Merge pull request swiftlang#59171 from AnthonyLatsis/init-delegation-optional

CSGen, SILGen: Fix delegations to `Optional` initializers

Author: AnthonyLatsis

lib/SILGen/SILGenExpr.cpp

@@ -4166,23 +4166,31 @@ RValue RValueEmitter::visitRebindSelfInConstructorExpr(
   auto ctorDecl = cast<ConstructorDecl>(selfDecl->getDeclContext());
   auto selfIfaceTy = ctorDecl->getDeclContext()->getSelfInterfaceType();
   auto selfTy = ctorDecl->mapTypeIntoContext(selfIfaceTy);
-  
-  auto newSelfTy = E->getSubExpr()->getType();
-  bool outerIsOptional = false;
-  bool innerIsOptional = false;
-  auto objTy = newSelfTy->getOptionalObjectType();
-  if (objTy) {
-    outerIsOptional = true;
-    newSelfTy = objTy;
-
-    // "try? self.init()" can give us two levels of optional if the initializer
-    // we delegate to is failable.
-    objTy = newSelfTy->getOptionalObjectType();
-    if (objTy) {
-      innerIsOptional = true;
-      newSelfTy = objTy;
+
+  bool isChaining; // Ignored
+  auto *otherCtor = E->getCalledConstructor(isChaining)->getDecl();
+  assert(otherCtor);
+
+  auto getOptionalityDepth = [](Type ty) {
+    unsigned level = 0;
+    Type objTy = ty->getOptionalObjectType();
+    while (objTy) {
+      ++level;
+      objTy = objTy->getOptionalObjectType();
     }
-  }
+
+    return level;
+  };
+
+  // The optionality depth of the 'new self' value. This can be '2' if the ctor
+  // we are delegating/chaining to is both throwing and failable, or more if
+  // 'self' is optional.
+  auto srcOptionalityDepth = getOptionalityDepth(E->getSubExpr()->getType());
+
+  // The optionality depth of the result type of the enclosing initializer in
+  // this context.
+  const auto destOptionalityDepth = getOptionalityDepth(
+      ctorDecl->mapTypeIntoContext(ctorDecl->getResultInterfaceType()));
 
   // The subexpression consumes the current 'self' binding.
   assert(SGF.SelfInitDelegationState == SILGenFunction::NormalSelf
@@ -4199,13 +4207,25 @@ RValue RValueEmitter::visitRebindSelfInConstructorExpr(
     SGF.emitAddressOfLocalVarDecl(E, selfDecl, selfTy->getCanonicalType(),
                                   SGFAccessKind::Write).getLValueAddress();
 
-  // Handle a nested optional case (see above).
-  if (innerIsOptional)
+  // Flatten a nested optional if 'new self' is a deeper optional than we
+  // can return.
+  if (srcOptionalityDepth > destOptionalityDepth) {
+    assert(destOptionalityDepth > 0);
+    assert(otherCtor->isFailable() && otherCtor->hasThrows());
+
+    --srcOptionalityDepth;
     newSelf = flattenOptional(SGF, E, newSelf);
 
-  // If both the delegated-to initializer and our enclosing initializer can
-  // fail, deal with the failure.
-  if (outerIsOptional && ctorDecl->isFailable()) {
+    assert(srcOptionalityDepth == destOptionalityDepth &&
+           "Flattening a single level was not enough?");
+  }
+
+  // If the enclosing ctor is failable and the optionality depths match, switch
+  // on 'new self' to either return 'nil' or continue with the projected value.
+  if (srcOptionalityDepth == destOptionalityDepth && ctorDecl->isFailable()) {
+    assert(destOptionalityDepth > 0);
+    assert(otherCtor->isFailable() || otherCtor->hasThrows());
+
     SILBasicBlock *someBB = SGF.createBasicBlock();
 
     auto hasValue = SGF.emitDoesOptionalHaveValue(E, newSelf.getValue());
@@ -4224,7 +4244,7 @@ RValue RValueEmitter::visitRebindSelfInConstructorExpr(
                                     SGF.getTypeLowering(newSelf.getType()),
                                                     SGFContext());
   }
-  
+
   // If we called a constructor that requires a downcast, perform the downcast.
   auto destTy = SGF.getLoweredType(selfTy);
   if (newSelf.getType() != destTy) {

lib/Sema/CSApply.cpp

@@ -2237,23 +2237,18 @@ namespace {
 
       // The constructor was opened with the allocating type, not the
       // initializer type. Map the former into the latter.
-      auto resultTy = solution.simplifyType(openedFullType);
+      auto *resultTy =
+          solution.simplifyType(openedFullType)->castTo<FunctionType>();
 
-      auto selfTy = getBaseType(resultTy->castTo<FunctionType>());
-
-      // Also replace the result type with the base type, so that calls
-      // to constructors defined in a superclass will know to cast the
-      // result to the derived type.
-      resultTy = resultTy->replaceCovariantResultType(selfTy, 2);
+      const auto selfTy = getBaseType(resultTy);
 
       ParameterTypeFlags flags;
       if (!selfTy->hasReferenceSemantics())
         flags = flags.withInOut(true);
 
       auto selfParam = AnyFunctionType::Param(selfTy, Identifier(), flags);
-      resultTy = FunctionType::get({selfParam},
-                                   resultTy->castTo<FunctionType>()->getResult(),
-                                   resultTy->castTo<FunctionType>()->getExtInfo());
+      resultTy = FunctionType::get({selfParam}, resultTy->getResult(),
+                                   resultTy->getExtInfo());
 
       // Build the constructor reference.
       Expr *ctorRef = cs.cacheType(

lib/Sema/CSGen.cpp

@@ -1700,9 +1700,48 @@ namespace {
       if (!optTy)
         return Type();
 
-      // Prior to Swift 5, 'try?' always adds an additional layer of optionality,
-      // even if the sub-expression was already optional.
-      if (CS.getASTContext().LangOpts.isSwiftVersionAtLeast(5)) {
+      bool isDelegationToOptionalInit = false;
+      {
+        Expr *e = expr->getSubExpr();
+        while (true) {
+          e = e->getSemanticsProvidingExpr();
+
+          // Look through force-value expressions.
+          if (auto *FVE = dyn_cast<ForceValueExpr>(e)) {
+            e = FVE->getSubExpr();
+            continue;
+          }
+
+          break;
+        }
+
+        if (auto *CE = dyn_cast<CallExpr>(e)) {
+          if (auto *UDE = dyn_cast<UnresolvedDotExpr>(CE->getFn())) {
+            if (!CS.getType(UDE->getBase())->is<AnyMetatypeType>()) {
+              auto overload =
+                  CS.findSelectedOverloadFor(CS.getConstraintLocator(
+                      UDE, ConstraintLocator::ConstructorMember));
+              if (overload) {
+                auto *decl = overload->choice.getDeclOrNull();
+                if (decl && isa<ConstructorDecl>(decl) &&
+                    decl->getDeclContext()
+                        ->getSelfNominalTypeDecl()
+                        ->isOptionalDecl())
+                  isDelegationToOptionalInit = true;
+              }
+            }
+          }
+        }
+      }
+
+      // Prior to Swift 5, 'try?' always adds an additional layer of
+      // optionality, even if the sub-expression was already optional.
+      //
+      // NB Keep adding the additional layer in Swift 5 and on if this 'try?'
+      // applies to a delegation to an 'Optional' initializer, or else we won't
+      // discern the difference between a failure and a constructed value.
+      if (CS.getASTContext().LangOpts.isSwiftVersionAtLeast(5) &&
+          !isDelegationToOptionalInit) {
         CS.addConstraint(ConstraintKind::Conversion,
                          CS.getType(expr->getSubExpr()), optTy,
                          CS.getConstraintLocator(expr));