Assert that a single scope is passed to for_scope

compiler/rustc_session/src/session.rs

@@ -1523,16 +1523,25 @@ pub trait RemapFileNameExt {
     where
         Self: 'a;
 
-    fn for_scope(&self, sess: &Session, scopes: RemapPathScopeComponents) -> Self::Output<'_>;
+    /// Returns a possibly remapped filename based on the passed scope and remap cli options.
+    ///
+    /// One and only one scope should be passed to this method. For anything related to
+    /// "codegen" see the [`RemapFileNameExt::for_codegen`] method.
+    fn for_scope(&self, sess: &Session, scope: RemapPathScopeComponents) -> Self::Output<'_>;
 
+    /// Return a possibly remapped filename, to be used in "codegen" related parts.
     fn for_codegen(&self, sess: &Session) -> Self::Output<'_>;
 }
 
 impl RemapFileNameExt for rustc_span::FileName {
     type Output<'a> = rustc_span::FileNameDisplay<'a>;
 
-    fn for_scope(&self, sess: &Session, scopes: RemapPathScopeComponents) -> Self::Output<'_> {
-        if sess.opts.unstable_opts.remap_path_scope.contains(scopes) {
+    fn for_scope(&self, sess: &Session, scope: RemapPathScopeComponents) -> Self::Output<'_> {
+        assert!(
+            scope.bits().count_ones() == 1,
+            "one and only one scope should be passed to for_scope"
+        );
+        if sess.opts.unstable_opts.remap_path_scope.contains(scope) {
             self.prefer_remapped_unconditionaly()
         } else {
             self.prefer_local()
@@ -1551,8 +1560,12 @@ impl RemapFileNameExt for rustc_span::FileName {
 impl RemapFileNameExt for rustc_span::RealFileName {
     type Output<'a> = &'a Path;
 
-    fn for_scope(&self, sess: &Session, scopes: RemapPathScopeComponents) -> Self::Output<'_> {
-        if sess.opts.unstable_opts.remap_path_scope.contains(scopes) {
+    fn for_scope(&self, sess: &Session, scope: RemapPathScopeComponents) -> Self::Output<'_> {
+        assert!(
+            scope.bits().count_ones() == 1,
+            "one and only one scope should be passed to for_scope"
+        );
+        if sess.opts.unstable_opts.remap_path_scope.contains(scope) {
             self.remapped_path_if_available()
         } else {
             self.local_path_if_available()