Validate crate name in CLI option --extern

compiler/rustc_session/src/config.rs

@@ -2451,6 +2451,19 @@ 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());

compiler/rustc_session/src/session.rs

@@ -1710,6 +1710,15 @@ impl EarlyErrorHandler {
         self.handler.struct_fatal(msg).emit()
     }
 
+    #[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>) {

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
+    }
+}

tests/run-make/incr-foreign-head-span/Makefile

@@ -15,7 +15,7 @@ INCR=$(TMPDIR)/incr
 all:
 	cp first_crate.rs second_crate.rs $(TMPDIR)
 	$(RUSTC) $(TMPDIR)/first_crate.rs  -C incremental=$(INCR) --target $(TARGET) --crate-type lib
-	$(RUSTC) $(TMPDIR)/second_crate.rs -C incremental=$(INCR) --target $(TARGET)  --extern first-crate=$(TMPDIR) --crate-type lib
+	$(RUSTC) $(TMPDIR)/second_crate.rs -C incremental=$(INCR) --target $(TARGET)  --extern first_crate=$(TMPDIR)/libfirst_crate.rlib --crate-type lib
 	rm $(TMPDIR)/first_crate.rs
 	$(RUSTC) $(TMPDIR)/second_crate.rs  -C incremental=$(INCR) --target $(TARGET) --cfg second_run --crate-type lib
 

tests/ui/extern-flag/invalid-crate-name-dashed.rs

@@ -0,0 +1,10 @@
+// compile-flags: --extern=my-awesome-library=libawesome.rlib
+// error-pattern: crate name `my-awesome-library` passed to `--extern` is not a valid ASCII identifier
+// error-pattern: consider replacing the dashes with underscores: `my_awesome_library`
+
+// In a sense, this is a regression test for issue #113035. We no longer suggest
+// `pub use my-awesome-library::*;` (sic!) as we outright ban this crate name.
+
+pub use my_awesome_library::*;
+
+fn main() {}

tests/ui/extern-flag/invalid-crate-name-dashed.stderr

@@ -0,0 +1,4 @@
+error: crate name `my-awesome-library` passed to `--extern` is not a valid ASCII identifier
+  |
+  = help: consider replacing the dashes with underscores: `my_awesome_library`
+

tests/ui/extern-flag/invalid-crate-name-non-ascii.rs

@@ -0,0 +1,4 @@
+// compile-flags: --extern čɍαţē=libnon_ascii.rlib
+// error-pattern: crate name `čɍαţē` passed to `--extern` is not a valid ASCII identifier
+
+fn main() {}

tests/ui/extern-flag/invalid-crate-name-non-ascii.stderr

@@ -0,0 +1,2 @@
+error: crate name `čɍαţē` passed to `--extern` is not a valid ASCII identifier
+

tests/ui/extern-flag/invalid-crate-name.rs

@@ -0,0 +1,4 @@
+// compile-flags: --extern=?#1%$
+// error-pattern: crate name `?#1%$` passed to `--extern` is not a valid ASCII identifier
+
+fn main() {}

tests/ui/extern-flag/invalid-crate-name.stderr

@@ -0,0 +1,2 @@
+error: crate name `?#1%$` passed to `--extern` is not a valid ASCII identifier
+

tests/ui/rust-2018/trait-import-suggestions.rs

@@ -1,6 +1,6 @@
 // edition:2018
 // aux-build:trait-import-suggestions.rs
-// compile-flags:--extern trait-import-suggestions
+// compile-flags:--extern trait_import_suggestions
 
 mod foo {
     mod foobar {