refactor: prepare to associate multiple spans with a module.

compiler/rustc_ast/src/ast.rs

@@ -2317,11 +2317,24 @@ pub enum ModKind {
     /// or with definition outlined to a separate file `mod foo;` and already loaded from it.
     /// The inner span is from the first token past `{` to the last token until `}`,
     /// or from the first to the last token in the loaded file.
-    Loaded(Vec<P<Item>>, Inline, Span),
+    Loaded(Vec<P<Item>>, Inline, ModSpans),
     /// Module with definition outlined to a separate file `mod foo;` but not yet loaded from it.
     Unloaded,
 }
 
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub struct ModSpans {
+    /// `inner_span` covers the body of the module; for a file module, its the whole file.
+    /// For an inline module, its the span inside the `{ ... }`, not including the curly braces.
+    pub inner_span: Span,
+}
+
+impl Default for ModSpans {
+    fn default() -> ModSpans {
+        ModSpans { inner_span: Default::default() }
+    }
+}
+
 /// Foreign module declaration.
 ///
 /// E.g., `extern { .. }` or `extern "C" { .. }`.

compiler/rustc_ast/src/mut_visit.rs

@@ -1009,7 +1009,7 @@ pub fn noop_visit_item_kind<T: MutVisitor>(kind: &mut ItemKind, vis: &mut T) {
         ItemKind::Mod(unsafety, mod_kind) => {
             visit_unsafety(unsafety, vis);
             match mod_kind {
-                ModKind::Loaded(items, _inline, inner_span) => {
+                ModKind::Loaded(items, _inline, ModSpans { inner_span }) => {
                     vis.visit_span(inner_span);
                     items.flat_map_in_place(|item| vis.flat_map_item(item));
                 }