[Constraint system] Record application targets for statement conditions.

We’ll need this to generate constraints for statement conditions within the
constraint system. This is unused boilerplate at the moment.

Author: DougGregor

lib/Sema/CSSolver.cpp

@@ -172,6 +172,8 @@ Solution ConstraintSystem::finalize() {
   solution.contextualTypes.assign(
       contextualTypes.begin(), contextualTypes.end());
 
+  solution.stmtConditionTargets = stmtConditionTargets;
+
   for (auto &e : CheckedConformances)
     solution.Conformances.push_back({e.first, e.second});
 
@@ -243,6 +245,12 @@ 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);
+  }
+
   // Register the conformances checked along the way to arrive to solution.
   for (auto &conformance : solution.Conformances)
     CheckedConformances.push_back(conformance);
@@ -455,6 +463,7 @@ ConstraintSystem::SolverScope::SolverScope(ConstraintSystem &cs)
   numResolvedOverloads = cs.ResolvedOverloads.size();
   numInferredClosureTypes = cs.ClosureTypes.size();
   numContextualTypes = cs.contextualTypes.size();
+  numStmtConditionTargets = cs.stmtConditionTargets.size();
 
   PreviousScore = cs.CurrentScore;
 
@@ -532,6 +541,9 @@ ConstraintSystem::SolverScope::~SolverScope() {
   // Remove any contextual types.
   truncate(cs.contextualTypes, numContextualTypes);
 
+  // Remove any statement condition types.
+  truncate(cs.stmtConditionTargets, numStmtConditionTargets);
+
   // Reset the previous score.
   cs.CurrentScore = PreviousScore;
 

lib/Sema/ConstraintSystem.h

@@ -868,6 +868,10 @@ 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;
+
   std::vector<std::pair<ConstraintLocator *, ProtocolConformanceRef>>
       Conformances;
 
@@ -1487,6 +1491,10 @@ 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;
+
   /// Contextual type information for expressions that are part of this
   /// constraint system.
   llvm::MapVector<const Expr *, ContextualTypeInfo> contextualTypes;
@@ -2068,6 +2076,9 @@ class ConstraintSystem {
     /// The length of \c contextualTypes.
     unsigned numContextualTypes;
 
+    /// The length of \c stmtConditionTargets.
+    unsigned numStmtConditionTargets;
+
     /// The previous score.
     Score PreviousScore;
 
@@ -2355,6 +2366,22 @@ 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});
+  }
+
+  Optional<SolutionApplicationTarget> getStmtConditionTarget(
+      const StmtConditionElement *element) const {
+    auto known = stmtConditionTargets.find(element);
+    if (known == stmtConditionTargets.end())
+      return None;
+    return known->second;
+  }
+
   /// Retrieve the constraint locator for the given anchor and
   /// path, uniqued.
   ConstraintLocator *