Remove rustc_serialize_exclude_null

Author: Manishearth

src/libsyntax/feature_gate.rs

@@ -846,11 +846,6 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                                        is just used for rustc unit tests \
                                                        and will never be stable",
                                                       cfg_fn!(rustc_attrs))),
-    ("rustc_serialize_exclude_null", Normal, Gated(Stability::Unstable,
-                                             "rustc_attrs",
-                                             "the `#[rustc_serialize_exclude_null]` attribute \
-                                              is an internal-only feature",
-                                             cfg_fn!(rustc_attrs))),
     ("rustc_synthetic", Whitelisted, Gated(Stability::Unstable,
                                                       "rustc_attrs",
                                                       "this attribute \

src/libsyntax_ext/deriving/encodable.rs

@@ -190,7 +190,7 @@ fn encodable_substructure(cx: &mut ExtCtxt,
         Struct(_, ref fields) => {
             let emit_struct_field = cx.ident_of("emit_struct_field");
             let mut stmts = Vec::new();
-            for (i, &FieldInfo { name, ref self_, span, attrs, .. }) in fields.iter().enumerate() {
+            for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
                 let name = match name {
                     Some(id) => id.name,
                     None => Symbol::intern(&format!("_field{}", i)),
@@ -213,17 +213,7 @@ fn encodable_substructure(cx: &mut ExtCtxt,
                     cx.expr(span, ExprKind::Ret(Some(call)))
                 };
 
-                // This exists for https://github.com/rust-lang/rust/pull/47540
-                //
-                // If we decide to stabilize that flag this can be removed
-                let expr = if attrs.iter().any(|a| a.check_name("rustc_serialize_exclude_null")) {
-                    let is_some = cx.ident_of("is_some");
-                    let condition = cx.expr_method_call(span, self_.clone(), is_some, vec![]);
-                    cx.expr_if(span, condition, call, None)
-                } else {
-                    call
-                };
-                let stmt = cx.stmt_expr(expr);
+                let stmt = cx.stmt_expr(call);
                 stmts.push(stmt);
             }