Rollup merge of #91694 - euclio:stability-improvements, r=GuillaumeGomez

rustdoc: decouple stability and const-stability

This PR tweaks the stability rendering code to consider stability and const-stability separately. This fixes two issues:

- Stabilities that match the enclosing item are now always omitted, even if the item has const-stability as well (#90552)
- Const-stable unstable functions will now have their (const-) stability rendered.

Fixes #90552.

src/test/rustdoc/const-display.rs

@@ -67,3 +67,20 @@ impl Foo {
     #[rustc_const_stable(feature = "rust1", since = "1.2.0")]
     pub const fn stable_impl() -> u32 { 42 }
 }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Bar;
+
+impl Bar {
+    // Do not show non-const stabilities that are the same as the enclosing item.
+    // @matches 'foo/struct.Bar.html' '//span[@class="since"]' '^const: 1.2.0$'
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "rust1", since = "1.2.0")]
+    pub const fn stable_impl() -> u32 { 42 }
+
+    // Show const-stability even for unstable functions.
+    // @matches 'foo/struct.Bar.html' '//span[@class="since"]' '^const: 1.3.0$'
+    #[unstable(feature = "foo2", issue = "none")]
+    #[rustc_const_stable(feature = "rust1", since = "1.3.0")]
+    pub const fn const_stable_unstable() -> u32 { 42 }
+}

src/test/rustdoc/deref-const-fn.rs

@@ -13,7 +13,7 @@ pub struct Bar;
 
 impl Bar {
     // @has - '//*[@id="method.len"]' 'pub const fn len(&self) -> usize'
-    // @has - '//*[@id="method.len"]//span[@class="since"]' '1.0.0 (const: 1.0.0)'
+    // @has - '//*[@id="method.len"]//span[@class="since"]' 'const: 1.0.0'
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "rust1", since = "1.0.0")]
     pub const fn len(&self) -> usize { 0 }