4 files changed, 45 insertions, 7 deletions
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 956ae149e55..d29ab02c1a6 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -2475,6 +2475,19 @@ pub fn parse_externs(
             Some((opts, name)) => (Some(opts), name.to_string()),
         };
 
+        if !crate::utils::is_ascii_ident(&name) {
+            let mut error = handler.early_struct_error(format!(
+                "crate name `{name}` passed to `--extern` is not a valid ASCII identifier"
+            ));
+            let adjusted_name = name.replace("-", "_");
+            if crate::utils::is_ascii_ident(&adjusted_name) {
+                error.help(format!(
+                    "consider replacing the dashes with underscores: `{adjusted_name}`"
+                ));
+            }
+            error.emit();
+        }
+
         let path = path.map(|p| CanonicalizedPath::new(p));
 
         let entry = externs.entry(name.to_owned());
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 5a6def1958b..23f2be632b2 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -20,7 +20,7 @@ use std::collections::BTreeMap;
 
 use std::collections::hash_map::DefaultHasher;
 use std::hash::Hasher;
-use std::num::NonZeroUsize;
+use std::num::{IntErrorKind, NonZeroUsize};
 use std::path::PathBuf;
 use std::str;
 
@@ -387,7 +387,7 @@ mod desc {
         "`all` (default), `except-unused-generics`, `except-unused-functions`, or `off`";
     pub const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub const parse_unpretty: &str = "`string` or `string=string`";
-    pub const parse_treat_err_as_bug: &str = "either no value or a number bigger than 0";
+    pub const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
     pub const parse_trait_solver: &str =
         "one of the supported solver modes (`classic`, `next`, or `next-coherence`)";
     pub const parse_lto: &str =
@@ -986,10 +986,16 @@ mod parse {
 
     pub(crate) fn parse_treat_err_as_bug(slot: &mut Option<NonZeroUsize>, v: Option<&str>) -> bool {
         match v {
-            Some(s) => {
-                *slot = s.parse().ok();
-                slot.is_some()
-            }
+            Some(s) => match s.parse() {
+                Ok(val) => {
+                    *slot = Some(val);
+                    true
+                }
+                Err(e) => {
+                    *slot = None;
+                    e.kind() == &IntErrorKind::Zero
+                }
+            },
             None => {
                 *slot = NonZeroUsize::new(1);
                 true
@@ -1846,7 +1852,8 @@ written to standard error output)"),
     trap_unreachable: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "generate trap instructions for unreachable intrinsics (default: use target setting, usually yes)"),
     treat_err_as_bug: Option<NonZeroUsize> = (None, parse_treat_err_as_bug, [TRACKED],
-        "treat error number `val` that occurs as bug"),
+        "treat the `val`th error that occurs as bug (default if not specified: 0 - don't treat errors as bugs. \
+        default if specified without a value: 1 - treat the first error as bug)"),
     trim_diagnostic_paths: bool = (true, parse_bool, [UNTRACKED],
         "in diagnostics, use heuristics to shorten paths referring to items"),
     tune_cpu: Option<String> = (None, parse_opt_string, [TRACKED],
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 86f4e7b48da..b484978eed2 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1726,6 +1726,15 @@ impl EarlyErrorHandler {
 
     #[allow(rustc::untranslatable_diagnostic)]
     #[allow(rustc::diagnostic_outside_of_impl)]
+    pub(crate) fn early_struct_error(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, !> {
+        self.handler.struct_fatal(msg)
+    }
+
+    #[allow(rustc::untranslatable_diagnostic)]
+    #[allow(rustc::diagnostic_outside_of_impl)]
     pub fn early_warn(&self, msg: impl Into<DiagnosticMessage>) {
         self.handler.struct_warn(msg).emit()
     }
diff --git a/compiler/rustc_session/src/utils.rs b/compiler/rustc_session/src/utils.rs
index f76c69af526..aea7c6c2842 100644
--- a/compiler/rustc_session/src/utils.rs
+++ b/compiler/rustc_session/src/utils.rs
@@ -158,3 +158,12 @@ pub fn extra_compiler_flags() -> Option<(Vec<String>, bool)> {
 
     if !result.is_empty() { Some((result, excluded_cargo_defaults)) } else { None }
 }
+
+pub(crate) fn is_ascii_ident(string: &str) -> bool {
+    let mut chars = string.chars();
+    if let Some(start) = chars.next() && (start.is_ascii_alphabetic() || start == '_') {
+        chars.all(|char| char.is_ascii_alphanumeric() || char == '_')
+    } else {
+        false
+    }
+}