Auto merge of #88574 - camelid:box-genericarg-const, r=GuillaumeGomez

rustdoc: Box `GenericArg::Const` to reduce enum size

This should reduce the amount of memory allocated in the common cases
where the `GenericArg` is a lifetime or type.

src/librustdoc/clean/mod.rs

@@ -1789,7 +1789,7 @@ impl Clean<GenericArgs> for hir::GenericArgs<'_> {
                         }
                         hir::GenericArg::Lifetime(_) => GenericArg::Lifetime(Lifetime::elided()),
                         hir::GenericArg::Type(ty) => GenericArg::Type(ty.clean(cx)),
-                        hir::GenericArg::Const(ct) => GenericArg::Const(ct.clean(cx)),
+                        hir::GenericArg::Const(ct) => GenericArg::Const(Box::new(ct.clean(cx))),
                         hir::GenericArg::Infer(_inf) => GenericArg::Infer,
                     })
                     .collect(),

src/librustdoc/clean/types.rs

@@ -2012,10 +2012,15 @@ impl Path {
 crate enum GenericArg {
     Lifetime(Lifetime),
     Type(Type),
-    Const(Constant),
+    Const(Box<Constant>),
     Infer,
 }
 
+// `GenericArg` can occur many times in a single `Path`, so make sure it
+// doesn't increase in size unexpectedly.
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+rustc_data_structures::static_assert_size!(GenericArg, 80);
+
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 crate enum GenericArgs {
     AngleBracketed { args: Vec<GenericArg>, bindings: Vec<TypeBinding> },

src/librustdoc/clean/utils.rs

@@ -121,7 +121,7 @@ fn external_generic_args(
                 ty_kind = Some(ty.kind());
                 Some(GenericArg::Type(ty.clean(cx)))
             }
-            GenericArgKind::Const(ct) => Some(GenericArg::Const(ct.clean(cx))),
+            GenericArgKind::Const(ct) => Some(GenericArg::Const(Box::new(ct.clean(cx)))),
         })
         .collect();
 

src/librustdoc/json/conversions.rs

@@ -139,7 +139,7 @@ impl FromWithTcx<clean::GenericArg> for GenericArg {
         match arg {
             Lifetime(l) => GenericArg::Lifetime(l.0.to_string()),
             Type(t) => GenericArg::Type(t.into_tcx(tcx)),
-            Const(c) => GenericArg::Const(c.into_tcx(tcx)),
+            Const(box c) => GenericArg::Const(c.into_tcx(tcx)),
             Infer => GenericArg::Infer,
         }
     }