Path evaluation to protobuf plugin.

third_party/protobuf/proto_library.gni

 # Copyright 2014 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.
 
 # Compile a protocol buffer.
 #
 # Protobuf parameters:
 #
 #   proto_out_dir (optional)
 #       Specifies the path suffix that output files are generated under. This
@@ skipping 14 matching lines @@
 #   cc_generator_options (optional)
 #       List of extra flags passed to the protocol compiler.  If you need to
 #       add an EXPORT macro to a protobuf's C++ header, set the
 #       'cc_generator_options' variable with the value:
 #       'dllexport_decl=FOO_EXPORT:' (note trailing colon).
 #
 #       It is likely you also need to #include a file for the above EXPORT
 #       macro to work (see cc_include) and set
 #       component_build_force_source_set = true.
 #
-#   generator_plugin (optional)
-#       Name of plugin executable which generates custom cc stubs.
-#       Plugin itself should be dependency of the invoker.
+#   generator_plugin_label (optional)
+#       GN label for plugin executable which generates custom cc stubs.
 #
-#   generator_plugin_suffix (required if generator_plugin set)
+#   generator_plugin_suffix (required if generator_plugin_label set)
 #       Suffix (before extension) for generated .cc and .h files.
 #
 #   generator_plugin_options (optional)
 #       Extra flags passed to the plugin. See cc_generator_options.
 #
 #   cc_include (optional)
 #       String listing an extra include that should be passed.
 #       Example: cc_include = "foo/bar.h"
 #
 #   deps (optional)
@@ skipping 109 matching lines @@
       outputs += [
         "$out_dir/{{source_name_part}}.pb.cc",
         "$out_dir/{{source_name_part}}.pb.h",
       ]
       args += [
         "--cpp_out",
         "$cc_generator_options$rel_out_dir",  # Separated by colon.
       ]
     }
 
-    if (defined(invoker.generator_plugin)) {
-      generator_plugin = invoker.generator_plugin
+    if (defined(invoker.generator_plugin_label)) {
+      generator_plugin_label = invoker.generator_plugin_label
       generator_plugin_suffix = invoker.generator_plugin_suffix
       if (defined(invoker.generator_plugin_options)) {
         generator_plugin_options = invoker.generator_plugin_options
       } else {
         generator_plugin_options = ""
       }
       outputs += [
         "$out_dir/{{source_name_part}}$generator_plugin_suffix.cc",
         "$out_dir/{{source_name_part}}$generator_plugin_suffix.h",
       ]
+
+      # 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
+      # also Windows executables have .exe at the end.
+
+      plugin_host_label = generator_plugin_label + "($host_toolchain)"
+      plugin_path = get_label_info(plugin_host_label, "root_out_dir") + "/" +
+                    get_label_info(plugin_host_label, "name")
+      if (host_os == "win") {
+        plugin_path += ".exe"
+      }
+
+      # Need "./" for script to find plugin binary (working dir is not on PATH).
       args += [
         "--plugin",
-        "protoc-gen-plugin=./$generator_plugin",
+        "protoc-gen-plugin=./" + rebase_path(plugin_path, root_build_dir),
         "--plugin_out",
         "$generator_plugin_options$rel_out_dir",  # Separated by colon.
       ]
     }
 
     deps = [
       protoc_label,
     ]
+    if (defined(plugin_host_label)) {
+      deps += [ plugin_host_label ]
+    }
 
     # The deps may have steps that have to run before running protobuf.
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
   }
 
   if (defined(invoker.component_build_force_source_set) &&
       invoker.component_build_force_source_set &&
       is_component_build) {
@@ skipping 28 matching lines @@
       ":$action_name",
     ]
 
     # This will link any libraries in the deps (the use of invoker.deps in the
     # action won't link it).
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
   }
 }