From d777cb84e2d27a5f44eab94854b74fea33034bb4 Mon Sep 17 00:00:00 2001
From: Ellen <supbscripter@gmail.com>
Date: Sat, 7 Aug 2021 18:44:36 +0100
Subject: [PATCH] less opt in const param of

---
 compiler/rustc_typeck/src/collect/type_of.rs |  7 ++++--
 src/test/ui/const-generics/enum-variants.rs  | 24 ++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/const-generics/enum-variants.rs

diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs
index 96b3fa9aa0143..7083b11f7d0ac 100644
--- a/compiler/rustc_typeck/src/collect/type_of.rs
+++ b/compiler/rustc_typeck/src/collect/type_of.rs
@@ -190,8 +190,12 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                 // Try to use the segment resolution if it is valid, otherwise we
                 // default to the path resolution.
                 let res = segment.res.filter(|&r| r != Res::Err).unwrap_or(path.res);
+                use def::CtorOf;
                 let generics = match res {
-                    Res::Def(DefKind::Ctor(..), def_id) => {
+                    Res::Def(DefKind::Ctor(CtorOf::Variant, _), def_id) => {
+                        tcx.generics_of(tcx.parent(def_id).and_then(|def_id| tcx.parent(def_id)).unwrap())
+                    }
+                    Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Struct, _), def_id) => {
                         tcx.generics_of(tcx.parent(def_id).unwrap())
                     }
                     // Other `DefKind`s don't have generics and would ICE when calling
@@ -200,7 +204,6 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                         DefKind::Struct
                         | DefKind::Union
                         | DefKind::Enum
-                        | DefKind::Variant
                         | DefKind::Trait
                         | DefKind::OpaqueTy
                         | DefKind::TyAlias
diff --git a/src/test/ui/const-generics/enum-variants.rs b/src/test/ui/const-generics/enum-variants.rs
new file mode 100644
index 0000000000000..a82db1c4b3217
--- /dev/null
+++ b/src/test/ui/const-generics/enum-variants.rs
@@ -0,0 +1,24 @@
+// check-pass
+pub enum Foo<const N: usize> {
+    Variant,
+    Variant2(),
+    Variant3{},
+}
+
+struct Bar<const N: usize>;
+struct Bar2<const N: usize>();
+struct Bar3<const N: usize> {}
+
+fn main() {
+    let _ = Foo::Variant::<1>;
+    let _ = Foo::Variant2::<1>();
+    let _ = Foo::Variant3::<1>{};
+
+    let _ = Foo::<1>::Variant;
+    let _ = Foo::<1>::Variant2();
+    let _ = Foo::<1>::Variant3{};
+
+    let _ = Bar::<1>;
+    let _ = Bar2::<1>();
+    let _ = Bar3::<1>{};
+}