[ConstraintSystem] NFC: Remove obsolete Fix struct

Also clean up `ConstraintSystem` interface from the storage
supporing `Fix` such as missing types, decl names, conformances etc.

Author: xedin

lib/Sema/Constraint.cpp

@@ -471,89 +471,6 @@ StringRef swift::constraints::getName(ConversionRestrictionKind kind) {
   llvm_unreachable("bad conversion restriction kind");
 }
 
-Fix Fix::getForcedDowncast(ConstraintSystem &cs, Type toType) {
-  unsigned index = cs.FixedTypes.size();
-  cs.FixedTypes.push_back(toType);
-  return Fix(FixKind::ForceDowncast, index);
-}
-
-Fix Fix::getUnwrapOptionalBase(ConstraintSystem &cs, DeclName memberName) {
-  unsigned index = cs.FixedDeclNames.size();
-  cs.FixedDeclNames.push_back(memberName);
-  return Fix(FixKind::UnwrapOptionalBase, index);
-}
-
-Fix Fix::fixArgumentLabels(ConstraintSystem &cs,
-                           ArrayRef<Identifier> newLabels) {
-  unsigned index = cs.FixedArgLabels.size();
-  cs.FixedArgLabels.push_back(newLabels);
-  return Fix(FixKind::RelabelArguments, index);
-}
-
-Type Fix::getTypeArgument(ConstraintSystem &cs) const {
-  assert(getKind() == FixKind::ForceDowncast);
-  return cs.FixedTypes[Data];
-}
-
-/// If this fix has a name argument, retrieve it.
-DeclName Fix::getDeclNameArgument(ConstraintSystem &cs) const {
-  assert(getKind() == FixKind::UnwrapOptionalBase);
-  return cs.FixedDeclNames[Data];
-}
-
-ArrayRef<Identifier> Fix::getArgumentLabels(ConstraintSystem &cs) const {
-  assert(getKind() == FixKind::RelabelArguments);
-  return cs.FixedArgLabels[Data];
-}
-
-/// If this fix has optional result info, retrieve it.
-bool Fix::isUnwrapOptionalBaseByOptionalChaining(ConstraintSystem &cs) const {
-  assert(getKind() == FixKind::UnwrapOptionalBase);
-
-  // Assumes that these fixes are always created in pairs, with the first
-  // created non-optional and the second with an added optional.
-  return (Data % 2) == 1;
-}
-
-StringRef Fix::getName(FixKind kind) {
-  switch (kind) {
-  case FixKind::ForceOptional:
-    return "fix: force optional";
-  case FixKind::UnwrapOptionalBase:
-  case FixKind::UnwrapOptionalBaseWithOptionalResult:
-    return "fix: unwrap optional base of member lookup";
-  case FixKind::ForceDowncast:
-    return "fix: force downcast";
-  case FixKind::AddressOf:
-    return "fix: add address-of";
-  case FixKind::CoerceToCheckedCast:
-    return "fix: as to as!";
-  case FixKind::ExplicitlyEscaping:
-    return "fix: add @escaping";
-  case FixKind::RelabelArguments:
-    return "fix: re-label argument(s)";
-  case FixKind::AddConformance:
-    return "fix: add missing protocol conformance";
-  }
-
-  llvm_unreachable("Unhandled FixKind in switch.");
-}
-
-void Fix::print(llvm::raw_ostream &Out, ConstraintSystem *cs) const {
-  Out << '[' << getName(getKind());
-
-  if (getKind() == FixKind::ForceDowncast && cs) {
-    Out << " as! ";
-    Out << getTypeArgument(*cs).getString();
-  }
-  Out << ']';
-}
-
-void Fix::dump(ConstraintSystem *cs) const {
-  print(llvm::errs(), cs);
-  llvm::errs() << "\n";
-}
-
 /// Recursively gather the set of type variables referenced by this constraint.
 static void
 gatherReferencedTypeVars(Constraint *constraint,

lib/Sema/Constraint.h

@@ -226,64 +226,6 @@ enum RememberChoice_t : bool {
   RememberChoice = true
 };
 
-/// Describes a fix that can be applied to a constraint before visiting it.
-class Fix {
-  FixKind Kind;
-  uint16_t Data;
-
-  Fix(FixKind kind, uint16_t data) : Kind(kind), Data(data){ }
-
-  uint16_t getData() const { return Data; }
-
-  friend class Constraint;
-
-public:
-  Fix(FixKind kind) : Kind(kind), Data(0) {
-    assert(kind != FixKind::ForceDowncast && "Use getForceDowncast()");
-    assert(kind != FixKind::UnwrapOptionalBase &&
-           "Use getUnwrapOptionalBase()");
-  }
-
-  /// Produce a new fix that performs a forced downcast to the given type.
-  static Fix getForcedDowncast(ConstraintSystem &cs, Type toType);
-
-  /// Produce a new fix that unwraps an optional base for an access to a member
-  /// with the given name.
-  static Fix getUnwrapOptionalBase(ConstraintSystem &cs, DeclName memberName);
-
-  /// Produce a new fix that re-labels existing arguments so they much
-  /// what parameters expect.
-  static Fix fixArgumentLabels(ConstraintSystem &cs,
-                               ArrayRef<Identifier> newLabels);
-
-  /// Retrieve the kind of fix.
-  FixKind getKind() const { return Kind; }
-
-  /// If this fix has a type argument, retrieve it.
-  Type getTypeArgument(ConstraintSystem &cs) const;
-
-  /// If this fix has a name argument, retrieve it.
-  DeclName getDeclNameArgument(ConstraintSystem &cs) const;
-
-  /// If this fix is an argument re-labeling, retrieve new labels.
-  ArrayRef<Identifier> getArgumentLabels(ConstraintSystem &cs) const;
-
-  /// If this fix has optional result info, retrieve it.
-  bool isUnwrapOptionalBaseByOptionalChaining(ConstraintSystem &cs) const;
-
-  /// Return a string representation of a fix.
-  static llvm::StringRef getName(FixKind kind);
-
-  void print(llvm::raw_ostream &Out, ConstraintSystem *cs) const;
-
-  LLVM_ATTRIBUTE_DEPRECATED(void dump(ConstraintSystem *cs) const 
-                              LLVM_ATTRIBUTE_USED,
-                            "only for use within the debugger");
-
-  bool operator==(Fix const &b) { return Kind == b.Kind && Data == b.Data; }
-};
-
-
 /// \brief A constraint between two type variables.
 class Constraint final : public llvm::ilist_node<Constraint>,
     private llvm::TrailingObjects<Constraint, TypeVariableType *> {

lib/Sema/ConstraintSystem.h

@@ -1010,21 +1010,6 @@ class ConstraintSystem {
   /// The set of fixes applied to make the solution work.
   llvm::SmallVector<ConstraintFix *, 4> Fixes;
 
-  /// Types used in fixes.
-  std::vector<Type> FixedTypes;
-
-  /// Declaration names used in fixes.
-  std::vector<DeclName> FixedDeclNames;
-
-  /// Argument labels fixed by the constraint solver.
-  SmallVector<std::vector<Identifier>, 4> FixedArgLabels;
-
-  /// Conformances which solver "fixed" to help with
-  /// diagnosing problems related to generic requirements.
-  llvm::SmallDenseMap<std::pair<Expr *, unsigned>,
-                      std::pair<TypeBase *, ProtocolDecl *>>
-      MissingConformances;
-
   /// \brief The set of remembered disjunction choices used to reach
   /// the current constraint system.
   SmallVector<std::pair<ConstraintLocator*, unsigned>, 32>
@@ -1522,12 +1507,6 @@ class ConstraintSystem {
   /// able to emit an error message, or false if none of the fixits worked out.
   bool applySolutionFixes(Expr *E, const Solution &solution);
 
-  /// \brief Apply the specified Fix to this solution, producing a fix-it hint
-  /// diagnostic for it and returning true.  If the fix-it hint turned out to be
-  /// bogus, this returns false and doesn't emit anything.
-  bool applySolutionFix(Expr *expr, const Solution &solution,
-                        std::pair<Fix, ConstraintLocator *> &fix);
-
   /// \brief If there is more than one viable solution,
   /// attempt to pick the best solution and remove all of the rest.
   ///