From 8a2e4262e88bede44cfc5a3ab54e5b88442d6ed2 Mon Sep 17 00:00:00 2001
From: Bastian Kauschke <bastian_kauschke@hotmail.de>
Date: Thu, 23 Jul 2020 10:15:02 +0200
Subject: [PATCH] stop sorting generic params

---
 src/librustc_ast_lowering/lib.rs | 15 +--------------
 src/librustc_typeck/collect.rs   | 21 +++++----------------
 2 files changed, 6 insertions(+), 30 deletions(-)

diff --git a/src/librustc_ast_lowering/lib.rs b/src/librustc_ast_lowering/lib.rs
index b5d3beb4f8a..b631686324b 100644
--- a/src/librustc_ast_lowering/lib.rs
+++ b/src/librustc_ast_lowering/lib.rs
@@ -936,20 +936,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 })
             });
 
-        let mut lowered_params: Vec<_> =
-            lowered_generics.params.into_iter().chain(in_band_defs).collect();
-
-        // FIXME(const_generics): the compiler doesn't always cope with
-        // unsorted generic parameters at the moment, so we make sure
-        // that they're ordered correctly here for now. (When we chain
-        // the `in_band_defs`, we might make the order unsorted.)
-        lowered_params.sort_by_key(|param| match param.kind {
-            hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
-            hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
-            hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
-        });
-
-        lowered_generics.params = lowered_params.into();
+        lowered_generics.params = lowered_generics.params.into_iter().chain(in_band_defs).collect();
 
         let lowered_generics = lowered_generics.into_generics(self.arena);
         (lowered_generics, res)
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index cb9348a9521..5953863cb3c 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -1362,13 +1362,9 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
     let type_start = own_start - has_self as u32 + params.len() as u32;
     let mut i = 0;
 
-    // FIXME(const_generics): a few places in the compiler expect generic params
-    // to be in the order lifetimes, then type params, then const params.
-    //
-    // To prevent internal errors in case const parameters are supplied before
-    // type parameters we first add all type params, then all const params.
-    params.extend(ast_generics.params.iter().filter_map(|param| {
-        if let GenericParamKind::Type { ref default, synthetic, .. } = param.kind {
+    params.extend(ast_generics.params.iter().filter_map(|param| match param.kind {
+        GenericParamKind::Lifetime { .. } => None,
+        GenericParamKind::Type { ref default, synthetic, .. } => {
             if !allow_defaults && default.is_some() {
                 if !tcx.features().default_type_parameter_fallback {
                     tcx.struct_span_lint_hir(
@@ -1378,7 +1374,7 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
                         |lint| {
                             lint.build(
                                 "defaults for type parameters are only allowed in \
-                                        `struct`, `enum`, `type`, or `trait` definitions.",
+                                            `struct`, `enum`, `type`, or `trait` definitions.",
                             )
                             .emit();
                         },
@@ -1403,13 +1399,8 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
             };
             i += 1;
             Some(param_def)
-        } else {
-            None
         }
-    }));
-
-    params.extend(ast_generics.params.iter().filter_map(|param| {
-        if let GenericParamKind::Const { .. } = param.kind {
+        GenericParamKind::Const { .. } => {
             let param_def = ty::GenericParamDef {
                 index: type_start + i as u32,
                 name: param.name.ident().name,
@@ -1419,8 +1410,6 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
             };
             i += 1;
             Some(param_def)
-        } else {
-            None
         }
     }));