[CSSimplify] If pack type has holes - its shape is a hole

Propagating holes to the shape helps avoid spurious diagnostics
about same-shape requirement failures.

Resolves: rdar://107675464

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -13280,6 +13280,14 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyShapeOfConstraint(
       return formUnsolved();
   }
 
+  if (type1->hasPlaceholder()) {
+    if (!shouldAttemptFixes())
+      return SolutionKind::Error;
+
+    recordTypeVariablesAsHoles(type2);
+    return SolutionKind::Solved;
+  }
+
   auto shape = type1->getReducedShape();
   addConstraint(ConstraintKind::Bind, shape, type2, locator);
   return SolutionKind::Solved;

test/Constraints/pack-expansion-expressions.swift

@@ -50,8 +50,15 @@ protocol P {
   var value: A { get }
 
   func f(_ self: Self) -> Self
+
+  func makeA() -> A
+}
+
+extension P {
+  func makeA() -> [Self] { return [self] }
 }
 
+
 func outerArchetype<each T, U>(t: repeat each T, u: U) where repeat each T: P {
   let _: (repeat (each T.A, U)) = (repeat ((each t).value, u))
 }
@@ -428,3 +435,15 @@ func test_partually_flattened_expansions() {
   _ = S().fn(t: 1, "hi", u: false, 1.0) // Ok
   _ = S<Int, String>().fn(t: 1, "hi", u: false, 1.0) // Ok
 }
+
+// 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) {
+    return (repeat (each value).makeA()) // Ok
+  }
+
+  func test_misplaced_each<each T: P>(_ value: repeat each T) -> (repeat each T.A) {
+    return (repeat each value.makeA())
+    // expected-error@-1 {{pack reference 'each T' can only appear in pack expansion}}
+  }
+}