swift-mirror/lib/AST/Substitution.cpp

//===--- Substitution.cpp - Type substitutions ----------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
//  This file implements the Substitution class and operations on it.
//
//===----------------------------------------------------------------------===//

#include "swift/AST/Substitution.h"

#include "swift/AST/ASTContext.h"
#include "swift/AST/GenericEnvironment.h"
#include "swift/AST/Module.h"
#include "swift/AST/Types.h"
#include "llvm/ADT/DenseMap.h"

using namespace swift;

bool Substitution::operator==(const Substitution &other) const {
  // The archetypes may be missing, but we can compare them directly
  // because archetypes are always canonical.
  return
    Replacement->getCanonicalType() == other.Replacement->getCanonicalType() &&
    Conformance.equals(other.Conformance);
}

Substitution::Substitution(Type Replacement,
                           ArrayRef<ProtocolConformanceRef> Conformance)
  : Replacement(Replacement), Conformance(Conformance)
{
  // The replacement type must be materializable.
  assert(Replacement->isMaterializable()
         && "cannot substitute with a non-materializable type");
}

Substitution Substitution::subst(Module *module,
                                 GenericSignature *sig,
                                 GenericEnvironment *env,
                                 ArrayRef<Substitution> subs) const {
  TypeSubstitutionMap subMap;
  ArchetypeConformanceMap conformanceMap;

  assert(sig && env);
  env->getSubstitutionMap(module, sig, subs, subMap, conformanceMap);
  return subst(module, subMap, conformanceMap);
}

static Optional<ProtocolConformanceRef>
lookupArchetypeConformance(ProtocolDecl *proto,
                           ArrayRef<ProtocolConformanceRef> conformances) {
  for (ProtocolConformanceRef found : conformances) {
    auto foundProto = found.getRequirement();
    if (foundProto == proto) {
      return found;
    } else if (foundProto->inheritsFrom(proto)) {
      if (found.isConcrete()) {
        return ProtocolConformanceRef(
          found.getConcrete()->getInheritedConformance(proto));
      }

      return found;
    }
  }

  return None;
}

static Optional<ProtocolConformanceRef>
lookupArchetypeConformance(ArchetypeType *replacement,
                           ProtocolDecl *proto,
                           ArchetypeConformanceMap &conformanceMap) {
  // Check for conformances for the type that apply to the original
  // substituted archetype.
  auto it = conformanceMap.find(replacement);
  if (it != conformanceMap.end()) {
    if (auto conformance = lookupArchetypeConformance(proto, it->second)) {
      return conformance;
    }
  }

  // Check if we have substitutions for the parent.
  if (auto *parent = replacement->getParent()) {
    auto *assocType = replacement->getAssocType();
    auto *parentProto = assocType->getProtocol();
    auto conformance =
        lookupArchetypeConformance(parent, parentProto, conformanceMap);

    if (conformance) {
      if (!conformance->isConcrete())
        return ProtocolConformanceRef(proto);

      auto sub = conformance->getConcrete()->getTypeWitnessSubstAndDecl(
          assocType, nullptr).first;

      return lookupArchetypeConformance(proto, sub.getConformances());
    }
  }

  return None;
}

Substitution Substitution::subst(Module *module,
                                 TypeSubstitutionMap &subMap,
                                 ArchetypeConformanceMap &conformanceMap) const {
  // Substitute the replacement.
  Type substReplacement = Replacement.subst(module, subMap, None);
  assert(substReplacement && "substitution replacement failed");

  if (substReplacement->isEqual(Replacement))
    return *this;

  if (Conformance.empty()) {
    return {substReplacement, Conformance};
  }

  bool conformancesChanged = false;
  SmallVector<ProtocolConformanceRef, 4> substConformances;
  substConformances.reserve(Conformance.size());

  for (auto c : Conformance) {
    // If we have a concrete conformance, we need to substitute the
    // conformance to apply to the new type.
    if (c.isConcrete()) {
      auto substC = c.getConcrete()->subst(module, substReplacement,
                                           subMap, conformanceMap);
      substConformances.push_back(ProtocolConformanceRef(substC));
      if (c != substConformances.back())
        conformancesChanged = true;
      continue;
    }

    // Otherwise, we may need to fill in the conformance.
    ProtocolDecl *proto = c.getAbstract();
    Optional<ProtocolConformanceRef> conformance;

    // If the original type was an archetype, check the conformance map.
    if (auto replacementArch = Replacement->getAs<ArchetypeType>()) {
      conformance = lookupArchetypeConformance(replacementArch, proto,
                                               conformanceMap);
    }

    // If that didn't find anything, we can still synthesize AnyObject
    // conformances from thin air.  FIXME: gross.
    if (!conformance &&
        proto->isSpecificProtocol(KnownProtocolKind::AnyObject)) {
      auto classDecl
        = substReplacement->getClassOrBoundGenericClass();
      SmallVector<ProtocolConformance *, 1> lookupResults;
      classDecl->lookupConformance(classDecl->getParentModule(),
                                   proto, lookupResults);
      conformance = ProtocolConformanceRef(lookupResults.front());
    }

    if (conformance) {
      if (conformance->isConcrete())
        conformancesChanged = true;
      substConformances.push_back(*conformance);
    } else {
      assert(substReplacement->hasDependentProtocolConformances() &&
             "couldn't find concrete conformance for concrete type?");
      substConformances.push_back(ProtocolConformanceRef(proto));
    }
  }
  assert(substConformances.size() == Conformance.size());

  ArrayRef<ProtocolConformanceRef> substConfs;
  if (conformancesChanged)
    substConfs = module->getASTContext().AllocateCopy(substConformances);
  else
    substConfs = Conformance;

  return Substitution{substReplacement, substConfs};
}