rustdoc: Show "const" for const-unstable if also overall unstable

If a const function is unstable overall (and thus, in all circumstances
I know of, also const-unstable), we should show the option to use it as
const. You need to enable a feature to use the function at all anyway.

If the function is stabilized without also being const-stabilized, then
we do not show the const keyword and instead show "const: unstable" in
the version info.

2 files changed, 17 insertions, 4 deletions

diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 1d0bc328641..8ee4cc5c75e 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -928,9 +928,11 @@ fn assoc_method(
     // FIXME: Once https://github.com/rust-lang/rust/issues/67792 is implemented, we can remove
     // this condition.
     let constness = match render_mode {
-        RenderMode::Normal => {
-            print_constness_with_space(&header.constness, meth.const_stability(tcx))
-        }
+        RenderMode::Normal => print_constness_with_space(
+            &header.constness,
+            meth.stable_since(tcx),
+            meth.const_stability(tcx),
+        ),
         RenderMode::ForDeref { .. } => "",
     };
     let asyncness = header.asyncness.print_with_space();
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index c7a23aa8503..c5b88c7a951 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -615,7 +615,18 @@ fn extra_info_tags<'a, 'tcx: 'a>(
 fn item_function(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, f: &clean::Function) {
     let tcx = cx.tcx();
     let header = it.fn_header(tcx).expect("printing a function which isn't a function");
-    let constness = print_constness_with_space(&header.constness, it.const_stability(tcx));
+    debug!(
+        "item_function/const: {:?} {:?} {:?} {:?}",
+        it.name,
+        &header.constness,
+        it.stable_since(tcx),
+        it.const_stability(tcx),
+    );
+    let constness = print_constness_with_space(
+        &header.constness,
+        it.stable_since(tcx),
+        it.const_stability(tcx),
+    );
     let safety = header.safety.print_with_space();
     let abi = print_abi_with_space(header.abi).to_string();
     let asyncness = header.asyncness.print_with_space();