[WIP] Resolve: refactor define into define_local and define_extern

compiler/rustc_expand/src/base.rs

@@ -1042,7 +1042,7 @@ pub trait ResolverExpand {
     fn next_node_id(&mut self) -> NodeId;
     fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId;
 
-    fn resolve_dollar_crates(&mut self);
+    fn resolve_dollar_crates(&self);
     fn visit_ast_fragment_with_placeholders(
         &mut self,
         expn_id: LocalExpnId,

compiler/rustc_hir/src/def.rs

@@ -295,6 +295,12 @@ impl DefKind {
         }
     }
 
+    /// This is a "module" in name resolution sense.
+    #[inline]
+    pub fn is_module_like(self) -> bool {
+        matches!(self, DefKind::Mod | DefKind::Enum | DefKind::Trait)
+    }
+
     #[inline]
     pub fn is_fn_like(self) -> bool {
         matches!(
@@ -720,6 +726,15 @@ impl<Id> Res<Id> {
         }
     }
 
+    /// If this is a "module" in name resolution sense, return its `DefId`.
+    #[inline]
+    pub fn module_like_def_id(&self) -> Option<DefId> {
+        match self {
+            Res::Def(def_kind, def_id) if def_kind.is_module_like() => Some(*def_id),
+            _ => None,
+        }
+    }
+
     /// A human readable name for the res kind ("function", "module", etc.).
     pub fn descr(&self) -> &'static str {
         match *self {

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -3,7 +3,7 @@ use std::mem;
 use std::sync::Arc;
 
 use rustc_attr_data_structures::Deprecation;
-use rustc_hir::def::{CtorKind, DefKind, Res};
+use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_middle::arena::ArenaAllocatable;
@@ -510,10 +510,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
                         }
                         Entry::Vacant(entry) => {
                             entry.insert(parent);
-                            if matches!(
-                                child.res,
-                                Res::Def(DefKind::Mod | DefKind::Enum | DefKind::Trait, _)
-                            ) {
+                            if child.res.module_like_def_id().is_some() {
                                 bfs_queue.push_back(def_id);
                             }
                         }

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -3454,9 +3454,7 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
                         collect_fn(&child.ident, ns, def_id);
                     }
 
-                    if matches!(defkind, DefKind::Mod | DefKind::Enum | DefKind::Trait)
-                        && seen_defs.insert(def_id)
-                    {
+                    if defkind.is_module_like() && seen_defs.insert(def_id) {
                         queue.push(def_id);
                     }
                 }