rustdoc: Do not expect doc(primitive) modules to always exist

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -80,10 +80,10 @@ impl Res {
         }
     }
 
-    fn def_id(self, tcx: TyCtxt<'_>) -> DefId {
+    fn def_id(self, tcx: TyCtxt<'_>) -> Option<DefId> {
         match self {
-            Res::Def(_, id) => id,
-            Res::Primitive(prim) => *PrimitiveType::primitive_locations(tcx).get(&prim).unwrap(),
+            Res::Def(_, id) => Some(id),
+            Res::Primitive(prim) => PrimitiveType::primitive_locations(tcx).get(&prim).copied(),
         }
     }
 
@@ -1127,10 +1127,10 @@ impl LinkCollector<'_, '_> {
                     }
                 }
 
-                Some(ItemLink {
+                res.def_id(self.cx.tcx).map(|page_id| ItemLink {
                     link: ori_link.link.clone(),
                     link_text: link_text.clone(),
-                    page_id: res.def_id(self.cx.tcx),
+                    page_id,
                     fragment,
                 })
             }

src/librustdoc/passes/collect_intra_doc_links/early.rs

@@ -48,7 +48,6 @@ pub(crate) fn early_resolve_intra_doc_links(
     link_resolver.resolve_doc_links_local(&krate.attrs);
     link_resolver.process_module_children_or_reexports(CRATE_DEF_ID.to_def_id());
     visit::walk_crate(&mut link_resolver, krate);
-    link_resolver.process_extern_impls();
 
     // 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.
@@ -58,6 +57,8 @@ pub(crate) fn early_resolve_intra_doc_links(
         link_resolver.resolver.resolve_rustdoc_path(extern_name, TypeNS, parent_scope);
     }
 
+    link_resolver.process_extern_impls();
+
     ResolverCaches {
         markdown_links: Some(link_resolver.markdown_links),
         doc_link_resolutions: link_resolver.doc_link_resolutions,

src/test/rustdoc/intra-doc/no-doc-primitive.rs

@@ -0,0 +1,15 @@
+// Crate tree without a `doc(primitive)` module for primitive type linked to by a doc link.
+
+#![deny(rustdoc::broken_intra_doc_links)]
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+#![rustc_coherence_is_core]
+#![crate_type = "rlib"]
+
+// @has no_doc_primitive/index.html
+//! A [`char`] and its [`char::len_utf8`].
+impl char {
+    pub fn len_utf8(self) -> usize {
+        42
+    }
+}