rustdoc: Compute enum discriminant on demand

src/librustdoc/clean/mod.rs

@@ -1787,10 +1787,7 @@ pub(crate) fn clean_visibility(vis: ty::Visibility) -> Visibility {
 pub(crate) fn clean_variant_def<'tcx>(variant: &ty::VariantDef, cx: &mut DocContext<'tcx>) -> Item {
     let kind = match variant.ctor_kind {
         CtorKind::Const => Variant::CLike(match variant.discr {
-            ty::VariantDiscr::Explicit(def_id) => Some(Discriminant {
-                expr: None,
-                value: print_evaluated_const(cx.tcx, def_id, false).unwrap(),
-            }),
+            ty::VariantDiscr::Explicit(def_id) => Some(Discriminant { expr: None, value: def_id }),
             ty::VariantDiscr::Relative(_) => None,
         }),
         CtorKind::Fn => Variant::Tuple(
@@ -1820,16 +1817,9 @@ fn clean_variant_data<'tcx>(
         hir::VariantData::Tuple(..) => {
             Variant::Tuple(variant.fields().iter().map(|x| clean_field(x, cx)).collect())
         }
-        hir::VariantData::Unit(..) => Variant::CLike(disr_expr.map(|disr| {
-            Discriminant {
-                expr: Some(print_const_expr(cx.tcx, disr.body)),
-                value: print_evaluated_const(
-                    cx.tcx,
-                    cx.tcx.hir().local_def_id(disr.hir_id).to_def_id(),
-                    false,
-                )
-                .unwrap(),
-            }
+        hir::VariantData::Unit(..) => Variant::CLike(disr_expr.map(|disr| Discriminant {
+            expr: Some(disr.body),
+            value: cx.tcx.hir().local_def_id(disr.hir_id).to_def_id(),
         })),
     }
 }

src/librustdoc/clean/types.rs

@@ -2116,8 +2116,20 @@ impl Variant {
 pub(crate) struct Discriminant {
     // In the case of cross crate re-exports, we don't have the nessesary information
     // to reconstruct the expression of the discriminant, only the value.
-    pub(crate) expr: Option<String>,
-    pub(crate) value: String,
+    pub(super) expr: Option<BodyId>,
+    pub(super) value: DefId,
+}
+
+impl Discriminant {
+    /// Will be `None` in the case of cross-crate reexports, and may be
+    /// simplified
+    pub(crate) fn expr(&self, tcx: TyCtxt<'_>) -> Option<String> {
+        self.expr.map(|body| print_const_expr(tcx, body))
+    }
+    /// Will always be a machine readable number, without underscores or suffixes.
+    pub(crate) fn value(&self, tcx: TyCtxt<'_>) -> String {
+        print_evaluated_const(tcx, self.value, false).unwrap()
+    }
 }
 
 /// Small wrapper around [`rustc_span::Span`] that adds helper methods

src/librustdoc/json/conversions.rs

@@ -662,7 +662,7 @@ impl FromWithTcx<clean::Variant> for Variant {
     fn from_tcx(variant: clean::Variant, tcx: TyCtxt<'_>) -> Self {
         use clean::Variant::*;
         match variant {
-            CLike(disr) => Variant::Plain(disr.map(convert_discriminant)),
+            CLike(disr) => Variant::Plain(disr.map(|disr| disr.into_tcx(tcx))),
             Tuple(fields) => Variant::Tuple(
                 fields
                     .into_iter()
@@ -678,13 +678,15 @@ impl FromWithTcx<clean::Variant> for Variant {
     }
 }
 
-fn convert_discriminant(disr: clean::Discriminant) -> Discriminant {
-    Discriminant {
-        // expr is only none if going throught the inlineing path, which gets
-        // `rustc_middle` types, not `rustc_hir`, but because JSON never inlines
-        // the expr is always some.
-        expr: disr.expr.unwrap(),
-        value: disr.value,
+impl FromWithTcx<clean::Discriminant> for Discriminant {
+    fn from_tcx(disr: clean::Discriminant, tcx: TyCtxt<'_>) -> Self {
+        Discriminant {
+            // expr is only none if going throught the inlineing path, which gets
+            // `rustc_middle` types, not `rustc_hir`, but because JSON never inlines
+            // the expr is always some.
+            expr: disr.expr(tcx).unwrap(),
+            value: disr.value(tcx),
+        }
     }
 }