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/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);
}

static void
getSubstitutionMaps(GenericParamList *context,
                    ArrayRef<Substitution> subs,
                    TypeSubstitutionMap &typeMap,
                    ArchetypeConformanceMap &conformanceMap) {
  for (auto arch : context->getAllNestedArchetypes()) {
    auto sub = subs.front();
    subs = subs.slice(1);

    // Save the conformances from the substitution so that we can substitute
    // them into substitutions that map between archetypes.
    conformanceMap[arch] = sub.getConformances();
    typeMap[arch] = sub.getReplacement();
  }
  assert(subs.empty() && "did not use all substitutions?!");
}

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,
                                 GenericParamList *context,
                                 ArrayRef<Substitution> subs) const {
  TypeSubstitutionMap subMap;
  ArchetypeConformanceMap conformanceMap;
  getSubstitutionMaps(context, subs,
                      subMap, conformanceMap);
  return subst(module, subs, subMap, conformanceMap);
}

Substitution Substitution::subst(Module *module,
                                 ArrayRef<Substitution> subs,
                                 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, subs,
                                           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>()) {
      // Check for conformances for the type that apply to the original
      // substituted archetype.
      auto it = conformanceMap.find(replacementArch);
      assert(it != conformanceMap.end());
      for (ProtocolConformanceRef found : it->second) {
        auto foundProto = found.getRequirement();
        if (foundProto == proto) {
          conformance = found;
          break;
        } else if (foundProto->inheritsFrom(proto)) {
          if (found.isConcrete()) {
            conformance = ProtocolConformanceRef(
              found.getConcrete()->getInheritedConformance(proto));
          } else {
            conformance = found;
          }
          break;
        }
      }
    }

    // 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};
}

SubstitutionIterator::SubstitutionIterator(GenericParamList *params,
                                           ArrayRef<Substitution> subs)
  : Archetypes(params->getAllArchetypes()), Subs(subs) {
}