bindings: Generate entries for .cpp/.h files from IDL dictionaries in GN

By auto-generating those entries, we can stop requiring people to manually
update lists such as |generated_core_dictionary_files| every time Blink's
lists of IDL dictionary files change.

Since the names of the generated .cpp/.h follow a fixed, specific format
that only depends on their respective IDL file's path and file name, we can
use GN itself to do some path introspection and generate the file names we
want in idl_impl().

While here, change the names of idl_impl()'s required arguments to make
their purpose more explicit: it is not immediately obvious that we
differentiate unions and callback functions from dictionary files in terms
of where the latter are generated and their file names, as well as why
idl_impl() only expects non-dictionary files in its outputs list. A good
next step would be generating dictionary impl files separately from unions
and callbacks to avoid the confusion altogether.

Bug: 725996
Change-Id: I41b06e8d71f33b21d77944216fcb07d0557ac47b
Reviewed-on: https://chromium-review.googlesource.com/517795
Commit-Queue: Raphael Kubo da Costa (rakuco) <raphael.kubo.da.costa@intel.com>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#476262}

third_party/WebKit/Source/bindings/modules/v8/BUILD.gn

@@ -27,11 +27,10 @@ idl_compiler("generate_bindings_modules_v8_interfaces") {
 }
 
 idl_impl("bindings_modules_impl_generated") {
-  sources = modules_dictionary_idl_files
-  outputs = bindings_modules_generated_union_type_files +
-            generated_modules_dictionary_files +
-            generated_modules_callback_function_files
-  output_dir = bindings_modules_v8_output_dir
+  dict_idls = modules_dictionary_idl_files
+  non_dict_outputs = bindings_modules_generated_union_type_files +
+                     generated_modules_callback_function_files
+  non_dict_output_dir = bindings_modules_v8_output_dir
   target_component = "modules"
 }
 

third_party/WebKit/Source/bindings/scripts/scripts.gni

@@ -245,12 +245,17 @@ template("idl_compiler") {
   }
 }
 
-# Runs the idl_compiler to generate IDL dictionary and union impl files.
+# Runs idl_compiler.py to generate IDL dictionary impl files, unions and
+# callback functions.
 #
 # Parameters:
-#   sources = a list of IDL files to process
-#   outputs = a list of files to write to
-#   output_dir = the directory to put the output files
+#   dict_idls = a list of dictionary IDL files to process. the callback and
+#               union IDL file names are already known and do not need to be
+#               specified.
+#   non_dict_outputs = a list of files generated from callback functions and
+#                      unions. the list of files generated from |dict_idls| is
+#                      added automatically and does not need to be specified.
+#   non_dict_output_dir = the directory to put the non-dict output files.
 #   target_component = component to generate code for
 template("idl_impl") {
   dictionary_impl_output_dir = "$root_gen_dir/blink/"
@@ -258,7 +263,7 @@ template("idl_impl") {
   action(target_name) {
     script = "//third_party/WebKit/Source/bindings/scripts/idl_compiler.py"
     idl_files_list = "$target_gen_dir/${target_name}_file_list.tmp"
-    write_file(idl_files_list, rebase_path(invoker.sources, root_build_dir))
+    write_file(idl_files_list, rebase_path(invoker.dict_idls, root_build_dir))
 
     inputs = idl_lexer_parser_files + idl_compiler_files  # to be explicit (covered by parsetab)
     inputs += [
@@ -267,14 +272,27 @@ template("idl_impl") {
       "$bindings_scripts_output_dir/cached_jinja_templates.stamp",
       "$bindings_dir/IDLExtendedAttributes.txt",
     ]
-    inputs += [ idl_files_list ] + invoker.sources
-    outputs = invoker.outputs
+    inputs += [ idl_files_list ] + invoker.dict_idls
+    outputs = invoker.non_dict_outputs
+
+    # Derive the names of the generated dictionary impl files. Contrary to
+    # generated interfaces, callbacks and unions, these files go to
+    # $root_gen_dir/blink/{core,modules}/<module name>/<IDLName>.{cpp,h}.
+    foreach(dict_idl, invoker.dict_idls) {
+      rel_path = rebase_path(dict_idl, "//third_party/WebKit/Source")
+      impl_dir = get_path_info(rel_path, "dir")
+      idl_name = get_path_info(rel_path, "name")
+      outputs += [
+        "${dictionary_impl_output_dir}$impl_dir/$idl_name.cpp",
+        "${dictionary_impl_output_dir}$impl_dir/$idl_name.h",
+      ]
+    }
 
     args = [
       "--cache-dir",
       rebase_path(bindings_scripts_output_dir, root_build_dir),
       "--output-dir",
-      rebase_path(invoker.output_dir, root_build_dir),
+      rebase_path(invoker.non_dict_output_dir, root_build_dir),
       "--impl-output-dir",
       rebase_path(dictionary_impl_output_dir, root_build_dir),
       "--info-dir",