[AutoDiff] SR-12526: cross-module @derivative deserialization

include/swift/AST/ASTTypeIDZone.def

@@ -29,6 +29,7 @@ SWIFT_TYPEID(Type)
 SWIFT_TYPEID(TypePair)
 SWIFT_TYPEID(TypeWitnessAndDecl)
 SWIFT_TYPEID(Witness)
+SWIFT_TYPEID_NAMED(AbstractFunctionDecl *, AbstractFunctionDecl)
 SWIFT_TYPEID_NAMED(ClosureExpr *, ClosureExpr)
 SWIFT_TYPEID_NAMED(CodeCompletionCallbacksFactory *,
                    CodeCompletionCallbacksFactory)

include/swift/AST/Attr.h

@@ -1865,6 +1865,7 @@ class DerivativeAttr final
     : public DeclAttribute,
       private llvm::TrailingObjects<DerivativeAttr, ParsedAutoDiffParameter> {
   friend TrailingObjects;
+  friend class DerivativeAttrOriginalDeclRequest;
 
   /// The base type for the referenced original declaration. This field is
   /// non-null only for parsed attributes that reference a qualified original
@@ -1873,8 +1874,24 @@ class DerivativeAttr final
   TypeRepr *BaseTypeRepr;
   /// The original function name.
   DeclNameRefWithLoc OriginalFunctionName;
-  /// The original function declaration, resolved by the type checker.
-  AbstractFunctionDecl *OriginalFunction = nullptr;
+  /// The original function.
+  ///
+  /// The states are:
+  /// - nullptr:
+  ///   The original function is unknown. The typechecker is responsible for
+  ///   eventually resolving it.
+  /// - AbstractFunctionDecl:
+  ///   The original function is known to be this `AbstractFunctionDecl`.
+  /// - LazyMemberLoader:
+  ///   This `LazyMemberLoader` knows how to resolve the original function.
+  ///   `ResolverContextData` is an additional piece of data that the
+  ///   `LazyMemberLoader` needs.
+  // TODO(TF-1235): Making `DerivativeAttr` immutable will simplify this by
+  // removing the `AbstractFunctionDecl` state.
+  llvm::PointerUnion<AbstractFunctionDecl *, LazyMemberLoader *> OriginalFunction;
+  /// Data representing the original function declaration. See doc comment for
+  /// `OriginalFunction`.
+  uint64_t ResolverContextData = 0;
   /// The number of parsed differentiability parameters specified in 'wrt:'.
   unsigned NumParsedParameters = 0;
   /// The differentiability parameter indices, resolved by the type checker.
@@ -1907,12 +1924,10 @@ class DerivativeAttr final
   DeclNameRefWithLoc getOriginalFunctionName() const {
     return OriginalFunctionName;
   }
-  AbstractFunctionDecl *getOriginalFunction() const {
-    return OriginalFunction;
-  }
-  void setOriginalFunction(AbstractFunctionDecl *decl) {
-    OriginalFunction = decl;
-  }
+  AbstractFunctionDecl *getOriginalFunction(ASTContext &context) const;
+  void setOriginalFunction(AbstractFunctionDecl *decl);
+  void setOriginalFunctionResolver(LazyMemberLoader *resolver,
+                                   uint64_t resolverContextData);
 
   AutoDiffDerivativeFunctionKind getDerivativeKind() const {
     assert(Kind && "Derivative function kind has not yet been resolved");

include/swift/AST/LazyResolver.h

@@ -106,6 +106,12 @@ class alignas(void*) LazyMemberLoader {
   loadDynamicallyReplacedFunctionDecl(const DynamicReplacementAttr *DRA,
                                       uint64_t contextData) = 0;
 
+  /// Returns the referenced original declaration for a `@derivative(of:)`
+  /// attribute.
+  virtual AbstractFunctionDecl *
+  loadReferencedFunctionDecl(const DerivativeAttr *DA,
+                             uint64_t contextData) = 0;
+
   /// Returns the type for a given @_typeEraser() attribute.
   virtual Type loadTypeEraserType(const TypeEraserAttr *TRA,
                                   uint64_t contextData) = 0;

include/swift/AST/TypeCheckRequests.h

@@ -2130,6 +2130,26 @@ class DifferentiableAttributeTypeCheckRequest
   void cacheResult(IndexSubset *value) const;
 };
 
+/// Resolves the referenced original declaration for a `@derivative` attribute.
+class DerivativeAttrOriginalDeclRequest
+    : public SimpleRequest<DerivativeAttrOriginalDeclRequest,
+                           AbstractFunctionDecl *(DerivativeAttr *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  AbstractFunctionDecl *evaluate(Evaluator &evaluator,
+                                 DerivativeAttr *attr) const;
+
+public:
+  // Caching.
+  bool isCached() const { return true; }
+};
+
 /// Checks whether a type eraser has a viable initializer.
 class TypeEraserHasViableInitRequest
     : public SimpleRequest<TypeEraserHasViableInitRequest,

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -49,6 +49,9 @@ SWIFT_REQUEST(TypeChecker, DefaultTypeRequest,
 SWIFT_REQUEST(TypeChecker, DifferentiableAttributeTypeCheckRequest,
               IndexSubset *(DifferentiableAttr *),
               SeparatelyCached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, DerivativeAttrOriginalDeclRequest,
+              AbstractFunctionDecl *(DerivativeAttr *),
+              Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, TypeEraserHasViableInitRequest,
               bool(TypeEraserAttr *, ProtocolDecl *),
               Cached, NoLocationInfo)

lib/AST/Attr.cpp

@@ -21,6 +21,7 @@
 #include "swift/AST/Expr.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/IndexSubset.h"
+#include "swift/AST/LazyResolver.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/ParameterList.h"
 #include "swift/AST/TypeCheckRequests.h"
@@ -1750,6 +1751,26 @@ DerivativeAttr *DerivativeAttr::create(ASTContext &context, bool implicit,
                                   std::move(originalName), parameterIndices);
 }
 
+AbstractFunctionDecl *
+DerivativeAttr::getOriginalFunction(ASTContext &context) const {
+  return evaluateOrDefault(
+      context.evaluator,
+      DerivativeAttrOriginalDeclRequest{const_cast<DerivativeAttr *>(this)},
+      nullptr);
+}
+
+void DerivativeAttr::setOriginalFunction(AbstractFunctionDecl *decl) {
+  assert(!OriginalFunction && "cannot overwrite original function");
+  OriginalFunction = decl;
+}
+
+void DerivativeAttr::setOriginalFunctionResolver(
+    LazyMemberLoader *resolver, uint64_t resolverContextData) {
+  assert(!OriginalFunction && "cannot overwrite original function");
+  OriginalFunction = resolver;
+  ResolverContextData = resolverContextData;
+}
+
 TransposeAttr::TransposeAttr(bool implicit, SourceLoc atLoc,
                              SourceRange baseRange, TypeRepr *baseTypeRepr,
                              DeclNameRefWithLoc originalName,

lib/ClangImporter/ImporterImpl.h

@@ -1290,6 +1290,12 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
     llvm_unreachable("unimplemented for ClangImporter");
   }
 
+  AbstractFunctionDecl *
+  loadReferencedFunctionDecl(const DerivativeAttr *DA,
+                             uint64_t contextData) override {
+    llvm_unreachable("unimplemented for ClangImporter");
+  }
+
   Type loadTypeEraserType(const TypeEraserAttr *TRA,
                           uint64_t contextData) override {
     llvm_unreachable("unimplemented for ClangImporter");

lib/SILGen/SILGen.cpp

@@ -791,7 +791,7 @@ void SILGenModule::emitDifferentiabilityWitnessesForFunction(
         vjp = F;
         break;
       }
-      auto *origAFD = derivAttr->getOriginalFunction();
+      auto *origAFD = derivAttr->getOriginalFunction(getASTContext());
       auto origDeclRef =
           SILDeclRef(origAFD).asForeign(requiresForeignEntryPoint(origAFD));
       auto *origFn = getFunction(origDeclRef, NotForDefinition);

lib/Sema/TypeCheckAttr.cpp

@@ -3705,8 +3705,6 @@ getTransposeOriginalFunctionType(AnyFunctionType *transposeFnType,
   return originalType;
 }
 
-
-
 /// Given a `@differentiable` attribute, attempts to resolve the original
 /// `AbstractFunctionDecl` for which it is registered, using the declaration
 /// on which it is actually declared. On error, emits diagnostic and returns
@@ -4454,6 +4452,21 @@ void AttributeChecker::visitDerivativeAttr(DerivativeAttr *attr) {
     attr->setInvalid();
 }
 
+AbstractFunctionDecl *
+DerivativeAttrOriginalDeclRequest::evaluate(Evaluator &evaluator,
+                                            DerivativeAttr *attr) const {
+  // If the typechecker has resolved the original function, return it.
+  if (auto *FD = attr->OriginalFunction.dyn_cast<AbstractFunctionDecl *>())
+    return FD;
+
+  // If the function can be lazily resolved, do so now.
+  if (auto *Resolver = attr->OriginalFunction.dyn_cast<LazyMemberLoader *>())
+    return Resolver->loadReferencedFunctionDecl(attr,
+                                                attr->ResolverContextData);
+
+  return nullptr;
+}
+
 /// Returns true if the given type's `TangentVector` is equal to itself in the
 /// given module.
 static bool tangentVectorEqualsSelf(Type type, DeclContext *DC) {

lib/Serialization/Deserialization.cpp

@@ -4379,7 +4379,6 @@ llvm::Error DeclDeserializer::deserializeDeclAttributes() {
 
         DeclNameRefWithLoc origName{
             DeclNameRef(MF.getDeclBaseName(origNameId)), DeclNameLoc()};
-        auto *origDecl = cast<AbstractFunctionDecl>(MF.getDecl(origDeclId));
         auto derivativeKind =
             getActualAutoDiffDerivativeFunctionKind(rawDerivativeKind);
         if (!derivativeKind)
@@ -4392,7 +4391,7 @@ llvm::Error DeclDeserializer::deserializeDeclAttributes() {
         auto *derivativeAttr =
             DerivativeAttr::create(ctx, isImplicit, SourceLoc(), SourceRange(),
                                    /*baseType*/ nullptr, origName, indices);
-        derivativeAttr->setOriginalFunction(origDecl);
+        derivativeAttr->setOriginalFunctionResolver(&MF, origDeclId);
         derivativeAttr->setDerivativeKind(*derivativeKind);
         Attr = derivativeAttr;
         break;
@@ -5941,6 +5940,12 @@ ValueDecl *ModuleFile::loadDynamicallyReplacedFunctionDecl(
   return cast<ValueDecl>(getDecl(contextData));
 }
 
+AbstractFunctionDecl *
+ModuleFile::loadReferencedFunctionDecl(const DerivativeAttr *DA,
+                                       uint64_t contextData) {
+  return cast<AbstractFunctionDecl>(getDecl(contextData));
+}
+
 Type ModuleFile::loadTypeEraserType(const TypeEraserAttr *TRA,
                                     uint64_t contextData) {
   return getType(contextData);

lib/Serialization/ModuleFile.h

@@ -882,6 +882,10 @@ class ModuleFile
   loadDynamicallyReplacedFunctionDecl(const DynamicReplacementAttr *DRA,
                                       uint64_t contextData) override;
 
+  virtual AbstractFunctionDecl *
+  loadReferencedFunctionDecl(const DerivativeAttr *DA,
+                             uint64_t contextData) override;
+
   virtual Type loadTypeEraserType(const TypeEraserAttr *TRA,
                                   uint64_t contextData) override;
 

lib/Serialization/Serialization.cpp

@@ -2417,12 +2417,13 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     case DAK_Derivative: {
       auto abbrCode = S.DeclTypeAbbrCodes[DerivativeDeclAttrLayout::Code];
       auto *attr = cast<DerivativeAttr>(DA);
-      assert(attr->getOriginalFunction() &&
+      auto &ctx = S.getASTContext();
+      assert(attr->getOriginalFunction(ctx) &&
              "`@derivative` attribute should have original declaration set "
              "during construction or parsing");
       auto origName = attr->getOriginalFunctionName().Name.getBaseName();
       IdentifierID origNameId = S.addDeclBaseNameRef(origName);
-      DeclID origDeclID = S.addDeclRef(attr->getOriginalFunction());
+      DeclID origDeclID = S.addDeclRef(attr->getOriginalFunction(ctx));
       auto derivativeKind =
           getRawStableAutoDiffDerivativeFunctionKind(attr->getDerivativeKind());
       auto *parameterIndices = attr->getParameterIndices();
@@ -4862,7 +4863,7 @@ static void recordDerivativeFunctionConfig(
          attr->getDerivativeGenericSignature()});
   }
   for (auto *attr : AFD->getAttrs().getAttributes<DerivativeAttr>()) {
-    auto *origAFD = attr->getOriginalFunction();
+    auto *origAFD = attr->getOriginalFunction(ctx);
     auto mangledName = ctx.getIdentifier(Mangler.mangleDeclAsUSR(origAFD, ""));
     derivativeConfigs[mangledName].insert(
         {ctx.getIdentifier(attr->getParameterIndices()->getString()),

lib/TBDGen/TBDGen.cpp

@@ -665,7 +665,7 @@ void TBDGenVisitor::visitAbstractFunctionDecl(AbstractFunctionDecl *AFD) {
   for (const auto *derivativeAttr :
        AFD->getAttrs().getAttributes<DerivativeAttr>())
     addDerivativeConfiguration(
-        derivativeAttr->getOriginalFunction(),
+        derivativeAttr->getOriginalFunction(AFD->getASTContext()),
         AutoDiffConfig(derivativeAttr->getParameterIndices(),
                        IndexSubset::get(AFD->getASTContext(), 1, {0}),
                        AFD->getGenericSignature()));

test/AutoDiff/Sema/DerivativeRegistrationCrossModule/Inputs/a.swift

@@ -1,7 +1,3 @@
 public struct Struct {
   public func method(_ x: Float) -> Float { x }
-
-  public static func +(_ lhs: Self, rhs: Self) -> Self {
-    lhs
-  }
 }

test/AutoDiff/Sema/DerivativeRegistrationCrossModule/Inputs/b.swift

@@ -10,12 +10,4 @@ extension Struct: Differentiable {
   func vjpMethod(_ x: Float) -> (value: Float, pullback: (Float) -> Float) {
     (x, { $0 })
   }
-
-  @usableFromInline
-  @derivative(of: +)
-  static func vjpAdd(_ lhs: Self, rhs: Self) -> (
-    value: Self, pullback: (TangentVector) -> (TangentVector, TangentVector)
-  ) {
-    (lhs + rhs, { v in (v, v) })
-  }
 }

test/AutoDiff/Sema/DerivativeRegistrationCrossModule/main.swift

@@ -1,14 +1,17 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -emit-module -primary-file %S/Inputs/a.swift -emit-module-path %t/a.swiftmodule
 // RUN: %target-swift-frontend -emit-module -primary-file %S/Inputs/b.swift -emit-module-path %t/b.swiftmodule -I %t
-// RUN: not --crash %target-swift-frontend-typecheck -verify -I %t %s
+// "-verify-ignore-unknown" is for "<unknown>:0: note: 'init()' declared here"
+// RUN: %target-swift-frontend-typecheck -verify -verify-ignore-unknown -I %t %s
 
 // SR-12526: Fix cross-module deserialization crash involving `@derivative` attribute.
 
 import a
 import b
 
 func foo(_ s: Struct) {
+  // Without this error, SR-12526 does not trigger.
+  // expected-error @+1 {{'Struct' initializer is inaccessible due to 'internal' protection level}}
   _ = Struct()
   _ = s.method(1)
 }