Use extension trait derive

compiler/rustc_trait_selection/src/regions.rs

@@ -3,20 +3,14 @@ use rustc_infer::infer::{InferCtxt, RegionResolutionError};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::ObligationCause;
 
-pub trait InferCtxtRegionExt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
     /// Resolve regions, using the deep normalizer to normalize any type-outlives
     /// obligations in the process. This is in `rustc_trait_selection` because
     /// we need to normalize.
     ///
     /// Prefer this method over `resolve_regions_with_normalize`, unless you are
     /// doing something specific for normalization.
-    fn resolve_regions(
-        &self,
-        outlives_env: &OutlivesEnvironment<'tcx>,
-    ) -> Vec<RegionResolutionError<'tcx>>;
-}
-
-impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
     fn resolve_regions(
         &self,
         outlives_env: &OutlivesEnvironment<'tcx>,