Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 1858 insertions, 0 deletions

diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
new file mode 100644
index 000000000..735017aa5
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -0,0 +1,1655 @@
+//! Some code that abstracts away much of the boilerplate of writing
+//! `derive` instances for traits. Among other things it manages getting
+//! access to the fields of the 4 different sorts of structs and enum
+//! variants, as well as creating the method and impl ast instances.
+//!
+//! Supported features (fairly exhaustive):
+//!
+//! - Methods taking any number of parameters of any type, and returning
+//!   any type, other than vectors, bottom and closures.
+//! - Generating `impl`s for types with type parameters and lifetimes
+//!   (e.g., `Option<T>`), the parameters are automatically given the
+//!   current trait as a bound. (This includes separate type parameters
+//!   and lifetimes for methods.)
+//! - Additional bounds on the type parameters (`TraitDef.additional_bounds`)
+//!
+//! The most important thing for implementors is the `Substructure` and
+//! `SubstructureFields` objects. The latter groups 5 possibilities of the
+//! arguments:
+//!
+//! - `Struct`, when `Self` is a struct (including tuple structs, e.g
+//!   `struct T(i32, char)`).
+//! - `EnumMatching`, when `Self` is an enum and all the arguments are the
+//!   same variant of the enum (e.g., `Some(1)`, `Some(3)` and `Some(4)`)
+//! - `EnumTag` when `Self` is an enum, for comparing the enum tags.
+//! - `StaticEnum` and `StaticStruct` for static methods, where the type
+//!   being derived upon is either an enum or struct respectively. (Any
+//!   argument with type Self is just grouped among the non-self
+//!   arguments.)
+//!
+//! In the first two cases, the values from the corresponding fields in
+//! all the arguments are grouped together.
+//!
+//! The non-static cases have `Option<ident>` in several places associated
+//! with field `expr`s. This represents the name of the field it is
+//! associated with. It is only not `None` when the associated field has
+//! an identifier in the source code. For example, the `x`s in the
+//! following snippet
+//!
+//! ```rust
+//! # #![allow(dead_code)]
+//! struct A { x : i32 }
+//!
+//! struct B(i32);
+//!
+//! enum C {
+//!     C0(i32),
+//!     C1 { x: i32 }
+//! }
+//! ```
+//!
+//! The `i32`s in `B` and `C0` don't have an identifier, so the
+//! `Option<ident>`s would be `None` for them.
+//!
+//! In the static cases, the structure is summarized, either into the just
+//! spans of the fields or a list of spans and the field idents (for tuple
+//! structs and record structs, respectively), or a list of these, for
+//! enums (one for each variant). For empty struct and empty enum
+//! variants, it is represented as a count of 0.
+//!
+//! # "`cs`" functions
+//!
+//! The `cs_...` functions ("combine substructure") are designed to
+//! make life easier by providing some pre-made recipes for common
+//! threads; mostly calling the function being derived on all the
+//! arguments and then combining them back together in some way (or
+//! letting the user chose that). They are not meant to be the only
+//! way to handle the structures that this code creates.
+//!
+//! # Examples
+//!
+//! The following simplified `PartialEq` is used for in-code examples:
+//!
+//! ```rust
+//! trait PartialEq {
+//!     fn eq(&self, other: &Self) -> bool;
+//! }
+//! impl PartialEq for i32 {
+//!     fn eq(&self, other: &i32) -> bool {
+//!         *self == *other
+//!     }
+//! }
+//! ```
+//!
+//! Some examples of the values of `SubstructureFields` follow, using the
+//! above `PartialEq`, `A`, `B` and `C`.
+//!
+//! ## Structs
+//!
+//! When generating the `expr` for the `A` impl, the `SubstructureFields` is
+//!
+//! ```{.text}
+//! Struct(vec![FieldInfo {
+//!            span: <span of x>
+//!            name: Some(<ident of x>),
+//!            self_: <expr for &self.x>,
+//!            other: vec![<expr for &other.x]
+//!          }])
+//! ```
+//!
+//! For the `B` impl, called with `B(a)` and `B(b)`,
+//!
+//! ```{.text}
+//! Struct(vec![FieldInfo {
+//!           span: <span of `i32`>,
+//!           name: None,
+//!           self_: <expr for &a>
+//!           other: vec![<expr for &b>]
+//!          }])
+//! ```
+//!
+//! ## Enums
+//!
+//! When generating the `expr` for a call with `self == C0(a)` and `other
+//! == C0(b)`, the SubstructureFields is
+//!
+//! ```{.text}
+//! EnumMatching(0, <ast::Variant for C0>,
+//!              vec![FieldInfo {
+//!                 span: <span of i32>
+//!                 name: None,
+//!                 self_: <expr for &a>,
+//!                 other: vec![<expr for &b>]
+//!               }])
+//! ```
+//!
+//! For `C1 {x}` and `C1 {x}`,
+//!
+//! ```{.text}
+//! EnumMatching(1, <ast::Variant for C1>,
+//!              vec![FieldInfo {
+//!                 span: <span of x>
+//!                 name: Some(<ident of x>),
+//!                 self_: <expr for &self.x>,
+//!                 other: vec![<expr for &other.x>]
+//!                }])
+//! ```
+//!
+//! For the tags,
+//!
+//! ```{.text}
+//! EnumTag(
+//!     &[<ident of self tag>, <ident of other tag>], <expr to combine with>)
+//! ```
+//! Note that this setup doesn't allow for the brute-force "match every variant
+//! against every other variant" approach, which is bad because it produces a
+//! quadratic amount of code (see #15375).
+//!
+//! ## Static
+//!
+//! A static method on the types above would result in,
+//!
+//! ```{.text}
+//! StaticStruct(<ast::VariantData of A>, Named(vec![(<ident of x>, <span of x>)]))
+//!
+//! StaticStruct(<ast::VariantData of B>, Unnamed(vec![<span of x>]))
+//!
+//! StaticEnum(<ast::EnumDef of C>,
+//!            vec![(<ident of C0>, <span of C0>, Unnamed(vec![<span of i32>])),
+//!                 (<ident of C1>, <span of C1>, Named(vec![(<ident of x>, <span of x>)]))])
+//! ```
+
+pub use StaticFields::*;
+pub use SubstructureFields::*;
+
+use std::cell::RefCell;
+use std::iter;
+use std::vec;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, EnumDef, Expr, Generics, PatKind};
+use rustc_ast::{GenericArg, GenericParamKind, VariantData};
+use rustc_attr as attr;
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::Span;
+
+use ty::{Bounds, Path, Ref, Self_, Ty};
+
+use crate::deriving;
+
+pub mod ty;
+
+pub struct TraitDef<'a> {
+    /// The span for the current #[derive(Foo)] header.
+    pub span: Span,
+
+    pub attributes: Vec<ast::Attribute>,
+
+    /// Path of the trait, including any type parameters
+    pub path: Path,
+
+    /// Additional bounds required of any type parameters of the type,
+    /// other than the current trait
+    pub additional_bounds: Vec<Ty>,
+
+    /// Any extra lifetimes and/or bounds, e.g., `D: serialize::Decoder`
+    pub generics: Bounds,
+
+    /// Can this trait be derived for unions?
+    pub supports_unions: bool,
+
+    pub methods: Vec<MethodDef<'a>>,
+
+    pub associated_types: Vec<(Ident, Ty)>,
+}
+
+pub struct MethodDef<'a> {
+    /// name of the method
+    pub name: Symbol,
+    /// List of generics, e.g., `R: rand::Rng`
+    pub generics: Bounds,
+
+    /// Is there is a `&self` argument? If not, it is a static function.
+    pub explicit_self: bool,
+
+    /// Arguments other than the self argument.
+    pub nonself_args: Vec<(Ty, Symbol)>,
+
+    /// Returns type
+    pub ret_ty: Ty,
+
+    pub attributes: Vec<ast::Attribute>,
+
+    /// Can we combine fieldless variants for enums into a single match arm?
+    /// If true, indicates that the trait operation uses the enum tag in some
+    /// way.
+    pub unify_fieldless_variants: bool,
+
+    pub combine_substructure: RefCell<CombineSubstructureFunc<'a>>,
+}
+
+/// All the data about the data structure/method being derived upon.
+pub struct Substructure<'a> {
+    /// ident of self
+    pub type_ident: Ident,
+    /// Verbatim access to any non-selflike arguments, i.e. arguments that
+    /// don't have type `&Self`.
+    pub nonselflike_args: &'a [P<Expr>],
+    pub fields: &'a SubstructureFields<'a>,
+}
+
+/// Summary of the relevant parts of a struct/enum field.
+pub struct FieldInfo {
+    pub span: Span,
+    /// None for tuple structs/normal enum variants, Some for normal
+    /// structs/struct enum variants.
+    pub name: Option<Ident>,
+    /// The expression corresponding to this field of `self`
+    /// (specifically, a reference to it).
+    pub self_expr: P<Expr>,
+    /// The expressions corresponding to references to this field in
+    /// the other selflike arguments.
+    pub other_selflike_exprs: Vec<P<Expr>>,
+}
+
+/// Fields for a static method
+pub enum StaticFields {
+    /// Tuple and unit structs/enum variants like this.
+    Unnamed(Vec<Span>, bool /*is tuple*/),
+    /// Normal structs/struct variants.
+    Named(Vec<(Ident, Span)>),
+}
+
+/// A summary of the possible sets of fields.
+pub enum SubstructureFields<'a> {
+    /// A non-static method with `Self` is a struct.
+    Struct(&'a ast::VariantData, Vec<FieldInfo>),
+
+    /// Matching variants of the enum: variant index, variant count, ast::Variant,
+    /// fields: the field name is only non-`None` in the case of a struct
+    /// variant.
+    EnumMatching(usize, usize, &'a ast::Variant, Vec<FieldInfo>),
+
+    /// The tag of an enum. The first field is a `FieldInfo` for the tags, as
+    /// if they were fields. The second field is the expression to combine the
+    /// tag expression with; it will be `None` if no match is necessary.
+    EnumTag(FieldInfo, Option<P<Expr>>),
+
+    /// A static method where `Self` is a struct.
+    StaticStruct(&'a ast::VariantData, StaticFields),
+
+    /// A static method where `Self` is an enum.
+    StaticEnum(&'a ast::EnumDef, Vec<(Ident, Span, StaticFields)>),
+}
+
+/// Combine the values of all the fields together. The last argument is
+/// all the fields of all the structures.
+pub type CombineSubstructureFunc<'a> =
+    Box<dyn FnMut(&mut ExtCtxt<'_>, Span, &Substructure<'_>) -> BlockOrExpr + 'a>;
+
+pub fn combine_substructure(
+    f: CombineSubstructureFunc<'_>,
+) -> RefCell<CombineSubstructureFunc<'_>> {
+    RefCell::new(f)
+}
+
+struct TypeParameter {
+    bound_generic_params: Vec<ast::GenericParam>,
+    ty: P<ast::Ty>,
+}
+
+// The code snippets built up for derived code are sometimes used as blocks
+// (e.g. in a function body) and sometimes used as expressions (e.g. in a match
+// arm). This structure avoids committing to either form until necessary,
+// avoiding the insertion of any unnecessary blocks.
+//
+// The statements come before the expression.
+pub struct BlockOrExpr(Vec<ast::Stmt>, Option<P<Expr>>);
+
+impl BlockOrExpr {
+    pub fn new_stmts(stmts: Vec<ast::Stmt>) -> BlockOrExpr {
+        BlockOrExpr(stmts, None)
+    }
+
+    pub fn new_expr(expr: P<Expr>) -> BlockOrExpr {
+        BlockOrExpr(vec![], Some(expr))
+    }
+
+    pub fn new_mixed(stmts: Vec<ast::Stmt>, expr: Option<P<Expr>>) -> BlockOrExpr {
+        BlockOrExpr(stmts, expr)
+    }
+
+    // Converts it into a block.
+    fn into_block(mut self, cx: &ExtCtxt<'_>, span: Span) -> P<ast::Block> {
+        if let Some(expr) = self.1 {
+            self.0.push(cx.stmt_expr(expr));
+        }
+        cx.block(span, self.0)
+    }
+
+    // Converts it into an expression.
+    fn into_expr(self, cx: &ExtCtxt<'_>, span: Span) -> P<Expr> {
+        if self.0.is_empty() {
+            match self.1 {
+                None => cx.expr_block(cx.block(span, vec![])),
+                Some(expr) => expr,
+            }
+        } else if self.0.len() == 1
+            && let ast::StmtKind::Expr(expr) = &self.0[0].kind
+            && self.1.is_none()
+        {
+            // There's only a single statement expression. Pull it out.
+            expr.clone()
+        } else {
+            // Multiple statements and/or expressions.
+            cx.expr_block(self.into_block(cx, span))
+        }
+    }
+}
+
+/// This method helps to extract all the type parameters referenced from a
+/// type. For a type parameter `<T>`, it looks for either a `TyPath` that
+/// is not global and starts with `T`, or a `TyQPath`.
+/// Also include bound generic params from the input type.
+fn find_type_parameters(
+    ty: &ast::Ty,
+    ty_param_names: &[Symbol],
+    cx: &ExtCtxt<'_>,
+) -> Vec<TypeParameter> {
+    use rustc_ast::visit;
+
+    struct Visitor<'a, 'b> {
+        cx: &'a ExtCtxt<'b>,
+        ty_param_names: &'a [Symbol],
+        bound_generic_params_stack: Vec<ast::GenericParam>,
+        type_params: Vec<TypeParameter>,
+    }
+
+    impl<'a, 'b> visit::Visitor<'a> for Visitor<'a, 'b> {
+        fn visit_ty(&mut self, ty: &'a ast::Ty) {
+            if let ast::TyKind::Path(_, ref path) = ty.kind {
+                if let Some(segment) = path.segments.first() {
+                    if self.ty_param_names.contains(&segment.ident.name) {
+                        self.type_params.push(TypeParameter {
+                            bound_generic_params: self.bound_generic_params_stack.clone(),
+                            ty: P(ty.clone()),
+                        });
+                    }
+                }
+            }
+
+            visit::walk_ty(self, ty)
+        }
+
+        // Place bound generic params on a stack, to extract them when a type is encountered.
+        fn visit_poly_trait_ref(
+            &mut self,
+            trait_ref: &'a ast::PolyTraitRef,
+            modifier: &'a ast::TraitBoundModifier,
+        ) {
+            let stack_len = self.bound_generic_params_stack.len();
+            self.bound_generic_params_stack
+                .extend(trait_ref.bound_generic_params.clone().into_iter());
+
+            visit::walk_poly_trait_ref(self, trait_ref, modifier);
+
+            self.bound_generic_params_stack.truncate(stack_len);
+        }
+
+        fn visit_mac_call(&mut self, mac: &ast::MacCall) {
+            self.cx.span_err(mac.span(), "`derive` cannot be used on items with type macros");
+        }
+    }
+
+    let mut visitor = Visitor {
+        cx,
+        ty_param_names,
+        bound_generic_params_stack: Vec::new(),
+        type_params: Vec::new(),
+    };
+    visit::Visitor::visit_ty(&mut visitor, ty);
+
+    visitor.type_params
+}
+
+impl<'a> TraitDef<'a> {
+    pub fn expand(
+        self,
+        cx: &mut ExtCtxt<'_>,
+        mitem: &ast::MetaItem,
+        item: &'a Annotatable,
+        push: &mut dyn FnMut(Annotatable),
+    ) {
+        self.expand_ext(cx, mitem, item, push, false);
+    }
+
+    pub fn expand_ext(
+        self,
+        cx: &mut ExtCtxt<'_>,
+        mitem: &ast::MetaItem,
+        item: &'a Annotatable,
+        push: &mut dyn FnMut(Annotatable),
+        from_scratch: bool,
+    ) {
+        match *item {
+            Annotatable::Item(ref item) => {
+                let is_packed = item.attrs.iter().any(|attr| {
+                    for r in attr::find_repr_attrs(&cx.sess, attr) {
+                        if let attr::ReprPacked(_) = r {
+                            return true;
+                        }
+                    }
+                    false
+                });
+                let has_no_type_params = match item.kind {
+                    ast::ItemKind::Struct(_, ref generics)
+                    | ast::ItemKind::Enum(_, ref generics)
+                    | ast::ItemKind::Union(_, ref generics) => !generics
+                        .params
+                        .iter()
+                        .any(|param| matches!(param.kind, ast::GenericParamKind::Type { .. })),
+                    _ => unreachable!(),
+                };
+                let container_id = cx.current_expansion.id.expn_data().parent.expect_local();
+                let always_copy = has_no_type_params && cx.resolver.has_derive_copy(container_id);
+
+                let newitem = match item.kind {
+                    ast::ItemKind::Struct(ref struct_def, ref generics) => self.expand_struct_def(
+                        cx,
+                        &struct_def,
+                        item.ident,
+                        generics,
+                        from_scratch,
+                        is_packed,
+                        always_copy,
+                    ),
+                    ast::ItemKind::Enum(ref enum_def, ref generics) => {
+                        // We ignore `is_packed`/`always_copy` here, because
+                        // `repr(packed)` enums cause an error later on.
+                        //
+                        // This can only cause further compilation errors
+                        // downstream in blatantly illegal code, so it
+                        // is fine.
+                        self.expand_enum_def(cx, enum_def, item.ident, generics, from_scratch)
+                    }
+                    ast::ItemKind::Union(ref struct_def, ref generics) => {
+                        if self.supports_unions {
+                            self.expand_struct_def(
+                                cx,
+                                &struct_def,
+                                item.ident,
+                                generics,
+                                from_scratch,
+                                is_packed,
+                                always_copy,
+                            )
+                        } else {
+                            cx.span_err(mitem.span, "this trait cannot be derived for unions");
+                            return;
+                        }
+                    }
+                    _ => unreachable!(),
+                };
+                // Keep the lint attributes of the previous item to control how the
+                // generated implementations are linted
+                let mut attrs = newitem.attrs.clone();
+                attrs.extend(
+                    item.attrs
+                        .iter()
+                        .filter(|a| {
+                            [
+                                sym::allow,
+                                sym::warn,
+                                sym::deny,
+                                sym::forbid,
+                                sym::stable,
+                                sym::unstable,
+                            ]
+                            .contains(&a.name_or_empty())
+                        })
+                        .cloned(),
+                );
+                push(Annotatable::Item(P(ast::Item { attrs, ..(*newitem).clone() })))
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    /// Given that we are deriving a trait `DerivedTrait` for a type like:
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// struct Struct<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z> where C: WhereTrait {
+    ///     a: A,
+    ///     b: B::Item,
+    ///     b1: <B as DeclaredTrait>::Item,
+    ///     c1: <C as WhereTrait>::Item,
+    ///     c2: Option<<C as WhereTrait>::Item>,
+    ///     ...
+    /// }
+    /// ```
+    ///
+    /// create an impl like:
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// impl<'a, ..., 'z, A, B: DeclaredTrait, C, ... Z> where
+    ///     C:                       WhereTrait,
+    ///     A: DerivedTrait + B1 + ... + BN,
+    ///     B: DerivedTrait + B1 + ... + BN,
+    ///     C: DerivedTrait + B1 + ... + BN,
+    ///     B::Item:                 DerivedTrait + B1 + ... + BN,
+    ///     <C as WhereTrait>::Item: DerivedTrait + B1 + ... + BN,
+    ///     ...
+    /// {
+    ///     ...
+    /// }
+    /// ```
+    ///
+    /// where B1, ..., BN are the bounds given by `bounds_paths`.'. Z is a phantom type, and
+    /// therefore does not get bound by the derived trait.
+    fn create_derived_impl(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        type_ident: Ident,
+        generics: &Generics,
+        field_tys: Vec<P<ast::Ty>>,
+        methods: Vec<P<ast::AssocItem>>,
+    ) -> P<ast::Item> {
+        let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
+
+        // Transform associated types from `deriving::ty::Ty` into `ast::AssocItem`
+        let associated_types = self.associated_types.iter().map(|&(ident, ref type_def)| {
+            P(ast::AssocItem {
+                id: ast::DUMMY_NODE_ID,
+                span: self.span,
+                ident,
+                vis: ast::Visibility {
+                    span: self.span.shrink_to_lo(),
+                    kind: ast::VisibilityKind::Inherited,
+                    tokens: None,
+                },
+                attrs: Vec::new(),
+                kind: ast::AssocItemKind::TyAlias(Box::new(ast::TyAlias {
+                    defaultness: ast::Defaultness::Final,
+                    generics: Generics::default(),
+                    where_clauses: (
+                        ast::TyAliasWhereClause::default(),
+                        ast::TyAliasWhereClause::default(),
+                    ),
+                    where_predicates_split: 0,
+                    bounds: Vec::new(),
+                    ty: Some(type_def.to_ty(cx, self.span, type_ident, generics)),
+                })),
+                tokens: None,
+            })
+        });
+
+        let Generics { mut params, mut where_clause, .. } =
+            self.generics.to_generics(cx, self.span, type_ident, generics);
+        where_clause.span = generics.where_clause.span;
+        let ctxt = self.span.ctxt();
+        let span = generics.span.with_ctxt(ctxt);
+
+        // Create the generic parameters
+        params.extend(generics.params.iter().map(|param| match &param.kind {
+            GenericParamKind::Lifetime { .. } => param.clone(),
+            GenericParamKind::Type { .. } => {
+                // I don't think this can be moved out of the loop, since
+                // a GenericBound requires an ast id
+                let bounds: Vec<_> =
+                    // extra restrictions on the generics parameters to the
+                    // type being derived upon
+                    self.additional_bounds.iter().map(|p| {
+                        cx.trait_bound(p.to_path(cx, self.span, type_ident, generics))
+                    }).chain(
+                        // require the current trait
+                        iter::once(cx.trait_bound(trait_path.clone()))
+                    ).chain(
+                        // also add in any bounds from the declaration
+                        param.bounds.iter().cloned()
+                    ).collect();
+
+                cx.typaram(param.ident.span.with_ctxt(ctxt), param.ident, vec![], bounds, None)
+            }
+            GenericParamKind::Const { ty, kw_span, .. } => {
+                let const_nodefault_kind = GenericParamKind::Const {
+                    ty: ty.clone(),
+                    kw_span: kw_span.with_ctxt(ctxt),
+
+                    // We can't have default values inside impl block
+                    default: None,
+                };
+                let mut param_clone = param.clone();
+                param_clone.kind = const_nodefault_kind;
+                param_clone
+            }
+        }));
+
+        // and similarly for where clauses
+        where_clause.predicates.extend(generics.where_clause.predicates.iter().map(|clause| {
+            match clause {
+                ast::WherePredicate::BoundPredicate(wb) => {
+                    let span = wb.span.with_ctxt(ctxt);
+                    ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
+                        span,
+                        ..wb.clone()
+                    })
+                }
+                ast::WherePredicate::RegionPredicate(wr) => {
+                    let span = wr.span.with_ctxt(ctxt);
+                    ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
+                        span,
+                        ..wr.clone()
+                    })
+                }
+                ast::WherePredicate::EqPredicate(we) => {
+                    let span = we.span.with_ctxt(ctxt);
+                    ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
+                        id: ast::DUMMY_NODE_ID,
+                        span,
+                        ..we.clone()
+                    })
+                }
+            }
+        }));
+
+        {
+            // Extra scope required here so ty_params goes out of scope before params is moved
+
+            let mut ty_params = params
+                .iter()
+                .filter(|param| matches!(param.kind, ast::GenericParamKind::Type { .. }))
+                .peekable();
+
+            if ty_params.peek().is_some() {
+                let ty_param_names: Vec<Symbol> =
+                    ty_params.map(|ty_param| ty_param.ident.name).collect();
+
+                for field_ty in field_tys {
+                    let field_ty_params = find_type_parameters(&field_ty, &ty_param_names, cx);
+
+                    for field_ty_param in field_ty_params {
+                        // if we have already handled this type, skip it
+                        if let ast::TyKind::Path(_, ref p) = field_ty_param.ty.kind {
+                            if p.segments.len() == 1
+                                && ty_param_names.contains(&p.segments[0].ident.name)
+                            {
+                                continue;
+                            };
+                        }
+                        let mut bounds: Vec<_> = self
+                            .additional_bounds
+                            .iter()
+                            .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                            .collect();
+
+                        // require the current trait
+                        bounds.push(cx.trait_bound(trait_path.clone()));
+
+                        let predicate = ast::WhereBoundPredicate {
+                            span: self.span,
+                            bound_generic_params: field_ty_param.bound_generic_params,
+                            bounded_ty: field_ty_param.ty,
+                            bounds,
+                        };
+
+                        let predicate = ast::WherePredicate::BoundPredicate(predicate);
+                        where_clause.predicates.push(predicate);
+                    }
+                }
+            }
+        }
+
+        let trait_generics = Generics { params, where_clause, span };
+
+        // Create the reference to the trait.
+        let trait_ref = cx.trait_ref(trait_path);
+
+        let self_params: Vec<_> = generics
+            .params
+            .iter()
+            .map(|param| match param.kind {
+                GenericParamKind::Lifetime { .. } => {
+                    GenericArg::Lifetime(cx.lifetime(param.ident.span.with_ctxt(ctxt), param.ident))
+                }
+                GenericParamKind::Type { .. } => {
+                    GenericArg::Type(cx.ty_ident(param.ident.span.with_ctxt(ctxt), param.ident))
+                }
+                GenericParamKind::Const { .. } => {
+                    GenericArg::Const(cx.const_ident(param.ident.span.with_ctxt(ctxt), param.ident))
+                }
+            })
+            .collect();
+
+        // Create the type of `self`.
+        let path = cx.path_all(self.span, false, vec![type_ident], self_params);
+        let self_type = cx.ty_path(path);
+
+        let attr = cx.attribute(cx.meta_word(self.span, sym::automatically_derived));
+        let opt_trait_ref = Some(trait_ref);
+
+        let mut a = vec![attr];
+        a.extend(self.attributes.iter().cloned());
+
+        cx.item(
+            self.span,
+            Ident::empty(),
+            a,
+            ast::ItemKind::Impl(Box::new(ast::Impl {
+                unsafety: ast::Unsafe::No,
+                polarity: ast::ImplPolarity::Positive,
+                defaultness: ast::Defaultness::Final,
+                constness: ast::Const::No,
+                generics: trait_generics,
+                of_trait: opt_trait_ref,
+                self_ty: self_type,
+                items: methods.into_iter().chain(associated_types).collect(),
+            })),
+        )
+    }
+
+    fn expand_struct_def(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        struct_def: &'a VariantData,
+        type_ident: Ident,
+        generics: &Generics,
+        from_scratch: bool,
+        is_packed: bool,
+        always_copy: bool,
+    ) -> P<ast::Item> {
+        let field_tys: Vec<P<ast::Ty>> =
+            struct_def.fields().iter().map(|field| field.ty.clone()).collect();
+
+        let methods = self
+            .methods
+            .iter()
+            .map(|method_def| {
+                let (explicit_self, selflike_args, nonselflike_args, nonself_arg_tys) =
+                    method_def.extract_arg_details(cx, self, type_ident, generics);
+
+                let body = if from_scratch || method_def.is_static() {
+                    method_def.expand_static_struct_method_body(
+                        cx,
+                        self,
+                        struct_def,
+                        type_ident,
+                        &nonselflike_args,
+                    )
+                } else {
+                    method_def.expand_struct_method_body(
+                        cx,
+                        self,
+                        struct_def,
+                        type_ident,
+                        &selflike_args,
+                        &nonselflike_args,
+                        is_packed,
+                        always_copy,
+                    )
+                };
+
+                method_def.create_method(
+                    cx,
+                    self,
+                    type_ident,
+                    generics,
+                    explicit_self,
+                    nonself_arg_tys,
+                    body,
+                )
+            })
+            .collect();
+
+        self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
+    }
+
+    fn expand_enum_def(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        enum_def: &'a EnumDef,
+        type_ident: Ident,
+        generics: &Generics,
+        from_scratch: bool,
+    ) -> P<ast::Item> {
+        let mut field_tys = Vec::new();
+
+        for variant in &enum_def.variants {
+            field_tys.extend(variant.data.fields().iter().map(|field| field.ty.clone()));
+        }
+
+        let methods = self
+            .methods
+            .iter()
+            .map(|method_def| {
+                let (explicit_self, selflike_args, nonselflike_args, nonself_arg_tys) =
+                    method_def.extract_arg_details(cx, self, type_ident, generics);
+
+                let body = if from_scratch || method_def.is_static() {
+                    method_def.expand_static_enum_method_body(
+                        cx,
+                        self,
+                        enum_def,
+                        type_ident,
+                        &nonselflike_args,
+                    )
+                } else {
+                    method_def.expand_enum_method_body(
+                        cx,
+                        self,
+                        enum_def,
+                        type_ident,
+                        selflike_args,
+                        &nonselflike_args,
+                    )
+                };
+
+                method_def.create_method(
+                    cx,
+                    self,
+                    type_ident,
+                    generics,
+                    explicit_self,
+                    nonself_arg_tys,
+                    body,
+                )
+            })
+            .collect();
+
+        self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
+    }
+}
+
+impl<'a> MethodDef<'a> {
+    fn call_substructure_method(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        type_ident: Ident,
+        nonselflike_args: &[P<Expr>],
+        fields: &SubstructureFields<'_>,
+    ) -> BlockOrExpr {
+        let span = trait_.span;
+        let substructure = Substructure { type_ident, nonselflike_args, fields };
+        let mut f = self.combine_substructure.borrow_mut();
+        let f: &mut CombineSubstructureFunc<'_> = &mut *f;
+        f(cx, span, &substructure)
+    }
+
+    fn get_ret_ty(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        generics: &Generics,
+        type_ident: Ident,
+    ) -> P<ast::Ty> {
+        self.ret_ty.to_ty(cx, trait_.span, type_ident, generics)
+    }
+
+    fn is_static(&self) -> bool {
+        !self.explicit_self
+    }
+
+    // The return value includes:
+    // - explicit_self: The `&self` arg, if present.
+    // - selflike_args: Expressions for `&self` (if present) and also any other
+    //   args with the same type (e.g. the `other` arg in `PartialEq::eq`).
+    // - nonselflike_args: Expressions for all the remaining args.
+    // - nonself_arg_tys: Additional information about all the args other than
+    //   `&self`.
+    fn extract_arg_details(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        type_ident: Ident,
+        generics: &Generics,
+    ) -> (Option<ast::ExplicitSelf>, Vec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
+        let mut selflike_args = Vec::new();
+        let mut nonselflike_args = Vec::new();
+        let mut nonself_arg_tys = Vec::new();
+        let span = trait_.span;
+
+        let explicit_self = if self.explicit_self {
+            let (self_expr, explicit_self) = ty::get_explicit_self(cx, span);
+            selflike_args.push(self_expr);
+            Some(explicit_self)
+        } else {
+            None
+        };
+
+        for (ty, name) in self.nonself_args.iter() {
+            let ast_ty = ty.to_ty(cx, span, type_ident, generics);
+            let ident = Ident::new(*name, span);
+            nonself_arg_tys.push((ident, ast_ty));
+
+            let arg_expr = cx.expr_ident(span, ident);
+
+            match ty {
+                // Selflike (`&Self`) arguments only occur in non-static methods.
+                Ref(box Self_, _) if !self.is_static() => selflike_args.push(arg_expr),
+                Self_ => cx.span_bug(span, "`Self` in non-return position"),
+                _ => nonselflike_args.push(arg_expr),
+            }
+        }
+
+        (explicit_self, selflike_args, nonselflike_args, nonself_arg_tys)
+    }
+
+    fn create_method(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        type_ident: Ident,
+        generics: &Generics,
+        explicit_self: Option<ast::ExplicitSelf>,
+        nonself_arg_tys: Vec<(Ident, P<ast::Ty>)>,
+        body: BlockOrExpr,
+    ) -> P<ast::AssocItem> {
+        let span = trait_.span;
+        // Create the generics that aren't for `Self`.
+        let fn_generics = self.generics.to_generics(cx, span, type_ident, generics);
+
+        let args = {
+            let self_arg = explicit_self.map(|explicit_self| {
+                let ident = Ident::with_dummy_span(kw::SelfLower).with_span_pos(span);
+                ast::Param::from_self(ast::AttrVec::default(), explicit_self, ident)
+            });
+            let nonself_args =
+                nonself_arg_tys.into_iter().map(|(name, ty)| cx.param(span, name, ty));
+            self_arg.into_iter().chain(nonself_args).collect()
+        };
+
+        let ret_type = self.get_ret_ty(cx, trait_, generics, type_ident);
+
+        let method_ident = Ident::new(self.name, span);
+        let fn_decl = cx.fn_decl(args, ast::FnRetTy::Ty(ret_type));
+        let body_block = body.into_block(cx, span);
+
+        let trait_lo_sp = span.shrink_to_lo();
+
+        let sig = ast::FnSig { header: ast::FnHeader::default(), decl: fn_decl, span };
+        let defaultness = ast::Defaultness::Final;
+
+        // Create the method.
+        P(ast::AssocItem {
+            id: ast::DUMMY_NODE_ID,
+            attrs: self.attributes.clone(),
+            span,
+            vis: ast::Visibility {
+                span: trait_lo_sp,
+                kind: ast::VisibilityKind::Inherited,
+                tokens: None,
+            },
+            ident: method_ident,
+            kind: ast::AssocItemKind::Fn(Box::new(ast::Fn {
+                defaultness,
+                sig,
+                generics: fn_generics,
+                body: Some(body_block),
+            })),
+            tokens: None,
+        })
+    }
+
+    /// The normal case uses field access.
+    /// ```
+    /// #[derive(PartialEq)]
+    /// # struct Dummy;
+    /// struct A { x: u8, y: u8 }
+    ///
+    /// // equivalent to:
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         self.x == other.x && self.y == other.y
+    ///     }
+    /// }
+    /// ```
+    /// But if the struct is `repr(packed)`, we can't use something like
+    /// `&self.x` because that might cause an unaligned ref. So for any trait
+    /// method that takes a reference, if the struct impls `Copy` then we use a
+    /// local block to force a copy:
+    /// ```
+    /// # struct A { x: u8, y: u8 }
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         // Desugars to `{ self.x }.eq(&{ other.y }) && ...`
+    ///         { self.x } == { other.y } && { self.y } == { other.y }
+    ///     }
+    /// }
+    /// impl Hash for A {
+    ///     fn hash<__H: ::core::hash::Hasher>(&self, state: &mut __H) -> () {
+    ///         ::core::hash::Hash::hash(&{ self.x }, state);
+    ///         ::core::hash::Hash::hash(&{ self.y }, state)
+    ///     }
+    /// }
+    /// ```
+    /// If the struct doesn't impl `Copy`, we use let-destructuring with `ref`:
+    /// ```
+    /// # struct A { x: u8, y: u8 }
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         let Self { x: ref __self_0_0, y: ref __self_0_1 } = *self;
+    ///         let Self { x: ref __self_1_0, y: ref __self_1_1 } = *other;
+    ///         *__self_0_0 == *__self_1_0 && *__self_0_1 == *__self_1_1
+    ///     }
+    /// }
+    /// ```
+    /// This latter case only works if the fields match the alignment required
+    /// by the `packed(N)` attribute. (We'll get errors later on if not.)
+    fn expand_struct_method_body<'b>(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'b>,
+        struct_def: &'b VariantData,
+        type_ident: Ident,
+        selflike_args: &[P<Expr>],
+        nonselflike_args: &[P<Expr>],
+        is_packed: bool,
+        always_copy: bool,
+    ) -> BlockOrExpr {
+        let span = trait_.span;
+        assert!(selflike_args.len() == 1 || selflike_args.len() == 2);
+
+        let mk_body = |cx, selflike_fields| {
+            self.call_substructure_method(
+                cx,
+                trait_,
+                type_ident,
+                nonselflike_args,
+                &Struct(struct_def, selflike_fields),
+            )
+        };
+
+        if !is_packed {
+            let selflike_fields =
+                trait_.create_struct_field_access_fields(cx, selflike_args, struct_def, false);
+            mk_body(cx, selflike_fields)
+        } else if always_copy {
+            let selflike_fields =
+                trait_.create_struct_field_access_fields(cx, selflike_args, struct_def, true);
+            mk_body(cx, selflike_fields)
+        } else {
+            // Neither packed nor copy. Need to use ref patterns.
+            let prefixes: Vec<_> =
+                (0..selflike_args.len()).map(|i| format!("__self_{}", i)).collect();
+            let addr_of = always_copy;
+            let selflike_fields =
+                trait_.create_struct_pattern_fields(cx, struct_def, &prefixes, addr_of);
+            let mut body = mk_body(cx, selflike_fields);
+
+            let struct_path = cx.path(span, vec![Ident::new(kw::SelfUpper, type_ident.span)]);
+            let use_ref_pat = is_packed && !always_copy;
+            let patterns =
+                trait_.create_struct_patterns(cx, struct_path, struct_def, &prefixes, use_ref_pat);
+
+            // Do the let-destructuring.
+            let mut stmts: Vec<_> = iter::zip(selflike_args, patterns)
+                .map(|(selflike_arg_expr, pat)| {
+                    let selflike_arg_expr = cx.expr_deref(span, selflike_arg_expr.clone());
+                    cx.stmt_let_pat(span, pat, selflike_arg_expr)
+                })
+                .collect();
+            stmts.extend(std::mem::take(&mut body.0));
+            BlockOrExpr(stmts, body.1)
+        }
+    }
+
+    fn expand_static_struct_method_body(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        struct_def: &VariantData,
+        type_ident: Ident,
+        nonselflike_args: &[P<Expr>],
+    ) -> BlockOrExpr {
+        let summary = trait_.summarise_struct(cx, struct_def);
+
+        self.call_substructure_method(
+            cx,
+            trait_,
+            type_ident,
+            nonselflike_args,
+            &StaticStruct(struct_def, summary),
+        )
+    }
+
+    /// ```
+    /// #[derive(PartialEq)]
+    /// # struct Dummy;
+    /// enum A {
+    ///     A1,
+    ///     A2(i32)
+    /// }
+    /// ```
+    /// is equivalent to:
+    /// ```
+    /// impl ::core::cmp::PartialEq for A {
+    ///     #[inline]
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         let __self_tag = ::core::intrinsics::discriminant_value(self);
+    ///         let __arg1_tag = ::core::intrinsics::discriminant_value(other);
+    ///         __self_tag == __arg1_tag &&
+    ///             match (self, other) {
+    ///                 (A::A2(__self_0), A::A2(__arg1_0)) =>
+    ///                     *__self_0 == *__arg1_0,
+    ///                 _ => true,
+    ///             }
+    ///     }
+    /// }
+    /// ```
+    /// Creates a tag check combined with a match for a tuple of all
+    /// `selflike_args`, with an arm for each variant with fields, possibly an
+    /// arm for each fieldless variant (if `!unify_fieldless_variants` is not
+    /// true), and possibly a default arm.
+    fn expand_enum_method_body<'b>(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'b>,
+        enum_def: &'b EnumDef,
+        type_ident: Ident,
+        selflike_args: Vec<P<Expr>>,
+        nonselflike_args: &[P<Expr>],
+    ) -> BlockOrExpr {
+        let span = trait_.span;
+        let variants = &enum_def.variants;
+
+        // Traits that unify fieldless variants always use the tag(s).
+        let uses_tags = self.unify_fieldless_variants;
+
+        // There is no sensible code to be generated for *any* deriving on a
+        // zero-variant enum. So we just generate a failing expression.
+        if variants.is_empty() {
+            return BlockOrExpr(vec![], Some(deriving::call_unreachable(cx, span)));
+        }
+
+        let prefixes = iter::once("__self".to_string())
+            .chain(
+                selflike_args
+                    .iter()
+                    .enumerate()
+                    .skip(1)
+                    .map(|(arg_count, _selflike_arg)| format!("__arg{}", arg_count)),
+            )
+            .collect::<Vec<String>>();
+
+        // Build a series of let statements mapping each selflike_arg
+        // to its discriminant value.
+        //
+        // e.g. for `PartialEq::eq` builds two statements:
+        // ```
+        // let __self_tag = ::core::intrinsics::discriminant_value(self);
+        // let __arg1_tag = ::core::intrinsics::discriminant_value(other);
+        // ```
+        let get_tag_pieces = |cx: &ExtCtxt<'_>| {
+            let tag_idents: Vec<_> = prefixes
+                .iter()
+                .map(|name| Ident::from_str_and_span(&format!("{}_tag", name), span))
+                .collect();
+
+            let mut tag_exprs: Vec<_> = tag_idents
+                .iter()
+                .map(|&ident| cx.expr_addr_of(span, cx.expr_ident(span, ident)))
+                .collect();
+
+            let self_expr = tag_exprs.remove(0);
+            let other_selflike_exprs = tag_exprs;
+            let tag_field = FieldInfo { span, name: None, self_expr, other_selflike_exprs };
+
+            let tag_let_stmts: Vec<_> = iter::zip(&tag_idents, &selflike_args)
+                .map(|(&ident, selflike_arg)| {
+                    let variant_value = deriving::call_intrinsic(
+                        cx,
+                        span,
+                        sym::discriminant_value,
+                        vec![selflike_arg.clone()],
+                    );
+                    cx.stmt_let(span, false, ident, variant_value)
+                })
+                .collect();
+
+            (tag_field, tag_let_stmts)
+        };
+
+        // There are some special cases involving fieldless enums where no
+        // match is necessary.
+        let all_fieldless = variants.iter().all(|v| v.data.fields().is_empty());
+        if all_fieldless {
+            if uses_tags && variants.len() > 1 {
+                // If the type is fieldless and the trait uses the tag and
+                // there are multiple variants, we need just an operation on
+                // the tag(s).
+                let (tag_field, mut tag_let_stmts) = get_tag_pieces(cx);
+                let mut tag_check = self.call_substructure_method(
+                    cx,
+                    trait_,
+                    type_ident,
+                    nonselflike_args,
+                    &EnumTag(tag_field, None),
+                );
+                tag_let_stmts.append(&mut tag_check.0);
+                return BlockOrExpr(tag_let_stmts, tag_check.1);
+            }
+
+            if variants.len() == 1 {
+                // If there is a single variant, we don't need an operation on
+                // the tag(s). Just use the most degenerate result.
+                return self.call_substructure_method(
+                    cx,
+                    trait_,
+                    type_ident,
+                    nonselflike_args,
+                    &EnumMatching(0, 1, &variants[0], Vec::new()),
+                );
+            };
+        }
+
+        // These arms are of the form:
+        // (Variant1, Variant1, ...) => Body1
+        // (Variant2, Variant2, ...) => Body2
+        // ...
+        // where each tuple has length = selflike_args.len()
+        let mut match_arms: Vec<ast::Arm> = variants
+            .iter()
+            .enumerate()
+            .filter(|&(_, v)| !(self.unify_fieldless_variants && v.data.fields().is_empty()))
+            .map(|(index, variant)| {
+                // A single arm has form (&VariantK, &VariantK, ...) => BodyK
+                // (see "Final wrinkle" note below for why.)
+
+                let addr_of = false; // because enums can't be repr(packed)
+                let fields =
+                    trait_.create_struct_pattern_fields(cx, &variant.data, &prefixes, addr_of);
+
+                let sp = variant.span.with_ctxt(trait_.span.ctxt());
+                let variant_path = cx.path(sp, vec![type_ident, variant.ident]);
+                let use_ref_pat = false; // because enums can't be repr(packed)
+                let mut subpats: Vec<_> = trait_.create_struct_patterns(
+                    cx,
+                    variant_path,
+                    &variant.data,
+                    &prefixes,
+                    use_ref_pat,
+                );
+
+                // `(VariantK, VariantK, ...)` or just `VariantK`.
+                let single_pat = if subpats.len() == 1 {
+                    subpats.pop().unwrap()
+                } else {
+                    cx.pat_tuple(span, subpats)
+                };
+
+                // For the BodyK, we need to delegate to our caller,
+                // passing it an EnumMatching to indicate which case
+                // we are in.
+                //
+                // Now, for some given VariantK, we have built up
+                // expressions for referencing every field of every
+                // Self arg, assuming all are instances of VariantK.
+                // Build up code associated with such a case.
+                let substructure = EnumMatching(index, variants.len(), variant, fields);
+                let arm_expr = self
+                    .call_substructure_method(
+                        cx,
+                        trait_,
+                        type_ident,
+                        nonselflike_args,
+                        &substructure,
+                    )
+                    .into_expr(cx, span);
+
+                cx.arm(span, single_pat, arm_expr)
+            })
+            .collect();
+
+        // Add a default arm to the match, if necessary.
+        let first_fieldless = variants.iter().find(|v| v.data.fields().is_empty());
+        let default = match first_fieldless {
+            Some(v) if self.unify_fieldless_variants => {
+                // We need a default case that handles all the fieldless
+                // variants. The index and actual variant aren't meaningful in
+                // this case, so just use dummy values.
+                Some(
+                    self.call_substructure_method(
+                        cx,
+                        trait_,
+                        type_ident,
+                        nonselflike_args,
+                        &EnumMatching(0, variants.len(), v, Vec::new()),
+                    )
+                    .into_expr(cx, span),
+                )
+            }
+            _ if variants.len() > 1 && selflike_args.len() > 1 => {
+                // Because we know that all the arguments will match if we reach
+                // the match expression we add the unreachable intrinsics as the
+                // result of the default which should help llvm in optimizing it.
+                Some(deriving::call_unreachable(cx, span))
+            }
+            _ => None,
+        };
+        if let Some(arm) = default {
+            match_arms.push(cx.arm(span, cx.pat_wild(span), arm));
+        }
+
+        // Create a match expression with one arm per discriminant plus
+        // possibly a default arm, e.g.:
+        //      match (self, other) {
+        //          (Variant1, Variant1, ...) => Body1
+        //          (Variant2, Variant2, ...) => Body2,
+        //          ...
+        //          _ => ::core::intrinsics::unreachable()
+        //      }
+        let get_match_expr = |mut selflike_args: Vec<P<Expr>>| {
+            let match_arg = if selflike_args.len() == 1 {
+                selflike_args.pop().unwrap()
+            } else {
+                cx.expr(span, ast::ExprKind::Tup(selflike_args))
+            };
+            cx.expr_match(span, match_arg, match_arms)
+        };
+
+        // If the trait uses the tag and there are multiple variants, we need
+        // to add a tag check operation before the match. Otherwise, the match
+        // is enough.
+        if uses_tags && variants.len() > 1 {
+            let (tag_field, mut tag_let_stmts) = get_tag_pieces(cx);
+
+            // Combine a tag check with the match.
+            let mut tag_check_plus_match = self.call_substructure_method(
+                cx,
+                trait_,
+                type_ident,
+                nonselflike_args,
+                &EnumTag(tag_field, Some(get_match_expr(selflike_args))),
+            );
+            tag_let_stmts.append(&mut tag_check_plus_match.0);
+            BlockOrExpr(tag_let_stmts, tag_check_plus_match.1)
+        } else {
+            BlockOrExpr(vec![], Some(get_match_expr(selflike_args)))
+        }
+    }
+
+    fn expand_static_enum_method_body(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        enum_def: &EnumDef,
+        type_ident: Ident,
+        nonselflike_args: &[P<Expr>],
+    ) -> BlockOrExpr {
+        let summary = enum_def
+            .variants
+            .iter()
+            .map(|v| {
+                let sp = v.span.with_ctxt(trait_.span.ctxt());
+                let summary = trait_.summarise_struct(cx, &v.data);
+                (v.ident, sp, summary)
+            })
+            .collect();
+        self.call_substructure_method(
+            cx,
+            trait_,
+            type_ident,
+            nonselflike_args,
+            &StaticEnum(enum_def, summary),
+        )
+    }
+}
+
+// general helper methods.
+impl<'a> TraitDef<'a> {
+    fn summarise_struct(&self, cx: &mut ExtCtxt<'_>, struct_def: &VariantData) -> StaticFields {
+        let mut named_idents = Vec::new();
+        let mut just_spans = Vec::new();
+        for field in struct_def.fields() {
+            let sp = field.span.with_ctxt(self.span.ctxt());
+            match field.ident {
+                Some(ident) => named_idents.push((ident, sp)),
+                _ => just_spans.push(sp),
+            }
+        }
+
+        let is_tuple = matches!(struct_def, ast::VariantData::Tuple(..));
+        match (just_spans.is_empty(), named_idents.is_empty()) {
+            (false, false) => {
+                cx.span_bug(self.span, "a struct with named and unnamed fields in generic `derive`")
+            }
+            // named fields
+            (_, false) => Named(named_idents),
+            // unnamed fields
+            (false, _) => Unnamed(just_spans, is_tuple),
+            // empty
+            _ => Named(Vec::new()),
+        }
+    }
+
+    fn create_struct_patterns(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        struct_path: ast::Path,
+        struct_def: &'a VariantData,
+        prefixes: &[String],
+        use_ref_pat: bool,
+    ) -> Vec<P<ast::Pat>> {
+        prefixes
+            .iter()
+            .map(|prefix| {
+                let pieces_iter =
+                    struct_def.fields().iter().enumerate().map(|(i, struct_field)| {
+                        let sp = struct_field.span.with_ctxt(self.span.ctxt());
+                        let binding_mode = if use_ref_pat {
+                            ast::BindingMode::ByRef(ast::Mutability::Not)
+                        } else {
+                            ast::BindingMode::ByValue(ast::Mutability::Not)
+                        };
+                        let ident = self.mk_pattern_ident(prefix, i);
+                        let path = ident.with_span_pos(sp);
+                        (
+                            sp,
+                            struct_field.ident,
+                            cx.pat(path.span, PatKind::Ident(binding_mode, path, None)),
+                        )
+                    });
+
+                let struct_path = struct_path.clone();
+                match *struct_def {
+                    VariantData::Struct(..) => {
+                        let field_pats = pieces_iter
+                            .map(|(sp, ident, pat)| {
+                                if ident.is_none() {
+                                    cx.span_bug(
+                                        sp,
+                                        "a braced struct with unnamed fields in `derive`",
+                                    );
+                                }
+                                ast::PatField {
+                                    ident: ident.unwrap(),
+                                    is_shorthand: false,
+                                    attrs: ast::AttrVec::new(),
+                                    id: ast::DUMMY_NODE_ID,
+                                    span: pat.span.with_ctxt(self.span.ctxt()),
+                                    pat,
+                                    is_placeholder: false,
+                                }
+                            })
+                            .collect();
+                        cx.pat_struct(self.span, struct_path, field_pats)
+                    }
+                    VariantData::Tuple(..) => {
+                        let subpats = pieces_iter.map(|(_, _, subpat)| subpat).collect();
+                        cx.pat_tuple_struct(self.span, struct_path, subpats)
+                    }
+                    VariantData::Unit(..) => cx.pat_path(self.span, struct_path),
+                }
+            })
+            .collect()
+    }
+
+    fn create_fields<F>(&self, struct_def: &'a VariantData, mk_exprs: F) -> Vec<FieldInfo>
+    where
+        F: Fn(usize, &ast::FieldDef, Span) -> Vec<P<ast::Expr>>,
+    {
+        struct_def
+            .fields()
+            .iter()
+            .enumerate()
+            .map(|(i, struct_field)| {
+                // For this field, get an expr for each selflike_arg. E.g. for
+                // `PartialEq::eq`, one for each of `&self` and `other`.
+                let sp = struct_field.span.with_ctxt(self.span.ctxt());
+                let mut exprs: Vec<_> = mk_exprs(i, struct_field, sp);
+                let self_expr = exprs.remove(0);
+                let other_selflike_exprs = exprs;
+                FieldInfo {
+                    span: sp.with_ctxt(self.span.ctxt()),
+                    name: struct_field.ident,
+                    self_expr,
+                    other_selflike_exprs,
+                }
+            })
+            .collect()
+    }
+
+    fn mk_pattern_ident(&self, prefix: &str, i: usize) -> Ident {
+        Ident::from_str_and_span(&format!("{}_{}", prefix, i), self.span)
+    }
+
+    fn create_struct_pattern_fields(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        struct_def: &'a VariantData,
+        prefixes: &[String],
+        addr_of: bool,
+    ) -> Vec<FieldInfo> {
+        self.create_fields(struct_def, |i, _struct_field, sp| {
+            prefixes
+                .iter()
+                .map(|prefix| {
+                    let ident = self.mk_pattern_ident(prefix, i);
+                    let expr = cx.expr_path(cx.path_ident(sp, ident));
+                    if addr_of { cx.expr_addr_of(sp, expr) } else { expr }
+                })
+                .collect()
+        })
+    }
+
+    fn create_struct_field_access_fields(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        selflike_args: &[P<Expr>],
+        struct_def: &'a VariantData,
+        copy: bool,
+    ) -> Vec<FieldInfo> {
+        self.create_fields(struct_def, |i, struct_field, sp| {
+            selflike_args
+                .iter()
+                .map(|selflike_arg| {
+                    // Note: we must use `struct_field.span` rather than `sp` in the
+                    // `unwrap_or_else` case otherwise the hygiene is wrong and we get
+                    // "field `0` of struct `Point` is private" errors on tuple
+                    // structs.
+                    let mut field_expr = cx.expr(
+                        sp,
+                        ast::ExprKind::Field(
+                            selflike_arg.clone(),
+                            struct_field.ident.unwrap_or_else(|| {
+                                Ident::from_str_and_span(&i.to_string(), struct_field.span)
+                            }),
+                        ),
+                    );
+                    if copy {
+                        field_expr = cx.expr_block(
+                            cx.block(struct_field.span, vec![cx.stmt_expr(field_expr)]),
+                        );
+                    }
+                    cx.expr_addr_of(sp, field_expr)
+                })
+                .collect()
+        })
+    }
+}
+
+/// The function passed to `cs_fold` is called repeatedly with a value of this
+/// type. It describes one part of the code generation. The result is always an
+/// expression.
+pub enum CsFold<'a> {
+    /// The basic case: a field expression for one or more selflike args. E.g.
+    /// for `PartialEq::eq` this is something like `self.x == other.x`.
+    Single(&'a FieldInfo),
+
+    /// The combination of two field expressions. E.g. for `PartialEq::eq` this
+    /// is something like `<field1 equality> && <field2 equality>`.
+    Combine(Span, P<Expr>, P<Expr>),
+
+    // The fallback case for a struct or enum variant with no fields.
+    Fieldless,
+}
+
+/// Folds over fields, combining the expressions for each field in a sequence.
+/// Statics may not be folded over.
+pub fn cs_fold<F>(
+    use_foldl: bool,
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substructure: &Substructure<'_>,
+    mut f: F,
+) -> P<Expr>
+where
+    F: FnMut(&mut ExtCtxt<'_>, CsFold<'_>) -> P<Expr>,
+{
+    match substructure.fields {
+        EnumMatching(.., all_fields) | Struct(_, all_fields) => {
+            if all_fields.is_empty() {
+                return f(cx, CsFold::Fieldless);
+            }
+
+            let (base_field, rest) = if use_foldl {
+                all_fields.split_first().unwrap()
+            } else {
+                all_fields.split_last().unwrap()
+            };
+
+            let base_expr = f(cx, CsFold::Single(base_field));
+
+            let op = |old, field: &FieldInfo| {
+                let new = f(cx, CsFold::Single(field));
+                f(cx, CsFold::Combine(field.span, old, new))
+            };
+
+            if use_foldl {
+                rest.iter().fold(base_expr, op)
+            } else {
+                rest.iter().rfold(base_expr, op)
+            }
+        }
+        EnumTag(tag_field, match_expr) => {
+            let tag_check_expr = f(cx, CsFold::Single(tag_field));
+            if let Some(match_expr) = match_expr {
+                if use_foldl {
+                    f(cx, CsFold::Combine(trait_span, tag_check_expr, match_expr.clone()))
+                } else {
+                    f(cx, CsFold::Combine(trait_span, match_expr.clone(), tag_check_expr))
+                }
+            } else {
+                tag_check_expr
+            }
+        }
+        StaticEnum(..) | StaticStruct(..) => cx.span_bug(trait_span, "static function in `derive`"),
+    }
+}
+
+/// Returns `true` if the type has no value fields
+/// (for an enum, no variant has any fields)
+pub fn is_type_without_fields(item: &Annotatable) -> bool {
+    if let Annotatable::Item(ref item) = *item {
+        match item.kind {
+            ast::ItemKind::Enum(ref enum_def, _) => {
+                enum_def.variants.iter().all(|v| v.data.fields().is_empty())
+            }
+            ast::ItemKind::Struct(ref variant_data, _) => variant_data.fields().is_empty(),
+            _ => false,
+        }
+    } else {
+        false
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
new file mode 100644
index 000000000..4d46f7cd4
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
@@ -0,0 +1,203 @@
+//! A mini version of ast::Ty, which is easier to use, and features an explicit `Self` type to use
+//! when specifying impls to be derived.
+
+pub use Ty::*;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, GenericArg, GenericParamKind, Generics, SelfKind};
+use rustc_expand::base::ExtCtxt;
+use rustc_span::source_map::{respan, DUMMY_SP};
+use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_span::Span;
+
+/// A path, e.g., `::std::option::Option::<i32>` (global). Has support
+/// for type parameters.
+#[derive(Clone)]
+pub struct Path {
+    path: Vec<Symbol>,
+    params: Vec<Box<Ty>>,
+    kind: PathKind,
+}
+
+#[derive(Clone)]
+pub enum PathKind {
+    Local,
+    Global,
+    Std,
+}
+
+impl Path {
+    pub fn new(path: Vec<Symbol>) -> Path {
+        Path::new_(path, Vec::new(), PathKind::Std)
+    }
+    pub fn new_local(path: Symbol) -> Path {
+        Path::new_(vec![path], Vec::new(), PathKind::Local)
+    }
+    pub fn new_(path: Vec<Symbol>, params: Vec<Box<Ty>>, kind: PathKind) -> Path {
+        Path { path, params, kind }
+    }
+
+    pub fn to_ty(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> P<ast::Ty> {
+        cx.ty_path(self.to_path(cx, span, self_ty, self_generics))
+    }
+    pub fn to_path(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> ast::Path {
+        let mut idents = self.path.iter().map(|s| Ident::new(*s, span)).collect();
+        let tys = self.params.iter().map(|t| t.to_ty(cx, span, self_ty, self_generics));
+        let params = tys.map(GenericArg::Type).collect();
+
+        match self.kind {
+            PathKind::Global => cx.path_all(span, true, idents, params),
+            PathKind::Local => cx.path_all(span, false, idents, params),
+            PathKind::Std => {
+                let def_site = cx.with_def_site_ctxt(DUMMY_SP);
+                idents.insert(0, Ident::new(kw::DollarCrate, def_site));
+                cx.path_all(span, false, idents, params)
+            }
+        }
+    }
+}
+
+/// A type. Supports pointers, Self, and literals.
+#[derive(Clone)]
+pub enum Ty {
+    Self_,
+    /// A reference.
+    Ref(Box<Ty>, ast::Mutability),
+    /// `mod::mod::Type<[lifetime], [Params...]>`, including a plain type
+    /// parameter, and things like `i32`
+    Path(Path),
+    /// For () return types.
+    Unit,
+}
+
+pub fn self_ref() -> Ty {
+    Ref(Box::new(Self_), ast::Mutability::Not)
+}
+
+impl Ty {
+    pub fn to_ty(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> P<ast::Ty> {
+        match self {
+            Ref(ty, mutbl) => {
+                let raw_ty = ty.to_ty(cx, span, self_ty, self_generics);
+                cx.ty_rptr(span, raw_ty, None, *mutbl)
+            }
+            Path(p) => p.to_ty(cx, span, self_ty, self_generics),
+            Self_ => cx.ty_path(self.to_path(cx, span, self_ty, self_generics)),
+            Unit => {
+                let ty = ast::TyKind::Tup(vec![]);
+                cx.ty(span, ty)
+            }
+        }
+    }
+
+    pub fn to_path(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        generics: &Generics,
+    ) -> ast::Path {
+        match *self {
+            Self_ => {
+                let params: Vec<_> = generics
+                    .params
+                    .iter()
+                    .map(|param| match param.kind {
+                        GenericParamKind::Lifetime { .. } => {
+                            GenericArg::Lifetime(ast::Lifetime { id: param.id, ident: param.ident })
+                        }
+                        GenericParamKind::Type { .. } => {
+                            GenericArg::Type(cx.ty_ident(span, param.ident))
+                        }
+                        GenericParamKind::Const { .. } => {
+                            GenericArg::Const(cx.const_ident(span, param.ident))
+                        }
+                    })
+                    .collect();
+
+                cx.path_all(span, false, vec![self_ty], params)
+            }
+            Path(ref p) => p.to_path(cx, span, self_ty, generics),
+            Ref(..) => cx.span_bug(span, "ref in a path in generic `derive`"),
+            Unit => cx.span_bug(span, "unit in a path in generic `derive`"),
+        }
+    }
+}
+
+fn mk_ty_param(
+    cx: &ExtCtxt<'_>,
+    span: Span,
+    name: Symbol,
+    attrs: &[ast::Attribute],
+    bounds: &[Path],
+    self_ident: Ident,
+    self_generics: &Generics,
+) -> ast::GenericParam {
+    let bounds = bounds
+        .iter()
+        .map(|b| {
+            let path = b.to_path(cx, span, self_ident, self_generics);
+            cx.trait_bound(path)
+        })
+        .collect();
+    cx.typaram(span, Ident::new(name, span), attrs.to_owned(), bounds, None)
+}
+
+/// Bounds on type parameters.
+#[derive(Clone)]
+pub struct Bounds {
+    pub bounds: Vec<(Symbol, Vec<Path>)>,
+}
+
+impl Bounds {
+    pub fn empty() -> Bounds {
+        Bounds { bounds: Vec::new() }
+    }
+    pub fn to_generics(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> Generics {
+        let params = self
+            .bounds
+            .iter()
+            .map(|t| {
+                let (name, ref bounds) = *t;
+                mk_ty_param(cx, span, name, &[], &bounds, self_ty, self_generics)
+            })
+            .collect();
+
+        Generics {
+            params,
+            where_clause: ast::WhereClause { has_where_token: false, predicates: Vec::new(), span },
+            span,
+        }
+    }
+}
+
+pub fn get_explicit_self(cx: &ExtCtxt<'_>, span: Span) -> (P<Expr>, ast::ExplicitSelf) {
+    // This constructs a fresh `self` path.
+    let self_path = cx.expr_self(span);
+    let self_ty = respan(span, SelfKind::Region(None, ast::Mutability::Not));
+    (self_path, self_ty)
+}