[Sema] Exclude private initialized vars from memberwise initializer

Exclude properties with initial values from the memberwise initializer
if they are less accessible than the most accessible property, up to
`internal`. Introduce a compatibility overload that continues to
include the same properties as before until the next language mode.

This is gated behind the `ExcludePrivateFromMemberwiseInit` feature.

rdar://122416579

Author: hamishknight

include/swift/AST/Decl.h

@@ -273,6 +273,15 @@ static_assert(uint8_t(SelfAccessKind::LastSelfAccessKind) <
               "Self Access Kind is too small to fit in SelfAccess kind bits. "
               "Please expand ");
 
+enum class MemberwiseInitKind {
+  /// The regular memberwise initializer.
+  Regular,
+  /// A compatibility memberwise initializer that includes all private
+  /// initialized variables. This only exists for migration purposes, and will
+  /// be removed in a future language mode.
+  Compatibility
+};
+
 enum class UsingSpecifier : uint8_t {
   MainActor,
   Nonisolated,
@@ -4634,9 +4643,10 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   ArrayRef<VarDecl *> getInitAccessorProperties() const;
 
   /// Return a collection of all properties that will be part of the memberwise
-  ///  initializer.
-  ArrayRef<VarDecl *> getMemberwiseInitProperties() const;
-  
+  /// initializer.
+  ArrayRef<VarDecl *>
+  getMemberwiseInitProperties(MemberwiseInitKind initKind) const;
+
   /// Establish a mapping between properties that could be iniitalized
   /// via other properties by means of init accessors. This mapping is
   /// one-to-many because we allow intersecting `initializes(...)`.
@@ -4679,11 +4689,11 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   }
 
   /// Whether this declaration has a synthesized memberwise initializer.
-  bool hasMemberwiseInitializer() const;
+  bool hasMemberwiseInitializer(MemberwiseInitKind initKind) const;
 
   /// Retrieves the synthesized memberwise initializer for this declaration,
   /// or \c nullptr if it does not have one.
-  ConstructorDecl *getMemberwiseInitializer() const;
+  ConstructorDecl *getMemberwiseInitializer(MemberwiseInitKind initKind) const;
 
   /// Retrieves the effective memberwise initializer for this declaration, or
   /// \c nullptr if it does not have one.
@@ -6967,7 +6977,9 @@ class VarDecl : public AbstractStorageDecl {
   /// actual declared property (which may or may not be considered "stored"
   /// as the moment) to the backing storage property. Otherwise, the stored
   /// backing property will be treated as the member-initialized property.
-  bool isMemberwiseInitialized(bool preferDeclaredProperties) const;
+  bool isMemberwiseInitialized(
+      MemberwiseInitKind initKind, bool preferDeclaredProperties,
+      std::optional<AccessLevel> minAccess = std::nullopt) const;
 
   /// Return the range of semantics attributes attached to this VarDecl.
   auto getSemanticsAttrs() const
@@ -7728,6 +7740,7 @@ class AbstractFunctionDecl : public GenericContext, public ValueDecl {
   enum class SILSynthesizeKind {
     None,
     MemberwiseInitializer,
+    CompatibilityMemberwiseInitializer,
     DistributedActorFactory
 
     // This enum currently needs to fit in a 2-bit bitfield.
@@ -8100,11 +8113,19 @@ class AbstractFunctionDecl : public GenericContext, public ValueDecl {
 
   /// Note that this is a memberwise initializer and thus the body will be
   /// generated by SILGen.
-  void setIsMemberwiseInitializer() {
+  void setIsMemberwiseInitializer(MemberwiseInitKind initKind) {
     assert(getBodyKind() == BodyKind::None);
     assert(isa<ConstructorDecl>(this));
     setBodyKind(BodyKind::SILSynthesize);
-    setSILSynthesizeKind(SILSynthesizeKind::MemberwiseInitializer);
+    switch (initKind) {
+    case MemberwiseInitKind::Regular:
+      setSILSynthesizeKind(SILSynthesizeKind::MemberwiseInitializer);
+      break;
+    case MemberwiseInitKind::Compatibility:
+      setSILSynthesizeKind(
+          SILSynthesizeKind::CompatibilityMemberwiseInitializer);
+      break;
+    }
   }
 
   /// Mark that the body should be filled in to be a factory method for creating
@@ -8140,9 +8161,20 @@ class AbstractFunctionDecl : public GenericContext, public ValueDecl {
   /// typechecking.
   bool isBodySkipped() const;
 
-  bool isMemberwiseInitializer() const {
-    return getBodyKind() == BodyKind::SILSynthesize
-        && getSILSynthesizeKind() == SILSynthesizeKind::MemberwiseInitializer;
+  /// Checks whether this is a memberwise initializer decl, and if so the kind,
+  /// otherwise \c std::nullopt.
+  std::optional<MemberwiseInitKind> isMemberwiseInitializer() const {
+    if (getBodyKind() != BodyKind::SILSynthesize)
+      return std::nullopt;
+
+    switch (getSILSynthesizeKind()) {
+    case SILSynthesizeKind::MemberwiseInitializer:
+      return MemberwiseInitKind::Regular;
+    case SILSynthesizeKind::CompatibilityMemberwiseInitializer:
+      return MemberwiseInitKind::Compatibility;
+    default:
+      return std::nullopt;
+    }
   }
 
   /// Determines whether this function represents a distributed actor
@@ -10196,9 +10228,22 @@ getAccessorNameForDiagnostic(AccessorDecl *accessor, bool article,
 StringRef getAccessorNameForDiagnostic(AccessorKind accessorKind, bool article,
                                        bool underscored);
 
-/// Retrieve a textual representation for a memberwise initializer in a given
-/// nominal decl.
-void printMemberwiseInit(NominalTypeDecl *nominal, llvm::raw_ostream &out);
+inline void simple_display(llvm::raw_ostream &out,
+                           MemberwiseInitKind initKind) {
+  switch (initKind) {
+  case MemberwiseInitKind::Regular:
+    out << "regular";
+    break;
+  case MemberwiseInitKind::Compatibility:
+    out << "compatibility";
+    break;
+  }
+}
+
+/// Retrieve a textual representation for a particular kind of memberwise
+/// initializer in a given nominal decl.
+void printMemberwiseInit(NominalTypeDecl *nominal, MemberwiseInitKind initKind,
+                         llvm::raw_ostream &out);
 
 void simple_display(llvm::raw_ostream &out,
                     OptionSet<NominalTypeDecl::LookupDirectFlags> options);

include/swift/AST/DiagnosticsSema.def

@@ -2706,6 +2706,15 @@ ERROR(spi_only_imports_not_enabled, none,
       "'@_spiOnly' requires setting the frontend flag '-experimental-spi-only-imports'",
       ())
 
+WARNING(warn_use_of_compat_memberwise_init,Deprecation,
+        "synthesized memberwise initializer no longer includes "
+        "%select{private properties with initial values|%1}0; uses of it "
+        "will be an error in a future Swift language mode", (bool, StringRef))
+NOTE(insert_compat_memberwise_init,none,
+     "insert an explicit implementation of the memberwise initializer",())
+NOTE(compat_memberwise_init_used_here,none,
+     "memberwise initializer used here",())
+
 // Access level on imports
 ERROR(access_level_on_import_unsupported, none,
       "The access level %0 is unsupported on imports: "

include/swift/AST/SourceFileExtras.h

@@ -23,6 +23,9 @@ class Decl;
 /// Extra information associated with a source file that is lazily created and
 /// stored in a separately-allocated side structure.
 struct SourceFileExtras {
+  /// Set of compatibility memberwise initializers that we have emitted a
+  /// warning for.
+  llvm::DenseSet<const ConstructorDecl *> DiagnosedCompatMemberwiseInits;
 };
 
 }

include/swift/AST/TypeCheckRequests.h

@@ -1990,19 +1990,39 @@ class InitAccessorPropertiesRequest :
 
 /// Request to obtain a list of properties that will be reflected in the parameters of a
 /// memberwise initializer.
-class MemberwiseInitPropertiesRequest :
-    public SimpleRequest<MemberwiseInitPropertiesRequest,
-                         ArrayRef<VarDecl *>(NominalTypeDecl *),
-                         RequestFlags::Cached> {
+class MemberwiseInitPropertiesRequest
+    : public SimpleRequest<MemberwiseInitPropertiesRequest,
+                           ArrayRef<VarDecl *>(NominalTypeDecl *,
+                                               MemberwiseInitKind),
+                           RequestFlags::Cached> {
 public:
   using SimpleRequest::SimpleRequest;
 
 private:
   friend SimpleRequest;
 
   // Evaluation.
-  ArrayRef<VarDecl *>
-  evaluate(Evaluator &evaluator, NominalTypeDecl *decl) const;
+  ArrayRef<VarDecl *> evaluate(Evaluator &evaluator, NominalTypeDecl *decl,
+                               MemberwiseInitKind initKind) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// The maximum access level the memberwise initializer can be for a given
+/// nominal decl.
+class MemberwiseInitMaxAccessLevel
+    : public SimpleRequest<MemberwiseInitMaxAccessLevel,
+                           AccessLevel(NominalTypeDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  AccessLevel evaluate(Evaluator &evaluator, NominalTypeDecl *nominal) const;
 
 public:
   bool isCached() const { return true; }
@@ -2843,7 +2863,8 @@ class HasUserDefinedDesignatedInitRequest
 
 /// Checks whether this type has a synthesized memberwise initializer.
 class HasMemberwiseInitRequest
-    : public SimpleRequest<HasMemberwiseInitRequest, bool(StructDecl *),
+    : public SimpleRequest<HasMemberwiseInitRequest,
+                           bool(StructDecl *, MemberwiseInitKind),
                            RequestFlags::Cached> {
 public:
   using SimpleRequest::SimpleRequest;
@@ -2852,7 +2873,8 @@ class HasMemberwiseInitRequest
   friend SimpleRequest;
 
   // Evaluation.
-  bool evaluate(Evaluator &evaluator, StructDecl *decl) const;
+  bool evaluate(Evaluator &evaluator, StructDecl *decl,
+                MemberwiseInitKind initKind) const;
 
 public:
   // Caching.
@@ -2862,7 +2884,8 @@ class HasMemberwiseInitRequest
 /// Synthesizes a memberwise initializer for a given type.
 class SynthesizeMemberwiseInitRequest
     : public SimpleRequest<SynthesizeMemberwiseInitRequest,
-                           ConstructorDecl *(NominalTypeDecl *),
+                           ConstructorDecl *(NominalTypeDecl *,
+                                             MemberwiseInitKind),
                            RequestFlags::Cached> {
 public:
   using SimpleRequest::SimpleRequest;
@@ -2871,7 +2894,8 @@ class SynthesizeMemberwiseInitRequest
   friend SimpleRequest;
 
   // Evaluation.
-  ConstructorDecl *evaluate(Evaluator &evaluator, NominalTypeDecl *decl) const;
+  ConstructorDecl *evaluate(Evaluator &evaluator, NominalTypeDecl *decl,
+                            MemberwiseInitKind initKind) const;
 
 public:
   // Caching.

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -342,7 +342,10 @@ SWIFT_REQUEST(TypeChecker, InitAccessorPropertiesRequest,
               ArrayRef<VarDecl *>(NominalTypeDecl *),
               Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, MemberwiseInitPropertiesRequest,
-              ArrayRef<VarDecl *>(NominalTypeDecl *),
+              ArrayRef<VarDecl *>(NominalTypeDecl *, MemberwiseInitKind),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, MemberwiseInitMaxAccessLevel,
+              AccessLevel(NominalTypeDecl *),
               Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, StructuralTypeRequest, Type(TypeAliasDecl *), Cached,
               NoLocationInfo)
@@ -394,7 +397,7 @@ SWIFT_REQUEST(TypeChecker, AreAllStoredPropertiesDefaultInitableRequest,
 SWIFT_REQUEST(TypeChecker, HasUserDefinedDesignatedInitRequest,
               bool(NominalTypeDecl *), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, HasMemberwiseInitRequest,
-              bool(StructDecl *), Cached, NoLocationInfo)
+              bool(StructDecl *, MemberwiseInitKind), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, BraceHasExplicitReturnStmtRequest,
               bool(const BraceStmt *),
               Cached, NoLocationInfo)
@@ -434,7 +437,8 @@ SWIFT_REQUEST(TypeChecker, SPIGroupsRequest,
               llvm::ArrayRef<Identifier>(Decl *),
               SeparatelyCached | SplitCached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, SynthesizeMemberwiseInitRequest,
-              ConstructorDecl *(NominalTypeDecl *), Cached, NoLocationInfo)
+              ConstructorDecl *(NominalTypeDecl *, MemberwiseInitKind),
+              Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, ResolveEffectiveMemberwiseInitRequest,
               ConstructorDecl *(NominalTypeDecl *), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, HasDefaultInitRequest,

include/swift/Basic/Features.def

@@ -533,6 +533,10 @@ EXPERIMENTAL_FEATURE(DefaultIsolationPerFile, false)
 /// Enable @_lifetime attribute
 SUPPRESSIBLE_EXPERIMENTAL_FEATURE(Lifetimes, true)
 
+/// Excludes '(file)private' properties with initial values from the memberwise
+/// initializer if there is a more accessible initializable property.
+EXPERIMENTAL_FEATURE(ExcludePrivateFromMemberwiseInit, true)
+
 /// Allow macro based aliases to be imported into Swift
 EXPERIMENTAL_FEATURE(ImportMacroAliases, true)