[CSBindings] Relax early conjunction solving rule related to outer declarations

Instead of checking that there are no references to external declarations,
let's check that all of such declarations have their types resolved.

Author: xedin

lib/Sema/CSBindings.cpp

@@ -1111,18 +1111,18 @@ bool BindingSet::favoredOverConjunction(Constraint *conjunction) const {
           }))
         return true;
 
-      // If conjunction references a single type variable (closure itself)
-      // it means that the builder is either not generic or has all of its
-      // generic parameter specified explicitly, and there are no references
-      // to declarations from outer context. Such conjunctions don't have to
-      // be delayed.
-      if (conjunction->getTypeVariables().size() == 1) {
-        assert(
-            conjunction->getTypeVariables()[0]->isEqual(CS.getType(closure)));
-        return false;
-      }
-
-      return true;
+      // Check whether conjunction has any unresolved type variables
+      // besides the variable that represents the closure.
+      //
+      // Conjunction could refer to declarations from outer context
+      // (i.e. a variable declared in the outer closure) or generic
+      // parameters of the builder type), if any of such references
+      // are not yet inferred the conjunction has to be delayed.
+      auto *closureType = CS.getType(closure)->castTo<TypeVariableType>();
+      return llvm::any_of(
+          conjunction->getTypeVariables(), [&](TypeVariableType *typeVar) {
+            return !(typeVar == closureType || CS.getFixedType(typeVar));
+          });
     }
   }