Update PINNED_CI_NIGHTLY (not LLVM_COMPATIBLE_NIGHTLY) (#7003)

By policy these are allowed (and usually supposed to be) separate:
`LLVM_COMPATIBLE_NIGHTLY` is *only* for tests constrained by LLVM
version, whereas `PINNED_CI_NIGHTLY` should be a recent nightly so that
nightly CI can keep passing. We should not be trying to maintain test
compatibility with rustc nightlies across 6 months.

We had these be the same for a while because JS CI was _additionally_
constrained by the WASM ABI changes; but that's been fixed for a while
now.

Making this PR from the ICU4X repo so I can run nightly CI on it.

This *should* fix JS and nostd nightly CI.

<!--
Thank you for your pull request to ICU4X!

Reminder: try to use [Conventional
Comments](https://conventionalcomments.org/) to make comments clearer.

Please see
https://github.com/unicode-org/icu4x/blob/main/CONTRIBUTING.md for
general
information on contributing to ICU4X.
-->

Author: Manishearth

Cargo.lock

@@ -18,7 +18,8 @@ default_to_workspace = false
 # The toolchain that CI is being run in. Allows tests to change under beta/nightly.
 CI_TOOLCHAIN = { value = "pinned-stable", condition = { env_not_set = ["CI_TOOLCHAIN"]}}
 # The pinned nightly toolchain for jobs that require a nightly compiler.
-PINNED_CI_NIGHTLY = { value = "nightly-2025-02-17", condition = { env_not_set = ["PINNED_CI_NIGHTLY"] } }
+PINNED_CI_NIGHTLY = { value = "nightly-2025-09-27", condition = { env_not_set = ["PINNED_CI_NIGHTLY"] } }
+LLVM_COMPATIBLE_NIGHTLY = { value = "nightly-2025-02-17", condition = { env_not_set = ["LLVM_COMPATIBLE_NIGHTLY"] } }
 
 [tasks.quick]
 description = "Run quick version of all lints and builds (useful before pushing to GitHub)"

Makefile.toml

@@ -43,10 +43,9 @@ When the nightly cronjob CI fails, ICU4X developers must fix it and ensure it do
 ICU4X pins Rust Nightlies in CI for multiple purposes:
 
  - `diplomat-coverage/src/main.rs`: Running the diplomat-coverage task, which uses unstable Rustdoc JSON output, requiring synchronization between the Rust version and the `rustdoc_types` dependency.
- - `PINNED_CI_NIGHTLY`: Running various FFI CI jobs that need _some_ Rust nightly to use build-std or other nightly features, without becoming beholden to arbitrary
+ - `PINNED_CI_NIGHTLY`: Running various FFI CI jobs that need a reasonably recent Rust nightly to use build-std or other nightly features, without becoming beholden to arbitrary specific version constraints.
  - `LLVM_COMPATIBLE_NIGHTLY`: Usage of `-Clinker-plugin-lto` in size-optimized tests where Rust and Clang need to be using compatible LLVM versions.
 
-
  ICU4X also runs its entire CI against the latest nightly once a day, reporting errors to Slack. These errors help us catch upstream breakages early, but ICU4X does not have any particular SLO against these being fixed. We guarantee we build on the latest stable as detailed in the first section of this page.
 
  The first two nightlies here can be updated whenever necessary to whatever nightly works. It not necessary to keep the nightly versions the same, though it is ideal to try. The choice of these nightlies does not have much of a direct impact on users.

documents/process/rust_versions.md

@@ -4,7 +4,7 @@
 
 export CARGO_TARGET_DIR ?= target
 
-PINNED_CI_NIGHTLY = "nightly-2025-02-17"
+PINNED_CI_NIGHTLY = "nightly-2025-09-27"
 
 all: buffer_data.postcard bin/tutorial_buffer.wasm
 

examples/cargo/buffer/Makefile

@@ -62,7 +62,7 @@ Future buildLib(
   final isNoStd = _isNoStdTarget(rustTarget);
 
   final nightly =
-      Platform.environment['PINNED_CI_NIGHTLY'] ?? 'nightly-2025-02-17';
+      Platform.environment['PINNED_CI_NIGHTLY'] ?? 'nightly-2025-09-27';
 
   if (buildStatic || isNoStd) {
     await runProcess('rustup', [
@@ -85,26 +85,30 @@ Future buildLib(
   final additionalFeatures = isNoStd
       ? ['libc_alloc', 'looping_panic_handler']
       : ['simple_logger'];
-  await runProcess('cargo', [
-    if (buildStatic || isNoStd) '+$nightly',
-    'rustc',
-    '--manifest-path=ffi/capi/Cargo.toml',
-    '--crate-type=${buildStatic ? 'staticlib' : 'cdylib'}',
-    '--release',
-    '--config=profile.release.panic="abort"',
-    '--config=profile.release.codegen-units=1',
-    '--no-default-features',
-    '--features=${{...cargoFeatures, ...additionalFeatures}.join(',')}',
-    if (isNoStd) '-Zbuild-std=core,alloc',
-    if (buildStatic || isNoStd) ...[
-      '-Zbuild-std=std,panic_abort',
-      '-Zbuild-std-features=panic_immediate_abort',
+  await runProcess(
+    'cargo',
+    [
+      if (buildStatic || isNoStd) '+$nightly',
+      'rustc',
+      '--manifest-path=ffi/capi/Cargo.toml',
+      '--crate-type=${buildStatic ? 'staticlib' : 'cdylib'}',
+      '--release',
+      '--config=profile.release.panic="abort"',
+      '--config=profile.release.codegen-units=1',
+      '--no-default-features',
+      '--features=${{...cargoFeatures, ...additionalFeatures}.join(',')}',
+      if (isNoStd) '-Zbuild-std=core,alloc',
+      if (buildStatic || isNoStd) ...['-Zbuild-std=std,panic_abort'],
+      '--target=$rustTarget',
+      '--',
+      '--emit',
+      'link=${out.toFilePath(windows: Platform.isWindows)}',
     ],
-    '--target=$rustTarget',
-    '--',
-    '--emit',
-    'link=${out.toFilePath(windows: Platform.isWindows)}',
-  ], workingDirectory: workingDirectory);
+    workingDirectory: workingDirectory,
+    environment: {
+      if (isNoStd) 'RUSTFLAGS': '-Zunstable-options -Cpanic=immediate-abort',
+    },
+  );
 }
 
 bool _isNoStdTarget(String target) =>
@@ -115,6 +119,7 @@ Future<void> runProcess(
   List<String> arguments, {
   Directory? workingDirectory,
   bool dryRun = false,
+  Map<String, String>? environment,
 }) async {
   print('----------');
   print('Running `$executable $arguments` in $workingDirectory');