[ConstraintSystem] Only record fixes that result in a correct solution.

It's probably harmless to record the ones for failures which later cause
us to back out in the solver, but it means we cannot easily set
breakpoints in places like recordFix and stop only in the places where
the fixes actually cause the solution to make progress.

Author: rudkx

lib/Sema/CSSimplify.cpp

@@ -4753,28 +4753,40 @@ ConstraintSystem::simplifyFixConstraint(Fix fix, Type type1, Type type2,
                                         ConstraintKind matchKind,
                                         TypeMatchOptions flags,
                                         ConstraintLocatorBuilder locator) {
-  if (recordFix(fix, locator))
-    return SolutionKind::Error;
-
   // Try with the fix.
   TypeMatchOptions subflags =
     getDefaultDecompositionOptions(flags) | TMF_ApplyingFix;
   switch (fix.getKind()) {
   case FixKind::ForceOptional:
-  case FixKind::OptionalChaining:
+  case FixKind::OptionalChaining: {
     // Assume that '!' was applied to the first type.
-    return matchTypes(type1->getRValueObjectType()->getOptionalObjectType(),
-                      type2, matchKind, subflags, locator);
+    auto result =
+        matchTypes(type1->getRValueObjectType()->getOptionalObjectType(), type2,
+                   matchKind, subflags, locator);
+    if (result == SolutionKind::Solved)
+      if (recordFix(fix, locator))
+        return SolutionKind::Error;
 
+    return result;
+  }
   case FixKind::ForceDowncast:
     // These work whenever they are suggested.
+    if (recordFix(fix, locator))
+      return SolutionKind::Error;
+
     return SolutionKind::Solved;
 
-  case FixKind::AddressOf:
+  case FixKind::AddressOf: {
     // Assume that '&' was applied to the first type, turning an lvalue into
     // an inout.
-    return matchTypes(InOutType::get(type1->getRValueType()), type2,
-                      matchKind, subflags, locator);
+    auto result = matchTypes(InOutType::get(type1->getRValueType()), type2,
+                             matchKind, subflags, locator);
+    if (result == SolutionKind::Solved)
+      if (recordFix(fix, locator))
+        return SolutionKind::Error;
+
+    return result;
+  }
 
   case FixKind::CoerceToCheckedCast:
     llvm_unreachable("handled elsewhere");