Sema: Remove BindingSet::operator bool

include/swift/Sema/CSBindings.h

@@ -469,10 +469,6 @@ public:
   /// checking.
   bool isViable(PotentialBinding &binding, bool isTransitive);
 
-  explicit operator bool() const {
-    return hasViableBindings() || isDirectHole();
-  }
-
   /// Determine whether this set has any "viable" (or non-hole) bindings.
   ///
   /// A viable binding could be - a direct or transitive binding

lib/Sema/CSBindings.cpp

@@ -1171,7 +1171,7 @@ std::optional<BindingSet> ConstraintSystem::determineBestBindings(
     if (shouldAttemptFixes() && typeVar->getImpl().canBindToHole())
       return true;
 
-    return bool(bindings);
+    return bindings.hasViableBindings() || bindings.isDirectHole();
   };
 
   // Now let's see if we could infer something for related type
@@ -1198,7 +1198,10 @@ std::optional<BindingSet> ConstraintSystem::determineBestBindings(
     if (!bindings.finalize(true))
       continue;
 
-    if (!bindings || !isViable)
+    if (!bindings.hasViableBindings() && !bindings.isDirectHole())
+      continue;
+
+    if (!isViable)
       continue;
 
     onCandidate(bindings);

lib/Sema/CSOptimizer.cpp

@@ -1105,7 +1105,9 @@ static void determineBestChoicesInContext(
       // Simply adding it as a binding won't work because if the second argument
       // is non-optional the overload that returns `T?` would still have a lower
       // score.
-      if (!bindingSet && isNilCoalescingOperator(disjunction)) {
+      if (!bindingSet.hasViableBindings() &&
+          !bindingSet.isDirectHole() &&
+          isNilCoalescingOperator(disjunction)) {
         auto &cg = cs.getConstraintGraph();
         if (llvm::any_of(cg[typeVar].getConstraints(),
                          [&typeVar](Constraint *constraint) {

lib/Sema/ConstraintGraph.cpp

@@ -921,7 +921,8 @@ bool ConstraintGraph::contractEdges() {
     // us enough information to decided on l-valueness.
     if (tyvar1->getImpl().canBindToInOut()) {
       bool isNotContractable = true;
-      if (auto bindings = CS.getBindingsFor(tyvar1)) {
+      auto bindings = CS.getBindingsFor(tyvar1);
+      if (bindings.hasViableBindings() || bindings.isDirectHole()) {
         // Holes can't be contracted.
         if (bindings.isHole())
           continue;