Fix rendering of stabilization version for trait implementors

src/librustdoc/html/render/mod.rs

@@ -2471,7 +2471,7 @@ fn item_function(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, f: &clean::
 fn render_implementor(
     cx: &Context<'_>,
     implementor: &Impl,
-    parent: &clean::Item,
+    trait_: &clean::Item,
     w: &mut Buffer,
     implementor_dups: &FxHashMap<Symbol, (DefId, bool)>,
     aliases: &[String],
@@ -2491,11 +2491,11 @@ fn render_implementor(
         w,
         cx,
         implementor,
-        parent,
+        trait_,
         AssocItemLink::Anchor(None),
         RenderMode::Normal,
-        implementor.impl_item.stable_since(cx.tcx()).as_deref(),
+        trait_.stable_since(cx.tcx()).as_deref(),
-        implementor.impl_item.const_stable_since(cx.tcx()).as_deref(),
+        trait_.const_stable_since(cx.tcx()).as_deref(),
         false,
         Some(use_absolute),
         false,

src/test/rustdoc/implementor-stable-version.rs

@@ -0,0 +1,19 @@
+#![crate_name = "foo"]
+
+#![feature(staged_api)]
+
+#[stable(feature = "bar", since = "OLD 1.0")]
+pub trait Bar {}
+
+#[stable(feature = "baz", since = "OLD 1.0")]
+pub trait Baz {}
+
+pub struct Foo;
+
+// @has foo/trait.Bar.html '//div[@id="implementors-list"]//span[@class="since"]' 'NEW 2.0'
+#[stable(feature = "foobar", since = "NEW 2.0")]
+impl Bar for Foo {}
+
+// @!has foo/trait.Baz.html '//div[@id="implementors-list"]//span[@class="since"]' 'OLD 1.0'
+#[stable(feature = "foobaz", since = "OLD 1.0")]
+impl Baz for Foo {}