[Sema] Requestify memberwise init synthesis

This commit adds two requests, one to compute
whether or not a decl should have a memberwise
initializer, and another to synthesize it.

include/swift/AST/ASTTypeIDZone.def

@@ -25,6 +25,7 @@ SWIFT_TYPEID(Requirement)
 SWIFT_TYPEID(ResilienceExpansion)
 SWIFT_TYPEID(Type)
 SWIFT_TYPEID(TypePair)
+SWIFT_TYPEID_NAMED(ConstructorDecl *, ConstructorDecl)
 SWIFT_TYPEID_NAMED(CustomAttr *, CustomAttr)
 SWIFT_TYPEID_NAMED(Decl *, Decl)
 SWIFT_TYPEID_NAMED(EnumDecl *, EnumDecl)

include/swift/AST/ASTTypeIDs.h

@@ -23,6 +23,7 @@ namespace swift {
 
 class AbstractFunctionDecl;
 class BraceStmt;
+class ConstructorDecl;
 class CustomAttr;
 class Decl;
 class EnumDecl;

include/swift/AST/Decl.h

@@ -3464,6 +3464,13 @@ public:
     });
   }
 
+  /// Whether this declaration has a synthesized memberwise initializer.
+  bool hasMemberwiseInitializer() const;
+
+  /// Retrieves the synthesized memberwise initializer for this declaration,
+  /// or \c nullptr if it does not have one.
+  ConstructorDecl *getMemberwiseInitializer() const;
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) {
     return D->getKind() >= DeclKind::First_NominalTypeDecl &&

include/swift/AST/TypeCheckRequests.h

@@ -1549,6 +1549,44 @@ public:
   bool isCached() const { return true; }
 };
 
+/// Checks whether this type has a synthesized memberwise initializer.
+class HasMemberwiseInitRequest
+    : public SimpleRequest<HasMemberwiseInitRequest, bool(StructDecl *),
+                           CacheKind::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  llvm::Expected<bool> evaluate(Evaluator &evaluator, StructDecl *decl) const;
+
+public:
+  // Caching.
+  bool isCached() const { return true; }
+};
+
+/// Synthesizes a memberwise initializer for a given type.
+class SynthesizeMemberwiseInitRequest
+    : public SimpleRequest<SynthesizeMemberwiseInitRequest,
+                           ConstructorDecl *(NominalTypeDecl *),
+                           CacheKind::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  llvm::Expected<ConstructorDecl *> evaluate(Evaluator &evaluator,
+                                             NominalTypeDecl *decl) const;
+
+public:
+  // Caching.
+  bool isCached() const { return true; }
+};
+
 // Allow AnyValue to compare two Type values, even though Type doesn't
 // support ==.
 template<>

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -169,3 +169,7 @@ SWIFT_REQUEST(TypeChecker, AreAllStoredPropertiesDefaultInitableRequest,
               bool(NominalTypeDecl *), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, HasUserDefinedDesignatedInitRequest,
               bool(NominalTypeDecl *), Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, HasMemberwiseInitRequest,
+              bool(StructDecl *), Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, SynthesizeMemberwiseInitRequest,
+              ConstructorDecl *(NominalTypeDecl *), Cached, NoLocationInfo)

lib/AST/Decl.cpp

@@ -3834,6 +3834,28 @@ StructDecl::StructDecl(SourceLoc StructLoc, Identifier Name, SourceLoc NameLoc,
   Bits.StructDecl.HasUnreferenceableStorage = false;
 }
 
+bool NominalTypeDecl::hasMemberwiseInitializer() const {
+  // Currently only structs can have memberwise initializers.
+  auto *sd = dyn_cast<StructDecl>(this);
+  if (!sd)
+    return false;
+
+  auto &ctx = getASTContext();
+  auto *mutableThis = const_cast<StructDecl *>(sd);
+  return evaluateOrDefault(ctx.evaluator, HasMemberwiseInitRequest{mutableThis},
+                           false);
+}
+
+ConstructorDecl *NominalTypeDecl::getMemberwiseInitializer() const {
+  if (!hasMemberwiseInitializer())
+    return nullptr;
+
+  auto &ctx = getASTContext();
+  auto *mutableThis = const_cast<NominalTypeDecl *>(this);
+  return evaluateOrDefault(
+      ctx.evaluator, SynthesizeMemberwiseInitRequest{mutableThis}, nullptr);
+}
+
 ClassDecl::ClassDecl(SourceLoc ClassLoc, Identifier Name, SourceLoc NameLoc,
                      MutableArrayRef<TypeLoc> Inherited,
                      GenericParamList *GenericParams, DeclContext *Parent)

lib/Sema/CodeSynthesis.cpp

@@ -871,36 +871,14 @@ static void addImplicitConstructorsToStruct(StructDecl *decl) {
          "User-defined structs cannot have unreferenceable storage");
 
   decl->setAddedImplicitInitializers();
-
-  // Check whether there is a user-declared constructor or an instance
-  // variable.
-  bool FoundMemberwiseInitializedProperty = false;
+  (void)decl->getMemberwiseInitializer();
 
   // If the user has already defined a designated initializer, then don't
-  // synthesize an initializer.
+  // synthesize a default initializer.
   auto &ctx = decl->getASTContext();
   if (hasUserDefinedDesignatedInit(ctx.evaluator, decl))
     return;
 
-  for (auto member : decl->getMembers()) {
-    if (auto var = dyn_cast<VarDecl>(member)) {
-      // If this is a backing storage property for a property wrapper,
-      // skip it.
-      if (var->getOriginalWrappedProperty())
-        continue;
-
-      if (var->isMemberwiseInitialized(/*preferDeclaredProperties=*/true))
-        FoundMemberwiseInitializedProperty = true;
-    }
-  }
-
-  if (FoundMemberwiseInitializedProperty) {
-    // Create the implicit memberwise constructor.
-    auto ctor = createImplicitConstructor(
-        decl, ImplicitConstructorKind::Memberwise, ctx);
-    decl->addMember(ctor);
-  }
-
   if (areAllStoredPropertiesDefaultInitializable(ctx.evaluator, decl))
     TypeChecker::defineDefaultConstructor(decl);
 }
@@ -1203,6 +1181,43 @@ void TypeChecker::synthesizeMemberForLookup(NominalTypeDecl *target,
   }
 }
 
+llvm::Expected<bool>
+HasMemberwiseInitRequest::evaluate(Evaluator &evaluator,
+                                   StructDecl *decl) const {
+  // Don't synthesize a memberwise init for imported decls.
+  if (decl->hasClangNode())
+    return false;
+
+  // If the user has already defined a designated initializer, then don't
+  // synthesize a memberwise init.
+  if (hasUserDefinedDesignatedInit(evaluator, decl))
+    return false;
+
+  for (auto *member : decl->getMembers()) {
+    if (auto *var = dyn_cast<VarDecl>(member)) {
+      // If this is a backing storage property for a property wrapper,
+      // skip it.
+      if (var->getOriginalWrappedProperty())
+        continue;
+
+      if (var->isMemberwiseInitialized(/*preferDeclaredProperties=*/true))
+        return true;
+    }
+  }
+  return false;
+}
+
+llvm::Expected<ConstructorDecl *>
+SynthesizeMemberwiseInitRequest::evaluate(Evaluator &evaluator,
+                                          NominalTypeDecl *decl) const {
+  // Create the implicit memberwise constructor.
+  auto &ctx = decl->getASTContext();
+  auto ctor =
+      createImplicitConstructor(decl, ImplicitConstructorKind::Memberwise, ctx);
+  decl->addMember(ctor);
+  return ctor;
+}
+
 /// Synthesizer callback for a function body consisting of "return".
 static std::pair<BraceStmt *, bool>
 synthesizeSingleReturnFunctionBody(AbstractFunctionDecl *afd, void *) {