[ConstraintSystem] Bail out of inference from default arguments if there

is no parameter list for the callee.

This can happen when the callee is a closure that has been assigned to
a variable.

Author: hborla

lib/Sema/CSSimplify.cpp

@@ -1753,10 +1753,12 @@ static ConstraintSystem::TypeMatchResult matchCallArguments(
 
       if (ctx.TypeCheckerOpts.EnableTypeInferenceFromDefaultArguments) {
         auto *paramList = getParameterList(callee);
-        auto *PD = paramList->get(paramIdx);
+        if (!paramList)
+          continue;
 
         // There is nothing to infer if parameter doesn't have any
         // generic parameters in its type.
+        auto *PD = paramList->get(paramIdx);
         if (!PD->getInterfaceType()->hasTypeParameter())
           continue;
 

test/expr/closure/basic.swift

@@ -1,4 +1,5 @@
 // RUN: %target-typecheck-verify-swift
+// RUN: %target-typecheck-verify-swift -enable-experimental-type-inference-from-defaults
 
 func takeIntToInt(_ f: (Int) -> Int) { }
 func takeIntIntToInt(_ f: (Int, Int) -> Int) { }