Go back to loading all external crates unconditionally

This *continues* to cause regressions. This code will be unnecessary
once access to the resolver happens fully before creating the tyctxt
(#83761), so load all crates unconditionally for now.

src/librustdoc/core.rs

@@ -16,13 +16,15 @@ use rustc_middle::hir::map::Map;
 use rustc_middle::middle::privacy::AccessLevels;
 use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
 use rustc_resolve as resolve;
+use rustc_resolve::Namespace::TypeNS;
 use rustc_session::config::{self, CrateType, ErrorOutputType};
 use rustc_session::lint;
 use rustc_session::DiagnosticOutput;
 use rustc_session::Session;
+use rustc_span::def_id::CRATE_DEF_INDEX;
 use rustc_span::source_map;
 use rustc_span::symbol::sym;
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 
 use std::cell::RefCell;
 use std::lazy::SyncLazy;
@@ -299,13 +301,43 @@ crate fn create_config(
 }
 
 crate fn create_resolver<'a>(
+    externs: config::Externs,
     queries: &Queries<'a>,
     sess: &Session,
 ) -> Rc<RefCell<interface::BoxedResolver>> {
     let (krate, resolver, _) = &*abort_on_err(queries.expansion(), sess).peek();
     let resolver = resolver.clone();
 
-    crate::passes::collect_intra_doc_links::load_intra_link_crates(resolver, krate)
+    let resolver = crate::passes::collect_intra_doc_links::load_intra_link_crates(resolver, krate);
+
+    // FIXME: somehow rustdoc is still missing crates even though we loaded all
+    // the known necessary crates. Load them all unconditionally until we find a way to fix this.
+    // DO NOT REMOVE THIS without first testing on the reproducer in
+    // https://github.com/jyn514/objr/commit/edcee7b8124abf0e4c63873e8422ff81beb11ebb
+    let extern_names: Vec<String> = externs
+        .iter()
+        .filter(|(_, entry)| entry.add_prelude)
+        .map(|(name, _)| name)
+        .cloned()
+        .collect();
+    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)
+                  }
+            }
+        });
+    });
+
+    resolver
 }
 
 crate fn run_global_ctxt(

src/librustdoc/lib.rs

@@ -755,6 +755,7 @@ fn main_options(options: config::Options) -> MainResult {
     let default_passes = options.default_passes;
     let output_format = options.output_format;
     // FIXME: fix this clone (especially render_options)
+    let externs = options.externs.clone();
     let manual_passes = options.manual_passes.clone();
     let render_options = options.render_options.clone();
     let scrape_examples_options = options.scrape_examples_options.clone();
@@ -773,7 +774,7 @@ fn main_options(options: config::Options) -> MainResult {
             // We need to hold on to the complete resolver, so we cause everything to be
             // cloned for the analysis passes to use. Suboptimal, but necessary in the
             // current architecture.
-            let resolver = core::create_resolver(queries, sess);
+            let resolver = core::create_resolver(externs, queries, sess);
 
             if sess.has_errors() {
                 sess.fatal("Compilation failed, aborting rustdoc");