[Constraint system] Generalize saved ASTNode -> solution target mapping.

We are currently only using the “solution targets” map for statement
conditions, but we will need it for more entities soon. Start generalizing
now.

Author: DougGregor

lib/Sema/CSApply.cpp

@@ -7461,7 +7461,7 @@ ExprWalker::rewriteTarget(SolutionApplicationTarget target) {
 
       case StmtConditionElement::CK_PatternBinding: {
         ConstraintSystem &cs = solution.getConstraintSystem();
-        auto target = *cs.getStmtConditionTarget(&condElement);
+        auto target = *cs.getSolutionApplicationTarget(&condElement);
         auto resolvedTarget = rewriteTarget(target);
         if (!resolvedTarget)
           return None;

lib/Sema/CSGen.cpp

@@ -4214,7 +4214,7 @@ bool ConstraintSystem::generateConstraints(StmtCondition condition,
       if (generateConstraints(target, FreeTypeVariableBinding::Disallow))
         return true;
 
-      setStmtConditionTarget(&condElement, target);
+      setSolutionApplicationTarget(&condElement, target);
       continue;
     }
     }

lib/Sema/CSSolver.cpp

@@ -172,7 +172,7 @@ Solution ConstraintSystem::finalize() {
   solution.contextualTypes.assign(
       contextualTypes.begin(), contextualTypes.end());
 
-  solution.stmtConditionTargets = stmtConditionTargets;
+  solution.solutionApplicationTargets = solutionApplicationTargets;
 
   for (auto &e : CheckedConformances)
     solution.Conformances.push_back({e.first, e.second});
@@ -246,9 +246,10 @@ void ConstraintSystem::applySolution(const Solution &solution) {
   }
 
   // Register the statement condition targets.
-  for (const auto &stmtConditionTarget : solution.stmtConditionTargets) {
-    if (!getStmtConditionTarget(stmtConditionTarget.first))
-      setStmtConditionTarget(stmtConditionTarget.first, stmtConditionTarget.second);
+  for (const auto &target : solution.solutionApplicationTargets) {
+    if (!getSolutionApplicationTarget(target.first))
+      setSolutionApplicationTarget(target.first, target.second);
+  }
   }
 
   // Register the conformances checked along the way to arrive to solution.
@@ -463,7 +464,7 @@ ConstraintSystem::SolverScope::SolverScope(ConstraintSystem &cs)
   numResolvedOverloads = cs.ResolvedOverloads.size();
   numInferredClosureTypes = cs.ClosureTypes.size();
   numContextualTypes = cs.contextualTypes.size();
-  numStmtConditionTargets = cs.stmtConditionTargets.size();
+  numSolutionApplicationTargets = cs.solutionApplicationTargets.size();
 
   PreviousScore = cs.CurrentScore;
 
@@ -541,8 +542,8 @@ ConstraintSystem::SolverScope::~SolverScope() {
   // Remove any contextual types.
   truncate(cs.contextualTypes, numContextualTypes);
 
-  // Remove any statement condition types.
-  truncate(cs.stmtConditionTargets, numStmtConditionTargets);
+  // Remove any solution application targets.
+  truncate(cs.solutionApplicationTargets, numSolutionApplicationTargets);
 
   // Reset the previous score.
   cs.CurrentScore = PreviousScore;

lib/Sema/ConstraintSystem.h

@@ -803,6 +803,10 @@ struct ContextualTypeInfo {
   Type getType() const { return typeLoc.getType(); }
 };
 
+
+/// Key to the constraint solver's mapping from AST nodes to their corresponding
+/// solution application targets.
+using SolutionApplicationTargetsKey = const StmtConditionElement *;
 /// A complete solution to a constraint system.
 ///
 /// A solution to a constraint system consists of type variable bindings to
@@ -868,9 +872,9 @@ class Solution {
   /// Contextual types introduced by this solution.
   std::vector<std::pair<const Expr *, ContextualTypeInfo>> contextualTypes;
 
-  /// Maps statement condition entries to their solution application targets.
-  llvm::MapVector<const StmtConditionElement *, SolutionApplicationTarget>
-    stmtConditionTargets;
+  /// Maps AST nodes to their solution application targets.
+  llvm::MapVector<SolutionApplicationTargetsKey, SolutionApplicationTarget>
+    solutionApplicationTargets;
 
   std::vector<std::pair<ConstraintLocator *, ProtocolConformanceRef>>
       Conformances;
@@ -1546,9 +1550,9 @@ class ConstraintSystem {
   llvm::DenseMap<std::pair<const KeyPathExpr *, unsigned>, TypeBase *>
       KeyPathComponentTypes;
 
-  /// Maps statement condition entries to their solution application targets.
-  llvm::MapVector<const StmtConditionElement *, SolutionApplicationTarget>
-    stmtConditionTargets;
+  /// Maps AST entries to their solution application targets.
+  llvm::MapVector<SolutionApplicationTargetsKey, SolutionApplicationTarget>
+    solutionApplicationTargets;
 
   /// Contextual type information for expressions that are part of this
   /// constraint system.
@@ -2131,8 +2135,8 @@ class ConstraintSystem {
     /// The length of \c contextualTypes.
     unsigned numContextualTypes;
 
-    /// The length of \c stmtConditionTargets.
-    unsigned numStmtConditionTargets;
+    /// The length of \c solutionApplicationTargets.
+    unsigned numSolutionApplicationTargets;
 
     /// The previous score.
     Score PreviousScore;
@@ -2421,18 +2425,18 @@ class ConstraintSystem {
     return CTP_Unused;
   }
 
-  void setStmtConditionTarget(
-      const StmtConditionElement *element, SolutionApplicationTarget target) {
-    assert(element != nullptr && "Expected non-null condition element!");
-    assert(stmtConditionTargets.count(element) == 0 &&
-           "Already set this condition target");
-    stmtConditionTargets.insert({element, target});
+  void setSolutionApplicationTarget(
+      SolutionApplicationTargetsKey key, SolutionApplicationTarget target) {
+    assert(key && "Expected non-null solution application target key!");
+    assert(solutionApplicationTargets.count(key) == 0 &&
+           "Already set this solution application target");
+    solutionApplicationTargets.insert({key, target});
   }
 
-  Optional<SolutionApplicationTarget> getStmtConditionTarget(
-      const StmtConditionElement *element) const {
-    auto known = stmtConditionTargets.find(element);
-    if (known == stmtConditionTargets.end())
+  Optional<SolutionApplicationTarget> getSolutionApplicationTarget(
+      SolutionApplicationTargetsKey key) const {
+    auto known = solutionApplicationTargets.find(key);
+    if (known == solutionApplicationTargets.end())
       return None;
     return known->second;
   }