[CS] Handle placeholder in buildDisjunctionForOptionalVsUnderlying

include/swift/Sema/ConstraintSystem.h

@@ -4527,60 +4527,8 @@ class ConstraintSystem {
   // Build a disjunction that attempts both T? and T for a particular
   // type binding. The choice of T? is preferred, and we will not
   // attempt T if we can type check with T?
-  void
-  buildDisjunctionForOptionalVsUnderlying(Type boundTy, Type type,
-                                          ConstraintLocator *locator) {
-    // NOTE: If we use other locator kinds for these disjunctions, we
-    // need to account for it in solution scores for forced-unwraps.
-    assert(locator->getPath().back().getKind() ==
-               ConstraintLocator::ImplicitlyUnwrappedDisjunctionChoice ||
-           locator->getPath().back().getKind() ==
-               ConstraintLocator::DynamicLookupResult);
-
-    // Create the constraint to bind to the optional type and make it
-    // the favored choice.
-    auto *bindToOptional =
-      Constraint::create(*this, ConstraintKind::Bind, boundTy, type, locator);
-    bindToOptional->setFavored();
-
-    Type underlyingType;
-    if (auto *fnTy = type->getAs<AnyFunctionType>())
-      underlyingType = replaceFinalResultTypeWithUnderlying(fnTy);
-    else if (auto *typeVar =
-                 type->getWithoutSpecifierType()->getAs<TypeVariableType>()) {
-      auto *locator = typeVar->getImpl().getLocator();
-
-      // If `type` hasn't been resolved yet, we need to allocate a type
-      // variable to represent an object type of a future optional, and
-      // add a constraint beetween `type` and `underlyingType` to model it.
-      underlyingType = createTypeVariable(
-          getConstraintLocator(locator, LocatorPathElt::GenericArgument(0)),
-          TVO_PrefersSubtypeBinding | TVO_CanBindToLValue |
-              TVO_CanBindToNoEscape);
-
-      // Using a `typeVar` here because l-value is going to be applied
-      // to the underlying type below.
-      addConstraint(ConstraintKind::OptionalObject, typeVar, underlyingType,
-                    locator);
-    } else {
-      underlyingType = type->getWithoutSpecifierType()->getOptionalObjectType();
-    }
-
-    assert(underlyingType);
-
-    if (type->is<LValueType>())
-      underlyingType = LValueType::get(underlyingType);
-    assert(!type->is<InOutType>());
-
-    auto *bindToUnderlying = Constraint::create(
-        *this, ConstraintKind::Bind, boundTy, underlyingType, locator);
-
-    llvm::SmallVector<Constraint *, 2> choices = {bindToOptional,
-                                                  bindToUnderlying};
-
-    // Create the disjunction
-    addDisjunctionConstraint(choices, locator, RememberChoice);
-  }
+  void buildDisjunctionForOptionalVsUnderlying(Type boundTy, Type ty,
+                                               ConstraintLocator *locator);
 
   // Build a disjunction for types declared IUO.
   void

lib/Sema/ConstraintSystem.cpp

@@ -2597,6 +2597,68 @@ bool ConstraintSystem::isAsynchronousContext(DeclContext *dc) {
   return false;
 }
 
+void ConstraintSystem::buildDisjunctionForOptionalVsUnderlying(
+    Type boundTy, Type ty, ConstraintLocator *locator) {
+  // NOTE: If we use other locator kinds for these disjunctions, we
+  // need to account for it in solution scores for forced-unwraps.
+  assert(locator->getPath().back().getKind() ==
+             ConstraintLocator::ImplicitlyUnwrappedDisjunctionChoice ||
+         locator->getPath().back().getKind() ==
+             ConstraintLocator::DynamicLookupResult);
+  assert(!ty->is<InOutType>());
+  auto rvalueTy = ty->getWithoutSpecifierType();
+
+  // If the type to bind is a placeholder, we can propagate it, as we don't know
+  // whether it can be optional or non-optional, and we would have already
+  // recorded a fix for it.
+  if (rvalueTy->isPlaceholder()) {
+    addConstraint(ConstraintKind::Bind, boundTy, ty, locator);
+    return;
+  }
+
+  // Create the constraint to bind to the optional type and make it the favored
+  // choice.
+  auto *bindToOptional =
+      Constraint::create(*this, ConstraintKind::Bind, boundTy, ty, locator);
+  bindToOptional->setFavored();
+
+  Type underlyingType;
+  if (auto *fnTy = ty->getAs<AnyFunctionType>())
+    underlyingType = replaceFinalResultTypeWithUnderlying(fnTy);
+  else if (auto *typeVar = rvalueTy->getAs<TypeVariableType>()) {
+    auto *locator = typeVar->getImpl().getLocator();
+
+    // If `ty` hasn't been resolved yet, we need to allocate a type variable to
+    // represent an object type of a future optional, and add a constraint
+    // between `ty` and `underlyingType` to model it.
+    underlyingType = createTypeVariable(
+        getConstraintLocator(locator, LocatorPathElt::GenericArgument(0)),
+        TVO_PrefersSubtypeBinding | TVO_CanBindToLValue |
+            TVO_CanBindToNoEscape);
+
+    // Using a `typeVar` here because l-value is going to be applied
+    // to the underlying type below.
+    addConstraint(ConstraintKind::OptionalObject, typeVar, underlyingType,
+                  locator);
+  } else {
+    underlyingType = rvalueTy->getOptionalObjectType();
+  }
+
+  assert(underlyingType);
+
+  if (ty->is<LValueType>())
+    underlyingType = LValueType::get(underlyingType);
+
+  auto *bindToUnderlying = Constraint::create(*this, ConstraintKind::Bind,
+                                              boundTy, underlyingType, locator);
+
+  llvm::SmallVector<Constraint *, 2> choices = {bindToOptional,
+                                                bindToUnderlying};
+
+  // Create the disjunction
+  addDisjunctionConstraint(choices, locator, RememberChoice);
+}
+
 void ConstraintSystem::bindOverloadType(
     const SelectedOverload &overload, Type boundType,
     ConstraintLocator *locator, DeclContext *useDC,

test/Constraints/iuo.swift

@@ -238,3 +238,12 @@ struct CurriedIUO {
     let _: Int = CurriedIUO.silly(self)()
   }
 }
+
+// SR-15219 (rdar://83352038): Make sure we don't crash if an IUO param becomes
+// a placeholder.
+func rdar83352038() {
+  func foo(_: UnsafeRawPointer) -> Undefined {} // expected-error {{cannot find type 'Undefined' in scope}}
+  let _ = { (cnode: AlsoUndefined!) -> UnsafeMutableRawPointer in // expected-error {{cannot find type 'AlsoUndefined' in scope}}
+    return foo(cnode)
+  }
+}