ast: Keep expansion status for out-of-line module items

Also remove `ast::Mod` which is mostly redundant now

compiler/rustc_ast/src/ast.rs

@@ -2299,21 +2299,22 @@ impl FnRetTy {
     }
 }
 
-/// Module declaration.
-///
-/// E.g., `mod foo;` or `mod foo { .. }`.
+#[derive(Clone, PartialEq, Encodable, Decodable, Debug)]
+pub enum Inline {
+    Yes,
+    No,
+}
+
+/// Module item kind.
 #[derive(Clone, Encodable, Decodable, Debug)]
-pub struct Mod {
-    /// A span from the first token past `{` to the last token until `}`.
-    /// For `mod foo;`, the inner span ranges from the first token
-    /// to the last token in the external file.
-    pub inner: Span,
-    /// `unsafe` keyword accepted syntactically for macro DSLs, but not
-    /// semantically by Rust.
-    pub unsafety: Unsafe,
-    pub items: Vec<P<Item>>,
-    /// `true` for `mod foo { .. }`; `false` for `mod foo;`.
-    pub inline: bool,
+pub enum ModKind {
+    /// Module with inlined definition `mod foo { ... }`,
+    /// 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),
+    /// Module with definition outlined to a separate file `mod foo;` but not yet loaded from it.
+    Unloaded,
 }
 
 /// Foreign module declaration.
@@ -2710,7 +2711,9 @@ pub enum ItemKind {
     /// A module declaration (`mod`).
     ///
     /// E.g., `mod foo;` or `mod foo { .. }`.
-    Mod(Mod),
+    /// `unsafe` keyword on modules is accepted syntactically for macro DSLs, but not
+    /// semantically by Rust.
+    Mod(Unsafe, ModKind),
     /// An external module (`extern`).
     ///
     /// E.g., `extern {}` or `extern "C" {}`.

compiler/rustc_ast/src/mut_visit.rs

@@ -913,11 +913,13 @@ pub fn noop_visit_item_kind<T: MutVisitor>(kind: &mut ItemKind, vis: &mut T) {
             vis.visit_generics(generics);
             visit_opt(body, |body| vis.visit_block(body));
         }
-        ItemKind::Mod(m) => {
-            let Mod { inner, unsafety: _, items, inline: _ } = m;
-            vis.visit_span(inner);
-            items.flat_map_in_place(|item| vis.flat_map_item(item));
-        }
+        ItemKind::Mod(_unsafety, mod_kind) => match mod_kind {
+            ModKind::Loaded(items, _inline, inner_span) => {
+                vis.visit_span(inner_span);
+                items.flat_map_in_place(|item| vis.flat_map_item(item));
+            }
+            ModKind::Unloaded => {}
+        },
         ItemKind::ForeignMod(nm) => vis.visit_foreign_mod(nm),
         ItemKind::GlobalAsm(_ga) => {}
         ItemKind::TyAlias(box TyAliasKind(_, generics, bounds, ty)) => {
@@ -1010,7 +1012,7 @@ pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
             id: DUMMY_NODE_ID,
             vis: item_vis,
             span,
-            kind: ItemKind::Mod(Mod { inner: span, unsafety: Unsafe::No, items, inline: true }),
+            kind: ItemKind::Mod(Unsafe::No, ModKind::Loaded(items, Inline::Yes, span)),
             tokens: None,
         });
         let items = vis.flat_map_item(item);
@@ -1021,7 +1023,9 @@ pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
         } else if len == 1 {
             let Item { attrs, span, kind, .. } = items.into_iter().next().unwrap().into_inner();
             match kind {
-                ItemKind::Mod(module) => Crate { attrs, items: module.items, span, proc_macros },
+                ItemKind::Mod(_, ModKind::Loaded(items, ..)) => {
+                    Crate { attrs, items, span, proc_macros }
+                }
                 _ => panic!("visitor converted a module to not a module"),
             }
         } else {

compiler/rustc_ast/src/visit.rs

@@ -290,7 +290,12 @@ pub fn walk_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a Item) {
             let kind = FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, body.as_deref());
             visitor.visit_fn(kind, item.span, item.id)
         }
-        ItemKind::Mod(ref module) => walk_list!(visitor, visit_item, &module.items),
+        ItemKind::Mod(_unsafety, ref mod_kind) => match mod_kind {
+            ModKind::Loaded(items, _inline, _inner_span) => {
+                walk_list!(visitor, visit_item, items)
+            }
+            ModKind::Unloaded => {}
+        },
         ItemKind::ForeignMod(ref foreign_module) => {
             walk_list!(visitor, visit_foreign_item, &foreign_module.items);
         }