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//! 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 crate::{deriving, errors};
use rustc_ast::ptr::P;
use rustc_ast::{
self as ast, BindingAnnotation, ByRef, EnumDef, Expr, GenericArg, GenericParamKind, Generics,
Mutability, PatKind, TyKind, VariantData,
};
use rustc_attr as attr;
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_session::lint::builtin::BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{Span, DUMMY_SP};
use std::cell::RefCell;
use std::iter;
use std::ops::Not;
use std::vec;
use thin_vec::{thin_vec, ThinVec};
use ty::{Bounds, Path, Ref, Self_, Ty};
pub mod ty;
pub struct TraitDef<'a> {
/// The span for the current #[derive(Foo)] header.
pub span: Span,
/// Path of the trait, including any type parameters
pub path: Path,
/// Whether to skip adding the current trait as a bound to the type parameters of the type.
pub skip_path_as_bound: bool,
/// Whether `Copy` is needed as an additional bound on type parameters in a packed struct.
pub needs_copy_as_bound_if_packed: bool,
/// Additional bounds required of any type parameters of the type,
/// other than the current trait
pub additional_bounds: Vec<Ty>,
/// Can this trait be derived for unions?
pub supports_unions: bool,
pub methods: Vec<MethodDef<'a>>,
pub associated_types: Vec<(Ident, Ty)>,
pub is_const: bool,
}
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: ast::AttrVec,
pub fieldless_variants_strategy: FieldlessVariantsStrategy,
pub combine_substructure: RefCell<CombineSubstructureFunc<'a>>,
}
/// How to handle fieldless enum variants.
#[derive(PartialEq)]
pub enum FieldlessVariantsStrategy {
/// Combine fieldless variants into a single match arm.
/// This assumes that relevant information has been handled
/// by looking at the enum's discriminant.
Unify,
/// Don't do anything special about fieldless variants. They are
/// handled like any other variant.
Default,
/// If all variants of the enum are fieldless, expand the special
/// `AllFieldLessEnum` substructure, so that the entire enum can be handled
/// at once.
SpecializeIfAllVariantsFieldless,
}
/// 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 where `Self` is a struct.
Struct(&'a ast::VariantData, Vec<FieldInfo>),
/// A non-static method handling the entire enum at once
/// (after it has been determined that none of the enum
/// variants has any fields).
AllFieldlessEnum(&'a ast::EnumDef),
/// 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: ThinVec<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(ThinVec<ast::Stmt>, Option<P<Expr>>);
impl BlockOrExpr {
pub fn new_stmts(stmts: ThinVec<ast::Stmt>) -> BlockOrExpr {
BlockOrExpr(stmts, None)
}
pub fn new_expr(expr: P<Expr>) -> BlockOrExpr {
BlockOrExpr(ThinVec::new(), Some(expr))
}
pub fn new_mixed(stmts: ThinVec<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, ThinVec::new())),
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: ThinVec<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(_, path) = &ty.kind
&& let Some(segment) = path.segments.first()
&& 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) {
let stack_len = self.bound_generic_params_stack.len();
self.bound_generic_params_stack.extend(trait_ref.bound_generic_params.iter().cloned());
visit::walk_poly_trait_ref(self, trait_ref);
self.bound_generic_params_stack.truncate(stack_len);
}
fn visit_mac_call(&mut self, mac: &ast::MacCall) {
self.cx.emit_err(errors::DeriveMacroCall { span: mac.span() });
}
}
let mut visitor = Visitor {
cx,
ty_param_names,
bound_generic_params_stack: ThinVec::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(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 newitem = match &item.kind {
ast::ItemKind::Struct(struct_def, generics) => self.expand_struct_def(
cx,
&struct_def,
item.ident,
generics,
from_scratch,
is_packed,
),
ast::ItemKind::Enum(enum_def, generics) => {
// We ignore `is_packed` 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(struct_def, generics) => {
if self.supports_unions {
self.expand_struct_def(
cx,
&struct_def,
item.ident,
generics,
from_scratch,
is_packed,
)
} else {
cx.emit_err(errors::DeriveUnion { span: mitem.span });
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>>,
is_packed: bool,
) -> 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: ast::AttrVec::new(),
kind: ast::AssocItemKind::Type(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 mut where_clause = ast::WhereClause::default();
where_clause.span = generics.where_clause.span;
let ctxt = self.span.ctxt();
let span = generics.span.with_ctxt(ctxt);
// Create the generic parameters
let params: ThinVec<_> = generics
.params
.iter()
.map(|param| match ¶m.kind {
GenericParamKind::Lifetime { .. } => param.clone(),
GenericParamKind::Type { .. } => {
// Extra restrictions on the generics parameters to the
// type being derived upon.
let bounds: Vec<_> = self
.additional_bounds
.iter()
.map(|p| {
cx.trait_bound(
p.to_path(cx, self.span, type_ident, generics),
self.is_const,
)
})
.chain(
// Add a bound for the current trait.
self.skip_path_as_bound
.not()
.then(|| cx.trait_bound(trait_path.clone(), self.is_const)),
)
.chain({
// Add a `Copy` bound if required.
if is_packed && self.needs_copy_as_bound_if_packed {
let p = deriving::path_std!(marker::Copy);
Some(cx.trait_bound(
p.to_path(cx, self.span, type_ident, generics),
self.is_const,
))
} else {
None
}
})
.chain(
// Also add in any bounds from the declaration.
param.bounds.iter().cloned(),
)
.collect();
cx.typaram(param.ident.span.with_ctxt(ctxt), param.ident, 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
}
})
.collect();
// 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 { 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(_, p) = &field_ty_param.ty.kind
&& let [sole_segment] = &*p.segments
&& ty_param_names.contains(&sole_segment.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),
self.is_const,
)
})
.collect();
// Require the current trait.
if !self.skip_path_as_bound {
bounds.push(cx.trait_bound(trait_path.clone(), self.is_const));
}
// Add a `Copy` bound if required.
if is_packed && self.needs_copy_as_bound_if_packed {
let p = deriving::path_std!(marker::Copy);
bounds.push(cx.trait_bound(
p.to_path(cx, self.span, type_ident, generics),
self.is_const,
));
}
if !bounds.is_empty() {
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 attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
let opt_trait_ref = Some(trait_ref);
cx.item(
self.span,
Ident::empty(),
attrs,
ast::ItemKind::Impl(Box::new(ast::Impl {
unsafety: ast::Unsafe::No,
polarity: ast::ImplPolarity::Positive,
defaultness: ast::Defaultness::Final,
constness: if self.is_const { ast::Const::Yes(DUMMY_SP) } else { 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,
) -> 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,
)
};
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, is_packed)
}
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();
let is_packed = false; // enums are never packed
self.create_derived_impl(cx, type_ident, generics, field_tys, methods, is_packed)
}
}
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>, ThinVec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
let mut selflike_args = ThinVec::new();
let mut nonselflike_args = Vec::new();
let mut nonself_arg_tys = Vec::new();
let span = trait_.span;
let explicit_self = self.explicit_self.then(|| {
let (self_expr, explicit_self) = ty::get_explicit_self(cx, span);
selflike_args.push(self_expr);
explicit_self
});
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, we use a local block to force a copy.
/// This requires that the field impl `Copy`.
/// ```rust,ignore (example)
/// # 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)
/// }
/// }
/// ```
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,
) -> BlockOrExpr {
assert!(selflike_args.len() == 1 || selflike_args.len() == 2);
let selflike_fields =
trait_.create_struct_field_access_fields(cx, selflike_args, struct_def, is_packed);
self.call_substructure_method(
cx,
trait_,
type_ident,
nonselflike_args,
&Struct(struct_def, selflike_fields),
)
}
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:
/// ```
/// #![feature(core_intrinsics)]
/// enum A {
/// A1,
/// A2(i32)
/// }
/// 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
/// `Unify`), 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,
mut selflike_args: ThinVec<P<Expr>>,
nonselflike_args: &[P<Expr>],
) -> BlockOrExpr {
assert!(
!selflike_args.is_empty(),
"static methods must use `expand_static_enum_method_body`",
);
let span = trait_.span;
let variants = &enum_def.variants;
// Traits that unify fieldless variants always use the tag(s).
let unify_fieldless_variants =
self.fieldless_variants_strategy == FieldlessVariantsStrategy::Unify;
// For zero-variant enum, this function body is unreachable. Generate
// `match *self {}`. This produces machine code identical to `unsafe {
// core::intrinsics::unreachable() }` while being safe and stable.
if variants.is_empty() {
selflike_args.truncate(1);
let match_arg = cx.expr_deref(span, selflike_args.pop().unwrap());
let match_arms = ThinVec::new();
let expr = cx.expr_match(span, match_arg, match_arms);
return BlockOrExpr(ThinVec::new(), Some(expr));
}
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!("{name}_tag"), 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: ThinVec<_> = iter::zip(&tag_idents, &selflike_args)
.map(|(&ident, selflike_arg)| {
let variant_value = deriving::call_intrinsic(
cx,
span,
sym::discriminant_value,
thin_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 variants.len() > 1 {
match self.fieldless_variants_strategy {
FieldlessVariantsStrategy::Unify => {
// 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);
}
FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless => {
return self.call_substructure_method(
cx,
trait_,
type_ident,
nonselflike_args,
&AllFieldlessEnum(enum_def),
);
}
FieldlessVariantsStrategy::Default => (),
}
} else 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: ThinVec<ast::Arm> = variants
.iter()
.enumerate()
.filter(|&(_, v)| !(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 fields = trait_.create_struct_pattern_fields(cx, &variant.data, &prefixes);
let sp = variant.span.with_ctxt(trait_.span.ctxt());
let variant_path = cx.path(sp, vec![type_ident, variant.ident]);
let by_ref = ByRef::No; // because enums can't be repr(packed)
let mut subpats = trait_.create_struct_patterns(
cx,
variant_path,
&variant.data,
&prefixes,
by_ref,
);
// `(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 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: ThinVec<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 unify_fieldless_variants && 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(ThinVec::new(), 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],
by_ref: ByRef,
) -> ThinVec<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 ident = self.mk_pattern_ident(prefix, i);
let path = ident.with_span_pos(sp);
(
sp,
struct_field.ident,
cx.pat(
path.span,
PatKind::Ident(
BindingAnnotation(by_ref, Mutability::Not),
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],
) -> Vec<FieldInfo> {
self.create_fields(struct_def, |i, _struct_field, sp| {
prefixes
.iter()
.map(|prefix| {
let ident = self.mk_pattern_ident(prefix, i);
cx.expr_path(cx.path_ident(sp, ident))
})
.collect()
})
}
fn create_struct_field_access_fields(
&self,
cx: &mut ExtCtxt<'_>,
selflike_args: &[P<Expr>],
struct_def: &'a VariantData,
is_packed: 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 is_packed {
// In general, fields in packed structs are copied via a
// block, e.g. `&{self.0}`. The two exceptions are `[u8]`
// and `str` fields, which cannot be copied and also never
// cause unaligned references. These exceptions are allowed
// to handle the `FlexZeroSlice` type in the `zerovec`
// crate within `icu4x-0.9.0`.
//
// Once use of `icu4x-0.9.0` has dropped sufficiently, this
// exception should be removed.
let is_simple_path = |ty: &P<ast::Ty>, sym| {
if let TyKind::Path(None, ast::Path { segments, .. }) = &ty.kind &&
let [seg] = segments.as_slice() &&
seg.ident.name == sym && seg.args.is_none()
{
true
} else {
false
}
};
let exception = if let TyKind::Slice(ty) = &struct_field.ty.kind &&
is_simple_path(ty, sym::u8)
{
Some("byte")
} else if is_simple_path(&struct_field.ty, sym::str) {
Some("string")
} else {
None
};
if let Some(ty) = exception {
cx.sess.parse_sess.buffer_lint_with_diagnostic(
BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
sp,
ast::CRATE_NODE_ID,
format!(
"{ty} slice in a packed struct that derives a built-in trait"
),
rustc_lint_defs::BuiltinLintDiagnostics::ByteSliceInPackedStructWithDerive
);
} else {
// Wrap the expression in `{...}`, causing a copy.
field_expr = cx.expr_block(
cx.block(struct_field.span, thin_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`"),
AllFieldlessEnum(..) => cx.span_bug(trait_span, "fieldless enum in `derive`"),
}
}