[Extensions] Add extension feature generation code

build/json_features.gni

+# Copyright 2016 The Chromium Authors. All rights reserved.

[Dirk Pranke, 2016/07/14 23:16:36]

Where is this template actually going to be used?

We generally don't want to put chromium-specific stuff in //build, as we want to
get //build to be a generic things that can be reused by other (non-chromium)
projects.

Can you move these to //tools/json_schema_compiler/json_features.gni or
something like that?

[Devlin, 2016/07/15 16:19:07]

This is going to be used from //chrome and //extensions.

I just copied where the other similar templates were. :) We can move this, as
long as there's no qualms about including tools/json_schema_compiler templates
from chromium sources.

Done.

[Dirk Pranke, 2016/07/15 19:16:37]

including //tools/json_schema_compiler is totally fine.

The location of the templates isn't totally consistent (and we're hopefully
making things better over time), but it is better to keep them by the code where
possible.

+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Generates the FeatureProviders files for extension features files.
+# The following variables are required:
+#   sources: The features.json files to use.
+#   feature_class: The name of the feature class to generate, e.g. APIFeature.
+#   provider_class: The name of the provider class to generate, e.g.
+#                   APIFeatureProvider.
+template("json_features") {
+  assert(defined(invoker.sources),
+         "\"sources\" must be defined for the $target_name template.")
+  assert(defined(invoker.feature_class),
+         "\"feature_class\" must be defined for the $target_name template.")
+  assert(defined(invoker.provider_class),
+         "\"provider_class\" must be defined for the $target_name template.")
+  feature_class = invoker.feature_class
+  provider_class = invoker.provider_class
+
+  compiler_root = "//tools/json_schema_compiler"
+  compiler_script = "$compiler_root/feature_compiler.py"
+  target = "${target_name}_json_features"
+
+  action(target) {
+    sources = invoker.sources
+    script = compiler_script

[Dirk Pranke, 2016/07/14 23:16:35]

I would get rid of compiler script and just refer to
"$compiler_root/feature_compiler.py" directly.

[Devlin, 2016/07/15 16:19:07]

Done.

+    inputs = []
+    outputs = [
+      "$target_gen_dir/$target_name.cc",
+      "$target_gen_dir/$target_name.h",
+    ]
+    rebased = rebase_path(invoker.sources, root_build_dir)
+    args = [
+             ".",
+             "$feature_class",
+             "$provider_class",
+             rebase_path(target_gen_dir, root_build_dir),
+             "$target",
+           ] + rebased
+  }
+
+  lib_sources = invoker.sources + get_target_outputs(":$target")
+  lib_public_deps = [ ":$target" ]
+  source_set(target_name) {
+    sources = lib_sources
+    public_deps = lib_public_deps

[Dirk Pranke, 2016/07/14 23:16:36]

similarly, just inline the values here.

[Devlin, 2016/07/15 16:19:07]

This seems to work for public deps, but trying to inline sources gives an error:
ERROR at //build/json_features.gni:43:33: Target not found in this context.
    sources = invoker.sources + get_target_outputs(":target")
                                ^---------------------------

(Done for public_deps)

[Dirk Pranke, 2016/07/15 19:16:37]

Did you drop the "$" ? I think (but am not positive) that it should work
otherwise.

But not a big deal either way.

[Devlin, 2016/07/15 21:03:01]

Works now using generated_files var.

+  }
+}