rustdoc-json: Expose Item stability

This is motivated by cargo-semver-checks wanting to work on the standard
library, but that requires being able to filter out breaking changes to
unstable items, so it can only flag breaking changes to stable items.
This in turn is motivated by
https://www.github.com/rust-lang/rust/issues/153486.

Author: aDotInTheVoid

src/librustdoc/json/conversions.rs

@@ -75,6 +75,7 @@ impl JsonRenderer<'_> {
             name: name.map(|sym| sym.to_string()),
             span: span.and_then(|span| span.into_json(self)),
             visibility: visibility.into_json(self),
+            stability: item.stability(self.tcx).into_json(self),
             docs,
             attrs,
             deprecation: deprecation.into_json(self),
@@ -203,6 +204,18 @@ impl FromClean<attrs::Deprecation> for Deprecation {
     }
 }
 
+impl FromClean<hir::Stability> for Stability {
+    fn from_clean(stab: &hir::Stability, _renderer: &JsonRenderer<'_>) -> Self {
+        Stability {
+            feature: stab.feature.to_string(),
+            level: match stab.level {
+                hir::StabilityLevel::Unstable { .. } => StabilityLevel::Unstable,
+                hir::StabilityLevel::Stable { .. } => StabilityLevel::Stable,
+            }
+        }
+    }
+}
+
 impl FromClean<clean::GenericArgs> for Option<Box<GenericArgs>> {
     fn from_clean(generic_args: &clean::GenericArgs, renderer: &JsonRenderer<'_>) -> Self {
         use clean::GenericArgs::*;

src/librustdoc/json/mod.rs

@@ -362,6 +362,6 @@ mod size_asserts {
     // tidy-alphabetical-end
 
     // These contains a `PathBuf`, which is different sizes on different OSes.
-    static_assert_size!(Item, 528 + size_of::<std::path::PathBuf>());
+    static_assert_size!(Item, 560 + size_of::<std::path::PathBuf>());
     static_assert_size!(ExternalCrate, 48 + size_of::<std::path::PathBuf>());
 }

src/rustdoc-json-types/lib.rs

@@ -114,8 +114,8 @@ pub type FxHashMap<K, V> = HashMap<K, V>; // re-export for use in src/librustdoc
 // will instead cause conflicts. See #94591 for more. (This paragraph and the "Latest feature" line
 // are deliberately not in a doc comment, because they need not be in public docs.)
 //
-// Latest feature: Add `ExternCrate::path`.
-pub const FORMAT_VERSION: u32 = 57;
+// Latest feature: Add `Item::stability`.
+pub const FORMAT_VERSION: u32 = 58;
 
 /// The root of the emitted JSON blob.
 ///
@@ -294,10 +294,30 @@ pub struct Item {
     pub attrs: Vec<Attribute>,
     /// Information about the item’s deprecation, if present.
     pub deprecation: Option<Deprecation>,
+
+    pub stability: Option<Stability>,
+
     /// The type-specific fields describing this item.
     pub inner: ItemEnum,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+pub struct Stability {
+    pub feature: String,
+    pub level: StabilityLevel,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[serde(rename_all = "snake_case")]
+pub enum StabilityLevel {
+    Stable,
+    Unstable,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
 #[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]

tests/rustdoc-json/attrs/stability/stable.rs

@@ -0,0 +1,7 @@
+#![feature(staged_api)]
+
+//@ is "$.index[?(@.name=='foo')].stability.level" '"stable"'
+//@ is "$.index[?(@.name=='foo')].stability.feature" '"eeeee"'
+//@ is "$.index[?(@.name=='foo')].attrs" []
+#[stable(since = "2.71.8", feature = "eeeee")]
+pub fn foo() {}

tests/rustdoc-json/attrs/stability/unmarked.rs

@@ -0,0 +1,3 @@
+//@ is "$.index[?(@.name=='foo')].stability" null
+//@ is "$.index[?(@.name=='foo')].attrs" []
+pub fn foo() {}

tests/rustdoc-json/attrs/stability/unstable.rs

@@ -0,0 +1,7 @@
+#![feature(staged_api)]
+
+//@ is "$.index[?(@.name=='foo')].stability.level" '"unstable"'
+//@ is "$.index[?(@.name=='foo')].stability.feature" '"delights"'
+//@ is "$.index[?(@.name=='foo')].attrs" []
+#[unstable(feature = "delights", issue = "26")]
+pub fn foo() {}