Rollup merge of #109109 - compiler-errors:polymorphize-foreign, r=Nilstrieb

Use `unused_generic_params` from crate metadata

Due to the way that `separate_provide_extern` interacted with the implementation of `<ty::InstanceDef<'tcx> as Key>::query_crate_is_local`, we actually never hit the foreign provider for `unused_generic_params`.

Additionally, since the *local* provider of `unused_generic_params` calls `should_polymorphize`, which always returns false if the def-id is foreign, this means that we never actually polymorphize monomorphic instances originating from foreign crates.

We don't actually encode `unused_generic_params` for items where all generics are used, so I had to tweak the foreign provider to fall back to `ty::UnusedGenericParams::new_all_used()` to avoid more ICEs when the above bugs were fixed.

1 files changed, 9 insertions, 1 deletions

diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 6c5e8863010..a9843395336 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -226,7 +226,15 @@ provide! { tcx, def_id, other, cdata,
     lookup_default_body_stability => { table }
     lookup_deprecation_entry => { table }
     params_in_repr => { table }
-    unused_generic_params => { table }
+    // FIXME: Could be defaulted, but `LazyValue<UnusedGenericParams>` is not `FixedSizeEncoding`..
+    unused_generic_params => {
+        cdata
+            .root
+            .tables
+            .unused_generic_params
+            .get(cdata, def_id.index)
+            .map_or_else(|| ty::UnusedGenericParams::new_all_used(), |lazy| lazy.decode((cdata, tcx)))
+    }
     opt_def_kind => { table_direct }
     impl_parent => { table }
     impl_polarity => { table_direct }