[CSSimplify] Adjust replaceTypeVariablesWithFreshPacks to propagate holes

If type variable that is being replaces allowed holes, the new one
should not lose this property.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -2412,13 +2412,16 @@ static PackType *replaceTypeVariablesWithFreshPacks(ConstraintSystem &cs,
       auto elementLoc = cs.getConstraintLocator(loc,
           LocatorPathElt::PackElement(freshTypeVars.size()));
       if (packExpansionElt != nullptr) {
-        auto *freshTypeVar =
-            cs.createTypeVariable(elementLoc, TVO_CanBindToPack);
+        auto *freshTypeVar = cs.createTypeVariable(
+            elementLoc,
+            TVO_CanBindToPack |
+                (typeVar->getImpl().canBindToHole() ? TVO_CanBindToHole : 0));
         freshTypeVars.push_back(PackExpansionType::get(
             freshTypeVar, packExpansionElt->getCountType()));
       } else {
-        freshTypeVars.push_back(
-            cs.createTypeVariable(elementLoc, /*options=*/0));
+        freshTypeVars.push_back(cs.createTypeVariable(
+            elementLoc,
+            typeVar->getImpl().canBindToHole() ? TVO_CanBindToHole : 0));
       }
     }
   }

test/Constraints/pack_expansion_types.swift

@@ -210,7 +210,7 @@ func concreteReturnFunctionInvalid() {
 }
 
 func patternInstantiationTupleTest1<each T>() -> (repeat Array<each T>) {}
-// expected-note@-1 2 {{in call to function 'patternInstantiationTupleTest1()'}}
+// expected-note@-1 {{in call to function 'patternInstantiationTupleTest1()'}}
 func patternInstantiationTupleTest2<each T, each U>() -> (repeat Dictionary<each T, each U>) {}
 
 func patternInstantiationFunctionTest1<each T>() -> (repeat Array<each T>) -> () {}
@@ -240,10 +240,9 @@ func patternInstantiationConcreteValid() {
 
 func patternInstantiationConcreteInvalid() {
   let _: Set<Int> = patternInstantiationTupleTest1()
-  // expected-error@-1 {{generic parameter 'each T' could not be inferred}}
-  // expected-error@-2 {{cannot convert value of type '(repeat Array<each T>)' to specified type 'Set<Int>'}}
+  // expected-error@-1 {{cannot convert value of type '(repeat Array<Pack{_}>)' to specified type 'Set<Int>'}}
 
-  let _: (Array<Int>, Set<String>) = patternInstantiationTupleTest1() // expected-error {{type of expression is ambiguous without more context}}
+  let _: (Array<Int>, Set<String>) = patternInstantiationTupleTest1() // expected-error {{'(repeat Array<Pack{Int, _}>)' is not convertible to '(Array<Int>, Set<String>)', tuples have a different number of elements}}
 }
 
 func patternInstantiationGenericValid<each T, each U>(t: repeat each T, u: repeat each U)
@@ -273,7 +272,7 @@ func patternInstantiationGenericInvalid<each T: Hashable>(t: repeat each T) {
   let _: (repeat Set<each T>) = patternInstantiationTupleTest1() // expected-error {{cannot convert value of type '(repeat Array<each T>)' to specified type '(repeat Set<each T>)}}
   // expected-error@-1 {{generic parameter 'each T' could not be inferred}}
 
-  let _: (repeat Array<each T>, Set<String>) = patternInstantiationTupleTest1() // expected-error {{type of expression is ambiguous without more context}}
+  let _: (repeat Array<each T>, Set<String>) = patternInstantiationTupleTest1() // expected-error {{'(repeat Array<Pack{repeat each T, _}>)' is not convertible to '(repeat Array<each T>, Set<String>)', tuples have a different number of elements}}
 }
 
 // rdar://107996926 - Vanishing metatype of tuple not supported