Fix error when using "extern crate self as"

crates/hir_def/src/nameres/path_resolution.rs

@@ -14,6 +14,7 @@
 
 use base_db::Edition;
 use hir_expand::name::Name;
+use hir_expand::name;
 use test_utils::mark;
 
 use crate::{
@@ -63,6 +64,11 @@ fn with(
 
 impl DefMap {
     pub(super) fn resolve_name_in_extern_prelude(&self, name: &Name) -> PerNs {
+        if name == &name!(self) {
+            return PerNs::types(ModuleId { krate: self.krate, local_id: self.root }.into(),
+                Visibility::Public,
+            );
+        }
         self.extern_prelude
             .get(name)
             .map_or(PerNs::none(), |&it| PerNs::types(it, Visibility::Public))

crates/hir_def/src/nameres/tests/diagnostics.rs

@@ -61,6 +61,21 @@ fn unresolved_extern_crate() {
     );
 }
 
+#[test]
+fn extern_crate_self_as() {
+    check_diagnostics(
+        r"
+        //- /lib.rs
+          extern crate doesnotexist;
+        //^^^^^^^^^^^^^^^^^^^^^^^^^^ unresolved extern crate
+        // Should not error.
+        extern crate self as foo;
+        struct Foo;
+        use foo::Foo as Bar;
+        ",
+    );
+}
+
 #[test]
 fn dedup_unresolved_import_from_unresolved_crate() {
     check_diagnostics(