Add GN template for generated extensions API targets.

extensions/generated_extensions_api.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.
+
+# Defines a static library corresponding to the output of schema compiler tools
+# over a set of extensions API schemas (IDL or JSON format.) The library target
+# has implicit hard dependencies on all schema files listed by the invoker and
+# is itself a hard dependency.
+#
+# Invocations of this template may use the following variables:
+#
+# schemas [required] A list of schema files to be compiled.

[brettw, 2014/04/24 18:29:44]

I'm thinking we should generally name this kind of thing "sources" so you never
have to remember what it's called for different template types.

[Ken Rockot(use gerrit already), 2014/04/24 19:39:54]

Debated this for a while myself. I agree with your reasoning. Done.

+#
+# root_namespace [required] The namespace in which generated API code is to be
+#     wrapped. C++ namespace syntax is accepted for nested namespace
+#     (e.g. "foo::bar::api").
+#
+# impl_dir [required] The path containing C++ implementations of API functions.
+#     This path is used as the root path when looking for
+#     {schema}/{schema}_api.h headers during the API bundle generation phase.
+#     Such headers, if found, are automatically included by the generated code.
+#
+# uncompiled_schemas [optional] A list of schema files which should not be
+#     compiled, but which should still be processed for API bundle generation.
+#
+# deps [optional] If any deps are specified they will be inherited by the
+#     static library target.
+#
+# The static libarary target also inherits the visibility and output_name
+# of its invoker.
+
+template("generated_extensions_api") {
+  assert(defined(invoker.schemas),
+         "\"schemas\" must be defined for the $target_name template.")
+  assert(defined(invoker.root_namespace),
+         "\"root_namespace\" must be defined for the $target_name template.")
+  assert(defined(invoker.impl_dir),
+         "\"impl_dir\" must be defined for the $target_name template.")
+
+  # Keep a copy of the target_name here since it will be trampled
+  # in nested targets.
+  target_visibility = ":$target_name"
+
+  generated_config_name = target_name + "_generated_config"
+  config(generated_config_name) {
+    include_dirs = [ target_gen_dir ]
+    visibility = target_visibility
+  }
+
+  schemas = invoker.schemas
+  root_namespace = invoker.root_namespace
+  impl_dir = invoker.impl_dir
+  uncompiled_schemas = []
+  if (defined(invoker.uncompiled_schemas)) {
+    uncompiled_schemas = invoker.uncompiled_schemas
+  }
+
+  compiler_root = "//tools/json_schema_compiler"
+  compiler_script = "$compiler_root/compiler.py"
+  compiler_sources = [
+      "$compiler_root/cc_generator.py",

[brettw, 2014/04/24 18:29:44]

Be consistent with the indenting. I would use 2 spaces here like you do below.

[Ken Rockot(use gerrit already), 2014/04/24 19:39:54]

Done. Force of habit from C++ style...

+      "$compiler_root/code.py",
+      "$compiler_root/compiler.py",
+      "$compiler_root/cpp_generator.py",
+      "$compiler_root/cpp_type_generator.py",
+      "$compiler_root/cpp_util.py",
+      "$compiler_root/h_generator.py",
+      "$compiler_root/idl_schema.py",
+      "$compiler_root/model.py",
+      "$compiler_root/util_cc_helper.py" ]

[brettw, 2014/04/24 18:29:44]

For these multiline lists, I put the ] on the next line and add a comma after
the last element so its easier to add and remove items.

[Ken Rockot(use gerrit already), 2014/04/24 19:39:54]

Done.

+
+  # This list mirrors the outputs that will be generated by the following
+  # action_foreach. It's used by the static_library target.
+  compiled_schema_outputs = process_file_template(
+      schemas,
+      [ "$target_gen_dir/{{source_name_part}}.cc",
+        "$target_gen_dir/{{source_name_part}}.h" ])
+
+  schema_generator_name = target_name + "_schema_generator"
+  action_foreach(schema_generator_name) {
+    script = compiler_script
+    hard_dep = true
+    source_prereqs = compiler_sources
+    sources = schemas
+    outputs = [
+      "$target_gen_dir/{{source_name_part}}.cc",
+      "$target_gen_dir/{{source_name_part}}.h" ]
+    args = [
+      "{{source}}",
+      "--root=" + rebase_path("//", root_build_dir),

[brettw, 2014/04/24 18:29:44]

FWIW I have no way to tell if this is correct other than the output works, so I
didn't look at the details of the commands you're running. I'm assuming we can
fix them if they need tweaking later.

[Ken Rockot(use gerrit already), 2014/04/24 19:39:54]

Yep. I' pretty confident the arguments are conceptually correct. My main concern
is that I'm not sure if rebase_path("//", root_build_dir) is the best/idiomatic
way to generate a string which means "the chromium src root relative to cwd" to
an external script.

+      "--destdir=" + rebase_path(root_gen_dir, root_build_dir),
+      "--namespace=$root_namespace",
+      "--generator=cpp" ]
+    visibility = target_visibility
+  }
+
+  bundle_generator_name = target_name + "_bundle_generator"
+  bundle_outputs = [
+      "$target_gen_dir/generated_api.cc",

[brettw, 2014/04/24 18:29:44]

Ditto previous comments.

+      "$target_gen_dir/generated_api.h",
+      "$target_gen_dir/generated_schemas.cc",
+      "$target_gen_dir/generated_schemas.h" ]
+  action(bundle_generator_name) {
+    script = compiler_script
+    hard_dep = true
+    source_prereqs = compiler_sources + schemas + uncompiled_schemas
+    outputs = bundle_outputs
+    args = [
+      "--root=" + rebase_path("//", root_build_dir),
+      "--destdir=" + rebase_path(root_gen_dir, root_build_dir),
+      "--namespace=$root_namespace",
+      "--generator=cpp-bundle",
+      "--impl-dir=" + rebase_path(impl_dir, "//")] +
+      rebase_path(schemas, root_build_dir) +
+      rebase_path(uncompiled_schemas, root_build_dir)
+  }
+
+  static_library(target_name) {

[brettw, 2014/04/24 18:29:44]

CAn this be a source_set instead of a static_library?

[Ken Rockot(use gerrit already), 2014/04/24 19:39:54]

I guess I don't see why it couldn't. Done.

Some day maybe we'd like APIs to be shared libraries, but that's neither here
nor there.

+    hard_dep = true
+    sources = compiled_schema_outputs + bundle_outputs
+    deps = [
+      ":$schema_generator_name",
+      ":$bundle_generator_name",
+      "//tools/json_schema_compiler:generated_api_util" ]
+
+    if (defined(invoker.deps)) {
+      deps += invoker.deps
+    }
+    direct_dependent_configs = [ ":$generated_config_name" ]
+
+    if (defined(invoker.visibility)) {
+      visibility = invoker.visibility
+    }
+    if (defined(invoker.output_name)) {
+      output_name = invoker.output_name
+    }
+  }
+}