[Serialization] Fix incorrect counting of value witnesses

lib/AST/ASTDumper.cpp

@@ -2743,6 +2743,35 @@ void ProtocolConformance::dump(llvm::raw_ostream &out, unsigned indent) const {
 
     printCommon("normal");
     // Maybe print information about the conforming context?
+    if (normal->isLazilyResolved()) {
+      out << " lazy";
+    } else {
+      forEachTypeWitness(nullptr, [&](const AssociatedTypeDecl *req,
+                                      Type ty, const TypeDecl *) -> bool {
+        out << '\n';
+        out.indent(indent + 2);
+        PrintWithColorRAII(out, ParenthesisColor) << '(';
+        out << "assoc_type req=" << req->getName() << " type=";
+        PrintWithColorRAII(out, TypeColor) << ty;
+        PrintWithColorRAII(out, ParenthesisColor) << ')';
+        return false;
+      });
+      normal->forEachValueWitness(nullptr, [&](const ValueDecl *req,
+                                               Witness witness) {
+        out << '\n';
+        out.indent(indent + 2);
+        PrintWithColorRAII(out, ParenthesisColor) << '(';
+        out << "value req=" << req->getFullName() << " witness=";
+        if (!witness) {
+          out << "(none)";
+        } else if (witness.getDecl() == req) {
+          out << "(dynamic)";
+        } else {
+          witness.getDecl()->dumpRef(out);
+        }
+        PrintWithColorRAII(out, ParenthesisColor) << ')';
+      });
+    }
 
     for (auto conformance : normal->getSignatureConformances()) {
       out << '\n';

lib/Serialization/Serialization.cpp

@@ -1296,6 +1296,7 @@ void Serializer::writeNormalConformance(
 
   conformance->forEachValueWitness(nullptr,
     [&](ValueDecl *req, Witness witness) {
+      ++numValueWitnesses;
       data.push_back(addDeclRef(req));
       data.push_back(addDeclRef(witness.getDecl()));
       assert(witness.getDecl() || req->getAttrs().hasAttribute<OptionalAttr>()
@@ -1319,11 +1320,10 @@ void Serializer::writeNormalConformance(
 
         // Requirements come at the end.
       } else {
-        data.push_back(0);
+        data.push_back(/*number of generic parameters*/0);
       }
 
       data.push_back(witness.getSubstitutions().size());
-      ++numValueWitnesses;
   });
 
   conformance->forEachTypeWitness(/*resolver=*/nullptr,

test/Serialization/cross_module_optional_protocol_reqt.swift

@@ -2,11 +2,28 @@
 // RUN: %target-swift-frontend -module-name cross_module_optional_protocol_reqt -c -emit-module-path %t/cross_module_optional_protocol_reqt~partial.swiftmodule -primary-file %s %S/Inputs/cross_module_optional_protocol_reqt_2.swift -import-objc-header %S/Inputs/cross_module_optional_protocol_reqt.h -o /dev/null
 // RUN: %target-swift-frontend -module-name cross_module_optional_protocol_reqt -c -emit-module-path %t/cross_module_optional_protocol_reqt_2~partial.swiftmodule %s -primary-file %S/Inputs/cross_module_optional_protocol_reqt_2.swift -import-objc-header %S/Inputs/cross_module_optional_protocol_reqt.h -o /dev/null
 // RUN: %target-swift-frontend -module-name cross_module_optional_protocol_reqt -emit-module -emit-module-path %t/cross_module_optional_protocol_reqt.swiftmodule %t/cross_module_optional_protocol_reqt~partial.swiftmodule %t/cross_module_optional_protocol_reqt_2~partial.swiftmodule -import-objc-header %S/Inputs/cross_module_optional_protocol_reqt.h
+// RUN: %target-swift-frontend -I %t -typecheck %s -DTEST -module-name main
 // REQUIRES: objc_interop
 
+#if TEST
+
+import cross_module_optional_protocol_reqt
+
+func test(_ foo: Foo) {
+  // At one point this forced deserialization of the conformance to ObjCProto,
+  // which was corrupted by the presence of the optional requirement with no
+  // witness.
+  foo.nonoptionalMethod()
+  foo.nonoptionalMethod2()
+}
+
+#else // TEST
+
 public protocol SwiftProto: ObjCProto {}
 
 public class Foo: ObjCFoo, SwiftProto {
   public func nonoptionalMethod() {}
   public func nonoptionalMethod2() {}
 }
+
+#endif // TEST