Revert "Revert "Don't load all extern crates unconditionally""

This reverts commit 5f0c54db4e.

src/librustdoc/core.rs

@@ -1,12 +1,12 @@
+use rustc_ast as ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::{self, Lrc};
 use rustc_driver::abort_on_err;
 use rustc_errors::emitter::{Emitter, EmitterWriter};
 use rustc_errors::json::JsonEmitter;
 use rustc_feature::UnstableFeatures;
-use rustc_hir::def::Namespace::TypeNS;
 use rustc_hir::def::Res;
-use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::HirId;
 use rustc_hir::{
     intravisit::{self, NestedVisitorMap, Visitor},
@@ -23,7 +23,7 @@ use rustc_session::DiagnosticOutput;
 use rustc_session::Session;
 use rustc_span::source_map;
 use rustc_span::symbol::sym;
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::Span;
 
 use std::cell::RefCell;
 use std::mem;
@@ -301,41 +301,16 @@ crate fn create_config(
 }
 
 crate fn create_resolver<'a>(
-    externs: config::Externs,
     queries: &Queries<'a>,
     sess: &Session,
 ) -> Rc<RefCell<interface::BoxedResolver>> {
-    let extern_names: Vec<String> = externs
-        .iter()
-        .filter(|(_, entry)| entry.add_prelude)
-        .map(|(name, _)| name)
-        .cloned()
-        .collect();
+    let (krate, resolver, _) = &*abort_on_err(queries.expansion(), sess).peek();
+    let resolver = resolver.clone();
 
-    let (_, resolver, _) = &*abort_on_err(queries.expansion(), sess).peek();
+    let mut loader = crate::passes::collect_intra_doc_links::IntraLinkCrateLoader::new(resolver);
+    ast::visit::walk_crate(&mut loader, krate);
 
-    // Before we actually clone it, let's force all the extern'd crates to
-    // actually be loaded, just in case they're only referred to inside
-    // intra-doc links
-    resolver.borrow_mut().access(|resolver| {
-        sess.time("load_extern_crates", || {
-            for extern_name in &extern_names {
-                debug!("loading extern crate {}", extern_name);
-                if let Err(()) = resolver
-                    .resolve_str_path_error(
-                        DUMMY_SP,
-                        extern_name,
-                        TypeNS,
-                        LocalDefId { local_def_index: CRATE_DEF_INDEX }.to_def_id(),
-                  ) {
-                    warn!("unable to resolve external crate {} (do you have an unused `--extern` crate?)", extern_name)
-                  }
-            }
-        });
-    });
-
-    // Now we're good to clone the resolver because everything should be loaded
-    resolver.clone()
+    loader.resolver
 }
 
 crate fn run_global_ctxt(