fix: add build.rs to crates with version-gated code lacking auto-detection

CONTRIBUTING.md

@@ -32,6 +32,47 @@ term health of the repository.
 * Please keep PRs limited to a single topic of change. This makes the PR easier to
   review, and easier to roll back, if that becomes necessary.
 
+## ICU version feature detection
+
+Several crates in this workspace contain code that is conditionally compiled
+based on the ICU library version, using attributes such as
+`#[cfg(feature = "icu_version_64_plus")]`.
+
+**There are two mechanisms by which these features are activated, and both
+must be kept in sync:**
+
+### 1. Automatic detection via `build.rs` (used when `icu_config` is active)
+
+Crates that have a `build.rs` call `rust_icu_release::run()`, which queries
+`pkg-config` for the installed ICU version and emits
+`cargo:rustc-cfg=feature="icu_version_XX_plus"` instructions. This activates
+the version features automatically when using the default feature set
+(`use-bindgen`, `icu_config`, `renaming`), so `cargo test` works without
+any explicit `--features` flags.
+
+**Every crate that contains `#[cfg(feature = "icu_version_XX_plus")]`-gated
+code MUST have a `build.rs`** that follows this pattern. Without it, the
+version-gated code is silently excluded from compilation and testing when
+the crate is built with default features, even if a modern ICU version is
+installed.
+
+Crates that currently have a `build.rs` for this purpose:
+`rust_icu_sys`, `rust_icu_udat`, `rust_icu_uloc`, `rust_icu_ulistformatter`,
+`rust_icu_unumberformatter`, `rust_icu_ecma402`.
+
+### 2. Explicit Cargo features (used when `icu_config` is inactive)
+
+When `icu_config` is disabled (e.g. when using pre-generated static bindgen
+files with `icu_version_in_env`), the version features must be passed
+explicitly via `--features=icu_version_64_plus,...`. The `build.rs` no-ops in
+this case. The CI `test-with-features` matrix job covers this path.
+
+### Adding a new crate with version-gated code
+
+If you add `#[cfg(feature = "icu_version_XX_plus")]` to a new crate, you must
+also add a `build.rs` (copy from any existing crate such as `rust_icu_uloc`)
+and add the corresponding `[build-dependencies]` to the crate's `Cargo.toml`.
+
 ## Community Guidelines
 
 This project follows [Google's Open Source Community

Makefile

@@ -104,11 +104,11 @@ macos-test:
 	    && PATH="$$ICU_PREFIX/bin:$$PATH" \
 	       PKG_CONFIG_PATH="$$ICU_PREFIX/lib/pkgconfig:$$PKG_CONFIG_PATH" \
 	       RUSTFLAGS="-L $$ICU_PREFIX/lib" \
-	       cargo test --no-default-features --features=use-bindgen,icu_config,renaming,icu_version_64_plus,icu_version_67_plus,icu_version_68_plus \
+	       cargo test \
 	    && PATH="$$ICU_PREFIX/bin:$$PATH" \
 	       PKG_CONFIG_PATH="$$ICU_PREFIX/lib/pkgconfig:$$PKG_CONFIG_PATH" \
 	       RUSTFLAGS="-L $$ICU_PREFIX/lib" \
-	       cargo test --no-default-features --features=use-bindgen,icu_config,renaming,icu_version_64_plus,icu_version_67_plus,icu_version_68_plus,static
+	       cargo test --features=static
 .PHONY: macos-test
 
 # Refreshes the static bindgen output (contents of ./rust_icu_sys/bindgen) based

rust_icu_ecma402/Cargo.toml

@@ -115,6 +115,10 @@ icu_version_69_max = [
   "rust_icu_ustring/icu_version_69_max",
 ]
 
+[build-dependencies]
+anyhow = "1.0"
+rust_icu_release = { path = "../rust_icu_release", version = "5.6.0" }
+
 [badges]
 maintenance = { status = "actively-developed" }
 is-it-maintained-issue-resolution = { repository = "google/rust_icu" }

rust_icu_ecma402/build.rs

@@ -0,0 +1,31 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! See LICENSE for licensing information.
+//!
+//! This build.rs script provides Cargo _features_ indicating the target ICU4C library version,
+//! enabling some conditionally compiled Rust code in this crate that depends on the particular
+//! ICU4C version.
+//!
+//! Please refer to README.md for instructions on how to build the library for your use.
+
+#[cfg(feature = "icu_config")]
+fn main() -> anyhow::Result<()> {
+    use rust_icu_release::run;
+    run()
+}
+
+/// No-op if icu_config is disabled.
+#[cfg(not(feature = "icu_config"))]
+fn main() {}

rust_icu_ulistformatter/Cargo.toml

@@ -70,6 +70,10 @@ icu_version_69_max = [
   "rust_icu_ustring/icu_version_69_max",
 ]
 
+[build-dependencies]
+anyhow = "1.0"
+rust_icu_release = { path = "../rust_icu_release", version = "5.6.0" }
+
 [badges]
 maintenance = { status = "actively-developed" }
 is-it-maintained-issue-resolution = { repository = "google/rust_icu" }

rust_icu_ulistformatter/build.rs

@@ -0,0 +1,31 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! See LICENSE for licensing information.
+//!
+//! This build.rs script provides Cargo _features_ indicating the target ICU4C library version,
+//! enabling some conditionally compiled Rust code in this crate that depends on the particular
+//! ICU4C version.
+//!
+//! Please refer to README.md for instructions on how to build the library for your use.
+
+#[cfg(feature = "icu_config")]
+fn main() -> anyhow::Result<()> {
+    use rust_icu_release::run;
+    run()
+}
+
+/// No-op if icu_config is disabled.
+#[cfg(not(feature = "icu_config"))]
+fn main() {}

rust_icu_unumberformatter/Cargo.toml

@@ -97,6 +97,10 @@ icu_version_69_max = [
   "rust_icu_ustring/icu_version_69_max",
 ]
 
+[build-dependencies]
+anyhow = "1.0"
+rust_icu_release = { path = "../rust_icu_release", version = "5.6.0" }
+
 [badges]
 maintenance = { status = "actively-developed" }
 is-it-maintained-issue-resolution = { repository = "google/rust_icu" }

rust_icu_unumberformatter/build.rs

@@ -0,0 +1,31 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! See LICENSE for licensing information.
+//!
+//! This build.rs script provides Cargo _features_ indicating the target ICU4C library version,
+//! enabling some conditionally compiled Rust code in this crate that depends on the particular
+//! ICU4C version.
+//!
+//! Please refer to README.md for instructions on how to build the library for your use.
+
+#[cfg(feature = "icu_config")]
+fn main() -> anyhow::Result<()> {
+    use rust_icu_release::run;
+    run()
+}
+
+/// No-op if icu_config is disabled.
+#[cfg(not(feature = "icu_config"))]
+fn main() {}