[Sema] Requestify inheritsSuperclassInitializers (#27936)

* [Sema] Factor out shouldAttemptInitializerSynthesis

This makes sure we don't attempt to synthesize
a memberwise or default initializer for an invalid
decl, or one in a module interface.

* [Sema] Requesify inheritsSuperclassInitializers

This commit introduces a request for computing
whether a class inherits both designated and
convenience initializers from its superclass.

The shared logic of finding initializers which the
subclass hasn't overriden has been factored out
into `collectNonOveriddenSuperclassInits`.

* Cleanup addImplicitInheritedConstructorsToClass

This commit removes some code that's no longer
needed. In addition, now that we've requestified
`inheritsSuperclassInitializers`, we can directly
diagnose on non-inherited required convenience
inits within the loop.

* Inherited init synthesis no longer deals with clang decls

Now that the computation of
`inheritsSuperclassInitializers` has been split off
into a request, we can avoid calling
`addImplicitInheritedConstructorsToClass` for clang
decls.

* Address review feedback

Continue to cache the InheritsSuperclassInits bit
on the AST.

Author: hamishknight

include/swift/AST/Decl.h

@@ -527,12 +527,13 @@ class alignas(1 << DeclAlignInBits) Decl {
     NumRequirementsInSignature : 16
   );
 
-  SWIFT_INLINE_BITFIELD(ClassDecl, NominalTypeDecl, 2+1+2+1+7+1+1+1+1+1+1,
+  SWIFT_INLINE_BITFIELD(ClassDecl, NominalTypeDecl, 2+1+1+2+1+7+1+1+1+1+1+1,
     /// The stage of the inheritance circularity check for this class.
     Circularity : 2,
 
     /// Whether this class inherits its superclass's convenience initializers.
     InheritsSuperclassInits : 1,
+    ComputedInheritsSuperclassInits : 1,
 
     /// \see ClassDecl::ForeignKind
     RawForeignKind : 2,
@@ -3810,9 +3811,24 @@ class ClassDecl final : public NominalTypeDecl {
     Bits.ClassDecl.HasForcedEmittedMembers = true;
   }
 
+  Optional<bool> getCachedInheritsSuperclassInitializers() const {
+    if (Bits.ClassDecl.ComputedInheritsSuperclassInits)
+      return Bits.ClassDecl.InheritsSuperclassInits;
+
+    return None;
+  }
+
+  /// Marks that this class inherits convenience initializers from its
+  /// superclass.
+  void setInheritsSuperclassInitializers(bool value) {
+    Bits.ClassDecl.InheritsSuperclassInits = value;
+    Bits.ClassDecl.ComputedInheritsSuperclassInits = true;
+  }
+
   friend class SuperclassDeclRequest;
   friend class SuperclassTypeRequest;
   friend class EmittedMembersRequest;
+  friend class InheritsSuperclassInitializersRequest;
   friend class TypeChecker;
 
 public:
@@ -3970,15 +3986,6 @@ class ClassDecl final : public NominalTypeDecl {
   /// from its superclass.
   bool inheritsSuperclassInitializers();
 
-  /// Marks that this class inherits convenience initializers from its
-  /// superclass.
-  ///
-  /// This is computed as part of adding implicit initializers.
-  void setInheritsSuperclassInitializers() {
-    assert(addedImplicitInitializers());
-    Bits.ClassDecl.InheritsSuperclassInits = true;
-  }
-
   /// Walks the class hierarchy starting from this class, checking various
   /// conditions.
   AncestryOptions checkAncestry() const;

include/swift/AST/TypeCheckRequests.h

@@ -1647,6 +1647,27 @@ class CompareDeclSpecializationRequest
   bool isCached() const { return true; }
 };
 
+/// Checks whether this declaration inherits its superclass' designated and
+/// convenience initializers.
+class InheritsSuperclassInitializersRequest
+    : public SimpleRequest<InheritsSuperclassInitializersRequest,
+                           bool(ClassDecl *), CacheKind::SeparatelyCached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  llvm::Expected<bool> evaluate(Evaluator &evaluator, ClassDecl *decl) const;
+
+public:
+  // Separate caching.
+  bool isCached() const { return true; }
+  Optional<bool> getCachedResult() const;
+  void cacheResult(bool value) const;
+};
+
 // Allow AnyValue to compare two Type values, even though Type doesn't
 // support ==.
 template<>

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -180,3 +180,5 @@ SWIFT_REQUEST(TypeChecker, HasDefaultInitRequest,
               bool(NominalTypeDecl *), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, SynthesizeDefaultInitRequest,
               ConstructorDecl *(NominalTypeDecl *), Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, InheritsSuperclassInitializersRequest,
+              bool(ClassDecl *), SeparatelyCached, NoLocationInfo)

lib/AST/Decl.cpp

@@ -3957,6 +3957,7 @@ ClassDecl::ClassDecl(SourceLoc ClassLoc, Identifier Name, SourceLoc NameLoc,
   Bits.ClassDecl.Circularity
     = static_cast<unsigned>(CircularityCheck::Unchecked);
   Bits.ClassDecl.InheritsSuperclassInits = 0;
+  Bits.ClassDecl.ComputedInheritsSuperclassInits = 0;
   Bits.ClassDecl.RawForeignKind = 0;
   Bits.ClassDecl.HasMissingDesignatedInitializers = 0;
   Bits.ClassDecl.ComputedHasMissingDesignatedInitializers = 0;
@@ -4072,31 +4073,16 @@ bool ClassDecl::isIncompatibleWithWeakReferences() const {
 }
 
 bool ClassDecl::inheritsSuperclassInitializers() {
-  // Check whether we already have a cached answer.
-  if (addedImplicitInitializers())
-    return Bits.ClassDecl.InheritsSuperclassInits;
-
   // If there's no superclass, there's nothing to inherit.
-  ClassDecl *superclassDecl;
-  if (!(superclassDecl = getSuperclassDecl())) {
-    setAddedImplicitInitializers();
-    return false;
-  }
-
-  // If the superclass has known-missing designated initializers, inheriting
-  // is unsafe.
-  if (superclassDecl->hasMissingDesignatedInitializers())
+  if (!getSuperclass())
     return false;
 
-  // Otherwise, do all the work of resolving constructors, which will also
-  // calculate the right answer.
-  if (auto *resolver = getASTContext().getLazyResolver())
-    resolver->resolveImplicitConstructors(this);
-
-  return Bits.ClassDecl.InheritsSuperclassInits;
+  auto &ctx = getASTContext();
+  auto *mutableThis = const_cast<ClassDecl *>(this);
+  return evaluateOrDefault(
+      ctx.evaluator, InheritsSuperclassInitializersRequest{mutableThis}, false);
 }
 
-
 AncestryOptions ClassDecl::checkAncestry() const {
   return AncestryOptions(evaluateOrDefault(getASTContext().evaluator,
                            ClassAncestryFlagsRequest{const_cast<ClassDecl *>(this)},

lib/AST/TypeCheckRequests.cpp

@@ -1057,3 +1057,17 @@ void swift::simple_display(llvm::raw_ostream &out,
   out << "precedence group " << desc.ident << " at ";
   desc.nameLoc.print(out, desc.dc->getASTContext().SourceMgr);
 }
+
+//----------------------------------------------------------------------------//
+// InheritsSuperclassInitializersRequest computation.
+//----------------------------------------------------------------------------//
+
+Optional<bool> InheritsSuperclassInitializersRequest::getCachedResult() const {
+  auto *decl = std::get<0>(getStorage());
+  return decl->getCachedInheritsSuperclassInitializers();
+}
+
+void InheritsSuperclassInitializersRequest::cacheResult(bool value) const {
+  auto *decl = std::get<0>(getStorage());
+  decl->setInheritsSuperclassInitializers(value);
+}