Address review comment

rust-lang/rust-clippy#13286 (comment)

Author: smoelius

clippy_lints/src/lifetimes.rs

@@ -506,8 +506,17 @@ struct LifetimeChecker<'cx, 'tcx, F> {
 }
 
 impl<'cx,'tcx,F>LifetimeChecker<'cx,'tcx,F>{
-fnnew(cx:&'cxLateContext<'tcx>,def_ids:Vec<LocalDefId>) -> LifetimeChecker<'cx,'tcx,F>{
-let map = def_ids.into_iter().map(|def_id| (def_id,Vec::new())).collect();
+fnnew(cx:&'cxLateContext<'tcx>,generics:&'tcxGenerics<'_>) -> LifetimeChecker<'cx,'tcx,F>{
+let map = generics
+.params
+.iter()
+.filter_map(|par| match par.kind{
+GenericParamKind::Lifetime{
+kind:LifetimeParamKind::Explicit,
+} => Some((par.def_id,Vec::new())),
+ _ => None,
+})
+.collect();
 Self{
  cx,
  map,
@@ -556,17 +565,7 @@ where
 }
 
 fnreport_extra_lifetimes<'tcx>(cx:&LateContext<'tcx>,func:&'tcxFnDecl<'_>,generics:&'tcxGenerics<'_>){
-let def_ids = generics
-.params
-.iter()
-.filter_map(|par| match par.kind{
-GenericParamKind::Lifetime{
-kind:LifetimeParamKind::Explicit,
-} => Some(par.def_id),
- _ => None,
-})
-.collect();
-letmut checker = LifetimeChecker::<hir_nested_filter::None>::new(cx, def_ids);
+letmut checker = LifetimeChecker::<hir_nested_filter::None>::new(cx, generics);
 
 walk_generics(&mut checker, generics);
 walk_fn_decl(&mut checker, func);
@@ -587,18 +586,7 @@ fn report_extra_lifetimes<'tcx>(cx: &LateContext<'tcx>, func: &'tcx FnDecl<'_>,
 }
 
 fnreport_extra_impl_lifetimes<'tcx>(cx:&LateContext<'tcx>,impl_:&'tcxImpl<'_>){
-let def_ids = impl_
-.generics
-.params
-.iter()
-.filter_map(|par| match par.kind{
-GenericParamKind::Lifetime{
-kind:LifetimeParamKind::Explicit,
-} => Some(par.def_id),
- _ => None,
-})
-.collect();
-letmut checker = LifetimeChecker::<middle_nested_filter::All>::new(cx, def_ids);
+letmut checker = LifetimeChecker::<middle_nested_filter::All>::new(cx, impl_.generics);
 
 walk_generics(&mut checker, impl_.generics);
 ifletSome(ref trait_ref) = impl_.of_trait{