Do not subst nonexistent lifetime in RPIT in recursive function

Author: zirconium-n

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -88,15 +88,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     Some(region) => {
                         let vid = self.universal_regions.to_region_vid(region);
                         subst_regions.push(vid);
-                        region
+                        Some(region)
                     }
                     None => {
                         subst_regions.push(vid);
-                        ty::Region::new_error_with_message(
-                            infcx.tcx,
-                            concrete_type.span,
-                            "opaque type with non-universal region substs",
-                        )
+                        None
                     }
                 }
             };
@@ -118,7 +114,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     return region;
                 }
                 let vid = self.to_region_vid(region);
-                to_universal_region(vid, &mut subst_regions)
+                to_universal_region(vid, &mut subst_regions).unwrap_or(region)
             });
             debug!(?universal_substs);
             debug!(?subst_regions);

tests/ui/impl-trait/recursive-impl-trait-type-direct-with-lifetime.rs

@@ -0,0 +1,10 @@
+// check-pass
+
+#![allow(unconditional_recursion)]
+
+fn test<'a>() -> impl Sized + 'a {
+    let r: i32 = test();
+    r
+}
+
+fn main() {}