forbid namespaced crate names with more than two segments

sq

Author: b-naber

compiler/rustc_resolve/src/ident.rs

@@ -211,25 +211,15 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     MacroRulesScope::Empty => Scope::ModuleNonGlobs(module.unwrap(), None),
                 },
                 Scope::ModuleNonGlobs(module, lint_id) => Scope::ModuleGlobs(module, lint_id),
-                Scope::ModuleGlobs(module, lint_id) if module_only => {
-                    Scope::NamespacedCrates(NamespacedCrateRoot::Mod(module), lint_id)
-                }
-                Scope::NamespacedCrates(..) if module_only | namespace_crate_only => break,
-                Scope::ModuleGlobs(module, lint_id) if module_and_extern_prelude => {
-                    Scope::NamespacedCrates(NamespacedCrateRoot::Mod(module), lint_id)
-                }
-                Scope::NamespacedCrates(..) if module_and_extern_prelude => match ns {
+                Scope::ModuleGlobs(module, lint_id) if module_only => break,
+                Scope::ModuleGlobs(module, lint_id) if module_and_extern_prelude => match ns {
                     TypeNS => {
                         ctxt.update_unchecked(|ctxt| ctxt.adjust(ExpnId::root()));
                         Scope::ExternPreludeItems
                     }
                     ValueNS | MacroNS => break,
                 },
                 Scope::ModuleGlobs(module, prev_lint_id) => {
-                    Scope::NamespacedCrates(NamespacedCrateRoot::Mod(module), prev_lint_id)
-                }
-                Scope::NamespacedCrates(namespace_crate_root, prev_lint_id) => {
-                    let module = namespace_crate_root.get_mod();
                     use_prelude = !module.no_implicit_prelude;
                     match self.hygienic_lexical_parent(module, &mut ctxt, derive_fallback_lint_id) {
                         Some((parent_module, lint_id)) => {
@@ -245,6 +235,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                     }
                 }
+                Scope::NamespacedCrates(..) => {
+                    assert!(namespace_crate_only);
+                    break;
+                }
                 Scope::MacroUsePrelude => Scope::StdLibPrelude,
                 Scope::BuiltinAttrs => break, // nowhere else to search
                 Scope::ExternPreludeItems => Scope::ExternPreludeFlags,

compiler/rustc_session/src/config/externs.rs

@@ -43,6 +43,13 @@ pub(crate) fn split_extern_opt<'a>(
         }
     };
 
+    // Reject paths with more than two segments.
+    if unstable_opts.namespaced_crates && crate_name.split("::").count() > 2 {
+        return Err(early_dcx.early_struct_fatal(format!(
+            "crate name `{crate_name}` passed to `--extern` has too many segments; namespaced crates currently support at most two segments"
+        )));
+    }
+
     if !valid_crate_name(&crate_name, unstable_opts) {
         let mut error = early_dcx.early_struct_fatal(format!(
             "crate name `{crate_name}` passed to `--extern` is not a valid ASCII identifier"