Mark rustc_driver::install_ice_hook unsafe

It modifies the environment.

Author: tbu-

compiler/rustc_driver_impl/src/lib.rs

@@ -1307,7 +1307,11 @@ fn ice_path() -> &'static Option<PathBuf> {
 /// internal features.
 ///
 /// A custom rustc driver can skip calling this to set up a custom ICE hook.
-pub fn install_ice_hook(
+///
+/// # Unsafety
+///
+/// This function modifies the environment and has the same safety as [`std::env::set_var`].
+pub unsafe fn install_ice_hook(
     bug_report_url: &'static str,
     extra_info: fn(&DiagCtxt),
 ) -> Arc<AtomicBool> {
@@ -1520,7 +1524,8 @@ pub fn main() -> ! {
     init_rustc_env_logger(&early_dcx);
     signal_handler::install();
     let mut callbacks = TimePassesCallbacks::default();
-    let using_internal_features = install_ice_hook(DEFAULT_BUG_REPORT_URL, |_| ());
+    // We're single-threaded at this point, so it's okay to call `install_ice_hook`.
+    let using_internal_features = unsafe { install_ice_hook(DEFAULT_BUG_REPORT_URL, |_| ()) };
     install_ctrlc_handler();
 
     let exit_code = catch_with_exit_code(|| {

src/tools/clippy/src/driver.rs

@@ -181,13 +181,16 @@ pub fn main() {
 
     rustc_driver::init_rustc_env_logger(&early_dcx);
 
-    let using_internal_features = rustc_driver::install_ice_hook(BUG_REPORT_URL, |handler| {
-        // FIXME: this macro calls unwrap internally but is called in a panicking context!  It's not
-        // as simple as moving the call from the hook to main, because `install_ice_hook` doesn't
-        // accept a generic closure.
-        let version_info = rustc_tools_util::get_version_info!();
-        handler.note(format!("Clippy version: {version_info}"));
-    });
+    // We're single-threaded at this point, so it's okay to call `install_ice_hook`.
+    let using_internal_features = unsafe {
+        rustc_driver::install_ice_hook(BUG_REPORT_URL, |handler| {
+            // FIXME: this macro calls unwrap internally but is called in a panicking context!  It's not
+            // as simple as moving the call from the hook to main, because `install_ice_hook` doesn't
+            // accept a generic closure.
+            let version_info = rustc_tools_util::get_version_info!();
+            handler.note(format!("Clippy version: {version_info}"));
+        })
+    };
 
     exit(rustc_driver::catch_with_exit_code(move || {
         let mut orig_args = rustc_driver::args::raw_args(&early_dcx)?;

src/tools/miri/src/bin/miri.rs

@@ -371,8 +371,11 @@ fn main() {
     // If the environment asks us to actually be rustc, then do that.
     if let Some(crate_kind) = env::var_os("MIRI_BE_RUSTC") {
         // Earliest rustc setup.
-        let using_internal_features =
-            rustc_driver::install_ice_hook(rustc_driver::DEFAULT_BUG_REPORT_URL, |_| ());
+        //
+        // We're single-threaded at this point, so it's okay to call `install_ice_hook`.
+        let using_internal_features = unsafe {
+            rustc_driver::install_ice_hook(rustc_driver::DEFAULT_BUG_REPORT_URL, |_| ())
+        };
         rustc_driver::init_rustc_env_logger(&early_dcx);
 
         let target_crate = if crate_kind == "target" {
@@ -393,8 +396,11 @@ fn main() {
     }
 
     // Add an ICE bug report hook.
-    let using_internal_features =
-        rustc_driver::install_ice_hook("https://github.com/rust-lang/miri/issues/new", |_| ());
+    //
+    // We're single-threaded at this point, so it's okay to call `install_ice_hook`.
+    let using_internal_features = unsafe {
+        rustc_driver::install_ice_hook("https://github.com/rust-lang/miri/issues/new", |_| ())
+    };
 
     // Init loggers the Miri way.
     init_early_loggers(&early_dcx);

src/tools/rustfmt/src/bin/main.rs

@@ -28,7 +28,10 @@ const BUG_REPORT_URL: &str = "https://github.com/rust-lang/rustfmt/issues/new?la
 extern crate rustc_driver;
 
 fn main() {
-    rustc_driver::install_ice_hook(BUG_REPORT_URL, |_| ());
+    // We're single-threaded at this point, so it's okay to call `install_ice_hook`.
+    unsafe {
+        rustc_driver::install_ice_hook(BUG_REPORT_URL, |_| ());
+    }
 
     tracing_subscriber::fmt()
         .with_env_filter(EnvFilter::from_env("RUSTFMT_LOG"))