Validate crate name in CLI option --extern

Author: fmease

compiler/rustc_session/Cargo.toml

@@ -19,6 +19,7 @@ rustc_span = { path = "../rustc_span" }
 rustc_fs_util = { path = "../rustc_fs_util" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_lint_defs = { path = "../rustc_lint_defs" }
+rustc_lexer = { path = "../rustc_lexer" }
 smallvec = "1.8.1"
 termize = "0.1.1"
 

compiler/rustc_session/src/config.rs

@@ -2451,6 +2451,19 @@ pub fn parse_externs(
             Some((opts, name)) => (Some(opts), name.to_string()),
         };
 
+        if !rustc_lexer::is_ident(&name) {
+            let mut error = handler.early_struct_error(format!(
+                "crate name `{name}` passed to `--extern` is not a valid identifier"
+            ));
+            let adjusted_name = name.replace("-", "_");
+            if rustc_lexer::is_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>) {

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

@@ -0,0 +1,7 @@
+// compile-flags: --extern=my-awesome-library=libawesome.rlib
+// error-pattern: crate name `my-awesome-library` passed to `--extern` is not a valid identifier
+// error-pattern: consider replacing the dashes with underscores: `my_awesome_library`
+
+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 identifier
+  |
+  = help: consider replacing the dashes with underscores: `my_awesome_library`
+

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 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 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 {