[CS] NFC: Remove SolutionApplicationToFunctionResult

This is now no longer needed.

Author: hamishknight

include/swift/Sema/ConstraintSystem.h

@@ -2080,15 +2080,6 @@ enum class ConstraintSystemPhase {
   Finalization
 };
 
-/// Describes the result of applying a solution to a given function.
-enum class SolutionApplicationToFunctionResult {
-  /// Application of the solution succeeded.
-  Success,
-  /// Application of the solution failed.
-  /// TODO: This should probably go away entirely.
-  Failure,
-};
-
 /// Retrieve the closure type from the constraint system.
 struct GetClosureType {
   ConstraintSystem &cs;
@@ -5543,8 +5534,8 @@ class ConstraintSystem {
   /// \param fn The function to which the solution is being applied.
   /// \param rewriter The rewriter to apply the solution with.
   ///
-  SolutionApplicationToFunctionResult
-  applySolution(AnyFunctionRef fn, SyntacticElementTargetRewriter &rewriter);
+  bool applySolution(AnyFunctionRef fn,
+                     SyntacticElementTargetRewriter &rewriter);
 
   /// Apply the given solution to the given closure body.
   ///

lib/Sema/CSApply.cpp

@@ -8907,13 +8907,7 @@ namespace {
     ///
     /// \returns true if an error occurred.
     bool rewriteFunction(AnyFunctionRef fn) {
-      switch (Rewriter.cs.applySolution(fn, *this)) {
-      case SolutionApplicationToFunctionResult::Success:
-        return false;
-
-      case SolutionApplicationToFunctionResult::Failure:
-        return true;
-      }
+      return Rewriter.cs.applySolution(fn, *this);
     }
 
     bool rewriteSingleValueStmtExpr(SingleValueStmtExpr *SVE) {

lib/Sema/CSSyntacticElement.cpp

@@ -2541,9 +2541,8 @@ static void applySolutionToClosurePropertyWrappers(ClosureExpr *closure,
   }
 }
 
-SolutionApplicationToFunctionResult
-ConstraintSystem::applySolution(AnyFunctionRef fn,
-                                SyntacticElementTargetRewriter &rewriter) {
+bool ConstraintSystem::applySolution(AnyFunctionRef fn,
+                                     SyntacticElementTargetRewriter &rewriter) {
   auto &solution = rewriter.getSolution();
   auto &cs = solution.getConstraintSystem();
   auto *closure = getAsExpr<ClosureExpr>(fn.getAbstractClosureExpr());
@@ -2590,14 +2589,10 @@ ConstraintSystem::applySolution(AnyFunctionRef fn,
     fn.setParsedBody(transform->transformedBody);
 
     ResultBuilderRewriter builderRewriter(fn, *transform, rewriter);
-    return builderRewriter.apply() ? SolutionApplicationToFunctionResult::Failure
-                                   : SolutionApplicationToFunctionResult::Success;
+    return builderRewriter.apply();
   }
   assert(closure && "Can only get here with a closure at the moment");
-
-  bool hadError = applySolutionToBody(closure, rewriter);
-  return hadError ? SolutionApplicationToFunctionResult::Failure
-                  : SolutionApplicationToFunctionResult::Success;
+  return applySolutionToBody(closure, rewriter);
 }
 
 bool ConstraintSystem::applySolutionToBody(