Sema: Availability checking needs to walk into PackConformances

Author: slavapestov

lib/Sema/TypeCheckAvailability.cpp

@@ -23,6 +23,7 @@
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/Initializer.h"
 #include "swift/AST/NameLookup.h"
+#include "swift/AST/PackConformance.h"
 #include "swift/AST/Pattern.h"
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/ProtocolConformance.h"
@@ -4011,7 +4012,18 @@ swift::diagnoseConformanceAvailability(SourceLoc loc,
                                        bool useConformanceAvailabilityErrorsOption) {
   assert(!where.isImplicit());
 
-  if (!conformance.isConcrete())
+  if (conformance.isPack()) {
+    bool diagnosed = false;
+    auto *pack = conformance.getPack();
+    for (auto patternConf : pack->getPatternConformances()) {
+      diagnosed |= diagnoseConformanceAvailability(
+          loc, patternConf, where, depTy, replacementTy,
+          useConformanceAvailabilityErrorsOption);
+    }
+    return diagnosed;
+  }
+
+  if (conformance.isInvalid() || conformance.isAbstract())
     return false;
 
   const ProtocolConformance *concreteConf = conformance.getConcrete();

test/Sema/pack_conformance_availability.swift

@@ -0,0 +1,14 @@
+// RUN: %target-typecheck-verify-swift
+
+func f<each T: P>(_: repeat each T) {}
+
+protocol P {}
+
+struct S {}
+
+@available(*, unavailable)
+extension S: P {}
+// expected-note@-1 {{conformance of 'S' to 'P' has been explicitly marked unavailable here}}
+
+f(S())
+// expected-error@-1 {{conformance of 'S' to 'P' is unavailable}}