Rust I18N Rewrite

build/deps/rust.MODULE.bazel

@@ -97,6 +97,14 @@ crate.annotation(
         "//:patches/rust/crates/hyper/parse-error-explanation.patch",
     ],
 )
+crate.annotation(
+    # rust_icu's checked-in bindings and symbol-renaming macro are selected by this value. Keep it
+    # synchronized with U_ICU_VERSION_MAJOR_NUM of the Chromium ICU commit pinned in
+    # build/deps/gen/deps.MODULE.bazel. ci/v8_update.py updates it; see docs/v8-updates.md.
+    build_script_env = {"BAZEL": "1"},
+    crate = "rust_icu_sys",
+    rustc_env = {"RUST_ICU_MAJOR_VERSION_NUMBER": "78"},
+)
 crate.from_cargo(
     # TODO(cleanup): This name is a bit misleading now that we don't vendor. We can clean it up as a
     # followup.

build/wd_rust_crate.bzl

@@ -66,6 +66,7 @@ def wd_rust_crate(
         deps = [],
         link_deps = [],
         proc_macro_deps = [],
+        rustc_env = {},
         data = [],
         test_env = {},
         test_tags = [],
@@ -174,6 +175,7 @@ def wd_rust_crate(
         srcs = srcs,
         deps = deps,
         link_deps = link_deps + ["@@//deps:rust_runtime"],
+        rustc_env = rustc_env,
         visibility = visibility,
         data = data,
         proc_macro_deps = proc_macro_deps,
@@ -195,6 +197,7 @@ def wd_rust_crate(
         size = test_size,
         tags = test_tags,
         crate_features = crate_features,
+        rustc_env = rustc_env,
         deps = test_deps,
         proc_macro_deps = test_proc_macro_deps,
     )

ci/v8_update.py

@@ -35,6 +35,14 @@
 # Keep the aligned markers in sync with the corresponding comments in
 # build/deps/deps.jsonc.
 
+# rust_icu_sys selects its bindings and versioned ICU symbol names from this
+# pin, which must match the major version of the ICU that V8 links.
+RUST_ICU_VERSION_PINS = (
+    ROOT / "build/deps/rust.MODULE.bazel",
+    ROOT / "src/rust/i18n/BUILD.bazel",
+)
+RUST_ICU_VERSION = re.compile(r'(?<="RUST_ICU_MAJOR_VERSION_NUMBER": ")\d+(?=")')
+
 
 def run(args, *, cwd=ROOT, check=True, env=None, stdout=None):
     print("+", shlex.join(map(str, args)), flush=True)
@@ -103,6 +111,41 @@ def _update_aligned_dependencies():
     DEPS.write_text(jsonc.dumps(doc) + "\n")
 
 
+def _icu_major_version(commit):
+    with urlopen(
+        "https://chromium.googlesource.com/chromium/deps/icu/+/"
+        f"{commit}/source/common/unicode/uvernum.h?format=TEXT",
+        timeout=30,
+    ) as response:
+        header = base64.b64decode(response.read()).decode()
+    match = re.search(
+        r"(?<=^#define U_ICU_VERSION_MAJOR_NUM )\d+$", header, re.MULTILINE
+    )
+    return match.group()
+
+
+def _update_rust_icu_version():
+    path, _ = V8_DEPENDENCIES["com_googlesource_chromium_icu"]
+    commit = _v8_dependency_commit(path, (CHECKOUT / "DEPS").read_text())
+    version = _icu_major_version(commit)
+    changed = False
+    for pin in RUST_ICU_VERSION_PINS:
+        text = pin.read_text()
+        old = RUST_ICU_VERSION.findall(text)
+        if len(old) != 1:
+            raise ValueError(
+                f"expected one RUST_ICU_MAJOR_VERSION_NUMBER in {pin}, found {len(old)}"
+            )
+        if old != [version]:
+            pin.write_text(RUST_ICU_VERSION.sub(version, text))
+            changed = True
+    if changed:
+        print(
+            f"Updated RUST_ICU_MAJOR_VERSION_NUMBER to {version}. Check that the pinned "
+            f"rust_icu_sys provides bindgen/lib_{version}.rs; update the crate if it does not."
+        )
+
+
 def _update_module(tag, patch_names):
     text = MODULE.read_text()
     text = re.sub(
@@ -220,6 +263,16 @@ def finish_update(target):
 
     _update_module(target, patch_names)
     _update_aligned_dependencies()
+    # The Rust ICU pin must match the ICU that Bazel builds, so regenerate the
+    # ICU repository from its new commit before deriving the pin.
+    run(
+        [
+            sys.executable,
+            ROOT / "build/deps/update-deps.py",
+            "com_googlesource_chromium_icu",
+        ]
+    )
+    _update_rust_icu_version()
 
 
 def parse_args():

deps/rust/Cargo.toml

@@ -76,6 +76,9 @@ pico-args = "0"
 rand = { version = "0.9", default-features = false, features = ["os_rng", "thread_rng"] }
 ruff_python_ast = { git = "https://github.com/astral-sh/ruff", tag = "0.12.1" }
 ruff_python_parser = { git = "https://github.com/astral-sh/ruff", tag = "0.12.1" }
+# Use rust_icu's checked-in bindings for the Chromium ICU version linked by workerd. ICU itself is
+# supplied by Bazel, so bindgen, icu-config, and rust_icu's library-linking features stay disabled.
+rust_icu_sys = { version = "5.8", default-features = false, features = ["renaming", "icu_version_in_env"] }
 # ring rather than aws-lc-rs: its crates.io package builds with plain cc (no cmake/NASM).
 rustls = { version = "0.23", default-features = false, features = ["ring", "std", "tls12"] }
 rustls-platform-verifier = "0.7"

docs/v8-updates.md

@@ -84,6 +84,13 @@ from the V8 directory.
     figure out what version of the github code V8 depends on. Instead, it should be safe
     to just bump these dependencies to the latest version on github.
 
+    If the new `com_googlesource_chromium_icu` commit changes `U_ICU_VERSION_MAJOR_NUM`
+    (in `source/common/unicode/uvernum.h`), update `RUST_ICU_MAJOR_VERSION_NUMBER` in both
+    `build/deps/rust.MODULE.bazel` and `src/rust/i18n/BUILD.bazel`. A stale value fails the
+    build with undefined `<function>_<version>` ICU symbols, or missing items in
+    `rust_icu_sys` if the two values disagree. If `rust_icu_sys` has no `bindgen/lib_<version>.rs`
+    for the new version, update the crate as well.
+
 11. Check workerd's tests pass with the updated V8.
 
      ```sh
@@ -122,6 +129,10 @@ rebases the patches, regenerates `patches/v8/*.patch`, and updates:
 - the `dragonbox`, `fast_float`, `fp16`, and `highway` commits in
   `build/deps/deps.jsonc`.
 
+It also regenerates `com_googlesource_chromium_icu` in `build/deps/gen/deps.MODULE.bazel`
+and sets `RUST_ICU_MAJOR_VERSION_NUMBER` in `build/deps/rust.MODULE.bazel` and
+`src/rust/i18n/BUILD.bazel` to the major version of the new ICU commit (see step 10).
+
 If the rebase stops because of conflicts, resolve and continue it in the temporary
 checkout:
 
@@ -143,7 +154,7 @@ python3 ci/v8_update.py finish <new_version>
 Do not run `finish` until the rebase has completed. It regenerates the patches and
 updates the pins listed above.
 
-The helper does not run `update-deps.py`. Compare the old and new V8 `DEPS` files for
+The helper runs `update-deps.py` only for ICU. Compare the old and new V8 `DEPS` files for
 changes to `dragonbox`, `fast_float`, `fp16`, `highway`, `perfetto`, and `simdutf`, then
 run the dependency updater for each changed revision:
 

src/rust/i18n/BUILD.bazel

@@ -0,0 +1,24 @@
+load("//:build/wd_rust_crate.bzl", "wd_rust_crate")
+
+wd_rust_crate(
+    name = "i18n",
+    cxx_bridge_deps = [
+        "//src/rust/jsg",
+        "@simdutf",
+        "@workerd-v8//:v8",
+    ],
+    cxx_bridge_src = "ffi.rs",
+    # ICU, which rust_icu_sys binds to, is linked through V8.
+    link_deps = ["@workerd-v8//:v8"],
+    # rust_icu_sys's `versioned_function!` expands in this crate and reads the ICU version from
+    # here. Keep it synchronized with the rust_icu_sys annotation in build/deps/rust.MODULE.bazel;
+    # ci/v8_update.py updates both.
+    rustc_env = {"RUST_ICU_MAJOR_VERSION_NUMBER": "78"},
+    test_deps = ["//src/rust/jsg-test"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//src/rust/jsg",
+        "@crates_vendor//:rust_icu_sys",
+        "@crates_vendor//:thiserror",
+    ],
+)