Sema: More accurate undo() of PotentialBindings::retract()

include/swift/Sema/CSBindings.h

@@ -71,15 +71,12 @@ enum class LiteralBindingKind : uint8_t {
 /// along with information that can be used to construct related
 /// bindings, e.g., the supertypes of a given type.
 struct PotentialBinding {
-  friend class BindingSet;
-
   /// The type to which the type variable can be bound.
   Type BindingType;
 
   /// The kind of bindings permitted.
   AllowedBindingKind Kind;
 
-protected:
   /// The source of the type information.
   ///
   /// Determines whether this binding represents a "hole" in
@@ -91,7 +88,6 @@ struct PotentialBinding {
                    PointerUnion<Constraint *, ConstraintLocator *> source)
       : BindingType(type), Kind(kind), BindingSource(source) {}
 
-public:
   PotentialBinding(Type type, AllowedBindingKind kind, Constraint *source)
       : PotentialBinding(
             type, kind,
@@ -219,25 +215,11 @@ struct LiteralRequirement {
 
 struct PotentialBindings {
   /// The set of all constraints that have been added via infer().
-  llvm::SmallPtrSet<Constraint *, 2> Constraints;
+  llvm::SmallSetVector<Constraint *, 2> Constraints;
 
   /// The set of potential bindings.
   llvm::SmallVector<PotentialBinding, 4> Bindings;
 
-  /// The set of protocol requirements placed on this type variable.
-  llvm::SmallVector<Constraint *, 4> Protocols;
-
-  /// The set of unique literal protocol requirements placed on this
-  /// type variable or inferred transitively through subtype chains.
-  ///
-  /// Note that ordering is important when it comes to bindings, we'd
-  /// like to add any "direct" default types first to attempt them
-  /// before transitive ones.
-  llvm::SmallPtrSet<Constraint *, 2> Literals;
-
-  /// The set of constraints which would be used to infer default types.
-  llvm::SmallPtrSet<Constraint *, 2> Defaults;
-
   /// The set of constraints which delay attempting this type variable.
   llvm::TinyPtrVector<Constraint *> DelayedBy;
 
@@ -247,22 +229,17 @@ struct PotentialBindings {
   /// bindings (contained in the binding type e.g. `Foo<$T0>`), or
   /// reachable through subtype/conversion  relationship e.g.
   /// `$T0 subtype of $T1` or `$T0 arg conversion $T1`.
-  llvm::SmallDenseSet<std::pair<TypeVariableType *, Constraint *>, 2>
-      AdjacentVars;
-
-  ASTNode AssociatedCodeCompletionToken = ASTNode();
+  llvm::SmallVector<std::pair<TypeVariableType *, Constraint *>, 2> AdjacentVars;
 
   /// A set of all not-yet-resolved type variables this type variable
   /// is a subtype of, supertype of or is equivalent to. This is used
   /// to determine ordering inside of a chain of subtypes to help infer
   /// transitive bindings  and protocol requirements.
-  llvm::SmallSetVector<std::pair<TypeVariableType *, Constraint *>, 4> SubtypeOf;
-  llvm::SmallSetVector<std::pair<TypeVariableType *, Constraint *>, 4> SupertypeOf;
-  llvm::SmallSetVector<std::pair<TypeVariableType *, Constraint *>, 4> EquivalentTo;
-
-  void addDefault(Constraint *constraint);
+  llvm::SmallVector<std::pair<TypeVariableType *, Constraint *>, 4> SubtypeOf;
+  llvm::SmallVector<std::pair<TypeVariableType *, Constraint *>, 4> SupertypeOf;
+  llvm::SmallVector<std::pair<TypeVariableType *, Constraint *>, 4> EquivalentTo;
 
-  void addLiteral(Constraint *constraint);
+  ASTNode AssociatedCodeCompletionToken = ASTNode();
 
   /// Add a potential binding to the list of bindings,
   /// coalescing supertype bounds when we are able to compute the meet.
@@ -385,28 +362,26 @@ class BindingSet {
 
 public:
   swift::SmallSetVector<PotentialBinding, 4> Bindings;
+
+  /// The set of protocol conformance requirements placed on this type variable.
+  llvm::SmallVector<Constraint *, 4> Protocols;
+
+  /// The set of unique literal protocol requirements placed on this
+  /// type variable or inferred transitively through subtype chains.
+  ///
+  /// Note that ordering is important when it comes to bindings, we'd
+  /// like to add any "direct" default types first to attempt them
+  /// before transitive ones.
   llvm::SmallMapVector<ProtocolDecl *, LiteralRequirement, 2> Literals;
+
   llvm::SmallDenseMap<CanType, Constraint *, 2> Defaults;
 
   /// The set of transitive protocol requirements inferred through
   /// subtype/conversion/equivalence relations with other type variables.
   std::optional<llvm::SmallPtrSet<Constraint *, 4>> TransitiveProtocols;
 
   BindingSet(ConstraintSystem &CS, TypeVariableType *TypeVar,
-             const PotentialBindings &info)
-      : CS(CS), TypeVar(TypeVar), Info(info) {
-    for (const auto &binding : info.Bindings)
-      addBinding(binding, /*isTransitive=*/false);
-
-    for (auto *literal : info.Literals)
-      addLiteralRequirement(literal);
-
-    for (auto *constraint : info.Defaults)
-      addDefault(constraint);
-
-    for (auto &entry : info.AdjacentVars)
-      AdjacentVars.insert(entry.first);
-  }
+             const PotentialBindings &info);
 
   ConstraintSystem &getConstraintSystem() const { return CS; }
 
@@ -512,7 +487,7 @@ class BindingSet {
   }
 
   ArrayRef<Constraint *> getConformanceRequirements() const {
-    return Info.Protocols;
+    return Protocols;
   }
 
   unsigned getNumViableLiteralBindings() const;

include/swift/Sema/CSTrail.def

@@ -38,6 +38,10 @@
 #define GRAPH_NODE_CHANGE(Name) CHANGE(Name)
 #endif
 
+#ifndef BINDING_RELATION_CHANGE
+#define BINDING_RELATION_CHANGE(Name) CHANGE(Name)
+#endif
+
 #ifndef SCORE_CHANGE
 #define SCORE_CHANGE(Name) CHANGE(Name)
 #endif
@@ -73,6 +77,12 @@ GRAPH_NODE_CHANGE(AddedConstraint)
 GRAPH_NODE_CHANGE(RemovedConstraint)
 GRAPH_NODE_CHANGE(InferredBindings)
 GRAPH_NODE_CHANGE(RetractedBindings)
+GRAPH_NODE_CHANGE(RetractedDelayedBy)
+
+BINDING_RELATION_CHANGE(RetractedAdjacentVar)
+BINDING_RELATION_CHANGE(RetractedSubtypeOf)
+BINDING_RELATION_CHANGE(RetractedSupertypeOf)
+BINDING_RELATION_CHANGE(RetractedEquivalentTo)
 
 SCORE_CHANGE(IncreasedScore)
 SCORE_CHANGE(DecreasedScore)
@@ -96,14 +106,16 @@ CHANGE(RecordedPotentialThrowSite)
 CHANGE(RecordedIsolatedParam)
 CHANGE(RecordedKeyPath)
 CHANGE(RetiredConstraint)
+CHANGE(RetractedBinding)
 
-LAST_CHANGE(RetiredConstraint)
+LAST_CHANGE(RetractedBinding)
 
 #undef LOCATOR_CHANGE
 #undef EXPR_CHANGE
 #undef CLOSURE_CHANGE
 #undef CONSTRAINT_CHANGE
 #undef GRAPH_NODE_CHANGE
+#undef BINDING_RELATION_CHANGE
 #undef SCORE_CHANGE
 #undef LAST_CHANGE
 #undef CHANGE

include/swift/Sema/CSTrail.h

@@ -38,6 +38,10 @@ namespace constraints {
 class Constraint;
 struct SyntacticElementTargetKey;
 
+namespace inference {
+struct PotentialBinding;
+}
+
 class SolverTrail {
 public:
 
@@ -89,6 +93,12 @@ class SolverTrail {
         TypeVariableType *OtherTypeVar;
       } Relation;
 
+      struct {
+        TypeVariableType *TypeVar;
+        TypeVariableType *OtherTypeVar;
+        Constraint *Constraint;
+      } BindingRelation;
+
       struct {
         /// The type variable being updated.
         TypeVariableType *TypeVar;
@@ -128,6 +138,15 @@ class SolverTrail {
         Constraint *Constraint;
       } Retiree;
 
+      struct {
+        TypeVariableType *TypeVar;
+
+        /// These two fields together with 'Options' above store the contents
+        /// of a PotentialBinding.
+        Type BindingType;
+        PointerUnion<Constraint *, ConstraintLocator *> BindingSource;
+      } Binding;
+
       ConstraintFix *TheFix;
       ConstraintLocator *TheLocator;
       PackExpansionType *TheExpansion;
@@ -155,6 +174,9 @@ class SolverTrail {
 #define SCORE_CHANGE(Name) static Change Name(ScoreKind kind, unsigned value);
 #define GRAPH_NODE_CHANGE(Name) static Change Name(TypeVariableType *typeVar, \
                                                    Constraint *constraint);
+#define BINDING_RELATION_CHANGE(Name) static Change Name(TypeVariableType *typeVar, \
+                                                         TypeVariableType *otherTypeVar, \
+                                                         Constraint *constraint);
 #include "swift/Sema/CSTrail.def"
 
     /// Create a change that added a type variable.
@@ -226,6 +248,11 @@ class SolverTrail {
     static Change RetiredConstraint(llvm::ilist<Constraint>::iterator where,
                                     Constraint *constraint);
 
+    /// Create a change that removed a binding from a type variable's potential
+    /// bindings.
+    static Change RetractedBinding(TypeVariableType *typeVar,
+                                   inference::PotentialBinding binding);
+
     /// Undo this change, reverting the constraint graph to the state it
     /// had prior to this change.
     ///

include/swift/Sema/ConstraintGraph.h

@@ -448,11 +448,6 @@ class ConstraintGraph {
   void unrelateTypeVariables(TypeVariableType *typeVar,
                              TypeVariableType *otherTypeVar);
 
-  /// Infer bindings from the given constraint.
-  ///
-  /// Note that this it only meant to be called by SolverTrail::Change::undo().
-  void inferBindings(TypeVariableType *typeVar, Constraint *constraint);
-
   /// Retract bindings from the given constraint.
   ///
   /// Note that this it only meant to be called by SolverTrail::Change::undo().