remove unused derives and variants

7 files changed, 56 insertions, 68 deletions

diff --git a/src/librustdoc/clean/cfg.rs b/src/librustdoc/clean/cfg.rs
index 67113787915..ad211763a6c 100644
--- a/src/librustdoc/clean/cfg.rs
+++ b/src/librustdoc/clean/cfg.rs
@@ -16,7 +16,7 @@ use syntax_pos::Span;
 
 use crate::html::escape::Escape;
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub enum Cfg {
     /// Accepts all configurations.
     True,
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 41a56756a14..3fe048a6986 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -223,7 +223,7 @@ impl<'a, 'tcx> Clean<Crate> for visit_ast::RustdocVisitor<'a, 'tcx> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct ExternalCrate {
     pub name: String,
     pub src: FileName,
@@ -355,7 +355,7 @@ impl Clean<ExternalCrate> for CrateNum {
 /// Anything with a source location and set of attributes and, optionally, a
 /// name. That is, anything that can be documented. This doesn't correspond
 /// directly to the AST's concept of an item; it's a strict superset.
-#[derive(Clone, RustcEncodable, RustcDecodable)]
+#[derive(Clone)]
 pub struct Item {
     /// Stringified span
     pub source: Span,
@@ -528,7 +528,7 @@ impl Item {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub enum ItemEnum {
     ExternCrateItem(String, Option<String>),
     ImportItem(Import),
@@ -594,7 +594,7 @@ impl ItemEnum {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Module {
     pub items: Vec<Item>,
     pub is_crate: bool,
@@ -731,7 +731,7 @@ impl<I: IntoIterator<Item=ast::NestedMetaItem>> NestedAttributesExt for I {
 /// Included files are kept separate from inline doc comments so that proper line-number
 /// information can be given when a doctest fails. Sugared doc comments and "raw" doc comments are
 /// kept separate because of issue #42760.
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum DocFragment {
     /// A doc fragment created from a `///` or `//!` doc comment.
     SugaredDoc(usize, syntax_pos::Span, String),
@@ -781,7 +781,7 @@ impl<'a> FromIterator<&'a DocFragment> for String {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Default)]
+#[derive(Clone, Debug, Default)]
 pub struct Attributes {
     pub doc_strings: Vec<DocFragment>,
     pub other_attrs: Vec<ast::Attribute>,
@@ -1048,7 +1048,7 @@ impl Clean<Attributes> for [ast::Attribute] {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum GenericBound {
     TraitBound(PolyTrait, hir::TraitBoundModifier),
     Outlives(Lifetime),
@@ -1231,7 +1231,7 @@ impl<'tcx> Clean<Option<Vec<GenericBound>>> for InternalSubsts<'tcx> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Lifetime(String);
 
 impl Lifetime {
@@ -1326,7 +1326,7 @@ impl Clean<Option<Lifetime>> for ty::RegionKind {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum WherePredicate {
     BoundPredicate { ty: Type, bounds: Vec<GenericBound> },
     RegionPredicate { lifetime: Lifetime, bounds: Vec<GenericBound> },
@@ -1464,7 +1464,7 @@ impl<'tcx> Clean<Type> for ty::ProjectionTy<'tcx> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum GenericParamDefKind {
     Lifetime,
     Type {
@@ -1498,7 +1498,7 @@ impl GenericParamDefKind {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct GenericParamDef {
     pub name: String,
 
@@ -1610,7 +1610,7 @@ impl Clean<GenericParamDef> for hir::GenericParam {
 }
 
 // maybe use a Generic enum and use Vec<Generic>?
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Default, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Default, Hash)]
 pub struct Generics {
     pub params: Vec<GenericParamDef>,
     pub where_predicates: Vec<WherePredicate>,
@@ -1874,7 +1874,7 @@ pub fn get_all_types(
     (all_types.into_iter().collect(), ret_types)
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Method {
     pub generics: Generics,
     pub decl: FnDecl,
@@ -1902,7 +1902,7 @@ impl<'a> Clean<Method> for (&'a hir::MethodSig, &'a hir::Generics, hir::BodyId,
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct TyMethod {
     pub header: hir::FnHeader,
     pub decl: FnDecl,
@@ -1911,7 +1911,7 @@ pub struct TyMethod {
     pub ret_types: Vec<Type>,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Function {
     pub decl: FnDecl,
     pub generics: Generics,
@@ -1952,7 +1952,7 @@ impl Clean<Item> for doctree::Function<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct FnDecl {
     pub inputs: Arguments,
     pub output: FunctionRetTy,
@@ -1989,7 +1989,7 @@ impl FnDecl {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Arguments {
     pub values: Vec<Argument>,
 }
@@ -2063,13 +2063,13 @@ impl<'tcx> Clean<FnDecl> for (DefId, ty::PolyFnSig<'tcx>) {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Argument {
     pub type_: Type,
     pub name: String,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Debug)]
+#[derive(Clone, PartialEq, Debug)]
 pub enum SelfTy {
     SelfValue,
     SelfBorrowed(Option<Lifetime>, Mutability),
@@ -2093,7 +2093,7 @@ impl Argument {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum FunctionRetTy {
     Return(Type),
     DefaultReturn,
@@ -2117,7 +2117,7 @@ impl GetDefId for FunctionRetTy {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Trait {
     pub auto: bool,
     pub unsafety: hir::Unsafety,
@@ -2153,7 +2153,7 @@ impl Clean<Item> for doctree::Trait<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct TraitAlias {
     pub generics: Generics,
     pub bounds: Vec<GenericBound>,
@@ -2437,7 +2437,7 @@ impl Clean<Item> for ty::AssocItem {
 }
 
 /// A trait reference, which may have higher ranked lifetimes.
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct PolyTrait {
     pub trait_: Type,
     pub generic_params: Vec<GenericParamDef>,
@@ -2446,7 +2446,7 @@ pub struct PolyTrait {
 /// A representation of a type suitable for hyperlinking purposes. Ideally, one can get the original
 /// type out of the AST/`TyCtxt` given one of these, if more information is needed. Most
 /// importantly, it does not preserve mutability or boxes.
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum Type {
     /// Structs/enums/traits (most that would be an `hir::TyKind::Path`).
     ResolvedPath {
@@ -2469,7 +2469,6 @@ pub enum Type {
     Array(Box<Type>, String),
     Never,
     CVarArgs,
-    Unique(Box<Type>),
     RawPointer(Mutability, Box<Type>),
     BorrowedRef {
         lifetime: Option<Lifetime>,
@@ -2491,7 +2490,7 @@ pub enum Type {
     ImplTrait(Vec<GenericBound>),
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Hash, Copy, Debug)]
+#[derive(Clone, PartialEq, Eq, Hash, Copy, Debug)]
 pub enum PrimitiveType {
     Isize, I8, I16, I32, I64, I128,
     Usize, U8, U16, U32, U64, U128,
@@ -2510,7 +2509,7 @@ pub enum PrimitiveType {
     CVarArgs,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Copy, Debug)]
+#[derive(Clone, Copy, Debug)]
 pub enum TypeKind {
     Enum,
     Function,
@@ -2520,7 +2519,6 @@ pub enum TypeKind {
     Struct,
     Union,
     Trait,
-    Variant,
     Typedef,
     Foreign,
     Macro,
@@ -3190,7 +3188,7 @@ impl Clean<Item> for ty::FieldDef {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, RustcDecodable, RustcEncodable, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug)]
 pub enum Visibility {
     Public,
     Inherited,
@@ -3219,7 +3217,7 @@ impl Clean<Option<Visibility>> for ty::Visibility {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Struct {
     pub struct_type: doctree::StructType,
     pub generics: Generics,
@@ -3227,7 +3225,7 @@ pub struct Struct {
     pub fields_stripped: bool,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Union {
     pub struct_type: doctree::StructType,
     pub generics: Generics,
@@ -3278,7 +3276,7 @@ impl Clean<Item> for doctree::Union<'_> {
 /// This is a more limited form of the standard Struct, different in that
 /// it lacks the things most items have (name, id, parameterization). Found
 /// only as a variant in an enum.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct VariantStruct {
     pub struct_type: doctree::StructType,
     pub fields: Vec<Item>,
@@ -3295,7 +3293,7 @@ impl Clean<VariantStruct> for ::rustc::hir::VariantData {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Enum {
     pub variants: IndexVec<VariantIdx, Item>,
     pub generics: Generics,
@@ -3321,7 +3319,7 @@ impl Clean<Item> for doctree::Enum<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Variant {
     pub kind: VariantKind,
 }
@@ -3384,7 +3382,7 @@ impl Clean<Item> for ty::VariantDef {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub enum VariantKind {
     CLike,
     Tuple(Vec<Type>),
@@ -3402,7 +3400,7 @@ impl Clean<VariantKind> for hir::VariantData {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Span {
     pub filename: FileName,
     pub loline: usize,
@@ -3448,7 +3446,7 @@ impl Clean<Span> for syntax_pos::Span {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Path {
     pub global: bool,
     pub res: Res,
@@ -3471,7 +3469,7 @@ impl Clean<Path> for hir::Path {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum GenericArg {
     Lifetime(Lifetime),
     Type(Type),
@@ -3488,7 +3486,7 @@ impl fmt::Display for GenericArg {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum GenericArgs {
     AngleBracketed {
         args: Vec<GenericArg>,
@@ -3528,7 +3526,7 @@ impl Clean<GenericArgs> for hir::GenericArgs {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct PathSegment {
     pub name: String,
     pub args: GenericArgs,
@@ -3553,7 +3551,6 @@ fn strip_type(ty: Type) -> Type {
         }
         Type::Slice(inner_ty) => Type::Slice(Box::new(strip_type(*inner_ty))),
         Type::Array(inner_ty, s) => Type::Array(Box::new(strip_type(*inner_ty)), s),
-        Type::Unique(inner_ty) => Type::Unique(Box::new(strip_type(*inner_ty))),
         Type::RawPointer(m, inner_ty) => Type::RawPointer(m, Box::new(strip_type(*inner_ty))),
         Type::BorrowedRef { lifetime, mutability, type_ } => {
             Type::BorrowedRef { lifetime, mutability, type_: Box::new(strip_type(*type_)) }
@@ -3625,7 +3622,7 @@ impl Clean<String> for InternedString {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Typedef {
     pub type_: Type,
     pub generics: Generics,
@@ -3649,7 +3646,7 @@ impl Clean<Item> for doctree::Typedef<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Existential {
     pub bounds: Vec<GenericBound>,
     pub generics: Generics,
@@ -3673,7 +3670,7 @@ impl Clean<Item> for doctree::Existential<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct BareFunctionDecl {
     pub unsafety: hir::Unsafety,
     pub generic_params: Vec<GenericParamDef>,
@@ -3695,7 +3692,7 @@ impl Clean<BareFunctionDecl> for hir::BareFnTy {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Static {
     pub type_: Type,
     pub mutability: Mutability,
@@ -3725,7 +3722,7 @@ impl Clean<Item> for doctree::Static<'_> {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub struct Constant {
     pub type_: Type,
     pub expr: String,
@@ -3749,7 +3746,7 @@ impl Clean<Item> for doctree::Constant<'_> {
     }
 }
 
-#[derive(Debug, Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Copy, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq, Copy, Hash)]
 pub enum Mutability {
     Mutable,
     Immutable,
@@ -3764,7 +3761,7 @@ impl Clean<Mutability> for hir::Mutability {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Copy, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Copy, Debug, Hash)]
 pub enum ImplPolarity {
     Positive,
     Negative,
@@ -3779,7 +3776,7 @@ impl Clean<ImplPolarity> for hir::ImplPolarity {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Impl {
     pub unsafety: hir::Unsafety,
     pub generics: Generics,
@@ -4003,7 +4000,7 @@ impl Clean<Vec<Item>> for doctree::Import<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub enum Import {
     // use source as str;
     Simple(String, ImportSource),
@@ -4011,7 +4008,7 @@ pub enum Import {
     Glob(ImportSource)
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct ImportSource {
     pub path: Path,
     pub did: Option<DefId>,
@@ -4227,7 +4224,7 @@ fn resolve_use_source(cx: &DocContext<'_>, path: Path) -> ImportSource {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Macro {
     pub source: String,
     pub imported_from: Option<String>,
@@ -4256,7 +4253,7 @@ impl Clean<Item> for doctree::Macro<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct ProcMacro {
     pub kind: MacroKind,
     pub helpers: Vec<String>,
@@ -4280,7 +4277,7 @@ impl Clean<Item> for doctree::ProcMacro<'_> {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Stability {
     pub level: stability::StabilityLevel,
     pub feature: Option<String>,
@@ -4290,7 +4287,7 @@ pub struct Stability {
     pub issue: Option<u32>,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Debug)]
 pub struct Deprecation {
     pub since: Option<String>,
     pub note: Option<String>,
@@ -4340,13 +4337,13 @@ impl Clean<Deprecation> for attr::Deprecation {
 
 /// An type binding on an associated type (e.g., `A = Bar` in `Foo<A = Bar>` or
 /// `A: Send + Sync` in `Foo<A: Send + Sync>`).
-#[derive(Clone, PartialEq, Eq, RustcDecodable, RustcEncodable, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct TypeBinding {
     pub name: String,
     pub kind: TypeBindingKind,
 }
 
-#[derive(Clone, PartialEq, Eq, RustcDecodable, RustcEncodable, Debug, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum TypeBindingKind {
     Equality {
         ty: Type,
diff --git a/src/librustdoc/doctree.rs b/src/librustdoc/doctree.rs
index 51deb4e9b97..2557b8d1627 100644
--- a/src/librustdoc/doctree.rs
+++ b/src/librustdoc/doctree.rs
@@ -78,7 +78,7 @@ impl Module<'hir> {
     }
 }
 
-#[derive(Debug, Clone, RustcEncodable, RustcDecodable, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub enum StructType {
     /// A braced struct
     Plain,
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index fa3bc3f5f4f..9e5cc03b831 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -737,9 +737,6 @@ fn fmt_type(t: &clean::Type, f: &mut fmt::Formatter<'_>, use_absolute: bool) ->
                 }
             }
         }
-        clean::Unique(..) => {
-            panic!("should have been cleaned")
-        }
     }
 }
 
diff --git a/src/librustdoc/html/item_type.rs b/src/librustdoc/html/item_type.rs
index 3f3f4c85e81..5f1a1b31616 100644
--- a/src/librustdoc/html/item_type.rs
+++ b/src/librustdoc/html/item_type.rs
@@ -110,7 +110,6 @@ impl From<clean::TypeKind> for ItemType {
             clean::TypeKind::Module     => ItemType::Module,
             clean::TypeKind::Static     => ItemType::Static,
             clean::TypeKind::Const      => ItemType::Constant,
-            clean::TypeKind::Variant    => ItemType::Variant,
             clean::TypeKind::Typedef    => ItemType::Typedef,
             clean::TypeKind::Foreign    => ItemType::ForeignType,
             clean::TypeKind::Macro      => ItemType::Macro,
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index f0aff961c67..2080637ecb4 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -5188,9 +5188,6 @@ fn collect_paths_for_type(first_ty: clean::Type) -> Vec<String> {
             clean::Type::Array(ty, _) => {
                 work.push_back(*ty);
             },
-            clean::Type::Unique(ty) => {
-                work.push_back(*ty);
-            },
             clean::Type::RawPointer(_, ty) => {
                 work.push_back(*ty);
             },
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 7a8b088020c..ba423300e02 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -42,8 +42,6 @@ extern crate test as testing;
 #[macro_use] extern crate log;
 extern crate rustc_errors as errors;
 
-extern crate serialize as rustc_serialize; // used by deriving
-
 use std::default::Default;
 use std::env;
 use std::panic;