AST: Handle PackConformance in SubstitutionMap::lookupConformance()

Author: slavapestov

lib/AST/SubstitutionMap.cpp

@@ -418,6 +418,16 @@ SubstitutionMap::lookupConformance(CanType type, ProtocolDecl *proto) const {
 
     // For the second step, we're looking into the requirement signature for
     // this protocol.
+    if (conformance.isPack()) {
+      auto pack = conformance.getPack();
+      conformance = ProtocolConformanceRef(
+          pack->getAssociatedConformance(step.first, step.second));
+      if (conformance.isInvalid())
+        return conformance;
+
+      continue;
+    }
+
     auto concrete = conformance.getConcrete();
     auto normal = concrete->getRootNormalConformance();
 

test/SILGen/variadic_generic_conformances.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -emit-silgen %s -disable-availability-checking
+
+protocol P {
+  associatedtype A: P
+}
+
+struct S: P {
+  typealias A = S
+}
+
+func f<each T: P>(_: repeat each T) -> (repeat each T.A.A.A.A) {}
+
+f(S(), S(), S())