *expr, Type toType,
+                                   ConstraintLocatorBuilder locator);
+
+    /// \brief Coerce an expression of unchecked optional type to its
+    /// underlying value type, in the correct way for an implicit
+    /// look-through.
+    Expr *coerceUncheckedOptionalToValue(Expr *expr, Type objTy,
+                                         ConstraintLocatorBuilder locator);
+
   public:
     /// \brief Build a reference to the given declaration.
     Expr *buildDeclRef(ValueDecl *decl, SourceLoc loc, Type openedType,
@@ -355,9 +366,17 @@ namespace {
       auto &tc = cs.getTypeChecker();
       auto &context = tc.Context;
 
+      Type baseTy = base->getType()->getRValueType();
+
+      // Handle accesses that implicitly look through UncheckedOptional<T>.
+      if (auto objTy = cs.lookThroughUncheckedOptionalType(baseTy)) {
+        base = coerceUncheckedOptionalToValue(base, objTy, locator);
+        if (!base) return nullptr;
+        baseTy = objTy;
+      }
+
       // Figure out the actual base type, and whether we have an instance of
       // that type or its metatype.
-      Type baseTy = base->getType()->getRValueType();
       bool baseIsInstance = true;
       if (auto baseMeta = baseTy->getAs<MetatypeType>()) {
         baseIsInstance = false;
@@ -677,6 +696,12 @@ namespace {
       auto &tc = cs.getTypeChecker();
       auto baseTy = base->getType()->getRValueType();
 
+      // Handle accesses that implicitly look through UncheckedOptional<T>.
+      if (auto objTy = cs.lookThroughUncheckedOptionalType(baseTy)) {
+        base = coerceUncheckedOptionalToValue(base, objTy, locator);
+        if (!base) return nullptr;
+      }
+
       // Figure out the index and result types.
       auto containerTy
         = subscript->getDeclContext()->getDeclaredTypeOfContext();
@@ -1490,13 +1515,22 @@ namespace {
                                      selected.openedType,
                                      cs.getConstraintLocator(expr, { }));
 
-      case OverloadChoiceKind::TupleIndex:
+      case OverloadChoiceKind::TupleIndex: {
+        auto base = expr->getBase();
+        auto baseTy = base->getType()->getRValueType();
+        if (auto objTy = cs.lookThroughUncheckedOptionalType(baseTy)) {
+          base = coerceUncheckedOptionalToValue(base, objTy,
+                                         cs.getConstraintLocator(base, { }));
+          if (!base) return nullptr;
+        }
+
         return new (cs.getASTContext()) TupleElementExpr(
-                                          expr->getBase(),
+                                          base,
                                           expr->getDotLoc(),
                                           selected.choice.getTupleIndex(),
                                           expr->getNameLoc(),
                                           simplifyType(expr->getType()));
+      }
 
       case OverloadChoiceKind::BaseType: {
         // FIXME: Losing ".0" sugar here.
@@ -1617,6 +1651,16 @@ namespace {
     }
 
     Expr *visitTupleElementExpr(TupleElementExpr *expr) {
+      // Handle accesses that implicitly look through UncheckedOptional<T>.
+      auto base = expr->getBase();
+      auto baseTy = base->getType()->getRValueType();
+      if (auto objTy = cs.lookThroughUncheckedOptionalType(baseTy)) {
+        base = coerceUncheckedOptionalToValue(base, objTy,
+                                              cs.getConstraintLocator(base, { }));
+        if (!base) return nullptr;
+        expr->setBase(base);
+      }
+
       simplifyExprType(expr);
       return expr;
     }
@@ -2653,6 +2697,47 @@ Expr *ExprRewriter::coerceViaUserConversion(Expr *expr, Type toType,
   return coerceToType(expr, toType, locator);
 }
 
+Expr *ExprRewriter::coerceOptionalToOptional(Expr *expr, Type toType,
+                                             ConstraintLocatorBuilder locator) {
+  auto &tc = cs.getTypeChecker();
+  Type fromType = expr->getType();
+  
+  auto fromGenericType = fromType->castTo<BoundGenericType>();
+  auto toGenericType = toType->castTo<BoundGenericType>();
+  assert(fromGenericType->getDecl()->classifyAsOptionalType());
+  assert(toGenericType->getDecl()->classifyAsOptionalType());
+  tc.requireOptionalIntrinsics(expr->getLoc());
+
+  Type fromValueType = fromGenericType->getGenericArgs()[0];
+  Type toValueType = toGenericType->getGenericArgs()[0];
+
+  expr = new (tc.Context) BindOptionalExpr(expr, expr->getSourceRange().End,
+                                           fromValueType);
+  expr->setImplicit(true);
+  expr = coerceToType(expr, toValueType, locator);
+  if (!expr) return nullptr;
+      
+  expr = new (tc.Context) InjectIntoOptionalExpr(expr, toType);
+      
+  expr = new (tc.Context) OptionalEvaluationExpr(expr, toType);
+  expr->setImplicit(true);
+  return expr;
+}
+
+Expr *ExprRewriter::coerceUncheckedOptionalToValue(Expr *expr, Type objTy,
+                                            ConstraintLocatorBuilder locator) {
+  // Coerce to an r-value.
+  auto rvalueTy = expr->getType()->getRValueType();
+  assert(rvalueTy->getUncheckedOptionalObjectType()->isEqual(objTy));
+
+  expr = coerceToType(expr, rvalueTy, /*bogus?*/ locator);
+  if (!expr) return nullptr;
+
+  expr = new (cs.getTypeChecker().Context) ForceValueExpr(expr, expr->getEndLoc());
+  expr->setType(objTy);
+  expr->setImplicit();
+  return expr;
+}
 
 Expr *ExprRewriter::coerceToType(Expr *expr, Type toType,
                                  ConstraintLocatorBuilder locator) {
@@ -2763,28 +2848,8 @@ Expr *ExprRewriter::coerceToType(Expr *expr, Type toType,
     }
 
     case ConversionRestrictionKind::UncheckedOptionalToOptional:
-    case ConversionRestrictionKind::OptionalToOptional: {
-      auto fromGenericType = fromType->castTo<BoundGenericType>();
-      auto toGenericType = toType->castTo<BoundGenericType>();
-      assert(fromGenericType->getDecl()->classifyAsOptionalType());
-      assert(toGenericType->getDecl()->classifyAsOptionalType());
-      tc.requireOptionalIntrinsics(expr->getLoc());
-
-      Type fromValueType = fromGenericType->getGenericArgs()[0];
-      Type toValueType = toGenericType->getGenericArgs()[0];
-      
-      expr = new (tc.Context) BindOptionalExpr(expr, expr->getSourceRange().End,
-                                               fromValueType);
-      expr->setImplicit(true);
-      expr = coerceToType(expr, toValueType, locator);
-      if (!expr) return nullptr;
-      
-      expr = new (tc.Context) InjectIntoOptionalExpr(expr, toType);
-      
-      expr = new (tc.Context) OptionalEvaluationExpr(expr, toType);
-      expr->setImplicit(true);
-      return expr;
-    }
+    case ConversionRestrictionKind::OptionalToOptional:
+      return coerceOptionalToOptional(expr, toType, locator);
 
     case ConversionRestrictionKind::User:
       return coerceViaUserConversion(expr, toType, locator);

lib/Sema/CSSimplify.cpp

@@ -1328,6 +1328,11 @@ ConstraintSystem::simplifyMemberConstraint(const Constraint &constraint) {
   Type baseTy = simplifyType(constraint.getFirstType());
   Type baseObjTy = baseTy->getRValueType();
 
+  // Try to look through UncheckedOptional<T>; the result is always an r-value.
+  if (auto objTy = lookThroughUncheckedOptionalType(baseObjTy)) {
+    baseTy = baseObjTy = objTy;
+  }
+
   // Dig out the instance type.
   bool isMetatype = false;
   Type instanceTy = baseObjTy;

lib/Sema/ConstraintSystem.cpp

@@ -1055,6 +1055,45 @@ void ConstraintSystem::resolveOverload(ConstraintLocator *locator,
   }
 }
 
+/// Given that we're accessing a member of an UncheckedOptional<T>, is
+/// the DC one of the special cases where we should not instead look at T?
+static bool isPrivilegedAccessToUncheckedOptional(DeclContext *DC,
+                                                  NominalTypeDecl *D) {
+  assert(D == DC->getASTContext().getUncheckedOptionalDecl());
+
+  // Walk up through the chain of current contexts.
+  for (; ; DC = DC->getParent()) {
+    assert(DC && "ran out of contexts before finding a module scope?");
+
+    // Look through local contexts.
+    if (DC->isLocalContext()) {
+      continue;
+
+    // If we're in a type context that's defining or extending
+    // UncheckedOptional<T>, we're privileged.
+    } else if (DC->isTypeContext()) {
+      if (DC->getDeclaredTypeInContext()->getAnyNominal() == D)
+        return true;
+
+    // Otherwise, we're privileged if we're within the same file that
+    // defines UncheckedOptional<T>.
+    } else {
+      assert(DC->isModuleScopeContext());
+      return (DC == D->getModuleScopeContext());
+    }
+  }
+}
+
+Type ConstraintSystem::lookThroughUncheckedOptionalType(Type type) {
+  if (auto boundTy = type->getAs<BoundGenericStructType>()) {
+    auto boundDecl = boundTy->getDecl();
+    if (boundDecl == TC.Context.getUncheckedOptionalDecl() &&
+        !isPrivilegedAccessToUncheckedOptional(DC, boundDecl))
+      return boundTy->getGenericArgs()[0];
+  }
+  return Type();
+}
+
 Type ConstraintSystem::simplifyType(Type type,
        llvm::SmallPtrSet<TypeVariableType *, 16> &substituting) {
   return type.transform([&](Type type) -> Type {

lib/Sema/ConstraintSystem.h

@@ -1510,6 +1510,11 @@ public:
   void addOverloadSet(Type boundType, ArrayRef<OverloadChoice> choices,
                       ConstraintLocator *locator);
 
+  /// If the given type is UncheckedOptional<T>, and we're in a context
+  /// that should transparently look through UncheckedOptional types,
+  /// return T.
+  Type lookThroughUncheckedOptionalType(Type type);
+
   /// \brief Retrieve the allocator used by this constraint system.
   llvm::BumpPtrAllocator &getAllocator() { return Allocator; }
 

test/Constraints/unchecked_optional.swift

@@ -0,0 +1,51 @@
+// RUN: %swift -parse -verify %s
+
+class A {
+  func do_a() {}
+
+  func do_b(x: Int) {}
+  func do_b(x: Float) {}
+
+  func do_c(x: Int) {} // expected-note {{found this candidate}}
+  func do_c(y: Int) {} // expected-note {{found this candidate}}
+}
+
+func test0(a : @unchecked A?) {
+  a.do_a()
+
+  a.do_b(1)
+  a.do_b(5.0)
+
+  a.do_c(1) // expected-error {{ambiguous use of 'do_c'}}
+  a.do_c(x: 1)
+}
+
+func test1(a : @unchecked A?) {
+  a?.do_a()
+
+  a?.do_b(1)
+  a?.do_b(5.0)
+
+  // FIXME: this should really get diagnosed like the above
+  a?.do_c(1) // expected-error {{expression does not type-check}}
+  a?.do_c(x: 1)
+}
+
+struct B {
+  var x : Int
+}
+
+func test2(var b : @unchecked B?) {
+  var x = b.x
+  b.x = x // expected-error {{cannot assign to the result of this expression}}
+}
+
+struct Subscriptable {
+  subscript(x : Int) -> Int {
+  get: return x
+  }
+}
+
+func test3(x: @unchecked Subscriptable?) -> Int {
+  return x[0]
+}