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 use syntax::attr;
 199 use syntax::ext::base::{Annotatable, ExtCtxt};
 200 use syntax::ext::build::AstBuilder;
 201 use syntax::codemap::{self, dummy_spanned, respan};
 202 use syntax::util::move_map::MoveMap;
 203 use syntax::ptr::P;
 204 use syntax::symbol::{Symbol, keywords};
 205 use syntax_pos::{DUMMY_SP, Span};
 206 use errors::Handler;
 207
 208 use self::ty::{LifetimeBounds, Path, Ptr, PtrTy, Self_, Ty};
 209
 210 use deriving;
 211
 212 pub mod ty;
 213
 214 pub struct TraitDef<'a> {
 215     /// The span for the current #[derive(Foo)] header.
 216     pub span: Span,
 217
 218     pub attributes: Vec<ast::Attribute>,
 219
 220     /// Path of the trait, including any type parameters
 221     pub path: Path<'a>,
 222
 223     /// Additional bounds required of any type parameters of the type,
 224     /// other than the current trait
 225     pub additional_bounds: Vec<Ty<'a>>,
 226
 227     /// Any extra lifetimes and/or bounds, e.g. `D: serialize::Decoder`
 228     pub generics: LifetimeBounds<'a>,
 229
 230     /// Is it an `unsafe` trait?
 231     pub is_unsafe: bool,
 232
 233     /// Can this trait be derived for unions?
 234     pub supports_unions: bool,
 235
 236     pub methods: Vec<MethodDef<'a>>,
 237
 238     pub associated_types: Vec<(ast::Ident, Ty<'a>)>,
 239 }
 240
 241
 242 pub struct MethodDef<'a> {
 243     /// name of the method
 244     pub name: &'a str,
 245     /// List of generics, e.g. `R: rand::Rng`
 246     pub generics: LifetimeBounds<'a>,
 247
 248     /// Whether there is a self argument (outer Option) i.e. whether
 249     /// this is a static function, and whether it is a pointer (inner
 250     /// Option)
 251     pub explicit_self: Option<Option<PtrTy<'a>>>,
 252
 253     /// Arguments other than the self argument
 254     pub args: Vec<Ty<'a>>,
 255
 256     /// Return type
 257     pub ret_ty: Ty<'a>,
 258
 259     pub attributes: Vec<ast::Attribute>,
 260
 261     // Is it an `unsafe fn`?
 262     pub is_unsafe: bool,
 263
 264     /// Can we combine fieldless variants for enums into a single match arm?
 265     pub unify_fieldless_variants: bool,
 266
 267     pub combine_substructure: RefCell<CombineSubstructureFunc<'a>>,
 268 }
 269
 270 /// All the data about the data structure/method being derived upon.
 271 pub struct Substructure<'a> {
 272     /// ident of self
 273     pub type_ident: Ident,
 274     /// ident of the method
 275     pub method_ident: Ident,
 276     /// dereferenced access to any `Self_` or `Ptr(Self_, _)` arguments
 277     pub self_args: &'a [P<Expr>],
 278     /// verbatim access to any other arguments
 279     pub nonself_args: &'a [P<Expr>],
 280     pub fields: &'a SubstructureFields<'a>,
 281 }
 282
 283 /// Summary of the relevant parts of a struct/enum field.
 284 pub struct FieldInfo<'a> {
 285     pub span: Span,
 286     /// None for tuple structs/normal enum variants, Some for normal
 287     /// structs/struct enum variants.
 288     pub name: Option<Ident>,
 289     /// The expression corresponding to this field of `self`
 290     /// (specifically, a reference to it).
 291     pub self_: P<Expr>,
 292     /// The expressions corresponding to references to this field in
 293     /// the other `Self` arguments.
 294     pub other: Vec<P<Expr>>,
 295     /// The attributes on the field
 296     pub attrs: &'a [ast::Attribute],
 297 }
 298
 299 /// Fields for a static method
 300 pub enum StaticFields {
 301     /// Tuple and unit structs/enum variants like this.
 302     Unnamed(Vec<Span>, bool /*is tuple*/),
 303     /// Normal structs/struct variants.
 304     Named(Vec<(Ident, Span)>),
 305 }
 306
 307 /// A summary of the possible sets of fields.
 308 pub enum SubstructureFields<'a> {
 309     Struct(&'a ast::VariantData, Vec<FieldInfo<'a>>),
 310     /// Matching variants of the enum: variant index, variant count, ast::Variant,
 311     /// fields: the field name is only non-`None` in the case of a struct
 312     /// variant.
 313     EnumMatching(usize, usize, &'a ast::Variant, Vec<FieldInfo<'a>>),
 314
 315     /// Non-matching variants of the enum, but with all state hidden from
 316     /// the consequent code.  The first component holds `Ident`s for all of
 317     /// the `Self` arguments; the second component is a slice of all of the
 318     /// variants for the enum itself, and the third component is a list of
 319     /// `Ident`s bound to the variant index values for each of the actual
 320     /// input `Self` arguments.
 321     EnumNonMatchingCollapsed(Vec<Ident>, &'a [ast::Variant], &'a [Ident]),
 322
 323     /// A static method where `Self` is a struct.
 324     StaticStruct(&'a ast::VariantData, StaticFields),
 325     /// A static method where `Self` is an enum.
 326     StaticEnum(&'a ast::EnumDef, Vec<(Ident, Span, StaticFields)>),
 327 }
 328
 329
 330
 331 /// Combine the values of all the fields together. The last argument is
 332 /// all the fields of all the structures.
 333 pub type CombineSubstructureFunc<'a> =
 334     Box<FnMut(&mut ExtCtxt, Span, &Substructure) -> P<Expr> + 'a>;
 335
 336 /// Deal with non-matching enum variants.  The tuple is a list of
 337 /// identifiers (one for each `Self` argument, which could be any of the
 338 /// variants since they have been collapsed together) and the identifiers
 339 /// holding the variant index value for each of the `Self` arguments.  The
 340 /// last argument is all the non-`Self` args of the method being derived.
 341 pub type EnumNonMatchCollapsedFunc<'a> =
 342     Box<FnMut(&mut ExtCtxt, Span, (&[Ident], &[Ident]), &[P<Expr>]) -> P<Expr> + 'a>;
 343
 344 pub fn combine_substructure<'a>(f: CombineSubstructureFunc<'a>)
 345                                 -> RefCell<CombineSubstructureFunc<'a>> {
 346     RefCell::new(f)
 347 }
 348
 349 /// This method helps to extract all the type parameters referenced from a
 350 /// type. For a type parameter `<T>`, it looks for either a `TyPath` that
 351 /// is not global and starts with `T`, or a `TyQPath`.
 352 fn find_type_parameters(ty: &ast::Ty,
 353                         ty_param_names: &[ast::Name],
 354                         span: Span,
 355                         cx: &ExtCtxt)
 356                         -> Vec<P<ast::Ty>> {
 357     use syntax::visit;
 358
 359     struct Visitor<'a, 'b: 'a> {
 360         cx: &'a ExtCtxt<'b>,
 361         span: Span,
 362         ty_param_names: &'a [ast::Name],
 363         types: Vec<P<ast::Ty>>,
 364     }
 365
 366     impl<'a, 'b> visit::Visitor<'a> for Visitor<'a, 'b> {
 367         fn visit_ty(&mut self, ty: &'a ast::Ty) {
 368             if let ast::TyKind::Path(_, ref path) = ty.node {
 369                 if let Some(segment) = path.segments.first() {
 370                     if self.ty_param_names.contains(&segment.identifier.name) {
 371                         self.types.push(P(ty.clone()));
 372                     }
 373                 }
 374             }
 375
 376             visit::walk_ty(self, ty)
 377         }
 378
 379         fn visit_mac(&mut self, mac: &ast::Mac) {
 380             let span = mac.span.with_ctxt(self.span.ctxt());
 381             self.cx.span_err(span, "`derive` cannot be used on items with type macros");
 382         }
 383     }
 384
 385     let mut visitor = Visitor {
 386         ty_param_names,
 387         types: Vec::new(),
 388         span,
 389         cx,
 390     };
 391
 392     visit::Visitor::visit_ty(&mut visitor, ty);
 393
 394     visitor.types
 395 }
 396
 397 impl<'a> TraitDef<'a> {
 398     pub fn expand(self,
 399                   cx: &mut ExtCtxt,
 400                   mitem: &ast::MetaItem,
 401                   item: &'a Annotatable,
 402                   push: &mut FnMut(Annotatable)) {
 403         self.expand_ext(cx, mitem, item, push, false);
 404     }
 405
 406     pub fn expand_ext(self,
 407                       cx: &mut ExtCtxt,
 408                       mitem: &ast::MetaItem,
 409                       item: &'a Annotatable,
 410                       push: &mut FnMut(Annotatable),
 411                       from_scratch: bool) {
 412         match *item {
 413             Annotatable::Item(ref item) => {
 414                 let is_packed = item.attrs.iter().any(|attr| {
 415                     attr::find_repr_attrs(&cx.parse_sess.span_diagnostic, attr)
 416                         .contains(&attr::ReprPacked)
 417                 });
 418                 let has_no_type_params = match item.node {
 419                     ast::ItemKind::Struct(_, ref generics) |
 420                     ast::ItemKind::Enum(_, ref generics) |
 421                     ast::ItemKind::Union(_, ref generics) => {
 422                         !generics.params.iter().any(|p| p.is_type_param())
 423                     }
 424                     _ => {
 425                         // Non-ADT derive is an error, but it should have been
 426                         // set earlier; see
 427                         // libsyntax/ext/expand.rs:MacroExpander::expand()
 428                         return;
 429                     }
 430                 };
 431                 let is_always_copy =
 432                     attr::contains_name(&item.attrs, "rustc_copy_clone_marker") &&
 433                     has_no_type_params;
 434                 let use_temporaries = is_packed && is_always_copy;
 435
 436                 let newitem = match item.node {
 437                     ast::ItemKind::Struct(ref struct_def, ref generics) => {
 438                         self.expand_struct_def(cx, &struct_def, item.ident, generics, from_scratch,
 439                                                use_temporaries)
 440                     }
 441                     ast::ItemKind::Enum(ref enum_def, ref generics) => {
 442                         // We ignore `use_temporaries` here, because
 443                         // `repr(packed)` enums cause an error later on.
 444                         //
 445                         // This can only cause further compilation errors
 446                         // downstream in blatantly illegal code, so it
 447                         // is fine.
 448                         self.expand_enum_def(cx, enum_def, &item.attrs,
 449                                              item.ident, generics, from_scratch)
 450                     }
 451                     ast::ItemKind::Union(ref struct_def, ref generics) => {
 452                         if self.supports_unions {
 453                             self.expand_struct_def(cx, &struct_def, item.ident,
 454                                                    generics, from_scratch,
 455                                                    use_temporaries)
 456                         } else {
 457                             cx.span_err(mitem.span,
 458                                         "this trait cannot be derived for unions");
 459                             return;
 460                         }
 461                     }
 462                     _ => unreachable!(),
 463                 };
 464                 // Keep the lint attributes of the previous item to control how the
 465                 // generated implementations are linted
 466                 let mut attrs = newitem.attrs.clone();
 467                 attrs.extend(item.attrs
 468                     .iter()
 469                     .filter(|a| {
 470                         a.name().is_some() && match &*a.name().unwrap().as_str() {
 471                             "allow" | "warn" | "deny" | "forbid" | "stable" | "unstable" => true,
 472                             _ => false,
 473                         }
 474                     })
 475                     .cloned());
 476                 push(Annotatable::Item(P(ast::Item { attrs: attrs, ..(*newitem).clone() })))
 477             }
 478             _ => {
 479                 // Non-Item derive is an error, but it should have been
 480                 // set earlier; see
 481                 // libsyntax/ext/expand.rs:MacroExpander::expand()
 482                 return;
 483             }
 484         }
 485     }
 486
 487     /// Given that we are deriving a trait `DerivedTrait` for a type like:
 488     ///
 489     /// ```ignore (only-for-syntax-highlight)
 490     /// struct Struct<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z> where C: WhereTrait {
 491     ///     a: A,
 492     ///     b: B::Item,
 493     ///     b1: <B as DeclaredTrait>::Item,
 494     ///     c1: <C as WhereTrait>::Item,
 495     ///     c2: Option<<C as WhereTrait>::Item>,
 496     ///     ...
 497     /// }
 498     /// ```
 499     ///
 500     /// create an impl like:
 501     ///
 502     /// ```ignore (only-for-syntax-highlight)
 503     /// impl<'a, ..., 'z, A, B: DeclaredTrait, C, ...  Z> where
 504     ///     C:                       WhereTrait,
 505     ///     A: DerivedTrait + B1 + ... + BN,
 506     ///     B: DerivedTrait + B1 + ... + BN,
 507     ///     C: DerivedTrait + B1 + ... + BN,
 508     ///     B::Item:                 DerivedTrait + B1 + ... + BN,
 509     ///     <C as WhereTrait>::Item: DerivedTrait + B1 + ... + BN,
 510     ///     ...
 511     /// {
 512     ///     ...
 513     /// }
 514     /// ```
 515     ///
 516     /// where B1, ..., BN are the bounds given by `bounds_paths`.'. Z is a phantom type, and
 517     /// therefore does not get bound by the derived trait.
 518     fn create_derived_impl(&self,
 519                            cx: &mut ExtCtxt,
 520                            type_ident: Ident,
 521                            generics: &Generics,
 522                            field_tys: Vec<P<ast::Ty>>,
 523                            methods: Vec<ast::ImplItem>)
 524                            -> P<ast::Item> {
 525         let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
 526
 527         // Transform associated types from `deriving::ty::Ty` into `ast::ImplItem`
 528         let associated_types = self.associated_types.iter().map(|&(ident, ref type_def)| {
 529             ast::ImplItem {
 530                 id: ast::DUMMY_NODE_ID,
 531                 span: self.span,
 532                 ident,
 533                 vis: respan(self.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
 534                 defaultness: ast::Defaultness::Final,
 535                 attrs: Vec::new(),
 536                 generics: Generics::default(),
 537                 node: ast::ImplItemKind::Type(type_def.to_ty(cx, self.span, type_ident, generics)),
 538                 tokens: None,
 539             }
 540         });
 541
 542         let Generics { mut params, mut where_clause, span } = self.generics
 543             .to_generics(cx, self.span, type_ident, generics);
 544
 545         // Create the generic parameters
 546         params.extend(generics.params.iter().map(|param| {
 547             match *param {
 548                 ref l @ GenericParam::Lifetime(_) => l.clone(),
 549                 GenericParam::Type(ref ty_param) => {
 550                     // I don't think this can be moved out of the loop, since
 551                     // a TyParamBound requires an ast id
 552                     let mut bounds: Vec<_> =
 553                         // extra restrictions on the generics parameters to the
 554                         // type being derived upon
 555                         self.additional_bounds.iter().map(|p| {
 556                             cx.typarambound(p.to_path(cx, self.span,
 557                                                         type_ident, generics))
 558                         }).collect();
 559
 560                     // require the current trait
 561                     bounds.push(cx.typarambound(trait_path.clone()));
 562
 563                     // also add in any bounds from the declaration
 564                     for declared_bound in ty_param.bounds.iter() {
 565                         bounds.push((*declared_bound).clone());
 566                     }
 567
 568                     GenericParam::Type(cx.typaram(self.span, ty_param.ident, vec![], bounds, None))
 569                 }
 570             }
 571         }));
 572
 573         // and similarly for where clauses
 574         where_clause.predicates.extend(generics.where_clause.predicates.iter().map(|clause| {
 575             match *clause {
 576                 ast::WherePredicate::BoundPredicate(ref wb) => {
 577                     ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 578                         span: self.span,
 579                         bound_generic_params: wb.bound_generic_params.clone(),
 580                         bounded_ty: wb.bounded_ty.clone(),
 581                         bounds: wb.bounds.iter().cloned().collect(),
 582                     })
 583                 }
 584                 ast::WherePredicate::RegionPredicate(ref rb) => {
 585                     ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 586                         span: self.span,
 587                         lifetime: rb.lifetime,
 588                         bounds: rb.bounds.iter().cloned().collect(),
 589                     })
 590                 }
 591                 ast::WherePredicate::EqPredicate(ref we) => {
 592                     ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 593                         id: ast::DUMMY_NODE_ID,
 594                         span: self.span,
 595                         lhs_ty: we.lhs_ty.clone(),
 596                         rhs_ty: we.rhs_ty.clone(),
 597                     })
 598                 }
 599             }
 600         }));
 601
 602         {
 603             // Extra scope required here so ty_params goes out of scope before params is moved
 604
 605             let mut ty_params = params.iter()
 606                 .filter_map(|param| match *param {
 607                     ast::GenericParam::Type(ref t) => Some(t),
 608                     _ => None,
 609                 })
 610                 .peekable();
 611
 612             if ty_params.peek().is_some() {
 613                 let ty_param_names: Vec<ast::Name> = ty_params
 614                     .map(|ty_param| ty_param.ident.name)
 615                     .collect();
 616
 617                 let mut processed_field_types = HashSet::new();
 618                 for field_ty in field_tys {
 619                     let tys = find_type_parameters(&field_ty, &ty_param_names, self.span, cx);
 620
 621                     for ty in tys {
 622                         // if we have already handled this type, skip it
 623                         if let ast::TyKind::Path(_, ref p) = ty.node {
 624                             if p.segments.len() == 1 &&
 625                             ty_param_names.contains(&p.segments[0].identifier.name) ||
 626                             processed_field_types.contains(&p.segments) {
 627                                 continue;
 628                             };
 629                             processed_field_types.insert(p.segments.clone());
 630                         }
 631                         let mut bounds: Vec<_> = self.additional_bounds
 632                             .iter()
 633                             .map(|p| {
 634                                 cx.typarambound(p.to_path(cx, self.span, type_ident, generics))
 635                             })
 636                             .collect();
 637
 638                         // require the current trait
 639                         bounds.push(cx.typarambound(trait_path.clone()));
 640
 641                         let predicate = ast::WhereBoundPredicate {
 642                             span: self.span,
 643                             bound_generic_params: Vec::new(),
 644                             bounded_ty: ty,
 645                             bounds,
 646                         };
 647
 648                         let predicate = ast::WherePredicate::BoundPredicate(predicate);
 649                         where_clause.predicates.push(predicate);
 650                     }
 651                 }
 652             }
 653         }
 654
 655         let trait_generics = Generics {
 656             params,
 657             where_clause,
 658             span,
 659         };
 660
 661         // Create the reference to the trait.
 662         let trait_ref = cx.trait_ref(trait_path);
 663
 664         // Create the type parameters on the `self` path.
 665         let self_ty_params = generics.params
 666             .iter()
 667             .filter_map(|param| match *param {
 668                 GenericParam::Type(ref ty_param)
 669                     => Some(cx.ty_ident(self.span, ty_param.ident)),
 670                 _ => None,
 671             })
 672             .collect();
 673
 674         let self_lifetimes: Vec<ast::Lifetime> = generics.params
 675             .iter()
 676             .filter_map(|param| match *param {
 677                 GenericParam::Lifetime(ref ld) => Some(ld.lifetime),
 678                 _ => None,
 679             })
 680             .collect();
 681
 682         // Create the type of `self`.
 683         let self_type = cx.ty_path(cx.path_all(self.span,
 684                                                false,
 685                                                vec![type_ident],
 686                                                self_lifetimes,
 687                                                self_ty_params,
 688                                                Vec::new()));
 689
 690         let attr = cx.attribute(self.span,
 691                                 cx.meta_word(self.span,
 692                                              Symbol::intern("automatically_derived")));
 693         // Just mark it now since we know that it'll end up used downstream
 694         attr::mark_used(&attr);
 695         let opt_trait_ref = Some(trait_ref);
 696         let unused_qual = {
 697             let word = cx.meta_list_item_word(self.span, Symbol::intern("unused_qualifications"));
 698             cx.attribute(self.span, cx.meta_list(self.span, Symbol::intern("allow"), vec![word]))
 699         };
 700
 701         let mut a = vec![attr, unused_qual];
 702         a.extend(self.attributes.iter().cloned());
 703
 704         let unsafety = if self.is_unsafe {
 705             ast::Unsafety::Unsafe
 706         } else {
 707             ast::Unsafety::Normal
 708         };
 709
 710         cx.item(self.span,
 711                 keywords::Invalid.ident(),
 712                 a,
 713                 ast::ItemKind::Impl(unsafety,
 714                                     ast::ImplPolarity::Positive,
 715                                     ast::Defaultness::Final,
 716                                     trait_generics,
 717                                     opt_trait_ref,
 718                                     self_type,
 719                                     methods.into_iter().chain(associated_types).collect()))
 720     }
 721
 722     fn expand_struct_def(&self,
 723                          cx: &mut ExtCtxt,
 724                          struct_def: &'a VariantData,
 725                          type_ident: Ident,
 726                          generics: &Generics,
 727                          from_scratch: bool,
 728                          use_temporaries: bool)
 729                          -> P<ast::Item> {
 730         let field_tys: Vec<P<ast::Ty>> = struct_def.fields()
 731             .iter()
 732             .map(|field| field.ty.clone())
 733             .collect();
 734
 735         let methods = self.methods
 736             .iter()
 737             .map(|method_def| {
 738                 let (explicit_self, self_args, nonself_args, tys) =
 739                     method_def.split_self_nonself_args(cx, self, type_ident, generics);
 740
 741                 let body = if from_scratch || method_def.is_static() {
 742                     method_def.expand_static_struct_method_body(cx,
 743                                                                 self,
 744                                                                 struct_def,
 745                                                                 type_ident,
 746                                                                 &self_args[..],
 747                                                                 &nonself_args[..])
 748                 } else {
 749                     method_def.expand_struct_method_body(cx,
 750                                                          self,
 751                                                          struct_def,
 752                                                          type_ident,
 753                                                          &self_args[..],
 754                                                          &nonself_args[..],
 755                                                          use_temporaries)
 756                 };
 757
 758                 method_def.create_method(cx,
 759                                          self,
 760                                          type_ident,
 761                                          generics,
 762                                          Abi::Rust,
 763                                          explicit_self,
 764                                          tys,
 765                                          body)
 766             })
 767             .collect();
 768
 769         self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
 770     }
 771
 772     fn expand_enum_def(&self,
 773                        cx: &mut ExtCtxt,
 774                        enum_def: &'a EnumDef,
 775                        type_attrs: &[ast::Attribute],
 776                        type_ident: Ident,
 777                        generics: &Generics,
 778                        from_scratch: bool)
 779                        -> P<ast::Item> {
 780         let mut field_tys = Vec::new();
 781
 782         for variant in &enum_def.variants {
 783             field_tys.extend(variant.node
 784                 .data
 785                 .fields()
 786                 .iter()
 787                 .map(|field| field.ty.clone()));
 788         }
 789
 790         let methods = self.methods
 791             .iter()
 792             .map(|method_def| {
 793                 let (explicit_self, self_args, nonself_args, tys) =
 794                     method_def.split_self_nonself_args(cx, self, type_ident, generics);
 795
 796                 let body = if from_scratch || method_def.is_static() {
 797                     method_def.expand_static_enum_method_body(cx,
 798                                                               self,
 799                                                               enum_def,
 800                                                               type_ident,
 801                                                               &self_args[..],
 802                                                               &nonself_args[..])
 803                 } else {
 804                     method_def.expand_enum_method_body(cx,
 805                                                        self,
 806                                                        enum_def,
 807                                                        type_attrs,
 808                                                        type_ident,
 809                                                        self_args,
 810                                                        &nonself_args[..])
 811                 };
 812
 813                 method_def.create_method(cx,
 814                                          self,
 815                                          type_ident,
 816                                          generics,
 817                                          Abi::Rust,
 818                                          explicit_self,
 819                                          tys,
 820                                          body)
 821             })
 822             .collect();
 823
 824         self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
 825     }
 826 }
 827
 828 fn find_repr_type_name(diagnostic: &Handler, type_attrs: &[ast::Attribute]) -> &'static str {
 829     let mut repr_type_name = "isize";
 830     for a in type_attrs {
 831         for r in &attr::find_repr_attrs(diagnostic, a) {
 832             repr_type_name = match *r {
 833                 attr::ReprPacked | attr::ReprSimd | attr::ReprAlign(_) | attr::ReprTransparent =>
 834                     continue,
 835
 836                 attr::ReprC => "i32",
 837
 838                 attr::ReprInt(attr::SignedInt(ast::IntTy::Isize)) => "isize",
 839                 attr::ReprInt(attr::SignedInt(ast::IntTy::I8)) => "i8",
 840                 attr::ReprInt(attr::SignedInt(ast::IntTy::I16)) => "i16",
 841                 attr::ReprInt(attr::SignedInt(ast::IntTy::I32)) => "i32",
 842                 attr::ReprInt(attr::SignedInt(ast::IntTy::I64)) => "i64",
 843                 attr::ReprInt(attr::SignedInt(ast::IntTy::I128)) => "i128",
 844
 845                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::Usize)) => "usize",
 846                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U8)) => "u8",
 847                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U16)) => "u16",
 848                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U32)) => "u32",
 849                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U64)) => "u64",
 850                 attr::ReprInt(attr::UnsignedInt(ast::UintTy::U128)) => "u128",
 851             }
 852         }
 853     }
 854     repr_type_name
 855 }
 856
 857 impl<'a> MethodDef<'a> {
 858     fn call_substructure_method(&self,
 859                                 cx: &mut ExtCtxt,
 860                                 trait_: &TraitDef,
 861                                 type_ident: Ident,
 862                                 self_args: &[P<Expr>],
 863                                 nonself_args: &[P<Expr>],
 864                                 fields: &SubstructureFields)
 865                                 -> P<Expr> {
 866         let substructure = Substructure {
 867             type_ident,
 868             method_ident: cx.ident_of(self.name),
 869             self_args,
 870             nonself_args,
 871             fields,
 872         };
 873         let mut f = self.combine_substructure.borrow_mut();
 874         let f: &mut CombineSubstructureFunc = &mut *f;
 875         f(cx, trait_.span, &substructure)
 876     }
 877
 878     fn get_ret_ty(&self,
 879                   cx: &mut ExtCtxt,
 880                   trait_: &TraitDef,
 881                   generics: &Generics,
 882                   type_ident: Ident)
 883                   -> P<ast::Ty> {
 884         self.ret_ty.to_ty(cx, trait_.span, type_ident, generics)
 885     }
 886
 887     fn is_static(&self) -> bool {
 888         self.explicit_self.is_none()
 889     }
 890
 891     fn split_self_nonself_args
 892         (&self,
 893          cx: &mut ExtCtxt,
 894          trait_: &TraitDef,
 895          type_ident: Ident,
 896          generics: &Generics)
 897          -> (Option<ast::ExplicitSelf>, Vec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
 898
 899         let mut self_args = Vec::new();
 900         let mut nonself_args = Vec::new();
 901         let mut arg_tys = Vec::new();
 902         let mut nonstatic = false;
 903
 904         let ast_explicit_self = self.explicit_self.as_ref().map(|self_ptr| {
 905             let (self_expr, explicit_self) = ty::get_explicit_self(cx, trait_.span, self_ptr);
 906
 907             self_args.push(self_expr);
 908             nonstatic = true;
 909
 910             explicit_self
 911         });
 912
 913         for (i, ty) in self.args.iter().enumerate() {
 914             let ast_ty = ty.to_ty(cx, trait_.span, type_ident, generics);
 915             let ident = cx.ident_of(&format!("__arg_{}", i));
 916             arg_tys.push((ident, ast_ty));
 917
 918             let arg_expr = cx.expr_ident(trait_.span, ident);
 919
 920             match *ty {
 921                 // for static methods, just treat any Self
 922                 // arguments as a normal arg
 923                 Self_ if nonstatic => {
 924                     self_args.push(arg_expr);
 925                 }
 926                 Ptr(ref ty, _) if **ty == Self_ && nonstatic => {
 927                     self_args.push(cx.expr_deref(trait_.span, arg_expr))
 928                 }
 929                 _ => {
 930                     nonself_args.push(arg_expr);
 931                 }
 932             }
 933         }
 934
 935         (ast_explicit_self, self_args, nonself_args, arg_tys)
 936     }
 937
 938     fn create_method(&self,
 939                      cx: &mut ExtCtxt,
 940                      trait_: &TraitDef,
 941                      type_ident: Ident,
 942                      generics: &Generics,
 943                      abi: Abi,
 944                      explicit_self: Option<ast::ExplicitSelf>,
 945                      arg_types: Vec<(Ident, P<ast::Ty>)>,
 946                      body: P<Expr>)
 947                      -> ast::ImplItem {
 948
 949         // create the generics that aren't for Self
 950         let fn_generics = self.generics.to_generics(cx, trait_.span, type_ident, generics);
 951
 952         let args = {
 953             let self_args = explicit_self.map(|explicit_self| {
 954                 ast::Arg::from_self(explicit_self,
 955                                     respan(trait_.span, keywords::SelfValue.ident()))
 956             });
 957             let nonself_args = arg_types.into_iter()
 958                 .map(|(name, ty)| cx.arg(trait_.span, name, ty));
 959             self_args.into_iter().chain(nonself_args).collect()
 960         };
 961
 962         let ret_type = self.get_ret_ty(cx, trait_, generics, type_ident);
 963
 964         let method_ident = cx.ident_of(self.name);
 965         let fn_decl = cx.fn_decl(args, ast::FunctionRetTy::Ty(ret_type));
 966         let body_block = cx.block_expr(body);
 967
 968         let unsafety = if self.is_unsafe {
 969             ast::Unsafety::Unsafe
 970         } else {
 971             ast::Unsafety::Normal
 972         };
 973
 974         // Create the method.
 975         ast::ImplItem {
 976             id: ast::DUMMY_NODE_ID,
 977             attrs: self.attributes.clone(),
 978             generics: fn_generics,
 979             span: trait_.span,
 980             vis: respan(trait_.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
 981             defaultness: ast::Defaultness::Final,
 982             ident: method_ident,
 983             node: ast::ImplItemKind::Method(ast::MethodSig {
 984                                                 abi,
 985                                                 unsafety,
 986                                                 constness:
 987                                                     dummy_spanned(ast::Constness::NotConst),
 988                                                 decl: fn_decl,
 989                                             },
 990                                             body_block),
 991             tokens: None,
 992         }
 993     }
 994
 995     /// ```
 996     /// #[derive(PartialEq)]
 997     /// # struct Dummy;
 998     /// struct A { x: i32, y: i32 }
 999     ///
1000     /// // equivalent to:
1001     /// impl PartialEq for A {
1002     ///     fn eq(&self, __arg_1: &A) -> bool {
1003     ///         match *self {
1004     ///             A {x: ref __self_0_0, y: ref __self_0_1} => {
1005     ///                 match *__arg_1 {
1006     ///                     A {x: ref __self_1_0, y: ref __self_1_1} => {
1007     ///                         __self_0_0.eq(__self_1_0) && __self_0_1.eq(__self_1_1)
1008     ///                     }
1009     ///                 }
1010     ///             }
1011     ///         }
1012     ///     }
1013     /// }
1014     ///
1015     /// // or if A is repr(packed) - note fields are matched by-value
1016     /// // instead of by-reference.
1017     /// impl PartialEq for A {
1018     ///     fn eq(&self, __arg_1: &A) -> bool {
1019     ///         match *self {
1020     ///             A {x: __self_0_0, y: __self_0_1} => {
1021     ///                 match __arg_1 {
1022     ///                     A {x: __self_1_0, y: __self_1_1} => {
1023     ///                         __self_0_0.eq(&__self_1_0) && __self_0_1.eq(&__self_1_1)
1024     ///                     }
1025     ///                 }
1026     ///             }
1027     ///         }
1028     ///     }
1029     /// }
1030     /// ```
1031     fn expand_struct_method_body<'b>(&self,
1032                                      cx: &mut ExtCtxt,
1033                                      trait_: &TraitDef<'b>,
1034                                      struct_def: &'b VariantData,
1035                                      type_ident: Ident,
1036                                      self_args: &[P<Expr>],
1037                                      nonself_args: &[P<Expr>],
1038                                      use_temporaries: bool)
1039                                      -> P<Expr> {
1040
1041         let mut raw_fields = Vec::new(); // Vec<[fields of self],
1042                                  // [fields of next Self arg], [etc]>
1043         let mut patterns = Vec::new();
1044         for i in 0..self_args.len() {
1045             let struct_path = cx.path(DUMMY_SP, vec![type_ident]);
1046             let (pat, ident_expr) = trait_.create_struct_pattern(cx,
1047                                                                  struct_path,
1048                                                                  struct_def,
1049                                                                  &format!("__self_{}", i),
1050                                                                  ast::Mutability::Immutable,
1051                                                                  use_temporaries);
1052             patterns.push(pat);
1053             raw_fields.push(ident_expr);
1054         }
1055
1056         // transpose raw_fields
1057         let fields = if !raw_fields.is_empty() {
1058             let mut raw_fields = raw_fields.into_iter().map(|v| v.into_iter());
1059             let first_field = raw_fields.next().unwrap();
1060             let mut other_fields: Vec<vec::IntoIter<_>> = raw_fields.collect();
1061             first_field.map(|(span, opt_id, field, attrs)| {
1062                     FieldInfo {
1063                         span,
1064                         name: opt_id,
1065                         self_: field,
1066                         other: other_fields.iter_mut()
1067                             .map(|l| {
1068                                 match l.next().unwrap() {
1069                                     (.., ex, _) => ex,
1070                                 }
1071                             })
1072                             .collect(),
1073                         attrs,
1074                     }
1075                 })
1076                 .collect()
1077         } else {
1078             cx.span_bug(trait_.span,
1079                         "no self arguments to non-static method in generic \
1080                          `derive`")
1081         };
1082
1083         // body of the inner most destructuring match
1084         let mut body = self.call_substructure_method(cx,
1085                                                      trait_,
1086                                                      type_ident,
1087                                                      self_args,
1088                                                      nonself_args,
1089                                                      &Struct(struct_def, fields));
1090
1091         // make a series of nested matches, to destructure the
1092         // structs. This is actually right-to-left, but it shouldn't
1093         // matter.
1094         for (arg_expr, pat) in self_args.iter().zip(patterns) {
1095             body = cx.expr_match(trait_.span,
1096                                  arg_expr.clone(),
1097                                  vec![cx.arm(trait_.span, vec![pat.clone()], body)])
1098         }
1099
1100         body
1101     }
1102
1103     fn expand_static_struct_method_body(&self,
1104                                         cx: &mut ExtCtxt,
1105                                         trait_: &TraitDef,
1106                                         struct_def: &VariantData,
1107                                         type_ident: Ident,
1108                                         self_args: &[P<Expr>],
1109                                         nonself_args: &[P<Expr>])
1110                                         -> P<Expr> {
1111         let summary = trait_.summarise_struct(cx, struct_def);
1112
1113         self.call_substructure_method(cx,
1114                                       trait_,
1115                                       type_ident,
1116                                       self_args,
1117                                       nonself_args,
1118                                       &StaticStruct(struct_def, summary))
1119     }
1120
1121     /// ```
1122     /// #[derive(PartialEq)]
1123     /// # struct Dummy;
1124     /// enum A {
1125     ///     A1,
1126     ///     A2(i32)
1127     /// }
1128     ///
1129     /// // is equivalent to
1130     ///
1131     /// impl PartialEq for A {
1132     ///     fn eq(&self, __arg_1: &A) -> ::bool {
1133     ///         match (&*self, &*__arg_1) {
1134     ///             (&A1, &A1) => true,
1135     ///             (&A2(ref self_0),
1136     ///              &A2(ref __arg_1_0)) => (*self_0).eq(&(*__arg_1_0)),
1137     ///             _ => {
1138     ///                 let __self_vi = match *self { A1(..) => 0, A2(..) => 1 };
1139     ///                 let __arg_1_vi = match *__arg_1 { A1(..) => 0, A2(..) => 1 };
1140     ///                 false
1141     ///             }
1142     ///         }
1143     ///     }
1144     /// }
1145     /// ```
1146     ///
1147     /// (Of course `__self_vi` and `__arg_1_vi` are unused for
1148     /// `PartialEq`, and those subcomputations will hopefully be removed
1149     /// as their results are unused.  The point of `__self_vi` and
1150     /// `__arg_1_vi` is for `PartialOrd`; see #15503.)
1151     fn expand_enum_method_body<'b>(&self,
1152                                    cx: &mut ExtCtxt,
1153                                    trait_: &TraitDef<'b>,
1154                                    enum_def: &'b EnumDef,
1155                                    type_attrs: &[ast::Attribute],
1156                                    type_ident: Ident,
1157                                    self_args: Vec<P<Expr>>,
1158                                    nonself_args: &[P<Expr>])
1159                                    -> P<Expr> {
1160         self.build_enum_match_tuple(cx,
1161                                     trait_,
1162                                     enum_def,
1163                                     type_attrs,
1164                                     type_ident,
1165                                     self_args,
1166                                     nonself_args)
1167     }
1168
1169
1170     /// Creates a match for a tuple of all `self_args`, where either all
1171     /// variants match, or it falls into a catch-all for when one variant
1172     /// does not match.
1173
1174     /// There are N + 1 cases because is a case for each of the N
1175     /// variants where all of the variants match, and one catch-all for
1176     /// when one does not match.
1177
1178     /// As an optimization we generate code which checks whether all variants
1179     /// match first which makes llvm see that C-like enums can be compiled into
1180     /// a simple equality check (for PartialEq).
1181
1182     /// The catch-all handler is provided access the variant index values
1183     /// for each of the self-args, carried in precomputed variables.
1184
1185     /// ```{.text}
1186     /// let __self0_vi = unsafe {
1187     ///     std::intrinsics::discriminant_value(&self) } as i32;
1188     /// let __self1_vi = unsafe {
1189     ///     std::intrinsics::discriminant_value(&arg1) } as i32;
1190     /// let __self2_vi = unsafe {
1191     ///     std::intrinsics::discriminant_value(&arg2) } as i32;
1192     ///
1193     /// if __self0_vi == __self1_vi && __self0_vi == __self2_vi && ... {
1194     ///     match (...) {
1195     ///         (Variant1, Variant1, ...) => Body1
1196     ///         (Variant2, Variant2, ...) => Body2,
1197     ///         ...
1198     ///         _ => ::core::intrinsics::unreachable()
1199     ///     }
1200     /// }
1201     /// else {
1202     ///     ... // catch-all remainder can inspect above variant index values.
1203     /// }
1204     /// ```
1205     fn build_enum_match_tuple<'b>(&self,
1206                                   cx: &mut ExtCtxt,
1207                                   trait_: &TraitDef<'b>,
1208                                   enum_def: &'b EnumDef,
1209                                   type_attrs: &[ast::Attribute],
1210                                   type_ident: Ident,
1211                                   self_args: Vec<P<Expr>>,
1212                                   nonself_args: &[P<Expr>])
1213                                   -> P<Expr> {
1214         let sp = trait_.span;
1215         let variants = &enum_def.variants;
1216
1217         let self_arg_names = self_args.iter()
1218             .enumerate()
1219             .map(|(arg_count, _self_arg)| {
1220                 if arg_count == 0 {
1221                     "__self".to_string()
1222                 } else {
1223                     format!("__arg_{}", arg_count)
1224                 }
1225             })
1226             .collect::<Vec<String>>();
1227
1228         let self_arg_idents = self_arg_names.iter()
1229             .map(|name| cx.ident_of(&name[..]))
1230             .collect::<Vec<ast::Ident>>();
1231
1232         // The `vi_idents` will be bound, solely in the catch-all, to
1233         // a series of let statements mapping each self_arg to an int
1234         // value corresponding to its discriminant.
1235         let vi_idents: Vec<ast::Ident> = self_arg_names.iter()
1236             .map(|name| {
1237                 let vi_suffix = format!("{}_vi", &name[..]);
1238                 cx.ident_of(&vi_suffix[..])
1239             })
1240             .collect::<Vec<ast::Ident>>();
1241
1242         // Builds, via callback to call_substructure_method, the
1243         // delegated expression that handles the catch-all case,
1244         // using `__variants_tuple` to drive logic if necessary.
1245         let catch_all_substructure =
1246             EnumNonMatchingCollapsed(self_arg_idents, &variants[..], &vi_idents[..]);
1247
1248         let first_fieldless = variants.iter().find(|v| v.node.data.fields().is_empty());
1249
1250         // These arms are of the form:
1251         // (Variant1, Variant1, ...) => Body1
1252         // (Variant2, Variant2, ...) => Body2
1253         // ...
1254         // where each tuple has length = self_args.len()
1255         let mut match_arms: Vec<ast::Arm> = variants.iter()
1256             .enumerate()
1257             .filter(|&(_, v)| !(self.unify_fieldless_variants && v.node.data.fields().is_empty()))
1258             .map(|(index, variant)| {
1259                 let mk_self_pat = |cx: &mut ExtCtxt, self_arg_name: &str| {
1260                     let (p, idents) = trait_.create_enum_variant_pattern(cx,
1261                                                      type_ident,
1262                                                      variant,
1263                                                      self_arg_name,
1264                                                      ast::Mutability::Immutable);
1265                     (cx.pat(sp, PatKind::Ref(p, ast::Mutability::Immutable)), idents)
1266                 };
1267
1268                 // A single arm has form (&VariantK, &VariantK, ...) => BodyK
1269                 // (see "Final wrinkle" note below for why.)
1270                 let mut subpats = Vec::with_capacity(self_arg_names.len());
1271                 let mut self_pats_idents = Vec::with_capacity(self_arg_names.len() - 1);
1272                 let first_self_pat_idents = {
1273                     let (p, idents) = mk_self_pat(cx, &self_arg_names[0]);
1274                     subpats.push(p);
1275                     idents
1276                 };
1277                 for self_arg_name in &self_arg_names[1..] {
1278                     let (p, idents) = mk_self_pat(cx, &self_arg_name[..]);
1279                     subpats.push(p);
1280                     self_pats_idents.push(idents);
1281                 }
1282
1283                 // Here is the pat = `(&VariantK, &VariantK, ...)`
1284                 let single_pat = cx.pat_tuple(sp, subpats);
1285
1286                 // For the BodyK, we need to delegate to our caller,
1287                 // passing it an EnumMatching to indicate which case
1288                 // we are in.
1289
1290                 // All of the Self args have the same variant in these
1291                 // cases.  So we transpose the info in self_pats_idents
1292                 // to gather the getter expressions together, in the
1293                 // form that EnumMatching expects.
1294
1295                 // The transposition is driven by walking across the
1296                 // arg fields of the variant for the first self pat.
1297                 let field_tuples = first_self_pat_idents.into_iter().enumerate()
1298                     // For each arg field of self, pull out its getter expr ...
1299                     .map(|(field_index, (sp, opt_ident, self_getter_expr, attrs))| {
1300                         // ... but FieldInfo also wants getter expr
1301                         // for matching other arguments of Self type;
1302                         // so walk across the *other* self_pats_idents
1303                         // and pull out getter for same field in each
1304                         // of them (using `field_index` tracked above).
1305                         // That is the heart of the transposition.
1306                         let others = self_pats_idents.iter().map(|fields| {
1307                             let (_, _opt_ident, ref other_getter_expr, _) =
1308                                 fields[field_index];
1309
1310                             // All Self args have same variant, so
1311                             // opt_idents are the same.  (Assert
1312                             // here to make it self-evident that
1313                             // it is okay to ignore `_opt_ident`.)
1314                             assert!(opt_ident == _opt_ident);
1315
1316                             other_getter_expr.clone()
1317                         }).collect::<Vec<P<Expr>>>();
1318
1319                         FieldInfo { span: sp,
1320                                     name: opt_ident,
1321                                     self_: self_getter_expr,
1322                                     other: others,
1323                                     attrs,
1324                         }
1325                     }).collect::<Vec<FieldInfo>>();
1326
1327                 // Now, for some given VariantK, we have built up
1328                 // expressions for referencing every field of every
1329                 // Self arg, assuming all are instances of VariantK.
1330                 // Build up code associated with such a case.
1331                 let substructure = EnumMatching(index, variants.len(), variant, field_tuples);
1332                 let arm_expr = self.call_substructure_method(cx,
1333                                                              trait_,
1334                                                              type_ident,
1335                                                              &self_args[..],
1336                                                              nonself_args,
1337                                                              &substructure);
1338
1339                 cx.arm(sp, vec![single_pat], arm_expr)
1340             })
1341             .collect();
1342
1343         let default = match first_fieldless {
1344             Some(v) if self.unify_fieldless_variants => {
1345                 // We need a default case that handles the fieldless variants.
1346                 // The index and actual variant aren't meaningful in this case,
1347                 // so just use whatever
1348                 let substructure = EnumMatching(0, variants.len(), v, Vec::new());
1349                 Some(self.call_substructure_method(cx,
1350                                                    trait_,
1351                                                    type_ident,
1352                                                    &self_args[..],
1353                                                    nonself_args,
1354                                                    &substructure))
1355             }
1356             _ if variants.len() > 1 && self_args.len() > 1 => {
1357                 // Since we know that all the arguments will match if we reach
1358                 // the match expression we add the unreachable intrinsics as the
1359                 // result of the catch all which should help llvm in optimizing it
1360                 Some(deriving::call_intrinsic(cx, sp, "unreachable", vec![]))
1361             }
1362             _ => None,
1363         };
1364         if let Some(arm) = default {
1365             match_arms.push(cx.arm(sp, vec![cx.pat_wild(sp)], arm));
1366         }
1367
1368         // We will usually need the catch-all after matching the
1369         // tuples `(VariantK, VariantK, ...)` for each VariantK of the
1370         // enum.  But:
1371         //
1372         // * when there is only one Self arg, the arms above suffice
1373         // (and the deriving we call back into may not be prepared to
1374         // handle EnumNonMatchCollapsed), and,
1375         //
1376         // * when the enum has only one variant, the single arm that
1377         // is already present always suffices.
1378         //
1379         // * In either of the two cases above, if we *did* add a
1380         //   catch-all `_` match, it would trigger the
1381         //   unreachable-pattern error.
1382         //
1383         if variants.len() > 1 && self_args.len() > 1 {
1384             // Build a series of let statements mapping each self_arg
1385             // to its discriminant value. If this is a C-style enum
1386             // with a specific repr type, then casts the values to
1387             // that type.  Otherwise casts to `i32` (the default repr
1388             // type).
1389             //
1390             // i.e. for `enum E<T> { A, B(1), C(T, T) }`, and a deriving
1391             // with three Self args, builds three statements:
1392             //
1393             // ```
1394             // let __self0_vi = unsafe {
1395             //     std::intrinsics::discriminant_value(&self) } as i32;
1396             // let __self1_vi = unsafe {
1397             //     std::intrinsics::discriminant_value(&arg1) } as i32;
1398             // let __self2_vi = unsafe {
1399             //     std::intrinsics::discriminant_value(&arg2) } as i32;
1400             // ```
1401             let mut index_let_stmts: Vec<ast::Stmt> = Vec::new();
1402
1403             // We also build an expression which checks whether all discriminants are equal
1404             // discriminant_test = __self0_vi == __self1_vi && __self0_vi == __self2_vi && ...
1405             let mut discriminant_test = cx.expr_bool(sp, true);
1406
1407             let target_type_name = find_repr_type_name(&cx.parse_sess.span_diagnostic, type_attrs);
1408
1409             let mut first_ident = None;
1410             for (&ident, self_arg) in vi_idents.iter().zip(&self_args) {
1411                 let self_addr = cx.expr_addr_of(sp, self_arg.clone());
1412                 let variant_value =
1413                     deriving::call_intrinsic(cx, sp, "discriminant_value", vec![self_addr]);
1414
1415                 let target_ty = cx.ty_ident(sp, cx.ident_of(target_type_name));
1416                 let variant_disr = cx.expr_cast(sp, variant_value, target_ty);
1417                 let let_stmt = cx.stmt_let(sp, false, ident, variant_disr);
1418                 index_let_stmts.push(let_stmt);
1419
1420                 match first_ident {
1421                     Some(first) => {
1422                         let first_expr = cx.expr_ident(sp, first);
1423                         let id = cx.expr_ident(sp, ident);
1424                         let test = cx.expr_binary(sp, BinOpKind::Eq, first_expr, id);
1425                         discriminant_test =
1426                             cx.expr_binary(sp, BinOpKind::And, discriminant_test, test)
1427                     }
1428                     None => {
1429                         first_ident = Some(ident);
1430                     }
1431                 }
1432             }
1433
1434             let arm_expr = self.call_substructure_method(cx,
1435                                                          trait_,
1436                                                          type_ident,
1437                                                          &self_args[..],
1438                                                          nonself_args,
1439                                                          &catch_all_substructure);
1440
1441             // Final wrinkle: the self_args are expressions that deref
1442             // down to desired places, but we cannot actually deref
1443             // them when they are fed as r-values into a tuple
1444             // expression; here add a layer of borrowing, turning
1445             // `(*self, *__arg_0, ...)` into `(&*self, &*__arg_0, ...)`.
1446             let borrowed_self_args = self_args.move_map(|self_arg| cx.expr_addr_of(sp, self_arg));
1447             let match_arg = cx.expr(sp, ast::ExprKind::Tup(borrowed_self_args));
1448
1449             // Lastly we create an expression which branches on all discriminants being equal
1450             //  if discriminant_test {
1451             //      match (...) {
1452             //          (Variant1, Variant1, ...) => Body1
1453             //          (Variant2, Variant2, ...) => Body2,
1454             //          ...
1455             //          _ => ::core::intrinsics::unreachable()
1456             //      }
1457             //  }
1458             //  else {
1459             //      <delegated expression referring to __self0_vi, et al.>
1460             //  }
1461             let all_match = cx.expr_match(sp, match_arg, match_arms);
1462             let arm_expr = cx.expr_if(sp, discriminant_test, all_match, Some(arm_expr));
1463             index_let_stmts.push(cx.stmt_expr(arm_expr));
1464             cx.expr_block(cx.block(sp, index_let_stmts))
1465         } else if variants.is_empty() {
1466             // As an additional wrinkle, For a zero-variant enum A,
1467             // currently the compiler
1468             // will accept `fn (a: &Self) { match   *a   { } }`
1469             // but rejects `fn (a: &Self) { match (&*a,) { } }`
1470             // as well as  `fn (a: &Self) { match ( *a,) { } }`
1471             //
1472             // This means that the strategy of building up a tuple of
1473             // all Self arguments fails when Self is a zero variant
1474             // enum: rustc rejects the expanded program, even though
1475             // the actual code tends to be impossible to execute (at
1476             // least safely), according to the type system.
1477             //
1478             // The most expedient fix for this is to just let the
1479             // code fall through to the catch-all.  But even this is
1480             // error-prone, since the catch-all as defined above would
1481             // generate code like this:
1482             //
1483             //     _ => { let __self0 = match *self { };
1484             //            let __self1 = match *__arg_0 { };
1485             //            <catch-all-expr> }
1486             //
1487             // Which is yields bindings for variables which type
1488             // inference cannot resolve to unique types.
1489             //
1490             // One option to the above might be to add explicit type
1491             // annotations.  But the *only* reason to go down that path
1492             // would be to try to make the expanded output consistent
1493             // with the case when the number of enum variants >= 1.
1494             //
1495             // That just isn't worth it.  In fact, trying to generate
1496             // sensible code for *any* deriving on a zero-variant enum
1497             // does not make sense.  But at the same time, for now, we
1498             // do not want to cause a compile failure just because the
1499             // user happened to attach a deriving to their
1500             // zero-variant enum.
1501             //
1502             // Instead, just generate a failing expression for the
1503             // zero variant case, skipping matches and also skipping
1504             // delegating back to the end user code entirely.
1505             //
1506             // (See also #4499 and #12609; note that some of the
1507             // discussions there influence what choice we make here;
1508             // e.g. if we feature-gate `match x { ... }` when x refers
1509             // to an uninhabited type (e.g. a zero-variant enum or a
1510             // type holding such an enum), but do not feature-gate
1511             // zero-variant enums themselves, then attempting to
1512             // derive Debug on such a type could here generate code
1513             // that needs the feature gate enabled.)
1514
1515             deriving::call_intrinsic(cx, sp, "unreachable", vec![])
1516         } else {
1517
1518             // Final wrinkle: the self_args are expressions that deref
1519             // down to desired places, but we cannot actually deref
1520             // them when they are fed as r-values into a tuple
1521             // expression; here add a layer of borrowing, turning
1522             // `(*self, *__arg_0, ...)` into `(&*self, &*__arg_0, ...)`.
1523             let borrowed_self_args = self_args.move_map(|self_arg| cx.expr_addr_of(sp, self_arg));
1524             let match_arg = cx.expr(sp, ast::ExprKind::Tup(borrowed_self_args));
1525             cx.expr_match(sp, match_arg, match_arms)
1526         }
1527     }
1528
1529     fn expand_static_enum_method_body(&self,
1530                                       cx: &mut ExtCtxt,
1531                                       trait_: &TraitDef,
1532                                       enum_def: &EnumDef,
1533                                       type_ident: Ident,
1534                                       self_args: &[P<Expr>],
1535                                       nonself_args: &[P<Expr>])
1536                                       -> P<Expr> {
1537         let summary = enum_def.variants
1538             .iter()
1539             .map(|v| {
1540                 let ident = v.node.name;
1541                 let sp = v.span.with_ctxt(trait_.span.ctxt());
1542                 let summary = trait_.summarise_struct(cx, &v.node.data);
1543                 (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::SpannedIdent>,
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(codemap::Spanned {
1617                 span: sp,
1618                 node: ident,
1619             });
1620             let val = cx.expr_path(cx.path_ident(sp, ident));
1621             let val = if use_temporaries {
1622                 val
1623             } else {
1624                 cx.expr_deref(sp, val)
1625             };
1626             let val = cx.expr(sp, ast::ExprKind::Paren(val));
1627
1628             ident_exprs.push((sp, struct_field.ident, val, &struct_field.attrs[..]));
1629         }
1630
1631         let subpats = self.create_subpatterns(cx, paths, mutbl, use_temporaries);
1632         let pattern = match *struct_def {
1633             VariantData::Struct(..) => {
1634                 let field_pats = subpats.into_iter()
1635                     .zip(&ident_exprs)
1636                     .map(|(pat, &(sp, ident, ..))| {
1637                         if ident.is_none() {
1638                             cx.span_bug(sp, "a braced struct with unnamed fields in `derive`");
1639                         }
1640                         codemap::Spanned {
1641                             span: pat.span.with_ctxt(self.span.ctxt()),
1642                             node: ast::FieldPat {
1643                                 ident: ident.unwrap(),
1644                                 pat,
1645                                 is_shorthand: false,
1646                                 attrs: ast::ThinVec::new(),
1647                             },
1648                         }
1649                     })
1650                     .collect();
1651                 cx.pat_struct(self.span, struct_path, field_pats)
1652             }
1653             VariantData::Tuple(..) => {
1654                 cx.pat_tuple_struct(self.span, struct_path, subpats)
1655             }
1656             VariantData::Unit(..) => {
1657                 cx.pat_path(self.span, struct_path)
1658             }
1659         };
1660
1661         (pattern, ident_exprs)
1662     }
1663
1664     fn create_enum_variant_pattern
1665         (&self,
1666          cx: &mut ExtCtxt,
1667          enum_ident: ast::Ident,
1668          variant: &'a ast::Variant,
1669          prefix: &str,
1670          mutbl: ast::Mutability)
1671          -> (P<ast::Pat>, Vec<(Span, Option<Ident>, P<Expr>, &'a [ast::Attribute])>) {
1672         let variant_ident = variant.node.name;
1673         let sp = variant.span.with_ctxt(self.span.ctxt());
1674         let variant_path = cx.path(sp, vec![enum_ident, variant_ident]);
1675         let use_temporaries = false; // enums can't be repr(packed)
1676         self.create_struct_pattern(cx, variant_path, &variant.node.data, prefix, mutbl,
1677                                    use_temporaries)
1678     }
1679 }
1680
1681 // helpful premade recipes
1682
1683 /// Fold the fields. `use_foldl` controls whether this is done
1684 /// left-to-right (`true`) or right-to-left (`false`).
1685 pub fn cs_fold<F>(use_foldl: bool,
1686                   mut f: F,
1687                   base: P<Expr>,
1688                   mut enum_nonmatch_f: EnumNonMatchCollapsedFunc,
1689                   cx: &mut ExtCtxt,
1690                   trait_span: Span,
1691                   substructure: &Substructure)
1692                   -> P<Expr>
1693     where F: FnMut(&mut ExtCtxt, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>
1694 {
1695     match *substructure.fields {
1696         EnumMatching(.., ref all_fields) |
1697         Struct(_, ref all_fields) => {
1698             if use_foldl {
1699                 all_fields.iter().fold(base, |old, field| {
1700                     f(cx, field.span, old, field.self_.clone(), &field.other)
1701                 })
1702             } else {
1703                 all_fields.iter().rev().fold(base, |old, field| {
1704                     f(cx, field.span, old, field.self_.clone(), &field.other)
1705                 })
1706             }
1707         }
1708         EnumNonMatchingCollapsed(ref all_args, _, tuple) => {
1709             enum_nonmatch_f(cx,
1710                             trait_span,
1711                             (&all_args[..], tuple),
1712                             substructure.nonself_args)
1713         }
1714         StaticEnum(..) | StaticStruct(..) => cx.span_bug(trait_span, "static function in `derive`"),
1715     }
1716 }
1717
1718
1719 /// Call the method that is being derived on all the fields, and then
1720 /// process the collected results. i.e.
1721 ///
1722 /// ```ignore (only-for-syntax-highlight)
1723 /// f(cx, span, vec![self_1.method(__arg_1_1, __arg_2_1),
1724 ///                  self_2.method(__arg_1_2, __arg_2_2)])
1725 /// ```
1726 #[inline]
1727 pub fn cs_same_method<F>(f: F,
1728                          mut enum_nonmatch_f: EnumNonMatchCollapsedFunc,
1729                          cx: &mut ExtCtxt,
1730                          trait_span: Span,
1731                          substructure: &Substructure)
1732                          -> P<Expr>
1733     where F: FnOnce(&mut ExtCtxt, Span, Vec<P<Expr>>) -> P<Expr>
1734 {
1735     match *substructure.fields {
1736         EnumMatching(.., ref all_fields) |
1737         Struct(_, ref all_fields) => {
1738             // call self_n.method(other_1_n, other_2_n, ...)
1739             let called = all_fields.iter()
1740                 .map(|field| {
1741                     cx.expr_method_call(field.span,
1742                                         field.self_.clone(),
1743                                         substructure.method_ident,
1744                                         field.other
1745                                             .iter()
1746                                             .map(|e| cx.expr_addr_of(field.span, e.clone()))
1747                                             .collect())
1748                 })
1749                 .collect();
1750
1751             f(cx, trait_span, called)
1752         }
1753         EnumNonMatchingCollapsed(ref all_self_args, _, tuple) => {
1754             enum_nonmatch_f(cx,
1755                             trait_span,
1756                             (&all_self_args[..], tuple),
1757                             substructure.nonself_args)
1758         }
1759         StaticEnum(..) | StaticStruct(..) => cx.span_bug(trait_span, "static function in `derive`"),
1760     }
1761 }
1762
1763 /// Return true if the type has no value fields
1764 /// (for an enum, no variant has any fields)
1765 pub fn is_type_without_fields(item: &Annotatable) -> bool {
1766     if let Annotatable::Item(ref item) = *item {
1767         match item.node {
1768             ast::ItemKind::Enum(ref enum_def, _) => {
1769                 enum_def.variants.iter().all(|v| v.node.data.fields().is_empty())
1770             }
1771             ast::ItemKind::Struct(ref variant_data, _) => variant_data.fields().is_empty(),
1772             _ => false,
1773         }
1774     } else {
1775         false
1776     }
1777 }