[CSSimplify] Allow conversions between tuples with pack expansions and Any

Don't attempt to wrap `Any` into a single-element tuple to match
against a tuple with pack expansions, this conversion would be
handled by existential promotion if it's allowed, otherwise it
would produce an error.

Resolves: rdar://109160060
(cherry picked from commit 181d2d1)

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -6885,9 +6885,13 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
   // becuase expansion could be defaulted to an empty pack which means
   // that under substitution that element would disappear and the type
   // would be just `(Int)`.
+  //
+  // Notable exception here is `Any` which doesn't require wrapping and
+  // would be handled by existental promotion in cases where it's allowed.
   if (isTupleWithUnresolvedPackExpansion(origType1) ||
       isTupleWithUnresolvedPackExpansion(origType2)) {
-    if (desugar1->is<TupleType>() != desugar2->is<TupleType>()) {
+    if (desugar1->is<TupleType>() != desugar2->is<TupleType>() &&
+        (!desugar1->isAny() && !desugar2->isAny())) {
       return matchTypes(
           desugar1->is<TupleType>() ? type1
                                     : TupleType::get({type1}, getASTContext()),

test/Constraints/pack-expansion-expressions.swift

@@ -453,6 +453,26 @@ func test_partually_flattened_expansions() {
   _ = S<Int, String>().fn(t: 1, "hi", u: false, 1.0) // Ok
 }
 
+// rdar://109160060 - tuple with pack expansions is not convertible to Any
+do {
+  func test1<each T>(_: repeat (each T).Type) -> (repeat each T) {}
+  print(test1(Int.self, String.self))
+
+  func test2<each T>(_ s: [Any], t: repeat (each T).Type) -> (repeat each T) {
+    var iter = s.makeIterator()
+    return (repeat (iter.next()! as! (each T)))
+  }
+
+  print(test2([]))
+  print(test2([1], t: Int.self))
+  print(test2([1, "hi"], t: Int.self, String.self))
+  print(test2([1, "hi", false], t: Int.self, String.self, Bool.self))
+
+  func test3<each T>(v: Any) -> (Int, repeat each T) {
+    return v // expected-error {{cannot convert return expression of type 'Any' to return type '(Int, repeat each T)'}}
+  }
+}
+
 // rdar://107675464 - misplaced `each` results in `type of expression is ambiguous without more context`
 do {
   func test_correct_each<each T: P>(_ value: repeat each T) -> (repeat each T.A) {