Bug 1854031 - Part 8. Update ICU4X document. r=TYLin

Depends on D193883

Differential Revision: https://phabricator.services.mozilla.com/D193886

intl/docs/icu4x.rst

@@ -13,18 +13,18 @@ Enabling ICU4X
 Updating the bundled ICU4X data
 ===============================
 
-ICU4X data is bundled directly as a rust crate in the ``intl/icu_testdata``. Although this crate is the same name as ICU4X's ``icu_testdata`` crate, it has customized data for Gecko.
+ICU4X data is bundled directly as a rust crate with ``compiled_data`` feature.
+
+But each ``icu_*_data`` crate has all locale data, so it might include unnecessary data. ``icu_segmenter`` uses custom crates in Gecko since it includes unnecessary data such as the word dictionaries for East Asian.
 
 The script ``intl/update-icu4x.sh`` can generate and update this binary data. If you want to add the new data type, you modify this script and then, run it.
 
-When using ICU4X 1.2.0 data, CLDR 43, and ICU4C 73.1, you have to run the following. The baked data is generated into ``intl/icu_testdata/data/baked``.
+When using ICU4X 1.4.0 data with the latest data that is hard-coded, you have to run the following. The baked data of ``icu_segmenter`` is generated into ``intl/icu_segmenter_data/data``.
 
 .. code:: bash
 
     $ cd $(TOPSRCDIR)/intl
-    $ ./update-icu4x.sh https://github.com/unicode-org/icu4x.git [email protected] 43.0.0 release-73-1
-
-ICU4X 1.3 will have new feature "``complied_data``" that replaces customized ``icu_testdata``. After upgrading to 1.3, we update this document too.
+    $ ./update-icu4x.sh https://github.com/unicode-org/icu4x.git [email protected] 44.0.0 release-74-1 1.4.0
 
 Updating ICU4X
 ==============
@@ -39,21 +39,14 @@ ICU4X provides ``icu_capi`` crate for C/C++ FFI. ``mozilla::intl::GetDataProvide
 Accessing the data provider from Rust
 =====================================
 
-``icu_testdata::any()`` returns any data provider.
-
-If you want to use unstable data provider from Rust, you should add it to ``intl/icu_testdata/src/lib.rs`` like the following, then use ``icu_testdata::unstable()``.
-
-.. code:: rust
-
-    pub fn unstable() -> UnstableDataProvider {
-        UnstableDataProvider
-    }
+Use ``compiled_data`` feature. You don't consider data provider.
 
 Adding new ICU4X features to Gecko
 ==================================
 
 To reduce build time and binary size, embedded ICU4X in Gecko is minimal configuration. If you have to add new features, you have to update some files.
 
 #. Adding the feature to ``icu_capi`` entry in ``js/src/rust/shared/Cargo.toml``.
-#. Modify ``intl/update-icu4x.sh`` to add generated ICU4X data.
-#. Modify ``intl/icu_testdata/Cargo.toml`` to add the data for enabled feature.
+#. Modify ``[features]`` section in ``intl/icu_capi/Cargo.toml`` to enable ``compiled_data`` feature of added crate.
+#. Modify the patch file for ``intl/icu_capi/Cargo.toml`` into ``intl/icu4x-patches``.
+#. (Optional) Modify ``intl/update-icu4x.sh`` to add generated ICU4X data if you want to modify ICU4X baked data.