Don't print "const" keyword on non-nightly build if rustc_const_unstable is used on the item

src/librustdoc/clean/mod.rs

@@ -1090,25 +1090,37 @@ impl Clean<TypeKind> for hir::def::DefKind {
 
 impl Clean<Item> for hir::TraitItem<'_> {
     fn clean(&self, cx: &DocContext<'_>) -> Item {
+        let local_did = cx.tcx.hir().local_def_id(self.hir_id);
         let inner = match self.kind {
             hir::TraitItemKind::Const(ref ty, default) => {
                 AssocConstItem(ty.clean(cx), default.map(|e| print_const_expr(cx, e)))
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Provided(body)) => {
-                MethodItem((sig, &self.generics, body, None).clean(cx))
+                let mut m = (sig, &self.generics, body, None).clean(cx);
+                if m.header.constness == hir::Constness::Const
+                    && !is_min_const_fn(cx.tcx, local_did.to_def_id())
+                {
+                    m.header.constness = hir::Constness::NotConst;
+                }
+                MethodItem(m)
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(ref names)) => {
                 let (generics, decl) = enter_impl_trait(cx, || {
                     (self.generics.clean(cx), (&*sig.decl, &names[..]).clean(cx))
                 });
                 let (all_types, ret_types) = get_all_types(&generics, &decl, cx);
-                TyMethodItem(TyMethod { header: sig.header, decl, generics, all_types, ret_types })
+                let mut t = TyMethod { header: sig.header, decl, generics, all_types, ret_types };
+                if t.header.constness == hir::Constness::Const
+                    && !is_min_const_fn(cx.tcx, local_did.to_def_id())
+                {
+                    t.header.constness = hir::Constness::NotConst;
+                }
+                TyMethodItem(t)
             }
             hir::TraitItemKind::Type(ref bounds, ref default) => {
                 AssocTypeItem(bounds.clean(cx), default.clean(cx))
             }
         };
-        let local_did = cx.tcx.hir().local_def_id(self.hir_id);
         Item {
             name: Some(self.ident.name.clean(cx)),
             attrs: self.attrs.clean(cx),
@@ -1124,20 +1136,26 @@ impl Clean<Item> for hir::TraitItem<'_> {
 
 impl Clean<Item> for hir::ImplItem<'_> {
     fn clean(&self, cx: &DocContext<'_>) -> Item {
+        let local_did = cx.tcx.hir().local_def_id(self.hir_id);
         let inner = match self.kind {
             hir::ImplItemKind::Const(ref ty, expr) => {
                 AssocConstItem(ty.clean(cx), Some(print_const_expr(cx, expr)))
             }
             hir::ImplItemKind::Fn(ref sig, body) => {
-                MethodItem((sig, &self.generics, body, Some(self.defaultness)).clean(cx))
+                let mut m = (sig, &self.generics, body, Some(self.defaultness)).clean(cx);
+                if m.header.constness == hir::Constness::Const
+                    && !is_min_const_fn(cx.tcx, local_did.to_def_id())
+                {
+                    m.header.constness = hir::Constness::NotConst;
+                }
+                MethodItem(m)
             }
             hir::ImplItemKind::TyAlias(ref ty) => {
                 let type_ = ty.clean(cx);
                 let item_type = type_.def_id().and_then(|did| inline::build_ty(cx, did));
                 TypedefItem(Typedef { type_, generics: Generics::default(), item_type }, true)
             }
         };
-        let local_did = cx.tcx.hir().local_def_id(self.hir_id);
         Item {
             name: Some(self.ident.name.clean(cx)),
             source: self.span.clean(cx),

src/test/rustdoc/const-display.rs

@@ -32,3 +32,12 @@ pub const unsafe fn bar2_gated() -> u32 { 42 }
 
 // @has 'foo/fn.bar_not_gated.html' '//pre' 'pub unsafe fn bar_not_gated() -> u32'
 pub const unsafe fn bar_not_gated() -> u32 { 42 }
+
+pub struct Foo;
+
+impl Foo {
+    // @has 'foo/struct.Foo.html' '//h4[@id="method.gated"]/code' 'pub unsafe fn gated() -> u32'
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature="foo", issue = "none")]
+    pub const unsafe fn gated() -> u32 { 42 }
+}