Encode optimized MIR of generators when emitting metadata

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1507,7 +1507,10 @@ impl EncodeContext<'a, 'tcx> {
             record!(self.tables.fn_sig[def_id] <- substs.as_closure().sig());
         }
         self.encode_generics(def_id.to_def_id());
-        let opt_mir = self.tcx.sess.opts.debugging_opts.always_encode_mir || self.emit_codegen_mir;
+        let opt_mir = // FIXME: Optimized MIR is necessary to determine the layout of generators.
+            matches!(ty.kind(), ty::Generator(..))
+            || self.tcx.sess.opts.debugging_opts.always_encode_mir
+            || self.emit_codegen_mir;
         if opt_mir {
             self.encode_optimized_mir(def_id);
             self.encode_promoted_mir(def_id);

src/test/ui/generator/auxiliary/metadata-sufficient-for-layout.rs

@@ -0,0 +1,11 @@
+// compile-flags: --emit metadata
+#![feature(generators, generator_trait)]
+
+use std::marker::Unpin;
+use std::ops::Generator;
+
+pub fn g() -> impl Generator<(), Yield = (), Return = ()> {
+    || {
+        yield;
+    }
+}

src/test/ui/generator/metadata-sufficient-for-layout.rs

@@ -0,0 +1,23 @@
+// Check that the layout of a generator is available when auxiliary crate
+// is compiled with --emit metadata.
+//
+// Regression test for #80998.
+//
+// aux-build:metadata-sufficient-for-layout.rs
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+#![feature(generator_trait)]
+
+extern crate metadata_sufficient_for_layout;
+
+use std::ops::Generator;
+
+type F = impl Generator<(), Yield = (), Return = ()>;
+
+// Static queries the layout of the generator.
+static A: Option<F> = None;
+
+fn f() -> F { metadata_sufficient_for_layout::g() }
+
+fn main() {}