Descriptor support in proto_library

This is needed in order to enable support for extension-based typed
tracing events. For more information, see
https://perfetto.dev/docs/design-docs/extensions

Change-Id: I43bd82ee1c94cf7ae5be0a1fd7db4104cf8ece6a
Bug: 161696674
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2332180Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Andrew Shulaev <ddrone@google.com>
Cr-Commit-Position: refs/heads/master@{#795191}

base/BUILD.gn

@@ -2147,7 +2147,10 @@ jumbo_component("base") {
 
     public_deps += [ "//third_party/perfetto:libperfetto" ]
 
-    deps += [ "//third_party/perfetto/include/perfetto/protozero" ]
+    deps += [
+      "//base/tracing/protos:chrome_track_event",
+      "//third_party/perfetto/include/perfetto/protozero",
+    ]
 
     all_dependent_configs += [ "//third_party/perfetto/gn:public_config" ]
 

base/tracing/protos/BUILD.gn

+# Copyright (c) 2020 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//third_party/protobuf/proto_library.gni")
+
+proto_library("chrome_track_event") {
+  proto_in_dir = "//"
+  import_dirs = [ "//third_party/perfetto/" ]
+  sources = [ "chrome_track_event.proto" ]
+  generate_cc = false
+  generate_python = false
+  generate_descriptor = "chrome_track_event.descriptor"
+}

base/tracing/protos/chrome_track_event.proto

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+import "third_party/perfetto/protos/perfetto/trace/track_event/track_event.proto";
+
+package perfetto.protos;
+
+enum ChromeAppState {
+  APP_STATE_FOREGROUND = 1;
+  APP_STATE_BACKGROUND = 2;
+}
+
+message ChromeTrackEvent {
+  // Extension range for Chrome: 1000-1099
+  extend TrackEvent { optional ChromeAppState chrome_app_state = 1000; }
+}

third_party/protobuf/proto_library.gni

@@ -160,6 +160,12 @@ template("proto_library") {
     generate_javascript = false
   }
 
+  if (defined(invoker.generate_descriptor)) {
+    generate_descriptor = invoker.generate_descriptor
+  } else {
+    generate_descriptor = ""
+  }
+
   if (defined(invoker.generator_plugin_label)) {
     # Straightforward way to get the name of executable doesn't work because
     # |root_out_dir| and |root_build_dir| may differ in cross-compilation and
@@ -235,37 +241,55 @@ template("proto_library") {
     js_out_dir = "$root_out_dir/jsproto/" + proto_out_dir
     rel_js_out_dir = rebase_path(js_out_dir, root_build_dir)
   }
+  if (generate_descriptor != "") {
+    descriptor_out =
+        "$root_gen_dir/" + proto_out_dir + "/" + generate_descriptor
+    rel_descriptor_out = rebase_path(descriptor_out, root_build_dir)
+  }
 
   protos = rebase_path(invoker.sources, proto_in_dir)
   protogens = []
   protogens_cc = []
   protogens_js = []
 
+  # Whether library should be generated.
+  # Library is not needed when proto_library is used to generate binary descriptor, in which case
+  # corresponding library target should be omitted entirely.
+  generate_library = generate_cc || generate_python || generate_with_plugin ||
+                     generate_javascript
+
   # List output files.
-  foreach(proto, protos) {
-    proto_dir = get_path_info(proto, "dir")
-    proto_name = get_path_info(proto, "name")
-    proto_path = proto_dir + "/" + proto_name
+  if (generate_library) {
+    foreach(proto, protos) {
+      proto_dir = get_path_info(proto, "dir")
+      proto_name = get_path_info(proto, "name")
+      proto_path = proto_dir + "/" + proto_name
 
-    if (generate_cc) {
-      protogens_cc += [
-        "$cc_out_dir/$proto_path.pb.h",
-        "$cc_out_dir/$proto_path.pb.cc",
-      ]
-    }
-    if (generate_python) {
-      protogens += [ "$py_out_dir/${proto_path}_pb2.py" ]
-    }
-    if (generate_with_plugin) {
-      foreach(suffix, generator_plugin_suffixes) {
-        protogens_cc += [ "$cc_out_dir/${proto_path}${suffix}" ]
+      if (generate_cc) {
+        protogens_cc += [
+          "$cc_out_dir/$proto_path.pb.h",
+          "$cc_out_dir/$proto_path.pb.cc",
+        ]
+      }
+      if (generate_python) {
+        protogens += [ "$py_out_dir/${proto_path}_pb2.py" ]
+      }
+      if (generate_with_plugin) {
+        foreach(suffix, generator_plugin_suffixes) {
+          protogens_cc += [ "$cc_out_dir/${proto_path}${suffix}" ]
+        }
+      }
+      if (generate_javascript) {
+        protogens_js += [ "$js_out_dir/${proto_path}.js" ]
       }
-    }
-    if (generate_javascript) {
-      protogens_js += [ "$js_out_dir/${proto_path}.js" ]
     }
   }
 
+  # If descriptor needs to be generated, it should be added to list of outputs once.
+  if (generate_descriptor != "") {
+    protogens += [ descriptor_out ]
+  }
+
   action_name = "${target_name}_gen"
   source_set_name = target_name
   javascript_name = "${target_name}_js"
@@ -346,6 +370,13 @@ template("proto_library") {
       }
     }
 
+    if (generate_descriptor != "") {
+      args += [
+        "--descriptor-set-out",
+        rel_descriptor_out,
+      ]
+    }
+
     if (defined(invoker.import_dirs)) {
       foreach(path, invoker.import_dirs) {
         args += [ "--import-dir=" + rebase_path(path, root_build_dir) ]
@@ -377,9 +408,12 @@ template("proto_library") {
     }
   }
 
-  # Option to disable building a library in component build.
-  if (defined(invoker.component_build_force_source_set) &&
-      invoker.component_build_force_source_set && is_component_build) {
+  if (!generate_library) {
+    # If only descriptor is required, just generate a group wrapper for action output.
+    link_target_type = "group"
+  } else if (defined(invoker.component_build_force_source_set) &&
+             invoker.component_build_force_source_set && is_component_build) {
+    # Option to disable building a library in component build.
     link_target_type = "source_set"
   } else {
     link_target_type = "static_library"
@@ -392,7 +426,7 @@ template("proto_library") {
   config_name = "${target_name}_config"
   config(config_name) {
     include_dirs = []
-    if (has_nested_dirs) {
+    if (has_nested_dirs && generate_cc) {
       include_dirs += [ cc_out_dir ]
     }
     if (defined(invoker.import_dirs)) {
@@ -428,21 +462,23 @@ template("proto_library") {
                              "visibility",
                            ])
 
-    sources = get_path_info(protogens_cc, "abspath")
+    if (generate_library) {
+      sources = get_path_info(protogens_cc, "abspath")
 
-    if (defined(invoker.remove_configs)) {
-      configs -= invoker.remove_configs
-    }
+      if (defined(invoker.remove_configs)) {
+        configs -= invoker.remove_configs
+      }
 
-    if (defined(invoker.extra_configs)) {
-      configs += invoker.extra_configs
-    }
+      if (defined(invoker.extra_configs)) {
+        configs += invoker.extra_configs
+      }
 
-    # Remove Sanitizer and coverage instrumentation for a performance boost when
-    # fuzzing, since the only fuzzers that use protobuf are libprotobuf-mutator
-    # based fuzzers, and they don't actually target protobuf code.
-    configs -= not_fuzzed_remove_configs
-    configs += [ "//build/config/sanitizers:not_fuzzed" ]
+      # Remove Sanitizer and coverage instrumentation for a performance boost when
+      # fuzzing, since the only fuzzers that use protobuf are libprotobuf-mutator
+      # based fuzzers, and they don't actually target protobuf code.
+      configs -= not_fuzzed_remove_configs
+      configs += [ "//build/config/sanitizers:not_fuzzed" ]
+    }
 
     public_configs = [ "//third_party/protobuf:using_proto" ]
     public_deps = []

tools/protoc_wrapper/protoc_wrapper.py

@@ -97,6 +97,8 @@ def main(argv):
   parser.add_argument("--import-dir", action="append", default=[],
                       help="Extra import directory for protos, can be repeated."
   )
+  parser.add_argument("--descriptor-set-out",
+                      help="Path to write a descriptor.")
   parser.add_argument("protos", nargs="+",
                       help="Input protobuf definition file(s).")
 
@@ -151,6 +153,9 @@ def main(argv):
 
   protoc_cmd += [os.path.join(proto_dir, name) for name in protos]
 
+  if options.descriptor_set_out:
+    protoc_cmd += ["--descriptor_set_out", options.descriptor_set_out]
+
   ret = subprocess.call(protoc_cmd)
   if ret != 0:
     if ret <= -100: