rustdoc: json: add support for variances

src/librustdoc/json/conversions.rs

@@ -454,9 +454,11 @@ impl FromWithTcx<clean::GenericParamDefKind> for GenericParamDefKind {
         use clean::GenericParamDefKind::*;
         match kind {
             Lifetime(param) => GenericParamDefKind::Lifetime {
+                variance: param.variance.map(|var| var.into_tcx(tcx)),
                 outlives: param.outlives.into_iter().map(convert_lifetime).collect(),
             },
             Type(param) => GenericParamDefKind::Type {
+                variance: param.variance.map(|var| var.into_tcx(tcx)),
                 bounds: param.bounds.into_tcx(tcx),
                 default: param.default.map(|ty| ty.into_tcx(tcx)),
                 synthetic: param.synthetic,
@@ -468,6 +470,17 @@ impl FromWithTcx<clean::GenericParamDefKind> for GenericParamDefKind {
     }
 }
 
+impl FromWithTcx<ty::Variance> for Variance {
+    fn from_tcx(variance: ty::Variance, _tcx: TyCtxt<'_>) -> Self {
+        match variance {
+            ty::Variance::Covariant => Self::Covariant,
+            ty::Variance::Invariant => Self::Invariant,
+            ty::Variance::Contravariant => Self::Contravariant,
+            ty::Variance::Bivariant => Self::Bivariant,
+        }
+    }
+}
+
 impl FromWithTcx<clean::WherePredicate> for WherePredicate {
     fn from_tcx(predicate: clean::WherePredicate, tcx: TyCtxt<'_>) -> Self {
         use clean::WherePredicate::*;

src/rustdoc-json-types/lib.rs

@@ -443,9 +443,11 @@ pub struct GenericParamDef {
 #[serde(rename_all = "snake_case")]
 pub enum GenericParamDefKind {
     Lifetime {
+        variance: Option<Variance>,
         outlives: Vec<String>,
     },
     Type {
+        variance: Option<Variance>,
         bounds: Vec<GenericBound>,
         default: Option<Type>,
         /// This is normally `false`, which means that this generic parameter is
@@ -480,6 +482,16 @@ pub enum GenericParamDefKind {
     },
 }
 
+// FIXME(fmease): docs
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum Variance {
+    Covariant,
+    Invariant,
+    Contravariant,
+    Bivariant,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum WherePredicate {