[CS] Preserve fatal scoring information across conjunction elements

We currently solve conjunction elements starting from a zero score,
but that means we can end up dropping `SK_Fix` and `SK_Hole` scoring
information, resulting in attempting to run CSApply on invalid
solutions. Make sure we preserve these score kinds both across
conjunction elements as well as propagating into non-isolated
conjunctions.

Author: hamishknight

lib/Sema/CSStep.cpp

@@ -803,21 +803,32 @@ bool ConjunctionStep::attempt(const ConjunctionElement &element) {
   // subsequent elements.
   CS.solverState->BestScore.reset();
 
+  // Make sure that element is solved in isolation by dropping scoring
+  // information. We do still need to preserve fatal score kinds below though.
+  CS.clearScore();
+
   // Apply solution inferred for all the previous elements
   // because this element could reference declarations
   // established in previous element(s).
+  Score PreviousScore;
   if (!Solutions.empty()) {
     assert(Solutions.size() == 1);
     // Note that solution is removed here. This is done
     // because we want build a single complete solution
     // incrementally.
-    CS.replaySolution(Solutions.pop_back_val(),
-                      /*shouldIncrementScore=*/false);
+    auto S = Solutions.pop_back_val();
+    CS.replaySolution(S, /*shouldIncrementScore=*/false);
+    PreviousScore = S.getFixedScore();
+  } else if (!Conjunction->isIsolated()) {
+    // If this isn't an isolated conjunction, we need to preserve outer fatal
+    // scoring information.
+    PreviousScore = OuterScore;
   }
 
-  // Make sure that element is solved in isolation
-  // by dropping all scoring information.
-  CS.clearScore();
+  // Preserve fatal scoring information to ensure they don't get dropped from
+  // the resulting solution.
+  for (auto kind : {SK_Fix, SK_Hole})
+    CS.increaseScore(kind, PreviousScore.Data[kind]);
 
   // Reset the scope and trail counters to avoid "too complex"
   // failures when closure has a lot of elements in the body.

lib/Sema/CSStep.h

@@ -858,6 +858,9 @@ class ConjunctionStep : public BindingStep<ConjunctionElementProducer> {
     void replaySolution(const Solution &solution);
   };
 
+  /// The score of the outer scope.
+  Score OuterScore;
+
   /// Best solution solver reached so far.
   std::optional<Score> BestScore;
 
@@ -901,7 +904,7 @@ class ConjunctionStep : public BindingStep<ConjunctionElementProducer> {
                   SmallVectorImpl<Solution> &solutions)
       : BindingStep(cs, {cs, conjunction},
                     conjunction->isIsolated() ? IsolatedSolutions : solutions),
-        BestScore(getBestScore()),
+        OuterScore(cs.CurrentScore), BestScore(getBestScore()),
         OuterNumSolverScopes(cs.NumSolverScopes, 0),
         OuterNumTrailSteps(cs.NumTrailSteps, 0),
         Conjunction(conjunction),

test/IDE/complete_in_closures.swift

@@ -543,8 +543,8 @@ func testCompleteAfterClosureWithIfExprThatContainErrors() {
   }#^AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS^#
 
   // AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS: Begin completions, 2 items
-  // AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS-DAG: Keyword[self]/CurrNominal:          .self[#() -> _#]; name=self
-  // AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS-DAG: Pattern/CurrModule/Flair[ArgLabels]: ()[#_#]; name=()
+  // AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS-DAG: Keyword[self]/CurrNominal:          .self[#() -> Void#]; name=self
+  // AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS-DAG: Pattern/CurrModule/Flair[ArgLabels]: ()[#Void#]; name=()
   // AFTER_CLOSURE_WITH_IF_EXPR_THAT_CONTAIN_ERRORS: End completions
 }
 

validation-test/compiler_crashers_2/2d5e95ea862946ed.swift renamed to validation-test/compiler_crashers_2_fixed/2d5e95ea862946ed.swift

@@ -1,5 +1,5 @@
 // {"kind":"typecheck","signature":"(anonymous namespace)::ExprWalker::walkToExprPost(swift::Expr*)","signatureAssert":"Assertion failed: (Ptr && \"Cannot dereference a null Type!\"), function operator->"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 func a {
   {
     \ b() a