[fidl][cpp] Fix hlcpp conversion w/ unknown interactions

We were missing Natural/HLCPP conversion rules for transport errors so
it wasn't possible to even build the hlcpp_conversion.h for FIDL
libraries with two-way flexible methods.

The type is the same between Natural and HLCPP bindings so the fix is
just to have a no-op conversion.

Change-Id: Ib4150db3bee55f98ba0f862e6072afed647ca767
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/934374
Fuchsia-Auto-Submit: Ian McKellar <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
API-Review: Adam Barth <[email protected]>
Reviewed-by: Mitchell Kember <[email protected]>

src/lib/fidl/cpp/fidl_cpp_hlcpp_conversion.api

@@ -1,3 +1,3 @@
 {
-  "pkg/fidl_cpp_hlcpp_conversion/include/lib/fidl/cpp/hlcpp_conversion.h": "a1a95b2ba032918a786ac281627b834f"
+  "pkg/fidl_cpp_hlcpp_conversion/include/lib/fidl/cpp/hlcpp_conversion.h": "d1bff0d7426fea5c89da263382bf5354"
 }

src/lib/fidl/cpp/include/lib/fidl/cpp/hlcpp_conversion.h

@@ -8,6 +8,7 @@
 #include <lib/fidl/cpp/box.h>
 #include <lib/fidl/cpp/enum.h>
 #include <lib/fidl/cpp/string.h>
+#include <lib/fidl/cpp/transport_err.h>
 #include <lib/fidl/cpp/wire/wire_types.h>
 
 #include <optional>
@@ -79,6 +80,16 @@ struct HLCPPToNaturalTraits<HLCPP, std::enable_if_t<std::is_base_of_v<zx::object
     final : public HLCPPToNaturalTraitsIdentical<HLCPP> {};
 #endif
 
+/* Natural to HLCPP types for transport errors */
+template <>
+struct NaturalToHLCPPTraits<::fidl::internal::TransportErr> final
+    : public NaturalToHLCPPTraitsIdentical<::fidl::internal::TransportErr> {};
+
+/* HLCPP to Natural types for transport errors */
+template <>
+struct HLCPPToNaturalTraits<::fidl::internal::TransportErr> final
+    : public HLCPPToNaturalTraitsIdentical<::fidl::internal::TransportErr> {};
+
 /* Natural to HLCPP traits for strings. */
 template <>
 struct NaturalToHLCPPTraits<std::string> final : public NaturalToHLCPPTraitsIdentical<std::string> {

src/lib/fidl/cpp/tests/hlcpp_conversion/BUILD.gn

@@ -25,6 +25,7 @@ test("fidl_hlcpp_conversion_tests_bin") {
   deps = [
     "fidl:test.enums.abc_cpp_hlcpp_conversion",
     "fidl:test.enums.xyz_cpp_hlcpp_conversion",
+    "fidl:test.protocols_cpp_hlcpp_conversion",
     "//sdk/testing/fidl/protocols_tests:test.protocol.connector_cpp",
     "//sdk/testing/fidl/protocols_tests:test.protocol.connector_cpp_hlcpp_conversion",
     "//sdk/testing/fidl/types_tests:test.types_cpp_hlcpp_conversion",

src/lib/fidl/cpp/tests/hlcpp_conversion/fidl/BUILD.gn

@@ -17,3 +17,9 @@ fidl("test.enums.xyz") {
   sources = [ "enums.xyz.test.fidl" ]
   enable_hlcpp = true
 }
+
+fidl("test.protocols") {
+  testonly = true
+  sources = [ "protocols.test.fidl" ]
+  enable_hlcpp = true
+}

src/lib/fidl/cpp/tests/hlcpp_conversion/fidl/protocols.test.fidl

@@ -0,0 +1,100 @@
+// Copyright 2023 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+library test.protocols;
+
+closed protocol ClosedProtocol {
+    strict StrictOneWay(struct {
+        arg int32;
+    });
+
+    strict StrictTwoWay(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    });
+
+    strict StrictTwoWayError(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    }) error int32;
+
+    strict -> OnStrictEvent(struct {
+        arg int32;
+    });
+};
+
+ajar protocol AjarProtocol {
+    strict StrictOneWay(struct {
+        arg int32;
+    });
+
+    strict StrictTwoWay(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    });
+
+    strict StrictTwoWayError(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    }) error int32;
+
+    strict -> OnStrictEvent(struct {
+        arg int32;
+    });
+
+    flexible FlexibleOneWay(struct {
+        arg int32;
+    });
+
+    flexible -> OnFlexibleEvent(struct {
+        arg int32;
+    });
+};
+
+
+open protocol OpenProtocol {
+    strict StrictOneWay(struct {
+        arg int32;
+    });
+
+    strict StrictTwoWay(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    });
+
+    strict StrictTwoWayError(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    }) error int32;
+
+    strict -> OnStrictEvent(struct {
+        arg int32;
+    });
+
+    flexible FlexibleOneWay(struct {
+        arg int32;
+    });
+
+    flexible -> OnFlexibleEvent(struct {
+        arg int32;
+    });
+
+    flexible FlexibleTwoWay(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    });
+
+    flexible FlexibleTwoWayError(struct {
+        arg int32;
+    }) -> (struct {
+        res int32;
+    }) error int32;
+};

src/lib/fidl/cpp/tests/hlcpp_conversion/protocol_endpoint_conversion_test.cc

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <fidl/test.protocols/cpp/hlcpp_conversion.h>
 #include <fidl/test.types/cpp/hlcpp_conversion.h>
 #include <lib/fidl/cpp/wire/channel.h>