Make orjson optional again

While 32 bit platform support is probably not going to come back,
this allows Anki to run on other architectures orjson doesn't support.

docs/new-platform.md

@@ -34,8 +34,15 @@ https://github.com/ankitects/anki/commit/db3308e788f20b188e84add40d6a1dce5bf726a
 build --action_env=PYTHON_SITE_PACKAGES=/path/to/site-packages
 ```
 
-- Anki uses the Python 'orjson' module. If it's not available on your system,
-  you will need to [patch it out](https://github.com/ankitects/anki/pull/752#issuecomment-748861582), and remove references to it in the build scripts.
+- Anki uses the Python 'orjson' module to speed up DB access. If you're on a
+  platform that can not build orjson, you can remove it from
+  pip/requirements.txt to skip it during running/building, but DB operations
+  will be slower.
+
+  The py_wheel() rule in pylib/anki/BUILD.bazel adds an orjson requirement to
+  the generated Anki wheel on x86_64. If you have removed orjson, you'll want to
+  remove that line. If you have successfully built orjson for another platform,
+  you'll want to adjust that line to include your platform.
 
 ## Rust
 

pylib/anki/BUILD.bazel

@@ -5,6 +5,7 @@ load("//pylib:protobuf.bzl", "py_proto_library_typed")
 load("@rules_python//experimental/python:wheel.bzl", "py_package", "py_wheel")
 load("@bazel_skylib//lib:selects.bzl", "selects")
 load("//:defs.bzl", "anki_version")
+load("//pylib:orjson.bzl", "orjson_if_available")
 
 copy_file(
     name = "buildinfo",
@@ -93,10 +94,9 @@ py_library(
         requirement("beautifulsoup4"),
         requirement("decorator"),
         requirement("distro"),
-        requirement("orjson"),
         requirement("protobuf"),
         requirement("requests"),
-    ],
+    ] + orjson_if_available(),
 )
 
 py_package(
@@ -123,7 +123,7 @@ py_wheel(
         "requests[socks]",
         "decorator",
         "protobuf",
-        "orjson",
+        'orjson; platform_machine == "x86_64"',
         'psutil; sys_platform == "win32"',
         'distro; sys_platform != "darwin" and sys_platform != "win32"',
     ],

pylib/anki/rsbackend.py

@@ -22,8 +22,6 @@ import os
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, Sequence, Union
 
-import orjson
-
 import anki._rsbridge
 import anki.backend_pb2 as pb
 import anki.buildinfo
@@ -53,8 +51,15 @@ SyncOutput = pb.SyncCollectionOut
 SyncStatus = pb.SyncStatusOut
 CountsForDeckToday = pb.CountsForDeckTodayOut
 
-to_json_bytes = orjson.dumps
-from_json_bytes = orjson.loads
+try:
+    import orjson
+
+    to_json_bytes = orjson.dumps
+    from_json_bytes = orjson.loads
+except:
+    print("orjson is missing; DB operations will be slower")
+    to_json_bytes = lambda obj: json.dumps(obj).encode("utf8")  # type: ignore
+    from_json_bytes = json.loads
 
 
 class Interrupted(Exception):

pylib/orjson.bzl

@@ -0,0 +1,9 @@
+load("@py_deps//:requirements.bzl", "requirement")
+
+def orjson_if_available():
+    "Include orjson if it's listed in requirements.txt."
+    target = requirement("orjson")
+    if "not_found" in target:
+        return []
+    else:
+        return [target]