[ConstraintSystem] openOpaqueType: remove logic that duplicates bindArchetypesFromContext

`openGenericParameters` calls `bindArchetypesFromContext` which would bind all of the
external generic parameters in the opaque type signature.

Resolves: rdar://107280056

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -1009,22 +1009,11 @@ Type ConstraintSystem::openOpaqueType(OpaqueTypeArchetypeType *opaque,
   // underlying return type.
   auto opaqueLocator = locator.withPathElement(
       LocatorPathElt::OpenedOpaqueArchetype(opaqueDecl));
+
   OpenedTypeMap replacements;
   openGeneric(DC, opaqueDecl->getOpaqueInterfaceGenericSignature(),
               opaqueLocator, replacements);
 
-  // If there is an outer generic signature, bind the outer parameters based
-  // on the substitutions in the opaque type.
-  auto subs = opaque->getSubstitutions();
-  if (auto genericSig = subs.getGenericSignature()) {
-    for (auto *genericParamPtr : genericSig.getGenericParams()) {
-      Type genericParam(genericParamPtr);
-      addConstraint(
-          ConstraintKind::Bind, openType(genericParam, replacements),
-          genericParam.subst(subs), opaqueLocator);
-    }
-  }
-
   recordOpenedTypes(opaqueLocatorKey, replacements);
 
   return openType(opaque->getInterfaceType(), replacements);

test/Constraints/pack-expansion-expressions.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -enable-experimental-feature VariadicGenerics
+// RUN: %target-typecheck-verify-swift -disable-availability-checking -enable-experimental-feature VariadicGenerics
 
 // REQUIRES: asserts
 
@@ -381,3 +381,18 @@ do {
   _ = Defaulted(t: "b", 0) // Ok
   _ = Defaulted(t: "c", 1.0, u: "d", 0) // Ok
 }
+
+// rdar://107280056 - "Ambiguous without more context" with opaque return type + variadics
+protocol Q {
+  associatedtype B
+}
+
+do {
+  struct G<each T>: Q {
+    typealias B = (repeat each T)
+  }
+
+  func f<each T>(_: repeat each T) -> some Q {
+    return G<repeat each T>() // Ok
+  }
+}