[ConstraintSystem] Simplify some logic around attempting fixes for Optionals.

Only record the fixes when they have made the solution to this point
successful.

Author: rudkx

lib/Sema/CSSimplify.cpp

@@ -4186,7 +4186,21 @@ ConstraintSystem::simplifyApplicableFnConstraint(
   ConstraintLocatorBuilder outerLocator =
     getConstraintLocator(anchor, parts, locator.getSummaryFlags());
 
-retry:
+  unsigned unwrapCount = 0;
+  if (shouldAttemptFixes()) {
+    // If we have an optional type, try forcing it to see if that
+    // helps. Note that we only deal with function and metatype types
+    // below, so there is no reason not to attempt to strip these off
+    // immediately.
+    while (auto objectType2 = desugar2->getOptionalObjectType()) {
+      type2 = objectType2;
+      desugar2 = type2->getDesugaredType();
+
+      // Track how many times we do this so that we can record a fix for each.
+      ++unwrapCount;
+    }
+  }
+
   // For a function, bind the output and convert the argument to the input.
   auto func1 = type1->castTo<FunctionType>();
   if (auto func2 = dyn_cast<FunctionType>(desugar2)) {
@@ -4214,6 +4228,11 @@ ConstraintSystem::simplifyApplicableFnConstraint(
           == SolutionKind::Error)
       return SolutionKind::Error;
 
+    // Record any fixes we attempted to get to the correct solution.
+    while (unwrapCount-- > 0)
+      if (recordFix(FixKind::ForceOptional, getConstraintLocator(locator)))
+        return SolutionKind::Error;
+
     return SolutionKind::Solved;
   }
 
@@ -4224,23 +4243,18 @@ ConstraintSystem::simplifyApplicableFnConstraint(
       return formUnsolved();
 
     // Construct the instance from the input arguments.
-    return simplifyConstructionConstraint(instance2, func1, subflags,
+    auto simplified = simplifyConstructionConstraint(instance2, func1, subflags,
                                           /*FIXME?*/ DC,
                                           FunctionRefKind::SingleApply,
                                           getConstraintLocator(outerLocator));
-  }
 
-  if (!shouldAttemptFixes())
-    return SolutionKind::Error;
-
-  // If we're coming from an optional type, unwrap the optional and try again.
-  if (auto objectType2 = desugar2->getOptionalObjectType()) {
-    if (recordFix(FixKind::ForceOptional, getConstraintLocator(locator)))
-      return SolutionKind::Error;
+    // Record any fixes we attempted to get to the correct solution.
+    if (simplified == SolutionKind::Solved)
+      while (unwrapCount-- > 0)
+        if (recordFix(FixKind::ForceOptional, getConstraintLocator(locator)))
+          return SolutionKind::Error;
 
-    type2 = objectType2;
-    desugar2 = type2->getDesugaredType();
-    goto retry;
+    return simplified;
   }
 
   return SolutionKind::Error;