Merge pull request swiftlang#42605 from xedin/abort-solver-on-too-complex

[CSStep] Abort any binding step when constraint system is 'too complex'

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -5494,6 +5494,9 @@ class ConstraintSystem {
   }
 
   bool getExpressionTooComplex(SmallVectorImpl<Solution> const &solutions) {
+    if (isExpressionAlreadyTooComplex)
+      return true;
+
     size_t solutionMemory = 0;
     for (auto const& s : solutions) {
       solutionMemory += s.getTotalMemory();

lib/Sema/CSStep.h

@@ -504,6 +504,11 @@ template <typename P> class BindingStep : public SolverStep {
 
 public:
   StepResult take(bool prevFailed) override {
+    // Before attempting the next choice, let's check whether the constraint
+    // system is too complex already.
+    if (CS.getExpressionTooComplex(Solutions))
+      return done(/*isSuccess=*/false);
+
     while (auto choice = Producer()) {
       if (shouldSkip(*choice))
         continue;