src/libsyntax_ext/deriving/generic/mod.rs

   1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Some code that abstracts away much of the boilerplate of writing
  12 //! `derive` instances for traits. Among other things it manages getting
  13 //! access to the fields of the 4 different sorts of structs and enum
  14 //! variants, as well as creating the method and impl ast instances.
  15 //!
  16 //! Supported features (fairly exhaustive):
  17 //!
  18 //! - Methods taking any number of parameters of any type, and returning
  19 //!   any type, other than vectors, bottom and closures.
  20 //! - Generating `impl`s for types with type parameters and lifetimes
  21 //!   (e.g. `Option<T>`), the parameters are automatically given the
  22 //!   current trait as a bound. (This includes separate type parameters
  23 //!   and lifetimes for methods.)
  24 //! - Additional bounds on the type parameters (`TraitDef.additional_bounds`)
  25 //!
  26 //! The most important thing for implementors is the `Substructure` and
  27 //! `SubstructureFields` objects. The latter groups 5 possibilities of the
  28 //! arguments:
  29 //!
  30 //! - `Struct`, when `Self` is a struct (including tuple structs, e.g
  31 //!   `struct T(i32, char)`).
  32 //! - `EnumMatching`, when `Self` is an enum and all the arguments are the
  33 //!   same variant of the enum (e.g. `Some(1)`, `Some(3)` and `Some(4)`)
  34 //! - `EnumNonMatchingCollapsed` when `Self` is an enum and the arguments
  35 //!   are not the same variant (e.g. `None`, `Some(1)` and `None`).
  36 //! - `StaticEnum` and `StaticStruct` for static methods, where the type
  37 //!   being derived upon is either an enum or struct respectively. (Any
  38 //!   argument with type Self is just grouped among the non-self
  39 //!   arguments.)
  40 //!
  41 //! In the first two cases, the values from the corresponding fields in
  42 //! all the arguments are grouped together. For `EnumNonMatchingCollapsed`
  43 //! this isn't possible (different variants have different fields), so the
  44 //! fields are inaccessible. (Previous versions of the deriving infrastructure
  45 //! had a way to expand into code that could access them, at the cost of
  46 //! generating exponential amounts of code; see issue #15375). There are no
  47 //! fields with values in the static cases, so these are treated entirely
  48 //! differently.
  49 //!
  50 //! The non-static cases have `Option<ident>` in several places associated
  51 //! with field `expr`s. This represents the name of the field it is
  52 //! associated with. It is only not `None` when the associated field has
  53 //! an identifier in the source code. For example, the `x`s in the
  54 //! following snippet
  55 //!
  56 //! ```rust
  57 //! # #![allow(dead_code)]
  58 //! struct A { x : i32 }
  59 //!
  60 //! struct B(i32);
  61 //!
  62 //! enum C {
  63 //!     C0(i32),
  64 //!     C1 { x: i32 }
  65 //! }
  66 //! ```
  67 //!
  68 //! The `i32`s in `B` and `C0` don't have an identifier, so the
  69 //! `Option<ident>`s would be `None` for them.
  70 //!
  71 //! In the static cases, the structure is summarised, either into the just
  72 //! spans of the fields or a list of spans and the field idents (for tuple
  73 //! structs and record structs, respectively), or a list of these, for
  74 //! enums (one for each variant). For empty struct and empty enum
  75 //! variants, it is represented as a count of 0.
  76 //!
  77 //! # "`cs`" functions
  78 //!
  79 //! The `cs_...` functions ("combine substructure) are designed to
  80 //! make life easier by providing some pre-made recipes for common
  81 //! threads; mostly calling the function being derived on all the
  82 //! arguments and then combining them back together in some way (or
  83 //! letting the user chose that). They are not meant to be the only
  84 //! way to handle the structures that this code creates.
  85 //!
  86 //! # Examples
  87 //!
  88 //! The following simplified `PartialEq` is used for in-code examples:
  89 //!
  90 //! ```rust
  91 //! trait PartialEq {
  92 //!     fn eq(&self, other: &Self) -> bool;
  93 //! }
  94 //! impl PartialEq for i32 {
  95 //!     fn eq(&self, other: &i32) -> bool {
  96 //!         *self == *other
  97 //!     }
  98 //! }
  99 //! ```
 100 //!
 101 //! Some examples of the values of `SubstructureFields` follow, using the
 102 //! above `PartialEq`, `A`, `B` and `C`.
 103 //!
 104 //! ## Structs
 105 //!
 106 //! When generating the `expr` for the `A` impl, the `SubstructureFields` is
 107 //!
 108 //! ```{.text}
 109 //! Struct(vec![FieldInfo {
 110 //!            span: <span of x>
 111 //!            name: Some(<ident of x>),
 112 //!            self_: <expr for &self.x>,
 113 //!            other: vec![<expr for &other.x]
 114 //!          }])
 115 //! ```
 116 //!
 117 //! For the `B` impl, called with `B(a)` and `B(b)`,
 118 //!
 119 //! ```{.text}
 120 //! Struct(vec![FieldInfo {
 121 //!           span: <span of `i32`>,
 122 //!           name: None,
 123 //!           self_: <expr for &a>
 124 //!           other: vec![<expr for &b>]
 125 //!          }])
 126 //! ```
 127 //!
 128 //! ## Enums
 129 //!
 130 //! When generating the `expr` for a call with `self == C0(a)` and `other
 131 //! == C0(b)`, the SubstructureFields is
 132 //!
 133 //! ```{.text}
 134 //! EnumMatching(0, <ast::Variant for C0>,
 135 //!              vec![FieldInfo {
 136 //!                 span: <span of i32>
 137 //!                 name: None,
 138 //!                 self_: <expr for &a>,
 139 //!                 other: vec![<expr for &b>]
 140 //!               }])
 141 //! ```
 142 //!
 143 //! For `C1 {x}` and `C1 {x}`,
 144 //!
 145 //! ```{.text}
 146 //! EnumMatching(1, <ast::Variant for C1>,
 147 //!              vec![FieldInfo {
 148 //!                 span: <span of x>
 149 //!                 name: Some(<ident of x>),
 150 //!                 self_: <expr for &self.x>,
 151 //!                 other: vec![<expr for &other.x>]
 152 //!                }])
 153 //! ```
 154 //!
 155 //! For `C0(a)` and `C1 {x}` ,
 156 //!
 157 //! ```{.text}
 158 //! EnumNonMatchingCollapsed(
 159 //!     vec![<ident of self>, <ident of __arg_1>],
 160 //!     &[<ast::Variant for C0>, <ast::Variant for C1>],
 161 //!     &[<ident for self index value>, <ident of __arg_1 index value>])
 162 //! ```
 163 //!
 164 //! It is the same for when the arguments are flipped to `C1 {x}` and
 165 //! `C0(a)`; the only difference is what the values of the identifiers
 166 //! <ident for self index value> and <ident of __arg_1 index value> will
 167 //! be in the generated code.
 168 //!
 169 //! `EnumNonMatchingCollapsed` deliberately provides far less information
 170 //! than is generally available for a given pair of variants; see #15375
 171 //! for discussion.
 172 //!
 173 //! ## Static
 174 //!
 175 //! A static method on the types above would result in,
 176 //!
 177 //! ```{.text}
 178 //! StaticStruct(<ast::VariantData of A>, Named(vec![(<ident of x>, <span of x>)]))
 179 //!
 180 //! StaticStruct(<ast::VariantData of B>, Unnamed(vec![<span of x>]))
 181 //!
 182 //! StaticEnum(<ast::EnumDef of C>,
 183 //!            vec![(<ident of C0>, <span of C0>, Unnamed(vec![<span of i32>])),
 184 //!                 (<ident of C1>, <span of C1>, Named(vec![(<ident of x>, <span of x>)]))])
 185 //! ```
 186
 187 pub use self::StaticFields::*;
 188 pub use self::SubstructureFields::*;
 189
 190 use std::cell::RefCell;
 191 use std::collections::HashSet;
 192 use std::vec;
 193
 194 use syntax::abi::Abi;
 195 use syntax::ast::{
 196     self, BinOpKind, EnumDef, Expr, GenericParam, Generics, Ident, PatKind, VariantData
 197 };
 198
 199 use syntax::attr;
 200 use syntax::ext::base::{Annotatable, ExtCtxt};
 201 use syntax::ext::build::AstBuilder;
 202 use syntax::codemap::{self, dummy_spanned, respan};
 203 use syntax::util::move_map::MoveMap;
 204 use syntax::ptr::P;
 205 use syntax::symbol::{Symbol, keywords};
 206 use syntax_pos::{DUMMY_SP, Span};
 207 use errors::Handler;
 208
 209 use self::ty::{LifetimeBounds, Path, Ptr, PtrTy, Self_, Ty};
 210
 211 use deriving;
 212
 213 pub mod ty;
 214
 215 pub struct TraitDef<'a> {
 216     /// The span for the current #[derive(Foo)] header.
 217     pub span: Span,
 218
 219     pub attributes: Vec<ast::Attribute>,
 220
 221     /// Path of the trait, including any type parameters
 222     pub path: Path<'a>,
 223
 224     /// Additional bounds required of any type parameters of the type,
 225     /// other than the current trait
 226     pub additional_bounds: Vec<Ty<'a>>,
 227
 228     /// Any extra lifetimes and/or bounds, e.g. `D: serialize::Decoder`
 229     pub generics: LifetimeBounds<'a>,
 230
 231     /// Is it an `unsafe` trait?
 232     pub is_unsafe: bool,
 233
 234     /// Can this trait be derived for unions?
 235     pub supports_unions: bool,
 236
 237     pub methods: Vec<MethodDef<'a>>,
 238
 239     pub associated_types: Vec<(ast::Ident, Ty<'a>)>,
 240 }
 241
 242
 243 pub struct MethodDef<'a> {
 244     /// name of the method
 245     pub name: &'a str,
 246     /// List of generics, e.g. `R: rand::Rng`
 247     pub generics: LifetimeBounds<'a>,
 248
 249     /// Whether there is a self argument (outer Option) i.e. whether
 250     /// this is a static function, and whether it is a pointer (inner
 251     /// Option)
 252     pub explicit_self: Option<Option<PtrTy<'a>>>,
 253
 254     /// Arguments other than the self argument
 255     pub args: Vec<Ty<'a>>,
 256
 257     /// Return type
 258     pub ret_ty: Ty<'a>,
 259
 260     pub attributes: Vec<ast::Attribute>,
 261
 262     // Is it an `unsafe fn`?
 263     pub is_unsafe: bool,
 264
 265     /// Can we combine fieldless variants for enums into a single match arm?
 266     pub unify_fieldless_variants: bool,
 267
 268     pub combine_substructure: RefCell<CombineSubstructureFunc<'a>>,
 269 }
 270
 271 /// All the data about the data structure/method being derived upon.
 272 pub struct Substructure<'a> {
 273     /// ident of self
 274     pub type_ident: Ident,
 275     /// ident of the method
 276     pub method_ident: Ident,
 277     /// dereferenced access to any `Self_` or `Ptr(Self_, _)` arguments
 278     pub self_args: &'a [P<Expr>],
 279     /// verbatim access to any other arguments
 280     pub nonself_args: &'a [P<Expr>],
 281     pub fields: &'a SubstructureFields<'a>,
 282 }
 283
 284 /// Summary of the relevant parts of a struct/enum field.
 285 pub struct FieldInfo<'a> {
 286     pub span: Span,
 287     /// None for tuple structs/normal enum variants, Some for normal
 288     /// structs/struct enum variants.
 289     pub name: Option<Ident>,
 290     /// The expression corresponding to this field of `self`
 291     /// (specifically, a reference to it).
 292     pub self_: P<Expr>,
 293     /// The expressions corresponding to references to this field in
 294     /// the other `Self` arguments.
 295     pub other: Vec<P<Expr>>,
 296     /// The attributes on the field
 297     pub attrs: &'a [ast::Attribute],
 298 }
 299
 300 /// Fields for a static method
 301 pub enum StaticFields {
 302     /// Tuple and unit structs/enum variants like this.
 303     Unnamed(Vec<Span>, bool /*is tuple*/),
 304     /// Normal structs/struct variants.
 305     Named(Vec<(Ident, Span)>),
 306 }
 307
 308 /// A summary of the possible sets of fields.
 309 pub enum SubstructureFields<'a> {
 310     Struct(&'a ast::VariantData, Vec<FieldInfo<'a>>),
 311     /// Matching variants of the enum: variant index, variant count, ast::Variant,
 312     /// fields: the field name is only non-`None` in the case of a struct
 313     /// variant.
 314     EnumMatching(usize, usize, &'a ast::Variant, Vec<FieldInfo<'a>>),
 315
 316     /// Non-matching variants of the enum, but with all state hidden from
 317     /// the consequent code.  The first component holds `Ident`s for all of
 318     /// the `Self` arguments; the second component is a slice of all of the
 319     /// variants for the enum itself, and the third component is a list of
 320     /// `Ident`s bound to the variant index values for each of the actual
 321     /// input `Self` arguments.
 322     EnumNonMatchingCollapsed(Vec<Ident>, &'a [ast::Variant], &'a [Ident]),
 323
 324     /// A static method where `Self` is a struct.
 325     StaticStruct(&'a ast::VariantData, StaticFields),
 326     /// A static method where `Self` is an enum.
 327     StaticEnum(&'a ast::EnumDef, Vec<(Ident, Span, StaticFields)>),
 328 }
 329
 330
 331
 332 /// Combine the values of all the fields together. The last argument is
 333 /// all the fields of all the structures.
 334 pub type CombineSubstructureFunc<'a> =
 335     Box<FnMut(&mut ExtCtxt, Span, &Substructure) -> P<Expr> + 'a>;
 336
 337 /// Deal with non-matching enum variants.  The tuple is a list of
 338 /// identifiers (one for each `Self` argument, which could be any of the
 339 /// variants since they have been collapsed together) and the identifiers
 340 /// holding the variant index value for each of the `Self` arguments.  The
 341 /// last argument is all the non-`Self` args of the method being derived.
 342 pub type EnumNonMatchCollapsedFunc<'a> =
 343     Box<FnMut(&mut ExtCtxt, Span, (&[Ident], &[Ident]), &[P<Expr>]) -> P<Expr> + 'a>;
 344
 345 pub fn combine_substructure<'a>(f: CombineSubstructureFunc<'a>)
 346                                 -> RefCell<CombineSubstructureFunc<'a>> {
 347     RefCell::new(f)
 348 }
 349
 350 /// This method helps to extract all the type parameters referenced from a
 351 /// type. For a type parameter `<T>`, it looks for either a `TyPath` that
 352 /// is not global and starts with `T`, or a `TyQPath`.
 353 fn find_type_parameters(ty: &ast::Ty,
 354                         ty_param_names: &[ast::Name],
 355                         span: Span,
 356                         cx: &ExtCtxt)
 357                         -> Vec<P<ast::Ty>> {
 358     use syntax::visit;
 359
 360     struct Visitor<'a, 'b: 'a> {
 361         cx: &'a ExtCtxt<'b>,
 362         span: Span,
 363         ty_param_names: &'a [ast::Name],
 364         types: Vec<P<ast::Ty>>,
 365     }
 366
 367     impl<'a, 'b> visit::Visitor<'a> for Visitor<'a, 'b> {
 368         fn visit_ty(&mut self, ty: &'a ast::Ty) {
 369             if let ast::TyKind::Path(_, ref path) = ty.node {
 370                 if let Some(segment) = path.segments.first() {
 371                     if self.ty_param_names.contains(&segment.ident.name) {
 372                         self.types.push(P(ty.clone()));
 373                     }
 374                 }
 375             }
 376
 377             visit::walk_ty(self, ty)
 378         }
 379
 380         fn visit_mac(&mut self, mac: &ast::Mac) {
 381             let span = mac.span.with_ctxt(self.span.ctxt());
 382             self.cx.span_err(span, "`derive` cannot be used on items with type macros");
 383         }
 384     }
 385
 386     let mut visitor = Visitor {
 387         ty_param_names,
 388         types: Vec::new(),
 389         span,
 390         cx,
 391     };
 392
 393     visit::Visitor::visit_ty(&mut visitor, ty);
 394
 395     visitor.types
 396 }
 397
 398 impl<'a> TraitDef<'a> {
 399     pub fn expand(self,
 400                   cx: &mut ExtCtxt,
 401                   mitem: &ast::MetaItem,
 402                   item: &'a Annotatable,
 403                   push: &mut FnMut(Annotatable)) {
 404         self.expand_ext(cx, mitem, item, push, false);
 405     }
 406
 407     pub fn expand_ext(self,
 408                       cx: &mut ExtCtxt,
 409                       mitem: &ast::MetaItem,
 410                       item: &'a Annotatable,
 411                       push: &mut FnMut(Annotatable),
 412                       from_scratch: bool) {
 413         match *item {
 414             Annotatable::Item(ref item) => {
 415                 let is_packed = item.attrs.iter().any(|attr| {
 416                     attr::find_repr_attrs(&cx.parse_sess.span_diagnostic, attr)
 417                         .contains(&attr::ReprPacked)
 418                 });
 419                 let has_no_type_params = match item.node {
 420                     ast::ItemKind::Struct(_, ref generics) |
 421                     ast::ItemKind::Enum(_, ref generics) |
 422                     ast::ItemKind::Union(_, ref generics) => {
 423                         !generics.params.iter().any(|p| p.is_type_param())
 424                     }
 425                     _ => {
 426                         // Non-ADT derive is an error, but it should have been
 427                         // set earlier; see
 428                         // libsyntax/ext/expand.rs:MacroExpander::expand()
 429                         return;
 430                     }
 431                 };
 432                 let is_always_copy =
 433                     attr::contains_name(&item.attrs, "rustc_copy_clone_marker") &&
 434                     has_no_type_params;
 435                 let use_temporaries = is_packed && is_always_copy;
 436
 437                 let newitem = match item.node {
 438                     ast::ItemKind::Struct(ref struct_def, ref generics) => {
 439                         self.expand_struct_def(cx, &struct_def, item.ident, generics, from_scratch,
 440                                                use_temporaries)
 441                     }
 442                     ast::ItemKind::Enum(ref enum_def, ref generics) => {
 443                         // We ignore `use_temporaries` here, because
 444                         // `repr(packed)` enums cause an error later on.
 445                         //
 446                         // This can only cause further compilation errors
 447                         // downstream in blatantly illegal code, so it
 448                         // is fine.
 449                         self.expand_enum_def(cx, enum_def, &item.attrs,
 450                                              item.ident, generics, from_scratch)
 451                     }
 452                     ast::ItemKind::Union(ref struct_def, ref generics) => {
 453                         if self.supports_unions {
 454                             self.expand_struct_def(cx, &struct_def, item.ident,
 455                                                    generics, from_scratch,
 456                                                    use_temporaries)
 457                         } else {
 458                             cx.span_err(mitem.span,
 459                                         "this trait cannot be derived for unions");
 460                             return;
 461                         }
 462                     }
 463                     _ => unreachable!(),
 464                 };
 465                 // Keep the lint attributes of the previous item to control how the
 466                 // generated implementations are linted
 467                 let mut attrs = newitem.attrs.clone();
 468                 attrs.extend(item.attrs
 469                     .iter()
 470                     .filter(|a| {
 471                         a.name().is_some() && match &*a.name().unwrap().as_str() {
 472                             "allow" | "warn" | "deny" | "forbid" | "stable" | "unstable" => true,
 473                             _ => false,
 474                         }
 475                     })
 476                     .cloned());
 477                 push(Annotatable::Item(P(ast::Item { attrs: attrs, ..(*newitem).clone() })))
 478             }
 479             _ => {
 480                 // Non-Item derive is an error, but it should have been
 481                 // set earlier; see
 482                 // libsyntax/ext/expand.rs:MacroExpander::expand()
 483                 return;
 484             }
 485         }
 486     }
 487
 488     /// Given that we are deriving a trait `DerivedTrait` for a type like:
 489     ///
 490     /// ```ignore (only-for-syntax-highlight)
 491     /// struct Struct<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z> where C: WhereTrait {
 492     ///     a: A,
 493     ///     b: B::Item,
 494     ///     b1: <B as DeclaredTrait>::Item,
 495     ///     c1: <C as WhereTrait>::Item,
 496     ///     c2: Option<<C as WhereTrait>::Item>,
 497     ///     ...
 498     /// }
 499     /// ```
 500     ///
 501     /// create an impl like:
 502     ///
 503     /// ```ignore (only-for-syntax-highlight)
 504     /// impl<'a, ..., 'z, A, B: DeclaredTrait, C, ...  Z> where
 505     ///     C:                       WhereTrait,
 506     ///     A: DerivedTrait + B1 + ... + BN,
 507     ///     B: DerivedTrait + B1 + ... + BN,
 508     ///     C: DerivedTrait + B1 + ... + BN,
 509     ///     B::Item:                 DerivedTrait + B1 + ... + BN,
 510     ///     <C as WhereTrait>::Item: DerivedTrait + B1 + ... + BN,
 511     ///     ...
 512     /// {
 513     ///     ...
 514     /// }
 515     /// ```
 516     ///
 517     /// where B1, ..., BN are the bounds given by `bounds_paths`.'. Z is a phantom type, and
 518     /// therefore does not get bound by the derived trait.
 519     fn create_derived_impl(&self,
 520                            cx: &mut ExtCtxt,
 521                            type_ident: Ident,
 522                            generics: &Generics,
 523                            field_tys: Vec<P<ast::Ty>>,
 524                            methods: Vec<ast::ImplItem>)
 525                            -> P<ast::Item> {
 526         let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
 527
 528         // Transform associated types from `deriving::ty::Ty` into `ast::ImplItem`
 529         let associated_types = self.associated_types.iter().map(|&(ident, ref type_def)| {
 530             ast::ImplItem {
 531                 id: ast::DUMMY_NODE_ID,
 532                 span: self.span,
 533                 ident,
 534                 vis: respan(self.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
 535                 defaultness: ast::Defaultness::Final,
 536                 attrs: Vec::new(),
 537                 generics: Generics::default(),
 538                 node: ast::ImplItemKind::Type(type_def.to_ty(cx, self.span, type_ident, generics)),
 539                 tokens: None,
 540             }
 541         });
 542
 543         let Generics { mut params, mut where_clause, span } = self.generics
 544             .to_generics(cx, self.span, type_ident, generics);
 545
 546         // Create the generic parameters
 547         params.extend(generics.params.iter().map(|param| {
 548             match *param {
 549                 ref l @ GenericParam::Lifetime(_) => l.clone(),
 550                 GenericParam::Type(ref ty_param) => {
 551                     // I don't think this can be moved out of the loop, since
 552                     // a TyParamBound requires an ast id
 553                     let mut bounds: Vec<_> =
 554                         // extra restrictions on the generics parameters to the
 555                         // type being derived upon
 556                         self.additional_bounds.iter().map(|p| {
 557                             cx.typarambound(p.to_path(cx, self.span,
 558                                                         type_ident, generics))
 559                         }).collect();
 560
 561                     // require the current trait
 562                     bounds.push(cx.typarambound(trait_path.clone()));
 563
 564                     // also add in any bounds from the declaration
 565                     for declared_bound in ty_param.bounds.iter() {
 566                         bounds.push((*declared_bound).clone());
 567                     }
 568
 569                     GenericParam::Type(cx.typaram(self.span, ty_param.ident, vec![], bounds, None))
 570                 }
 571             }
 572         }));
 573
 574         // and similarly for where clauses
 575         where_clause.predicates.extend(generics.where_clause.predicates.iter().map(|clause| {
 576             match *clause {
 577                 ast::WherePredicate::BoundPredicate(ref wb) => {
 578                     ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 579                         span: self.span,
 580                         bound_generic_params: wb.bound_generic_params.clone(),
 581                         bounded_ty: wb.bounded_ty.clone(),
 582                         bounds: wb.bounds.iter().cloned().collect(),
 583                     })
 584                 }
 585                 ast::WherePredicate::RegionPredicate(ref rb) => {
 586                     ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 587                         span: self.span,
 588                         lifetime: rb.lifetime,
 589                         bounds: rb.bounds.iter().cloned().collect(),
 590                     })
 591                 }
 592                 ast::WherePredicate::EqPredicate(ref we) => {
 593                     ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 594                         id: ast::DUMMY_NODE_ID,
 595                         span: self.span,
 596                         lhs_ty: we.lhs_ty.clone(),
 597                         rhs_ty: we.rhs_ty.clone(),
 598                     })
 599                 }
 600             }
 601         }));
 602
 603         {
 604             // Extra scope required here so ty_params goes out of scope before params is moved
 605
 606             let mut ty_params = params.iter()
 607                 .filter_map(|param| match *param {
 608                     ast::GenericParam::Type(ref t) => Some(t),
 609                     _ => None,
 610                 })
 611                 .peekable();
 612
 613             if ty_params.peek().is_some() {
 614                 let ty_param_names: Vec<ast::Name> = ty_params
 615                     .map(|ty_param| ty_param.ident.name)
 616                     .collect();
 617
 618                 let mut processed_field_types = HashSet::new();
 619                 for field_ty in field_tys {
 620                     let tys = find_type_parameters(&field_ty, &ty_param_names, self.span, cx);
 621
 622                     for ty in tys {
 623                         // if we have already handled this type, skip it
 624                         if let ast::TyKind::Path(_, ref p) = ty.node {
 625                             if p.segments.len() == 1 &&
 626                             ty_param_names.contains(&p.segments[0].ident.name) ||
 627                             processed_field_types.contains(&p.segments) {
 628                                 continue;
 629                             };
 630                             processed_field_types.insert(p.segments.clone());
 631                         }
 632                         let mut bounds: Vec<_> = self.additional_bounds
 633                             .iter()
 634                             .map(|p| {
 635                                 cx.typarambound(p.to_path(cx, self.span, type_ident, generics))
 636                             })
 637                             .collect();
 638
 639                         // require the current trait
 640                         bounds.push(cx.typarambound(trait_path.clone()));
 641
 642                         let predicate = ast::WhereBoundPredicate {
 643                             span: self.span,
 644                             bound_generic_params: Vec::new(),
 645                             bounded_ty: ty,
 646                             bounds,
 647                         };
 648
 649                         let predicate = ast::WherePredicate::BoundPredicate(predicate);
 650                         where_clause.predicates.push(predicate);
 651                     }
 652                 }
 653             }
 654         }
 655
 656         let trait_generics = Generics {
 657             params,
 658             where_clause,
 659             span,
 660         };
 661
 662         // Create the reference to the trait.
 663         let trait_ref = cx.trait_ref(trait_path);
 664
 665         // Create the type parameters on the `self` path.
 666         let self_ty_params = generics.params
 667             .iter()
 668             .filter_map(|param| match *param {
 669                 GenericParam::Type(ref ty_param)
 670                     => Some(cx.ty_ident(self.span, ty_param.ident)),
 671                 _ => None,
 672             })
 673             .collect();
 674
 675         let self_lifetimes: Vec<ast::Lifetime> = generics.params
 676             .iter()
 677             .filter_map(|param| match *param {
 678                 GenericParam::Lifetime(ref ld) => Some(ld.lifetime),
 679                 _ => None,
 680             })
 681             .collect();
 682
 683         // Create the type of `self`.
 684         let self_type = cx.ty_path(cx.path_all(self.span,
 685                                                false,
 686                                                vec![type_ident],
 687                                                self_lifetimes,
 688                                                self_ty_params,
 689                                                Vec::new()));
 690
 691         let attr = cx.attribute(self.span,
 692                                 cx.meta_word(self.span,
 693                                              Symbol::intern("automatically_derived")));
 694         // Just mark it now since we know that it'll end up used downstream
 695         attr::mark_used(&attr);
 696         let opt_trait_ref = Some(trait_ref);
 697         let unused_qual = {
 698             let word = cx.meta_list_item_word(self.span, Symbol::intern("unused_qualifications"));
 699             cx.attribute(self.span, cx.meta_list(self.span, Symbol::intern("allow"), vec![word]))
 700         };
 701
 702         let mut a = vec![attr, unused_qual];
 703         a.extend(self.attributes.iter().cloned());
 704
 705         let unsafety = if self.is_unsafe {
 706             ast::Unsafety::Unsafe
 707         } else {
 708             ast::Unsafety::Normal
 709         };
 710
 711         cx.item(self.span,
 712                 keywords::Invalid.ident(),
 713                 a,
 714                 ast::ItemKind::Impl(unsafety,
 715                                     ast::ImplPolarity::Positive,
 716                                     ast::Defaultness::Final,
 717                                     trait_generics,
 718                                     opt_trait_ref,
 719                                     self_type,
 720                                     methods.into_iter().chain(associated_types).collect()))
 721     }
 722
 723     fn expand_struct_def(&self,
 724                          cx: &mut ExtCtxt,
 725                          struct_def: &'a VariantData,
 726                          type_ident: Ident,
 727                          generics: &Generics,
 728                          from_scratch: bool,
 729                          use_temporaries: bool)
 730                          -> P<ast::Item> {
 731         let field_tys: Vec<P<ast::Ty>> = struct_def.fields()
 732             .iter()
 733             .map(|field| field.ty.clone())
 734             .collect();
 735
 736         let methods = self.methods
 737             .iter()
 738             .map(|method_def| {
 739                 let (explicit_self, self_args, nonself_args, tys) =
 740                     method_def.split_self_nonself_args(cx, self, type_ident, generics);
 741
 742                 let body = if from_scratch || method_def.is_static() {
 743                     method_def.expand_static_struct_method_body(cx,
 744                                                                 self,
 745                                                                 struct_def,
 746                                                                 type_ident,
 747                                                                 &self_args[..],
 748                                                                 &nonself_args[..])
 749                 } else {
 750                     method_def.expand_struct_method_body(cx,
 751                                                          self,
 752                                                          struct_def,
 753                                                          type_ident,
 754                                                          &self_args[..],
 755                                                          &nonself_args[..],
 756                                                          use_temporaries)
 757                 };
 758
 759                 method_def.create_method(cx,
 760                                          self,
 761                                          type_ident,
 762                                          generics,
 763                                          Abi::Rust,
 764                                          explicit_self,
 765                                          tys,
 766                                          body)
 767             })
 768             .collect();
 769
 770         self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
 771     }
 772
 773     fn expand_enum_def(&self,
 774                        cx: &mut ExtCtxt,
 775                        enum_def: &'a EnumDef,
 776                        type_attrs: &[ast::Attribute],
 777                        type_ident: Ident,
 778                        generics: &Generics,
 779                        from_scratch: bool)
 780                        -> P<ast::Item> {
 781         let mut field_tys = Vec::new();
 782
 783         for variant in &enum_def.variants {
 784             field_tys.extend(variant.node
 785                 .data
 786                 .fields()
 787                 .iter()
 788                 .map(|field| field.ty.clone()));
 789         }
 790
 791         let methods = self.methods
 792             .iter()
 793             .map(|method_def| {
 794                 let (explicit_self, self_args, nonself_args, tys) =
 795                     method_def.split_self_nonself_args(cx, self, type_ident, generics);
 796
 797                 let body = if from_scratch || method_def.is_static() {
 798                     method_def.expand_static_enum_method_body(cx,
 799                                                               self,
 800                                                               enum_def,
 801                                                               type_ident,
 802                                                               &self_args[..],
 803                                                               &nonself_args[..])
 804                 } else {
 805                     method_def.expand_enum_method_body(cx,
 806                                                        self,
 807                                                        enum_def,
 808                                                        type_attrs,
 809                                                        type_ident,
 810                                                        self_args,
 811                                                        &nonself_args[..])
 812                 };
 813
 814                 method_def.create_method(cx,
 815                                          self,
 816                                          type_ident,
 817                                          generics,
 818                                          Abi::Rust,
 819                                          explicit_self,
 820                                          tys,
 821                                          body)
 822             })
 823             .collect();
 824
 825         self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
 826     }
 827 }
 828
 829 fn find_repr_type_name(diagnostic: &Handler, type_attrs: &[ast::Attribute]) -> &'static str {
 830     let mut repr_type_name = "isize";
 831     for a in type_attrs {
 832         for r in &attr::find_repr_attrs(diagnostic, a) {
 833             repr_type_name = match *r {
 834                 attr::ReprPacked | attr::ReprSimd | attr::ReprAlign(_) | attr::ReprTransparent =>
 835                     continue,
 836
 837                 attr::ReprC => "i32",
 838
 839                 attr::ReprInt(attr::SignedInt(ast::IntTy::Isize)) => "isize",
 840                 attr::ReprInt(attr::SignedInt(ast::IntTy::I8)) => "i8",
 841                 attr::ReprInt(attr::SignedInt(ast::IntTy::I16)) => "i16",
 842                 attr::ReprInt(attr::SignedInt(ast::IntTy::I32)) => "i32",
 843                 attr::ReprInt(attr::SignedInt(ast::IntTy::I64)) => "i64",
 844                 attr::ReprInt(attr::SignedInt(ast::IntTy::I128)) => "i128",
 845
 846                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::Usize)) => "usize",
 847                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U8)) => "u8",
 848                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U16)) => "u16",
 849                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U32)) => "u32",
 850                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U64)) => "u64",
 851                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U128)) => "u128",
 852             }
 853         }
 854     }
 855     repr_type_name
 856 }
 857
 858 impl<'a> MethodDef<'a> {
 859     fn call_substructure_method(&self,
 860                                 cx: &mut ExtCtxt,
 861                                 trait_: &TraitDef,
 862                                 type_ident: Ident,
 863                                 self_args: &[P<Expr>],
 864                                 nonself_args: &[P<Expr>],
 865                                 fields: &SubstructureFields)
 866                                 -> P<Expr> {
 867         let substructure = Substructure {
 868             type_ident,
 869             method_ident: cx.ident_of(self.name),
 870             self_args,
 871             nonself_args,
 872             fields,
 873         };
 874         let mut f = self.combine_substructure.borrow_mut();
 875         let f: &mut CombineSubstructureFunc = &mut *f;
 876         f(cx, trait_.span, &substructure)
 877     }
 878
 879     fn get_ret_ty(&self,
 880                   cx: &mut ExtCtxt,
 881                   trait_: &TraitDef,
 882                   generics: &Generics,
 883                   type_ident: Ident)
 884                   -> P<ast::Ty> {
 885         self.ret_ty.to_ty(cx, trait_.span, type_ident, generics)
 886     }
 887
 888     fn is_static(&self) -> bool {
 889         self.explicit_self.is_none()
 890     }
 891
 892     fn split_self_nonself_args
 893         (&self,
 894          cx: &mut ExtCtxt,
 895          trait_: &TraitDef,
 896          type_ident: Ident,
 897          generics: &Generics)
 898          -> (Option<ast::ExplicitSelf>, Vec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
 899
 900         let mut self_args = Vec::new();
 901         let mut nonself_args = Vec::new();
 902         let mut arg_tys = Vec::new();
 903         let mut nonstatic = false;
 904
 905         let ast_explicit_self = self.explicit_self.as_ref().map(|self_ptr| {
 906             let (self_expr, explicit_self) = ty::get_explicit_self(cx, trait_.span, self_ptr);
 907
 908             self_args.push(self_expr);
 909             nonstatic = true;
 910
 911             explicit_self
 912         });
 913
 914         for (i, ty) in self.args.iter().enumerate() {
 915             let ast_ty = ty.to_ty(cx, trait_.span, type_ident, generics);
 916             let ident = cx.ident_of(&format!("__arg_{}", i));
 917             arg_tys.push((ident, ast_ty));
 918
 919             let arg_expr = cx.expr_ident(trait_.span, ident);
 920
 921             match *ty {
 922                 // for static methods, just treat any Self
 923                 // arguments as a normal arg
 924                 Self_ if nonstatic => {
 925                     self_args.push(arg_expr);
 926                 }
 927                 Ptr(ref ty, _) if **ty == Self_ && nonstatic => {
 928                     self_args.push(cx.expr_deref(trait_.span, arg_expr))
 929                 }
 930                 _ => {
 931                     nonself_args.push(arg_expr);
 932                 }
 933             }
 934         }
 935
 936         (ast_explicit_self, self_args, nonself_args, arg_tys)
 937     }
 938
 939     fn create_method(&self,
 940                      cx: &mut ExtCtxt,
 941                      trait_: &TraitDef,
 942                      type_ident: Ident,
 943                      generics: &Generics,
 944                      abi: Abi,
 945                      explicit_self: Option<ast::ExplicitSelf>,
 946                      arg_types: Vec<(Ident, P<ast::Ty>)>,
 947                      body: P<Expr>)
 948                      -> ast::ImplItem {
 949
 950         // create the generics that aren't for Self
 951         let fn_generics = self.generics.to_generics(cx, trait_.span, type_ident, generics);
 952
 953         let args = {
 954             let self_args = explicit_self.map(|explicit_self| {
 955                 ast::Arg::from_self(explicit_self,
 956                                     keywords::SelfValue.ident().with_span_pos(trait_.span))
 957             });
 958             let nonself_args = arg_types.into_iter()
 959                 .map(|(name, ty)| cx.arg(trait_.span, name, ty));
 960             self_args.into_iter().chain(nonself_args).collect()
 961         };
 962
 963         let ret_type = self.get_ret_ty(cx, trait_, generics, type_ident);
 964
 965         let method_ident = cx.ident_of(self.name);
 966         let fn_decl = cx.fn_decl(args, ast::FunctionRetTy::Ty(ret_type));
 967         let body_block = cx.block_expr(body);
 968
 969         let unsafety = if self.is_unsafe {
 970             ast::Unsafety::Unsafe
 971         } else {
 972             ast::Unsafety::Normal
 973         };
 974
 975         // Create the method.
 976         ast::ImplItem {
 977             id: ast::DUMMY_NODE_ID,
 978             attrs: self.attributes.clone(),
 979             generics: fn_generics,
 980             span: trait_.span,
 981             vis: respan(trait_.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
 982             defaultness: ast::Defaultness::Final,
 983             ident: method_ident,
 984             node: ast::ImplItemKind::Method(ast::MethodSig {
 985                                                 abi,
 986                                                 unsafety,
 987                                                 constness:
 988                                                     dummy_spanned(ast::Constness::NotConst),
 989                                                 decl: fn_decl,
 990                                             },
 991                                             body_block),
 992             tokens: None,
 993         }
 994     }
 995
 996     /// ```
 997     /// #[derive(PartialEq)]
 998     /// # struct Dummy;
 999     /// struct A { x: i32, y: i32 }
1000     ///
1001     /// // equivalent to:
1002     /// impl PartialEq for A {
1003     ///     fn eq(&self, __arg_1: &A) -> bool {
1004     ///         match *self {
1005     ///             A {x: ref __self_0_0, y: ref __self_0_1} => {
1006     ///                 match *__arg_1 {
1007     ///                     A {x: ref __self_1_0, y: ref __self_1_1} => {
1008     ///                         __self_0_0.eq(__self_1_0) && __self_0_1.eq(__self_1_1)
1009     ///                     }
1010     ///                 }
1011     ///             }
1012     ///         }
1013     ///     }
1014     /// }
1015     ///
1016     /// // or if A is repr(packed) - note fields are matched by-value
1017     /// // instead of by-reference.
1018     /// impl PartialEq for A {
1019     ///     fn eq(&self, __arg_1: &A) -> bool {
1020     ///         match *self {
1021     ///             A {x: __self_0_0, y: __self_0_1} => {
1022     ///                 match __arg_1 {
1023     ///                     A {x: __self_1_0, y: __self_1_1} => {
1024     ///                         __self_0_0.eq(&__self_1_0) && __self_0_1.eq(&__self_1_1)
1025     ///                     }
1026     ///                 }
1027     ///             }
1028     ///         }
1029     ///     }
1030     /// }
1031     /// ```
1032     fn expand_struct_method_body<'b>(&self,
1033                                      cx: &mut ExtCtxt,
1034                                      trait_: &TraitDef<'b>,
1035                                      struct_def: &'b VariantData,
1036                                      type_ident: Ident,
1037                                      self_args: &[P<Expr>],
1038                                      nonself_args: &[P<Expr>],
1039                                      use_temporaries: bool)
1040                                      -> P<Expr> {
1041
1042         let mut raw_fields = Vec::new(); // Vec<[fields of self],
1043                                  // [fields of next Self arg], [etc]>
1044         let mut patterns = Vec::new();
1045         for i in 0..self_args.len() {
1046             let struct_path = cx.path(DUMMY_SP, vec![type_ident]);
1047             let (pat, ident_expr) = trait_.create_struct_pattern(cx,
1048                                                                  struct_path,
1049                                                                  struct_def,
1050                                                                  &format!("__self_{}", i),
1051                                                                  ast::Mutability::Immutable,
1052                                                                  use_temporaries);
1053             patterns.push(pat);
1054             raw_fields.push(ident_expr);
1055         }
1056
1057         // transpose raw_fields
1058         let fields = if !raw_fields.is_empty() {
1059             let mut raw_fields = raw_fields.into_iter().map(|v| v.into_iter());
1060             let first_field = raw_fields.next().unwrap();
1061             let mut other_fields: Vec<vec::IntoIter<_>> = raw_fields.collect();
1062             first_field.map(|(span, opt_id, field, attrs)| {
1063                     FieldInfo {
1064                         span,
1065                         name: opt_id,
1066                         self_: field,
1067                         other: other_fields.iter_mut()
1068                             .map(|l| {
1069                                 match l.next().unwrap() {
1070                                     (.., ex, _) => ex,
1071                                 }
1072                             })
1073                             .collect(),
1074                         attrs,
1075                     }
1076                 })
1077                 .collect()
1078         } else {
1079             cx.span_bug(trait_.span,
1080                         "no self arguments to non-static method in generic \
1081                          `derive`")
1082         };
1083
1084         // body of the inner most destructuring match
1085         let mut body = self.call_substructure_method(cx,
1086                                                      trait_,
1087                                                      type_ident,
1088                                                      self_args,
1089                                                      nonself_args,
1090                                                      &Struct(struct_def, fields));
1091
1092         // make a series of nested matches, to destructure the
1093         // structs. This is actually right-to-left, but it shouldn't
1094         // matter.
1095         for (arg_expr, pat) in self_args.iter().zip(patterns) {
1096             body = cx.expr_match(trait_.span,
1097                                  arg_expr.clone(),
1098                                  vec![cx.arm(trait_.span, vec![pat.clone()], body)])
1099         }
1100
1101         body
1102     }
1103
1104     fn expand_static_struct_method_body(&self,
1105                                         cx: &mut ExtCtxt,
1106                                         trait_: &TraitDef,
1107                                         struct_def: &VariantData,
1108                                         type_ident: Ident,
1109                                         self_args: &[P<Expr>],
1110                                         nonself_args: &[P<Expr>])
1111                                         -> P<Expr> {
1112         let summary = trait_.summarise_struct(cx, struct_def);
1113
1114         self.call_substructure_method(cx,
1115                                       trait_,
1116                                       type_ident,
1117                                       self_args,
1118                                       nonself_args,
1119                                       &StaticStruct(struct_def, summary))
1120     }
1121
1122     /// ```
1123     /// #[derive(PartialEq)]
1124     /// # struct Dummy;
1125     /// enum A {
1126     ///     A1,
1127     ///     A2(i32)
1128     /// }
1129     ///
1130     /// // is equivalent to
1131     ///
1132     /// impl PartialEq for A {
1133     ///     fn eq(&self, __arg_1: &A) -> ::bool {
1134     ///         match (&*self, &*__arg_1) {
1135     ///             (&A1, &A1) => true,
1136     ///             (&A2(ref self_0),
1137     ///              &A2(ref __arg_1_0)) => (*self_0).eq(&(*__arg_1_0)),
1138     ///             _ => {
1139     ///                 let __self_vi = match *self { A1(..) => 0, A2(..) => 1 };
1140     ///                 let __arg_1_vi = match *__arg_1 { A1(..) => 0, A2(..) => 1 };
1141     ///                 false
1142     ///             }
1143     ///         }
1144     ///     }
1145     /// }
1146     /// ```
1147     ///
1148     /// (Of course `__self_vi` and `__arg_1_vi` are unused for
1149     /// `PartialEq`, and those subcomputations will hopefully be removed
1150     /// as their results are unused.  The point of `__self_vi` and
1151     /// `__arg_1_vi` is for `PartialOrd`; see #15503.)
1152     fn expand_enum_method_body<'b>(&self,
1153                                    cx: &mut ExtCtxt,
1154                                    trait_: &TraitDef<'b>,
1155                                    enum_def: &'b EnumDef,
1156                                    type_attrs: &[ast::Attribute],
1157                                    type_ident: Ident,
1158                                    self_args: Vec<P<Expr>>,
1159                                    nonself_args: &[P<Expr>])
1160                                    -> P<Expr> {
1161         self.build_enum_match_tuple(cx,
1162                                     trait_,
1163                                     enum_def,
1164                                     type_attrs,
1165                                     type_ident,
1166                                     self_args,
1167                                     nonself_args)
1168     }
1169
1170
1171     /// Creates a match for a tuple of all `self_args`, where either all
1172     /// variants match, or it falls into a catch-all for when one variant
1173     /// does not match.
1174
1175     /// There are N + 1 cases because is a case for each of the N
1176     /// variants where all of the variants match, and one catch-all for
1177     /// when one does not match.
1178
1179     /// As an optimization we generate code which checks whether all variants
1180     /// match first which makes llvm see that C-like enums can be compiled into
1181     /// a simple equality check (for PartialEq).
1182
1183     /// The catch-all handler is provided access the variant index values
1184     /// for each of the self-args, carried in precomputed variables.
1185
1186     /// ```{.text}
1187     /// let __self0_vi = unsafe {
1188     ///     std::intrinsics::discriminant_value(&self) } as i32;
1189     /// let __self1_vi = unsafe {
1190     ///     std::intrinsics::discriminant_value(&arg1) } as i32;
1191     /// let __self2_vi = unsafe {
1192     ///     std::intrinsics::discriminant_value(&arg2) } as i32;
1193     ///
1194     /// if __self0_vi == __self1_vi && __self0_vi == __self2_vi && ... {
1195     ///     match (...) {
1196     ///         (Variant1, Variant1, ...) => Body1
1197     ///         (Variant2, Variant2, ...) => Body2,
1198     ///         ...
1199     ///         _ => ::core::intrinsics::unreachable()
1200     ///     }
1201     /// }
1202     /// else {
1203     ///     ... // catch-all remainder can inspect above variant index values.
1204     /// }
1205     /// ```
1206     fn build_enum_match_tuple<'b>(&self,
1207                                   cx: &mut ExtCtxt,
1208                                   trait_: &TraitDef<'b>,
1209                                   enum_def: &'b EnumDef,
1210                                   type_attrs: &[ast::Attribute],
1211                                   type_ident: Ident,
1212                                   self_args: Vec<P<Expr>>,
1213                                   nonself_args: &[P<Expr>])
1214                                   -> P<Expr> {
1215         let sp = trait_.span;
1216         let variants = &enum_def.variants;
1217
1218         let self_arg_names = self_args.iter()
1219             .enumerate()
1220             .map(|(arg_count, _self_arg)| {
1221                 if arg_count == 0 {
1222                     "__self".to_string()
1223                 } else {
1224                     format!("__arg_{}", arg_count)
1225                 }
1226             })
1227             .collect::<Vec<String>>();
1228
1229         let self_arg_idents = self_arg_names.iter()
1230             .map(|name| cx.ident_of(&name[..]))
1231             .collect::<Vec<ast::Ident>>();
1232
1233         // The `vi_idents` will be bound, solely in the catch-all, to
1234         // a series of let statements mapping each self_arg to an int
1235         // value corresponding to its discriminant.
1236         let vi_idents: Vec<ast::Ident> = self_arg_names.iter()
1237             .map(|name| {
1238                 let vi_suffix = format!("{}_vi", &name[..]);
1239                 cx.ident_of(&vi_suffix[..])
1240             })
1241             .collect::<Vec<ast::Ident>>();
1242
1243         // Builds, via callback to call_substructure_method, the
1244         // delegated expression that handles the catch-all case,
1245         // using `__variants_tuple` to drive logic if necessary.
1246         let catch_all_substructure =
1247             EnumNonMatchingCollapsed(self_arg_idents, &variants[..], &vi_idents[..]);
1248
1249         let first_fieldless = variants.iter().find(|v| v.node.data.fields().is_empty());
1250
1251         // These arms are of the form:
1252         // (Variant1, Variant1, ...) => Body1
1253         // (Variant2, Variant2, ...) => Body2
1254         // ...
1255         // where each tuple has length = self_args.len()
1256         let mut match_arms: Vec<ast::Arm> = variants.iter()
1257             .enumerate()
1258             .filter(|&(_, v)| !(self.unify_fieldless_variants && v.node.data.fields().is_empty()))
1259             .map(|(index, variant)| {
1260                 let mk_self_pat = |cx: &mut ExtCtxt, self_arg_name: &str| {
1261                     let (p, idents) = trait_.create_enum_variant_pattern(cx,
1262                                                      type_ident,
1263                                                      variant,
1264                                                      self_arg_name,
1265                                                      ast::Mutability::Immutable);
1266                     (cx.pat(sp, PatKind::Ref(p, ast::Mutability::Immutable)), idents)
1267                 };
1268
1269                 // A single arm has form (&VariantK, &VariantK, ...) => BodyK
1270                 // (see "Final wrinkle" note below for why.)
1271                 let mut subpats = Vec::with_capacity(self_arg_names.len());
1272                 let mut self_pats_idents = Vec::with_capacity(self_arg_names.len() - 1);
1273                 let first_self_pat_idents = {
1274                     let (p, idents) = mk_self_pat(cx, &self_arg_names[0]);
1275                     subpats.push(p);
1276                     idents
1277                 };
1278                 for self_arg_name in &self_arg_names[1..] {
1279                     let (p, idents) = mk_self_pat(cx, &self_arg_name[..]);
1280                     subpats.push(p);
1281                     self_pats_idents.push(idents);
1282                 }
1283
1284                 // Here is the pat = `(&VariantK, &VariantK, ...)`
1285                 let single_pat = cx.pat_tuple(sp, subpats);
1286
1287                 // For the BodyK, we need to delegate to our caller,
1288                 // passing it an EnumMatching to indicate which case
1289                 // we are in.
1290
1291                 // All of the Self args have the same variant in these
1292                 // cases.  So we transpose the info in self_pats_idents
1293                 // to gather the getter expressions together, in the
1294                 // form that EnumMatching expects.
1295
1296                 // The transposition is driven by walking across the
1297                 // arg fields of the variant for the first self pat.
1298                 let field_tuples = first_self_pat_idents.into_iter().enumerate()
1299                     // For each arg field of self, pull out its getter expr ...
1300                     .map(|(field_index, (sp, opt_ident, self_getter_expr, attrs))| {
1301                         // ... but FieldInfo also wants getter expr
1302                         // for matching other arguments of Self type;
1303                         // so walk across the *other* self_pats_idents
1304                         // and pull out getter for same field in each
1305                         // of them (using `field_index` tracked above).
1306                         // That is the heart of the transposition.
1307                         let others = self_pats_idents.iter().map(|fields| {
1308                             let (_, _opt_ident, ref other_getter_expr, _) =
1309                                 fields[field_index];
1310
1311                             // All Self args have same variant, so
1312                             // opt_idents are the same.  (Assert
1313                             // here to make it self-evident that
1314                             // it is okay to ignore `_opt_ident`.)
1315                             assert!(opt_ident == _opt_ident);
1316
1317                             other_getter_expr.clone()
1318                         }).collect::<Vec<P<Expr>>>();
1319
1320                         FieldInfo { span: sp,
1321                                     name: opt_ident,
1322                                     self_: self_getter_expr,
1323                                     other: others,
1324                                     attrs,
1325                         }
1326                     }).collect::<Vec<FieldInfo>>();
1327
1328                 // Now, for some given VariantK, we have built up
1329                 // expressions for referencing every field of every
1330                 // Self arg, assuming all are instances of VariantK.
1331                 // Build up code associated with such a case.
1332                 let substructure = EnumMatching(index, variants.len(), variant, field_tuples);
1333                 let arm_expr = self.call_substructure_method(cx,
1334                                                              trait_,
1335                                                              type_ident,
1336                                                              &self_args[..],
1337                                                              nonself_args,
1338                                                              &substructure);
1339
1340                 cx.arm(sp, vec![single_pat], arm_expr)
1341             })
1342             .collect();
1343
1344         let default = match first_fieldless {
1345             Some(v) if self.unify_fieldless_variants => {
1346                 // We need a default case that handles the fieldless variants.
1347                 // The index and actual variant aren't meaningful in this case,
1348                 // so just use whatever
1349                 let substructure = EnumMatching(0, variants.len(), v, Vec::new());
1350                 Some(self.call_substructure_method(cx,
1351                                                    trait_,
1352                                                    type_ident,
1353                                                    &self_args[..],
1354                                                    nonself_args,
1355                                                    &substructure))
1356             }
1357             _ if variants.len() > 1 && self_args.len() > 1 => {
1358                 // Since we know that all the arguments will match if we reach
1359                 // the match expression we add the unreachable intrinsics as the
1360                 // result of the catch all which should help llvm in optimizing it
1361                 Some(deriving::call_intrinsic(cx, sp, "unreachable", vec![]))
1362             }
1363             _ => None,
1364         };
1365         if let Some(arm) = default {
1366             match_arms.push(cx.arm(sp, vec![cx.pat_wild(sp)], arm));
1367         }
1368
1369         // We will usually need the catch-all after matching the
1370         // tuples `(VariantK, VariantK, ...)` for each VariantK of the
1371         // enum.  But:
1372         //
1373         // * when there is only one Self arg, the arms above suffice
1374         // (and the deriving we call back into may not be prepared to
1375         // handle EnumNonMatchCollapsed), and,
1376         //
1377         // * when the enum has only one variant, the single arm that
1378         // is already present always suffices.
1379         //
1380         // * In either of the two cases above, if we *did* add a
1381         //   catch-all `_` match, it would trigger the
1382         //   unreachable-pattern error.
1383         //
1384         if variants.len() > 1 && self_args.len() > 1 {
1385             // Build a series of let statements mapping each self_arg
1386             // to its discriminant value. If this is a C-style enum
1387             // with a specific repr type, then casts the values to
1388             // that type.  Otherwise casts to `i32` (the default repr
1389             // type).
1390             //
1391             // i.e. for `enum E<T> { A, B(1), C(T, T) }`, and a deriving
1392             // with three Self args, builds three statements:
1393             //
1394             // ```
1395             // let __self0_vi = unsafe {
1396             //     std::intrinsics::discriminant_value(&self) } as i32;
1397             // let __self1_vi = unsafe {
1398             //     std::intrinsics::discriminant_value(&arg1) } as i32;
1399             // let __self2_vi = unsafe {
1400             //     std::intrinsics::discriminant_value(&arg2) } as i32;
1401             // ```
1402             let mut index_let_stmts: Vec<ast::Stmt> = Vec::new();
1403
1404             // We also build an expression which checks whether all discriminants are equal
1405             // discriminant_test = __self0_vi == __self1_vi && __self0_vi == __self2_vi && ...
1406             let mut discriminant_test = cx.expr_bool(sp, true);
1407
1408             let target_type_name = find_repr_type_name(&cx.parse_sess.span_diagnostic, type_attrs);
1409
1410             let mut first_ident = None;
1411             for (&ident, self_arg) in vi_idents.iter().zip(&self_args) {
1412                 let self_addr = cx.expr_addr_of(sp, self_arg.clone());
1413                 let variant_value =
1414                     deriving::call_intrinsic(cx, sp, "discriminant_value", vec![self_addr]);
1415
1416                 let target_ty = cx.ty_ident(sp, cx.ident_of(target_type_name));
1417                 let variant_disr = cx.expr_cast(sp, variant_value, target_ty);
1418                 let let_stmt = cx.stmt_let(sp, false, ident, variant_disr);
1419                 index_let_stmts.push(let_stmt);
1420
1421                 match first_ident {
1422                     Some(first) => {
1423                         let first_expr = cx.expr_ident(sp, first);
1424                         let id = cx.expr_ident(sp, ident);
1425                         let test = cx.expr_binary(sp, BinOpKind::Eq, first_expr, id);
1426                         discriminant_test =
1427                             cx.expr_binary(sp, BinOpKind::And, discriminant_test, test)
1428                     }
1429                     None => {
1430                         first_ident = Some(ident);
1431                     }
1432                 }
1433             }
1434
1435             let arm_expr = self.call_substructure_method(cx,
1436                                                          trait_,
1437                                                          type_ident,
1438                                                          &self_args[..],
1439                                                          nonself_args,
1440                                                          &catch_all_substructure);
1441
1442             // Final wrinkle: the self_args are expressions that deref
1443             // down to desired places, but we cannot actually deref
1444             // them when they are fed as r-values into a tuple
1445             // expression; here add a layer of borrowing, turning
1446             // `(*self, *__arg_0, ...)` into `(&*self, &*__arg_0, ...)`.
1447             let borrowed_self_args = self_args.move_map(|self_arg| cx.expr_addr_of(sp, self_arg));
1448             let match_arg = cx.expr(sp, ast::ExprKind::Tup(borrowed_self_args));
1449
1450             // Lastly we create an expression which branches on all discriminants being equal
1451             //  if discriminant_test {
1452             //      match (...) {
1453             //          (Variant1, Variant1, ...) => Body1
1454             //          (Variant2, Variant2, ...) => Body2,
1455             //          ...
1456             //          _ => ::core::intrinsics::unreachable()
1457             //      }
1458             //  }
1459             //  else {
1460             //      <delegated expression referring to __self0_vi, et al.>
1461             //  }
1462             let all_match = cx.expr_match(sp, match_arg, match_arms);
1463             let arm_expr = cx.expr_if(sp, discriminant_test, all_match, Some(arm_expr));
1464             index_let_stmts.push(cx.stmt_expr(arm_expr));
1465             cx.expr_block(cx.block(sp, index_let_stmts))
1466         } else if variants.is_empty() {
1467             // As an additional wrinkle, For a zero-variant enum A,
1468             // currently the compiler
1469             // will accept `fn (a: &Self) { match   *a   { } }`
1470             // but rejects `fn (a: &Self) { match (&*a,) { } }`
1471             // as well as  `fn (a: &Self) { match ( *a,) { } }`
1472             //
1473             // This means that the strategy of building up a tuple of
1474             // all Self arguments fails when Self is a zero variant
1475             // enum: rustc rejects the expanded program, even though
1476             // the actual code tends to be impossible to execute (at
1477             // least safely), according to the type system.
1478             //
1479             // The most expedient fix for this is to just let the
1480             // code fall through to the catch-all.  But even this is
1481             // error-prone, since the catch-all as defined above would
1482             // generate code like this:
1483             //
1484             //     _ => { let __self0 = match *self { };
1485             //            let __self1 = match *__arg_0 { };
1486             //            <catch-all-expr> }
1487             //
1488             // Which is yields bindings for variables which type
1489             // inference cannot resolve to unique types.
1490             //
1491             // One option to the above might be to add explicit type
1492             // annotations.  But the *only* reason to go down that path
1493             // would be to try to make the expanded output consistent
1494             // with the case when the number of enum variants >= 1.
1495             //
1496             // That just isn't worth it.  In fact, trying to generate
1497             // sensible code for *any* deriving on a zero-variant enum
1498             // does not make sense.  But at the same time, for now, we
1499             // do not want to cause a compile failure just because the
1500             // user happened to attach a deriving to their
1501             // zero-variant enum.
1502             //
1503             // Instead, just generate a failing expression for the
1504             // zero variant case, skipping matches and also skipping
1505             // delegating back to the end user code entirely.
1506             //
1507             // (See also #4499 and #12609; note that some of the
1508             // discussions there influence what choice we make here;
1509             // e.g. if we feature-gate `match x { ... }` when x refers
1510             // to an uninhabited type (e.g. a zero-variant enum or a
1511             // type holding such an enum), but do not feature-gate
1512             // zero-variant enums themselves, then attempting to
1513             // derive Debug on such a type could here generate code
1514             // that needs the feature gate enabled.)
1515
1516             deriving::call_intrinsic(cx, sp, "unreachable", vec![])
1517         } else {
1518
1519             // Final wrinkle: the self_args are expressions that deref
1520             // down to desired places, but we cannot actually deref
1521             // them when they are fed as r-values into a tuple
1522             // expression; here add a layer of borrowing, turning
1523             // `(*self, *__arg_0, ...)` into `(&*self, &*__arg_0, ...)`.
1524             let borrowed_self_args = self_args.move_map(|self_arg| cx.expr_addr_of(sp, self_arg));
1525             let match_arg = cx.expr(sp, ast::ExprKind::Tup(borrowed_self_args));
1526             cx.expr_match(sp, match_arg, match_arms)
1527         }
1528     }
1529
1530     fn expand_static_enum_method_body(&self,
1531                                       cx: &mut ExtCtxt,
1532                                       trait_: &TraitDef,
1533                                       enum_def: &EnumDef,
1534                                       type_ident: Ident,
1535                                       self_args: &[P<Expr>],
1536                                       nonself_args: &[P<Expr>])
1537                                       -> P<Expr> {
1538         let summary = enum_def.variants
1539             .iter()
1540             .map(|v| {
1541                 let sp = v.span.with_ctxt(trait_.span.ctxt());
1542                 let summary = trait_.summarise_struct(cx, &v.node.data);
1543                 (v.node.ident, sp, summary)
1544             })
1545             .collect();
1546         self.call_substructure_method(cx,
1547                                       trait_,
1548                                       type_ident,
1549                                       self_args,
1550                                       nonself_args,
1551                                       &StaticEnum(enum_def, summary))
1552     }
1553 }
1554
1555 // general helper methods.
1556 impl<'a> TraitDef<'a> {
1557     fn summarise_struct(&self, cx: &mut ExtCtxt, struct_def: &VariantData) -> StaticFields {
1558         let mut named_idents = Vec::new();
1559         let mut just_spans = Vec::new();
1560         for field in struct_def.fields() {
1561             let sp = field.span.with_ctxt(self.span.ctxt());
1562             match field.ident {
1563                 Some(ident) => named_idents.push((ident, sp)),
1564                 _ => just_spans.push(sp),
1565             }
1566         }
1567
1568         match (just_spans.is_empty(), named_idents.is_empty()) {
1569             (false, false) => {
1570                 cx.span_bug(self.span,
1571                             "a struct with named and unnamed \
1572                                           fields in generic `derive`")
1573             }
1574             // named fields
1575             (_, false) => Named(named_idents),
1576             // empty structs
1577             _ if struct_def.is_struct() => Named(named_idents),
1578             _ => Unnamed(just_spans, struct_def.is_tuple()),
1579         }
1580     }
1581
1582     fn create_subpatterns(&self,
1583                           cx: &mut ExtCtxt,
1584                           field_paths: Vec<ast::Ident>,
1585                           mutbl: ast::Mutability,
1586                           use_temporaries: bool)
1587                           -> Vec<P<ast::Pat>> {
1588         field_paths.iter()
1589             .map(|path| {
1590                 let binding_mode = if use_temporaries {
1591                     ast::BindingMode::ByValue(ast::Mutability::Immutable)
1592                 } else {
1593                     ast::BindingMode::ByRef(mutbl)
1594                 };
1595                 cx.pat(path.span,
1596                        PatKind::Ident(binding_mode, (*path).clone(), None))
1597             })
1598             .collect()
1599     }
1600
1601     fn create_struct_pattern
1602         (&self,
1603          cx: &mut ExtCtxt,
1604          struct_path: ast::Path,
1605          struct_def: &'a VariantData,
1606          prefix: &str,
1607          mutbl: ast::Mutability,
1608          use_temporaries: bool)
1609          -> (P<ast::Pat>, Vec<(Span, Option<Ident>, P<Expr>, &'a [ast::Attribute])>)
1610     {
1611         let mut paths = Vec::new();
1612         let mut ident_exprs = Vec::new();
1613         for (i, struct_field) in struct_def.fields().iter().enumerate() {
1614             let sp = struct_field.span.with_ctxt(self.span.ctxt());
1615             let ident = cx.ident_of(&format!("{}_{}", prefix, i));
1616             paths.push(ident.with_span_pos(sp));
1617             let val = cx.expr_path(cx.path_ident(sp, ident));
1618             let val = if use_temporaries {
1619                 val
1620             } else {
1621                 cx.expr_deref(sp, val)
1622             };
1623             let val = cx.expr(sp, ast::ExprKind::Paren(val));
1624
1625             ident_exprs.push((sp, struct_field.ident, val, &struct_field.attrs[..]));
1626         }
1627
1628         let subpats = self.create_subpatterns(cx, paths, mutbl, use_temporaries);
1629         let pattern = match *struct_def {
1630             VariantData::Struct(..) => {
1631                 let field_pats = subpats.into_iter()
1632                     .zip(&ident_exprs)
1633                     .map(|(pat, &(sp, ident, ..))| {
1634                         if ident.is_none() {
1635                             cx.span_bug(sp, "a braced struct with unnamed fields in `derive`");
1636                         }
1637                         codemap::Spanned {
1638                             span: pat.span.with_ctxt(self.span.ctxt()),
1639                             node: ast::FieldPat {
1640                                 ident: ident.unwrap(),
1641                                 pat,
1642                                 is_shorthand: false,
1643                                 attrs: ast::ThinVec::new(),
1644                             },
1645                         }
1646                     })
1647                     .collect();
1648                 cx.pat_struct(self.span, struct_path, field_pats)
1649             }
1650             VariantData::Tuple(..) => {
1651                 cx.pat_tuple_struct(self.span, struct_path, subpats)
1652             }
1653             VariantData::Unit(..) => {
1654                 cx.pat_path(self.span, struct_path)
1655             }
1656         };
1657
1658         (pattern, ident_exprs)
1659     }
1660
1661     fn create_enum_variant_pattern
1662         (&self,
1663          cx: &mut ExtCtxt,
1664          enum_ident: ast::Ident,
1665          variant: &'a ast::Variant,
1666          prefix: &str,
1667          mutbl: ast::Mutability)
1668          -> (P<ast::Pat>, Vec<(Span, Option<Ident>, P<Expr>, &'a [ast::Attribute])>) {
1669         let sp = variant.span.with_ctxt(self.span.ctxt());
1670         let variant_path = cx.path(sp, vec![enum_ident, variant.node.ident]);
1671         let use_temporaries = false; // enums can't be repr(packed)
1672         self.create_struct_pattern(cx, variant_path, &variant.node.data, prefix, mutbl,
1673                                    use_temporaries)
1674     }
1675 }
1676
1677 // helpful premade recipes
1678
1679 /// Fold the fields. `use_foldl` controls whether this is done
1680 /// left-to-right (`true`) or right-to-left (`false`).
1681 pub fn cs_fold<F>(use_foldl: bool,
1682                   mut f: F,
1683                   base: P<Expr>,
1684                   mut enum_nonmatch_f: EnumNonMatchCollapsedFunc,
1685                   cx: &mut ExtCtxt,
1686                   trait_span: Span,
1687                   substructure: &Substructure)
1688                   -> P<Expr>
1689     where F: FnMut(&mut ExtCtxt, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>
1690 {
1691     match *substructure.fields {
1692         EnumMatching(.., ref all_fields) |
1693         Struct(_, ref all_fields) => {
1694             if use_foldl {
1695                 all_fields.iter().fold(base, |old, field| {
1696                     f(cx, field.span, old, field.self_.clone(), &field.other)
1697                 })
1698             } else {
1699                 all_fields.iter().rev().fold(base, |old, field| {
1700                     f(cx, field.span, old, field.self_.clone(), &field.other)
1701                 })
1702             }
1703         }
1704         EnumNonMatchingCollapsed(ref all_args, _, tuple) => {
1705             enum_nonmatch_f(cx,
1706                             trait_span,
1707                             (&all_args[..], tuple),
1708                             substructure.nonself_args)
1709         }
1710         StaticEnum(..) | StaticStruct(..) => cx.span_bug(trait_span, "static function in `derive`"),
1711     }
1712 }
1713
1714
1715 /// Call the method that is being derived on all the fields, and then
1716 /// process the collected results. i.e.
1717 ///
1718 /// ```ignore (only-for-syntax-highlight)
1719 /// f(cx, span, vec![self_1.method(__arg_1_1, __arg_2_1),
1720 ///                  self_2.method(__arg_1_2, __arg_2_2)])
1721 /// ```
1722 #[inline]
1723 pub fn cs_same_method<F>(f: F,
1724                          mut enum_nonmatch_f: EnumNonMatchCollapsedFunc,
1725                          cx: &mut ExtCtxt,
1726                          trait_span: Span,
1727                          substructure: &Substructure)
1728                          -> P<Expr>
1729     where F: FnOnce(&mut ExtCtxt, Span, Vec<P<Expr>>) -> P<Expr>
1730 {
1731     match *substructure.fields {
1732         EnumMatching(.., ref all_fields) |
1733         Struct(_, ref all_fields) => {
1734             // call self_n.method(other_1_n, other_2_n, ...)
1735             let called = all_fields.iter()
1736                 .map(|field| {
1737                     cx.expr_method_call(field.span,
1738                                         field.self_.clone(),
1739                                         substructure.method_ident,
1740                                         field.other
1741                                             .iter()
1742                                             .map(|e| cx.expr_addr_of(field.span, e.clone()))
1743                                             .collect())
1744                 })
1745                 .collect();
1746
1747             f(cx, trait_span, called)
1748         }
1749         EnumNonMatchingCollapsed(ref all_self_args, _, tuple) => {
1750             enum_nonmatch_f(cx,
1751                             trait_span,
1752                             (&all_self_args[..], tuple),
1753                             substructure.nonself_args)
1754         }
1755         StaticEnum(..) | StaticStruct(..) => cx.span_bug(trait_span, "static function in `derive`"),
1756     }
1757 }
1758
1759 /// Return true if the type has no value fields
1760 /// (for an enum, no variant has any fields)
1761 pub fn is_type_without_fields(item: &Annotatable) -> bool {
1762     if let Annotatable::Item(ref item) = *item {
1763         match item.node {
1764             ast::ItemKind::Enum(ref enum_def, _) => {
1765                 enum_def.variants.iter().all(|v| v.node.data.fields().is_empty())
1766             }
1767             ast::ItemKind::Struct(ref variant_data, _) => variant_data.fields().is_empty(),
1768             _ => false,
1769         }
1770     } else {
1771         false
1772     }
1773 }