rustdoc: decouple stability and const-stability

src/librustdoc/html/render/mod.rs

@@ -792,6 +792,20 @@ fn assoc_type(
     }
 }
 
+/// Writes a span containing the versions at which an item became stable and/or const-stable. For
+/// example, if the item became stable at 1.0.0, and const-stable at 1.45.0, this function would
+/// write a span containing "1.0.0 (const: 1.45.0)".
+///
+/// Returns `true` if a stability annotation was rendered.
+///
+/// Stability and const-stability are considered separately. If the item is unstable, no version
+/// will be written. If the item is const-unstable, "const: unstable" will be appended to the
+/// span, with a link to the tracking issue if present. If an item's stability or const-stability
+/// version matches the version of its enclosing item, that version will be omitted.
+///
+/// Note that it is possible for an unstable function to be const-stable. In that case, the span
+/// will include the const-stable version, but no stable version will be emitted, as a natural
+/// consequence of the above rules.
 fn render_stability_since_raw(
     w: &mut Buffer,
     ver: Option<Symbol>,
@@ -799,51 +813,56 @@ fn render_stability_since_raw(
     containing_ver: Option<Symbol>,
     containing_const_ver: Option<Symbol>,
 ) -> bool {
-    let ver = ver.filter(|inner| !inner.is_empty());
+    let stable_version = ver.filter(|inner| !inner.is_empty() && Some(*inner) != containing_ver);
 
-    match (ver, const_stability) {
-        // stable and const stable
-        (Some(v), Some(ConstStability { level: StabilityLevel::Stable { since }, .. }))
+    let mut title = String::new();
+    let mut stability = String::new();
+
+    if let Some(ver) = stable_version {
+        stability.push_str(&ver.as_str());
+        title.push_str(&format!("Stable since Rust version {}", ver));
+    }
+
+    let const_title_and_stability = match const_stability {
+        Some(ConstStability { level: StabilityLevel::Stable { since }, .. })
             if Some(since) != containing_const_ver =>
         {
-            write!(
-                w,
-                "<span class=\"since\" title=\"Stable since Rust version {0}, const since {1}\">{0} (const: {1})</span>",
-                v, since
-            );
+            Some((format!("const since {}", since), format!("const: {}", since)))
         }
-        // stable and const unstable
-        (
-            Some(v),
-            Some(ConstStability { level: StabilityLevel::Unstable { issue, .. }, feature, .. }),
-        ) => {
-            write!(
-                w,
-                "<span class=\"since\" title=\"Stable since Rust version {0}, const unstable\">{0} (const: ",
-                v
-            );
-            if let Some(n) = issue {
-                write!(
-                    w,
-                    "<a href=\"https://github.com/rust-lang/rust/issues/{}\" title=\"Tracking issue for {}\">unstable</a>",
+        Some(ConstStability { level: StabilityLevel::Unstable { issue, .. }, feature, .. }) => {
+            let unstable = if let Some(n) = issue {
+                format!(
+                    r#"<a href="https://github.com/rust-lang/rust/issues/{}" title="Tracking issue for {}">unstable</a>"#,
                     n, feature
-                );
+                )
             } else {
-                write!(w, "unstable");
-            }
-            write!(w, ")</span>");
+                String::from("unstable")
+            };
+
+            Some((String::from("const unstable"), format!("const: {}", unstable)))
         }
-        // stable
-        (Some(v), _) if ver != containing_ver => {
-            write!(
-                w,
-                "<span class=\"since\" title=\"Stable since Rust version {0}\">{0}</span>",
-                v
-            );
+        _ => None,
+    };
+
+    if let Some((const_title, const_stability)) = const_title_and_stability {
+        if !title.is_empty() {
+            title.push_str(&format!(", {}", const_title));
+        } else {
+            title.push_str(&const_title);
+        }
+
+        if !stability.is_empty() {
+            stability.push_str(&format!(" ({})", const_stability));
+        } else {
+            stability.push_str(&const_stability);
         }
-        _ => return false,
     }
-    true
+
+    if !stability.is_empty() {
+        write!(w, r#"<span class="since" title="{}">{}</span>"#, title, stability);
+    }
+
+    !stability.is_empty()
 }
 
 fn render_assoc_item(

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 }