Revert "[mojo] Enable use of forward declarations of type-mapped mojo…

…m types"

This reverts commit 63b02ed.

Reason for revert: Looks like this broke compile on linux-chromeos-chrome:

https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/15690
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/15691
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/15692

Original change's description:
> [mojo] Enable use of forward declarations of type-mapped mojom types
>
> This makes it possible to reduce generated header sizes significantly
> when the full type is not necessary.
>
> For example, url_loader_factory.mojom defines an interface using the
> URLRequest mojom type, which is type-mapped to the C++ type
> ResourceRequest.
>
> Making it possible to forward declare ResourceRequest avoids the need
> to include url_request_mojom.h in url_loader_factory.mojom.h, which
> reduces the compiler input size for the chrome target on Linux by
> 1.3 GB, saving 19 CPU-minutes of compile time on my machine.
>
> Bug: 1226821, 242216
> Change-Id: I7ba187f714183ef5a7bc909458276aa4aeb05b2f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3008756
> Commit-Queue: Hans Wennborg <hans@chromium.org>
> Reviewed-by: Ken Rockot <rockot@google.com>
> Cr-Commit-Position: refs/heads/master@{#899267}

Bug: 1226821, 242216
Change-Id: I412b23efbe70b6e17c9d0c7e3ef031e3d33d6b07
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3011443
Auto-Submit: Scott Little <sclittle@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Trevor Perrier <perrier@chromium.org>
Reviewed-by: Scott Little <sclittle@chromium.org>
Reviewed-by: Trevor Perrier <perrier@chromium.org>
Owners-Override: Scott Little <sclittle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#899307}

mojo/public/tools/bindings/generate_type_mappings.py

@@ -82,7 +82,6 @@ def LoadCppTypemapConfig(path):
       for entry in config['types']:
         configs[entry['mojom']] = {
             'typename': entry['cpp'],
-            'forward_declaration': entry.get('forward_declaration', None),
             'public_headers': config.get('traits_headers', []),
             'traits_headers': config.get('traits_private_headers', []),
             'copyable_pass_by_value': entry.get('copyable_pass_by_value',

mojo/public/tools/bindings/generators/cpp_templates/module.h.tmpl

@@ -120,10 +120,6 @@ namespace {{variant}} {
 #endif
 {%- endif %}
 
-{%- for forward_declaration in typemap_forward_declarations %}
-{{forward_declaration}}
-{%- endfor %}
-
 {#--- WTF enum hashing #}
 {%- from "enum_macros.tmpl" import enum_hash_blink%}
 {%- if for_blink %}

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

@@ -331,12 +331,6 @@ def _GetJinjaExports(self):
     for interface in self.module.interfaces:
       all_enums.extend(interface.enums)
 
-    typemap_forward_declarations = []
-    for kind in self.module.imported_kinds.values():
-      forward_declaration = self._GetTypemappedForwardDeclaration(kind)
-      if forward_declaration:
-        typemap_forward_declarations.append(forward_declaration)
-
     return {
         "all_enums": all_enums,
         "contains_only_enums": self._ContainsOnlyEnums(),
@@ -350,7 +344,6 @@ def _GetJinjaExports(self):
         "extra_traits_headers": self._GetExtraTraitsHeaders(),
         "for_blink": self.for_blink,
         "imports": self.module.imports,
-        "typemap_forward_declarations": typemap_forward_declarations,
         "interfaces": self.module.interfaces,
         "kinds": self.module.kinds,
         "module": self.module,
@@ -573,12 +566,6 @@ def _IsTypemappedKind(self, kind):
     return hasattr(kind, "name") and \
         self._GetFullMojomNameForKind(kind) in self.typemap
 
-  def _GetTypemappedForwardDeclaration(self, kind):
-    if not self._IsTypemappedKind(kind):
-      return None
-    return self.typemap[self._GetFullMojomNameForKind(
-        kind)]["forward_declaration"]
-
   def _IsHashableKind(self, kind):
     """Check if the kind can be hashed.
 
@@ -742,11 +729,11 @@ def _IsFullHeaderRequiredForImport(self, imported_module):
     """Determines whether a given import module requires a full header include,
     or if the forward header is sufficient."""
 
-    # Type-mapped kinds may not have forward declarations, and nested kinds
-    # cannot be forward declared.
+    # Type-mapped kinds don't have forward declarations, and nested kinds cannot
+    # be forward declared.
+    # TODO(hans): Use forward declarations for type-mapped kinds.
     if any(kind.module == imported_module and (
-        (self._IsTypemappedKind(kind) and not self.
-         _GetTypemappedForwardDeclaration(kind)) or kind.parent_kind != None)
+        self._IsTypemappedKind(kind) or kind.parent_kind != None)
            for kind in self.module.imported_kinds.values()):
       return True
 

mojo/public/tools/bindings/mojom.gni

@@ -401,12 +401,6 @@ if (enable_scrambled_message_ids) {
 #             should be mapped in generated bindings. This is a string like
 #             "::base::Value" or "std::vector<::base::Value>".
 #
-#         forward_declaration (optional)
-#             A forward declaration of the C++ type, which bindings that don't
-#             need the full type definition can use to reduce the size of
-#             the generated code. This is a string like
-#             "namespace base { class Value; }".
-#
 #         move_only (optional)
 #             A boolean value (default false) which indicates whether the C++
 #             type is move-only. If true, generated bindings will pass the type

mojo/public/tools/bindings/validate_typemap_config.py

@@ -17,7 +17,7 @@ def CheckCppTypemapConfigs(target_name, config_filename, out_filename):
   ])
   _SUPPORTED_TYPE_KEYS = set([
       'mojom', 'cpp', 'copyable_pass_by_value', 'force_serialize', 'hashable',
-      'move_only', 'nullable_is_same_type', 'forward_declaration'
+      'move_only', 'nullable_is_same_type'
   ])
   with open(config_filename, 'r') as f:
     for config in json.load(f):

services/network/public/mojom/BUILD.gn

@@ -264,7 +264,6 @@ mojom("url_loader_base") {
         {
           mojom = "network.mojom.URLRequest"
           cpp = "::network::ResourceRequest"
-          forward_declaration = "namespace network { struct ResourceRequest; }"
         },
         {
           mojom = "network.mojom.URLRequestBody"