Provide more context for rustc +nightly -Zunstable-options on stable

compiler/rustc_codegen_cranelift/src/pretty_clif.rs

@@ -225,10 +225,10 @@ pub(crate) fn write_ir_file(
     let res = std::fs::File::create(clif_file_name).and_then(|mut file| write(&mut file));
     if let Err(err) = res {
         // Using early_warn as no Session is available here
-        rustc_session::early_warn(
+        let handler = rustc_session::EarlyErrorHandler::new(
             rustc_session::config::ErrorOutputType::default(),
-            format!("error writing ir file: {}", err),
         );
+        handler.early_warn(format!("error writing ir file: {}", err));
     }
 }
 

compiler/rustc_driver_impl/src/args.rs

@@ -3,6 +3,8 @@ use std::fmt;
 use std::fs;
 use std::io;
 
+use rustc_session::EarlyErrorHandler;
+
 fn arg_expand(arg: String) -> Result<Vec<String>, Error> {
     if let Some(path) = arg.strip_prefix('@') {
         let file = match fs::read_to_string(path) {
@@ -21,15 +23,12 @@ fn arg_expand(arg: String) -> Result<Vec<String>, Error> {
 /// **Note:** This function doesn't interpret argument 0 in any special way.
 /// If this function is intended to be used with command line arguments,
 /// `argv[0]` must be removed prior to calling it manually.
-pub fn arg_expand_all(at_args: &[String]) -> Vec<String> {
+pub fn arg_expand_all(handler: &EarlyErrorHandler, at_args: &[String]) -> Vec<String> {
     let mut args = Vec::new();
     for arg in at_args {
         match arg_expand(arg.clone()) {
             Ok(arg) => args.extend(arg),
-            Err(err) => rustc_session::early_error(
-                rustc_session::config::ErrorOutputType::default(),
-                format!("Failed to load argument file: {err}"),
-            ),
+            Err(err) => handler.early_error(format!("Failed to load argument file: {err}")),
         }
     }
     args