Detect nightly in icu_capi_freertos, bump to 1.2.1 (#3394)

* Fix freertos on modern nightlies

* Bump to 1.2.1

* fix

ffi/freertos/Cargo.toml

@@ -5,7 +5,7 @@
 [package]
 name = "icu_freertos"
 description = "C interface to ICU4X"
-version = "1.2.0"
+version = "1.2.1"
 authors = ["The ICU4X Project Developers"]
 edition = "2021"
 resolver = "2"
@@ -42,3 +42,6 @@ freertos-rust = "0.1.2"
 # Currently we don't enable anything here as WearOS loads data manually, but the feature remains for future use
 wearos = []
 default = ["icu_capi/default_components"]
+
+[build-dependencies]
+rustc_version = "0.4"

ffi/freertos/build.rs

@@ -0,0 +1,41 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use std::env;
+
+/// Returns whether the Rust compiler needs an `#[alloc_error_handler]`
+/// set. Returns None for cases where we cannot determine the nightly version of the
+/// compiler.
+fn needs_alloc_error_handler() -> Option<bool> {
+    use rustc_version::Channel;
+    let version = rustc_version::version_meta().ok()?;
+    if version.channel != Channel::Nightly {
+        // Ignore custom/dev toolchains, commit date
+        // may not be meaningful
+        return None;
+    }
+    let commit_date = version.commit_date?;
+
+    let year = commit_date.split('-').next()?.parse::<u32>().ok()?;
+
+    // alloc_error_handler became defaulted to the panic handler
+    // in December 2022. Since it still works until April 2023,
+    // we can be fuzzy with our dates and just set the boundary at
+    // 2022/2023
+    Some(year <= 2022)
+}
+
+fn main() {
+    match env::var("CARGO_CFG_TARGET_OS") {
+        Ok(v) if v == "none" => (),
+        // Only on target_os = none
+        _ => return,
+    };
+
+    if let Some(true) = needs_alloc_error_handler() {
+        println!("cargo:rustc-cfg=needs_alloc_error_handler");
+    }
+
+    // For unknown compilers, assume that the nightly is recent.
+}

ffi/freertos/src/lib.rs

@@ -2,6 +2,17 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+//! This crate is a shim that enables one to use icu4x on Cortex-M + FreeRTOS by setting up the
+//! relevant Rust runtime hooks.
+//!
+//! Note that compiling to this platform needs Rust nightly, and this crate attempts to
+//! build across multiple nightly versions.
+//!
+//! This crate has a build script that will attempt to detect the nightly version and configure
+//! things appropriately, where possible. Older nightlies will end up setting the
+//! `--cfg needs_alloc_error_handler` flag: if using a custom build system and a nightly from
+//! 2022 or earlier, please set this flag.
+
 // https://github.com/unicode-org/icu4x/blob/main/docs/process/boilerplate.md#library-annotations
 #![no_std]
 #![cfg_attr(
@@ -17,7 +28,10 @@
     )
 )]
 #![allow(clippy::upper_case_acronyms)]
-#![cfg_attr(target_os = "none", feature(alloc_error_handler))]
+#![cfg_attr(
+    all(target_os = "none", needs_alloc_error_handler),
+    feature(alloc_error_handler)
+)]
 
 // Necessary to for symbols to be linked in
 extern crate icu_capi;
@@ -27,21 +41,19 @@ extern crate icu_capi;
 mod stuff {
     extern crate alloc;
 
-    use alloc::alloc::Layout;
     use core::panic::PanicInfo;
-    use cortex_m::asm;
     use freertos_rust::FreeRtosAllocator;
 
     #[global_allocator]
     static GLOBAL: FreeRtosAllocator = FreeRtosAllocator;
 
+    #[cfg(needs_alloc_error_handler)] // this defaults to the panic handler on newer nightlies
     #[alloc_error_handler]
-    fn alloc_error(_layout: Layout) -> ! {
-        asm::bkpt();
+    fn alloc_error(_layout: alloc::alloc::Layout) -> ! {
+        cortex_m::asm::bkpt();
         loop {}
     }
 
-    #[cfg(target_os = "none")]
     #[panic_handler]
     fn panic(_info: &PanicInfo) -> ! {
         loop {}