GSB: Introduce a list of explicit as-written requirements

include/swift/AST/GenericSignature.h

@@ -362,8 +362,6 @@ class alignas(1 << TypeAlignInBits) GenericSignatureImpl final
   /// Return the canonical version of the given type under this generic
   /// signature.
   CanType getCanonicalTypeInContext(Type type) const;
-  CanType getCanonicalTypeInContext(Type type,
-                                    GenericSignatureBuilder &builder) const;
 
   bool isCanonicalTypeInContext(Type type) const;
   bool isCanonicalTypeInContext(Type type,

include/swift/AST/GenericSignatureBuilder.h

@@ -270,6 +270,7 @@ class GenericSignatureBuilder {
     struct CachedNestedType {
       unsigned numConformancesPresent;
       CanType superclassPresent;
+      CanType concreteTypePresent;
       llvm::TinyPtrVector<TypeDecl *> types;
     };
 
@@ -793,6 +794,13 @@ class GenericSignatureBuilder {
   /// Simplify the given dependent type down to its canonical representation.
   Type getCanonicalTypeParameter(Type type);
 
+  /// Replace any non-canonical dependent types in the given type with their
+  /// canonical representation. This is not a canonical type in the AST sense;
+  /// type sugar is preserved. The GenericSignature::getCanonicalTypeInContext()
+  /// method combines this with a subsequent getCanonicalType() call.
+  Type getCanonicalTypeInContext(Type type,
+                            TypeArrayView<GenericTypeParamType> genericParams);
+
   /// Verify the correctness of the given generic signature.
   ///
   /// This routine will test that the given generic signature is both minimal

lib/AST/GenericSignature.cpp

@@ -557,47 +557,6 @@ bool GenericSignatureImpl::isCanonicalTypeInContext(
   });
 }
 
-CanType GenericSignatureImpl::getCanonicalTypeInContext(
-    Type type, GenericSignatureBuilder &builder) const {
-  type = type->getCanonicalType();
-
-  // All the contextual canonicality rules apply to type parameters, so if the
-  // type doesn't involve any type parameters, it's already canonical.
-  if (!type->hasTypeParameter())
-    return CanType(type);
-
-  // Replace non-canonical type parameters.
-  type = type.transformRec([&](TypeBase *component) -> Optional<Type> {
-    if (!isa<GenericTypeParamType>(component) &&
-        !isa<DependentMemberType>(component))
-      return None;
-
-    // Find the equivalence class for this dependent type.
-    auto resolved = builder.maybeResolveEquivalenceClass(
-                      Type(component),
-                      ArchetypeResolutionKind::CompleteWellFormed,
-                      /*wantExactPotentialArchetype=*/false);
-    if (!resolved) return None;
-
-    if (auto concrete = resolved.getAsConcreteType())
-      return getCanonicalTypeInContext(concrete, builder);
-
-    auto equivClass = resolved.getEquivalenceClass(builder);
-    if (!equivClass) return None;
-
-    if (equivClass->concreteType) {
-      return getCanonicalTypeInContext(equivClass->concreteType, builder);
-    }
-
-    return equivClass->getAnchor(builder, getGenericParams());
-  });
-
-  auto result = type->getCanonicalType();
-
-  assert(isCanonicalTypeInContext(result, builder));
-  return result;
-}
-
 CanType GenericSignatureImpl::getCanonicalTypeInContext(Type type) const {
   type = type->getCanonicalType();
 
@@ -607,7 +566,7 @@ CanType GenericSignatureImpl::getCanonicalTypeInContext(Type type) const {
     return CanType(type);
 
   auto &builder = *getGenericSignatureBuilder();
-  return getCanonicalTypeInContext(type, builder);
+  return builder.getCanonicalTypeInContext(type, { })->getCanonicalType();
 }
 
 ArrayRef<CanTypeWrapper<GenericTypeParamType>>