swift-mirror/lib/Sema/CSTrail.cpp

//===--- CSTrail.cpp -  Tracking changes that can be undone ---------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file defines the \c SolverTrail class, which records the decisions taken
// while attempting to find a solution.
//
//===----------------------------------------------------------------------===//

#include "swift/Basic/Defer.h"
#include "swift/Basic/Statistic.h"
#include "swift/Sema/ConstraintGraph.h"
#include "swift/Sema/ConstraintSystem.h"
#include "swift/Sema/CSTrail.h"
#include "swift/Basic/Assertions.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/SaveAndRestore.h"
#include <algorithm>
#include <memory>
#include <numeric>

using namespace swift;
using namespace constraints;

#define DEBUG_TYPE "SolverTrail"

SolverTrail::~SolverTrail() {
  // If constraint system is in an invalid state, it's
  // possible that constraint graph is corrupted as well
  // so let's not attempt to check change log.
  if (!CS.inInvalidState())
    ASSERT(Changes.empty() && "Trail corrupted");
}

SolverTrail::Change
SolverTrail::Change::addedTypeVariable(TypeVariableType *typeVar) {
  Change result;
  result.Kind = ChangeKind::AddedTypeVariable;
  result.TypeVar = typeVar;
  return result;
}

SolverTrail::Change
SolverTrail::Change::addedConstraint(Constraint *constraint) {
  Change result;
  result.Kind = ChangeKind::AddedConstraint;
  result.TheConstraint = constraint;
  return result;
}

SolverTrail::Change
SolverTrail::Change::removedConstraint(Constraint *constraint) {
  Change result;
  result.Kind = ChangeKind::RemovedConstraint;
  result.TheConstraint = constraint;
  return result;
}

SolverTrail::Change
SolverTrail::Change::extendedEquivalenceClass(TypeVariableType *typeVar,
                                              unsigned prevSize) {
  Change result;
  result.Kind = ChangeKind::ExtendedEquivalenceClass;
  result.EquivClass.TypeVar = typeVar;
  result.EquivClass.PrevSize = prevSize;
  return result;
}

SolverTrail::Change
SolverTrail::Change::boundTypeVariable(TypeVariableType *typeVar,
                                       Type fixed) {
  Change result;
  result.Kind = ChangeKind::BoundTypeVariable;
  result.Binding.TypeVar = typeVar;
  result.Binding.FixedType = fixed.getPointer();
  return result;
}

SolverTrail::Change
SolverTrail::Change::introducedToInference(TypeVariableType *typeVar,
                                           Type fixed) {
  Change result;
  result.Kind = ChangeKind::IntroducedToInference;
  result.Binding.TypeVar = typeVar;
  result.Binding.FixedType = fixed.getPointer();
  return result;
}

SolverTrail::Change
SolverTrail::Change::updatedTypeVariable(
    TypeVariableType *typeVar,
    llvm::PointerUnion<TypeVariableType *, TypeBase *> parentOrFixed,
	  unsigned options) {
  Change result;
  result.Kind = ChangeKind::UpdatedTypeVariable;
  result.Update.TypeVar = typeVar;
  result.Update.ParentOrFixed = parentOrFixed;
  result.Update.Options = options;
  return result;
}

void SolverTrail::Change::undo(ConstraintSystem &cs) const {
  auto &cg = cs.getConstraintGraph();

  switch (Kind) {
  case ChangeKind::AddedTypeVariable:
    cg.removeNode(TypeVar);
    break;

  case ChangeKind::AddedConstraint:
    cg.removeConstraint(TheConstraint);
    break;

  case ChangeKind::RemovedConstraint:
    cg.addConstraint(TheConstraint);
    break;

  case ChangeKind::ExtendedEquivalenceClass: {
    auto &node = cg[EquivClass.TypeVar];
    node.truncateEquivalenceClass(EquivClass.PrevSize);
    break;
   }

  case ChangeKind::BoundTypeVariable:
    cg.unbindTypeVariable(Binding.TypeVar, Binding.FixedType);
    break;

  case ChangeKind::IntroducedToInference:
    cg.retractFromInference(Binding.TypeVar, Binding.FixedType);
    break;

  case ChangeKind::UpdatedTypeVariable:
    Update.TypeVar->getImpl().setRawOptions(Update.Options);
    Update.TypeVar->getImpl().ParentOrFixed = Update.ParentOrFixed;
    break;
  }
}

void SolverTrail::Change::dump(llvm::raw_ostream &out,
                               ConstraintSystem &cs,
                               unsigned indent) const {
  PrintOptions PO;
  PO.PrintTypesForDebugging = true;

  out.indent(indent);

  switch (Kind) {
  case ChangeKind::AddedTypeVariable:
    out << "(added type variable ";
    TypeVar->print(out, PO);
    out << ")\n";
    break;

  case ChangeKind::AddedConstraint:
    out << "(added constraint ";
    TheConstraint->print(out, &cs.getASTContext().SourceMgr, indent + 2);
    out << ")\n";
    break;

  case ChangeKind::RemovedConstraint:
    out << "(removed constraint ";
    TheConstraint->print(out, &cs.getASTContext().SourceMgr, indent + 2);
    out << ")\n";
    break;

  case ChangeKind::ExtendedEquivalenceClass: {
    out << "(equivalence ";
    EquivClass.TypeVar->print(out, PO);
    out << " " << EquivClass.PrevSize << ")\n";
    break;
   }

  case ChangeKind::BoundTypeVariable:
    out << "(bound type variable ";
    Binding.TypeVar->print(out, PO);
    out << " to fixed type ";
    Binding.FixedType->print(out, PO);
    out << ")\n";
    break;

  case ChangeKind::IntroducedToInference:
    out << "(introduced type variable ";
    Binding.TypeVar->print(out, PO);
    out << " with fixed type ";
    Binding.FixedType->print(out, PO);
    out << " to inference)\n";
    break;

  case ChangeKind::UpdatedTypeVariable:
    out << "(updated type variable ";
    Update.TypeVar->print(out, PO);

    auto parentOrFixed = Update.TypeVar->getImpl().ParentOrFixed;
    if (auto *parent = parentOrFixed.dyn_cast<TypeVariableType *>()) {
      out << " to parent ";
      parent->print(out, PO);
    }
    else {
      out << " to fixed type ";
      parentOrFixed.get<TypeBase *>()->print(out, PO);
    }
    out << " with options 0x";
    out.write_hex(Update.Options);
    out << ")\n";
    break;
  }
}

void SolverTrail::recordChange(Change change) {
  ASSERT(!UndoActive);
  Changes.push_back(change);
}

void SolverTrail::undo(unsigned toIndex) {
  // Don't attempt to rollback if constraint system ended up
  // in an invalid state.
  if (CS.inInvalidState())
    return;

  ASSERT(Changes.size() >= toIndex && "Trail corrupted");
  ASSERT(!UndoActive);
  UndoActive = true;

  for (unsigned i = Changes.size(); i > toIndex; i--) {
    auto change = Changes[i - 1];
    if (change.Kind == ChangeKind::UpdatedTypeVariable)
      change.undo(CS);
  }

  for (unsigned i = Changes.size(); i > toIndex; i--) {
    auto change = Changes[i - 1];
    if (change.Kind != ChangeKind::UpdatedTypeVariable)
      change.undo(CS);
  }

  Changes.resize(toIndex);
  UndoActive = false;
}

void SolverTrail::dumpActiveScopeChanges(llvm::raw_ostream &out,
                                         unsigned fromIndex,
                                         unsigned indent) const {
  out.indent(indent);
  out << "(changes:\n";

  for (unsigned i = fromIndex; i < Changes.size(); ++i)
    Changes[i].dump(out, CS, indent + 2);

  out.indent(indent);
  out << ")\n";
}