[ConstraintSystem] SE-0326: Temporarily prevent multi-statement closure inference in result builder contexts

Multi-statement closure inference doesn't play well with result builders
at the moment because it expects all of the information from the parent
statements to be inferred before solver starts working on the body of a
nested closure. Let's prevent inference for nested multi-statement closures
until result builders are ported to use conjunctions and solve the body
incrementally top-down instead of in one shot.

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -5913,8 +5913,13 @@ bool ConstraintSystem::participatesInInference(ClosureExpr *closure) const {
     return false;
 
   auto &ctx = closure->getASTContext();
-  return !closure->hasEmptyBody() &&
-         ctx.TypeCheckerOpts.EnableMultiStatementClosureInference;
+  if (closure->hasEmptyBody() ||
+      !ctx.TypeCheckerOpts.EnableMultiStatementClosureInference)
+    return false;
+
+  // If body is nested in a parent that has a function builder applied,
+  // let's prevent inference until result builders.
+  return !isInResultBuilderContext(closure);
 }
 
 TypeVarBindingProducer::TypeVarBindingProducer(BindingSet &bindings)