Eliminate witness markers

include/swift/AST/GenericSignature.h

@@ -31,71 +31,6 @@ class ProtocolType;
 class Substitution;
 class SubstitutionMap;
 
-/// Iterator that walks the generic parameter types declared in a generic
-/// signature and their dependent members.
-class GenericSignatureWitnessIterator {
-  ArrayRef<Requirement> p;
-
-  void checkValid() const {
-    assert(!p.empty() &&
-           p.front().getKind() == RequirementKind::WitnessMarker);
-  }
-
-  bool shouldSkip() const {
-    return (!p.empty() &&
-            p.front().getKind() != RequirementKind::WitnessMarker);
-  }
-
-public:
-  GenericSignatureWitnessIterator() = default;
-  GenericSignatureWitnessIterator(ArrayRef<Requirement> requirements)
-      : p(requirements) {
-    while (shouldSkip()) { p = p.slice(1); }
-  }
-
-  GenericSignatureWitnessIterator &operator++() {
-    checkValid();
-    do { p = p.slice(1); } while (shouldSkip());
-    return *this;
-  }
-
-  GenericSignatureWitnessIterator operator++(int) {
-    auto copy = *this;
-    ++(*this);
-    return copy;
-  }
-
-  Type operator*() const {
-    checkValid();
-    return p.front().getFirstType();
-  }
-
-  Type operator->() const {
-    checkValid();
-    return p.front().getFirstType();
-  }
-
-  bool operator==(const GenericSignatureWitnessIterator &o) {
-    return p.data() == o.p.data() && p.size() == o.p.size();
-  }
-
-  bool operator!=(const GenericSignatureWitnessIterator &o) {
-    return p.data() != o.p.data() || p.size() != o.p.size();
-  }
-
-  static GenericSignatureWitnessIterator emptyRange() {
-    return GenericSignatureWitnessIterator();
-  }
-
-  // Allow the witness iterator to be used with a ranged for.
-  GenericSignatureWitnessIterator begin() const {
-    return *this;
-  }
-  GenericSignatureWitnessIterator end() const {
-    return GenericSignatureWitnessIterator({p.end(), p.end()});
-  }
-};
-
 /// Describes the generic signature of a particular declaration, including
 /// both the generic type parameters and the requirements placed on those
 /// generic parameters.
@@ -207,12 +142,22 @@ class alignas(1 << TypeAlignInBits) GenericSignature final
                         const SubstitutionMap &subMap,
                         SmallVectorImpl<Substitution> &result) const;
 
-  /// Return a range that iterates through first all of the generic parameters
-  /// of the signature, followed by all of their recursive member types exposed
-  /// through protocol requirements.
-  GenericSignatureWitnessIterator getAllDependentTypes() const {
-    return GenericSignatureWitnessIterator(getRequirements());
-  }
+  /// Return a range that iterates through all of the types that require
+  /// substitution, which includes the generic parameter types as well as
+  /// other dependent types that require additional conformances.
+  SmallVector<Type, 4> getAllDependentTypes() const;
+
+  /// Enumerate all of the dependent types in the type signature that will
+  /// occur in substitution lists (in order), along with the set of
+  /// conformance requirements placed on that dependent type.
+  ///
+  /// \param fn Callback function that will receive each (type, requirements)
+  /// pair, in the order they occur within a list of substitutions. If this
+  /// returns \c true, the enumeration will be aborted.
+  ///
+  /// \returns true if any call to \c fn returned \c true, otherwise \c false.
+  bool enumeratePairedRequirements(
+         llvm::function_ref<bool(Type, ArrayRef<Requirement>)> fn) const;
 
   /// Determines whether this GenericSignature is canonical.
   bool isCanonical() const;

include/swift/AST/Requirement.h

@@ -35,12 +35,6 @@ enum class RequirementKind : unsigned {
   /// A same-type requirement T == U, where T and U are types that shall be
   /// equivalent.
   SameType,
-  /// A marker that indicates where the witness for the given (first)
-  /// type should be located.
-  ///
-  /// FIXME: This is a crutch used to help us eliminate various walks over
-  /// "all archetypes".
-  WitnessMarker
 
   // Note: there is code that packs this enum in a 2-bit bitfield.  Audit users
   // when adding enumerators.
@@ -56,10 +50,8 @@ class Requirement {
   /// Create a conformance or same-type requirement.
   Requirement(RequirementKind kind, Type first, Type second)
     : FirstTypeAndKind(first, kind), SecondType(second) {
-    if (kind != RequirementKind::WitnessMarker) {
-      assert(first);
-      assert(second);
-    }
+    assert(first);
+    assert(second);
   }
 
   /// \brief Determine the kind of requirement.

include/swift/Serialization/ModuleFormat.h

@@ -54,7 +54,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// in source control, you should also update the comment to briefly
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
-const uint16_t VERSION_MINOR = 282; // Last change: @_inlineable
+const uint16_t VERSION_MINOR = 283; // Last change: witness markers removed
 
 using DeclID = PointerEmbeddedInt<unsigned, 31>;
 using DeclIDField = BCFixed<31>;
@@ -236,9 +236,8 @@ static inline OperatorKind getStableFixity(DeclKind kind) {
 // VERSION_MAJOR.
 enum GenericRequirementKind : uint8_t {
   Conformance = 0,
-  SameType,
-  WitnessMarker,
-  Superclass
+  SameType    = 1,
+  Superclass  = 2,
 };
 using GenericRequirementKindField = BCFixed<2>;
 

lib/AST/ASTContext.cpp

@@ -3542,8 +3542,7 @@ void GenericSignature::Profile(llvm::FoldingSetNodeID &ID,
 
   for (auto &reqt : requirements) {
     ID.AddPointer(reqt.getFirstType().getPointer());
-    if (reqt.getKind() != RequirementKind::WitnessMarker)
-      ID.AddPointer(reqt.getSecondType().getPointer());
+    ID.AddPointer(reqt.getSecondType().getPointer());
     ID.AddInteger(unsigned(reqt.getKind()));
   }
 }
@@ -4056,8 +4055,7 @@ CanGenericSignature ASTContext::getSingleGenericParameterSignature() const {
     return theSig;
 
   auto param = GenericTypeParamType::get(0, 0, *this);
-  auto witnessReqt = Requirement(RequirementKind::WitnessMarker, param, Type());
-  auto sig = GenericSignature::get(param, witnessReqt);;
+  auto sig = GenericSignature::get(param, { });
   auto canonicalSig = CanGenericSignature(sig);
   Impl.SingleGenericParameterSignature = canonicalSig;
   return canonicalSig;

lib/AST/ASTPrinter.cpp

@@ -233,8 +233,6 @@ struct SynthesizedExtensionAnalyzer::Implementation {
     assert(Ext->getGenericSignature() && "No generic signature.");
     for (auto Req : Ext->getGenericSignature()->getRequirements()) {
       auto Kind = Req.getKind();
-      if (Kind == RequirementKind::WitnessMarker)
-        continue;
 
       Type First = Req.getFirstType().subst(
           M, subMap, SubstOptions());
@@ -251,9 +249,6 @@ struct SynthesizedExtensionAnalyzer::Implementation {
       Second = Second->getCanonicalType();
 
       switch (Kind) {
-        case RequirementKind::WitnessMarker:
-          break;
-
         case RequirementKind::Conformance:
         case RequirementKind::Superclass:
           if (!canPossiblyConvertTo(First, Second, *DC))
@@ -1208,7 +1203,6 @@ static unsigned getDepthOfRequirement(const Requirement &req) {
   switch (req.getKind()) {
   case RequirementKind::Conformance:
   case RequirementKind::Superclass:
-  case RequirementKind::WitnessMarker:
     return getDepthOfType(req.getFirstType());
 
   case RequirementKind::SameType: {
@@ -1337,9 +1331,6 @@ void PrintAST::printSingleDepthOfGenericSignature(
     // Print the requirements.
     bool isFirstReq = true;
     for (const auto &req : requirements) {
-      if (req.getKind() == RequirementKind::WitnessMarker)
-        continue;
-
       auto first = req.getFirstType();
       auto second = req.getSecondType();
 
@@ -1387,9 +1378,6 @@ void PrintAST::printRequirement(const Requirement &req) {
   case RequirementKind::SameType:
     Printer << " == ";
     break;
-
-  case RequirementKind::WitnessMarker:
-    llvm_unreachable("Handled above");
   }
   printType(req.getSecondType());
 }
@@ -4119,9 +4107,6 @@ void GenericSignature::dump() const {
 
 void Requirement::dump() const {
   switch (getKind()) {
-  case RequirementKind::WitnessMarker:
-    llvm::errs() << "witness_marker: ";
-    break;
   case RequirementKind::Conformance:
     llvm::errs() << "conforms_to: ";
     break;

lib/AST/ArchetypeBuilder.cpp

@@ -1517,9 +1517,6 @@ void ArchetypeBuilder::addRequirement(const Requirement &req,
   case RequirementKind::SameType:
     addSameTypeRequirement(req.getFirstType(), req.getSecondType(), source);
     return;
-
-  case RequirementKind::WitnessMarker:
-    return;
   }
 
   llvm_unreachable("Unhandled requirement?");
@@ -1569,9 +1566,6 @@ class ArchetypeBuilder::InferRequirementsWalker : public TypeWalker {
     RequirementSource source(RequirementSource::Inferred, Loc);
     for (const auto &req : genericSig->getRequirements()) {
       switch (req.getKind()) {
-      case RequirementKind::WitnessMarker:
-        break;
-
       case RequirementKind::SameType: {
         auto firstType = req.getFirstType().subst(
                            &Builder.getModule(),
@@ -1891,10 +1885,6 @@ void ArchetypeBuilder::enumerateRequirements(llvm::function_ref<
       continue;
     }
 
-    // Add the witness marker.
-    f(RequirementKind::WitnessMarker, archetype, Type(),
-      RequirementSource(RequirementSource::Explicit, SourceLoc()));
-
     // If we have a superclass, produce a superclass requirement
     if (Type superclass = archetype->getSuperclass()) {
       f(RequirementKind::Superclass, archetype, superclass,
@@ -1957,10 +1947,6 @@ void ArchetypeBuilder::dump(llvm::raw_ostream &out) {
       source.dump(out, &Context.SourceMgr);
       out << "]";
       break;
-
-    case RequirementKind::WitnessMarker:
-      out << "\n  " << archetype->getDebugName() << " witness marker";
-      break;
     }
   });
   out << "\n";
@@ -2046,15 +2032,6 @@ Type ArchetypeBuilder::substDependentType(Type type) {
 static void collectRequirements(ArchetypeBuilder &builder,
                                 ArrayRef<GenericTypeParamType *> params,
                                 SmallVectorImpl<Requirement> &requirements) {
-  // Don't emit WitnessMarker requirements for secondary types with
-  // no requirements.
-  auto dropRedundantWitnessMarker = [&]() {
-    if (!requirements.empty() &&
-        requirements.back().getKind() == RequirementKind::WitnessMarker &&
-        !requirements.back().getFirstType()->is<GenericTypeParamType>())
-      requirements.pop_back();
-  };
-
   builder.enumerateRequirements([&](RequirementKind kind,
           ArchetypeBuilder::PotentialArchetype *archetype,
           llvm::PointerUnion<Type, ArchetypeBuilder::PotentialArchetype *> type,
@@ -2078,12 +2055,6 @@ static void collectRequirements(ArchetypeBuilder &builder,
     if (depTy->hasError())
       return;
 
-    if (kind == RequirementKind::WitnessMarker) {
-      dropRedundantWitnessMarker();
-      requirements.push_back(Requirement(kind, depTy, Type()));
-      return;
-    }
-
     Type repTy;
     if (auto concreteTy = type.dyn_cast<Type>()) {
       // Maybe we were equated to a concrete type...
@@ -2099,8 +2070,6 @@ static void collectRequirements(ArchetypeBuilder &builder,
 
     requirements.push_back(Requirement(kind, depTy, repTy));
   });
-
-  dropRedundantWitnessMarker();
 }
 
 GenericSignature *ArchetypeBuilder::getGenericSignature() {

lib/AST/Builtins.cpp

@@ -196,14 +196,8 @@ getBuiltinGenericFunction(Identifier Id,
     GenericParamTypes.push_back(gp->getDeclaredType()
                                   ->castTo<GenericTypeParamType>());
   }
-  // Create witness markers for all of the generic param types.
-  SmallVector<Requirement, 2> requirements;
-  for (auto param : GenericParamTypes) {
-    requirements.push_back(Requirement(RequirementKind::WitnessMarker,
-                                       param, Type()));
-  }
   GenericSignature *Sig =
-      GenericSignature::get(GenericParamTypes, requirements);
+    GenericSignature::get(GenericParamTypes, { });
   GenericEnvironment *Env =
       GenericEnvironment::get(Context, GenericParamTypes,
                               InterfaceToArchetypeMap);