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derive(SmartPointer): rewrite bounds in where and generic bounds #127681

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244 changes: 227 additions & 17 deletions compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
Original file line number Diff line number Diff line change
@@ -1,14 +1,18 @@
use std::mem::swap;

use ast::ptr::P;
use ast::HasAttrs;
use rustc_ast::mut_visit::MutVisitor;
use rustc_ast::visit::BoundKind;
use rustc_ast::{
self as ast, GenericArg, GenericBound, GenericParamKind, ItemKind, MetaItem,
TraitBoundModifiers, VariantData,
TraitBoundModifiers, VariantData, WherePredicate,
};
use rustc_attr as attr;
use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
use rustc_span::{Span, Symbol};
use smallvec::{smallvec, SmallVec};
use thin_vec::{thin_vec, ThinVec};

Expand Down Expand Up @@ -141,33 +145,239 @@ pub fn expand_deriving_smart_ptr(
alt_self_params[pointee_param_idx] = GenericArg::Type(s_ty.clone());
let alt_self_type = cx.ty_path(cx.path_all(span, false, vec![name_ident], alt_self_params));

// # Add `Unsize<__S>` bound to `#[pointee]` at the generic parameter location
//
// Find the `#[pointee]` parameter and add an `Unsize<__S>` bound to it.
let mut impl_generics = generics.clone();
let pointee_ty_ident = generics.params[pointee_param_idx].ident;
let mut self_bounds;
{
let p = &mut impl_generics.params[pointee_param_idx];
let pointee = &mut impl_generics.params[pointee_param_idx];
self_bounds = pointee.bounds.clone();
let arg = GenericArg::Type(s_ty.clone());
let unsize = cx.path_all(span, true, path!(span, core::marker::Unsize), vec![arg]);
p.bounds.push(cx.trait_bound(unsize, false));
pointee.bounds.push(cx.trait_bound(unsize, false));
let mut attrs = thin_vec![];
swap(&mut p.attrs, &mut attrs);
p.attrs = attrs.into_iter().filter(|attr| !attr.has_name(sym::pointee)).collect();
swap(&mut pointee.attrs, &mut attrs);
// Drop `#[pointee]` attribute since it should not be recognized outside `derive(SmartPointer)`
pointee.attrs = attrs.into_iter().filter(|attr| !attr.has_name(sym::pointee)).collect();
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Can be done as a follow-up, but can't this be rewritten as .retain?

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Yes 👍

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If you're already making changes, please also change this.

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I have not forgotten.

Applied in appendix commit.

}

// Add the `__S: ?Sized` extra parameter to the impl block.
// # Rewrite generic parameter bounds
// For each bound `U: ..` in `struct<U: ..>`, make a new bound with `__S` in place of `#[pointee]`
// Example:
// ```
// struct<
// U: Trait<T>,
// #[pointee] T: Trait<T>,
// V: Trait<T>> ...
// ```
// ... generates this `impl` generic parameters
// ```
// impl<
// U: Trait<T> + Trait<__S>,
// T: Trait<T> + Unsize<__S>, // (**)
// __S: Trait<__S> + ?Sized, // (*)
// V: Trait<T> + Trait<__S>> ...
// ```
// The new bound marked with (*) has to be done separately.
// See next section
for (idx, (params, orig_params)) in
impl_generics.params.iter_mut().zip(&generics.params).enumerate()
{
// Default type parameters are rejected for `impl` block.
// We should drop them now.
match &mut params.kind {
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Move the comment from above into here, and split it up so each part (match &mut params.kind and for bound in &orig_params.bounds) is individually documented.

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Applied

ast::GenericParamKind::Const { default, .. } => *default = None,
ast::GenericParamKind::Type { default } => *default = None,
ast::GenericParamKind::Lifetime => {}
}
// We CANNOT rewrite `#[pointee]` type parameter bounds.
// This has been set in stone. (**)
// So we skip over it.
// Otherwise, we push extra bounds involving `__S`.
if idx != pointee_param_idx {
for bound in &orig_params.bounds {
let mut bound = bound.clone();
let mut substitution = TypeSubstitution {
from_name: pointee_ty_ident.name,
to_ty: &s_ty,
rewritten: false,
};
substitution.visit_param_bound(&mut bound, BoundKind::Bound);
if substitution.rewritten {
// We found use of `#[pointee]` somewhere,
// so we make a new bound using `__S` in place of `#[pointee]`
params.bounds.push(bound);
}
}
}
}

// # Insert `__S` type parameter
//
// We now insert `__S` with the missing bounds marked with (*) above.
// We should also write the bounds from `#[pointee]` to `__S` as required by `Unsize<__S>`.
let sized = cx.path_global(span, path!(span, core::marker::Sized));
let bound = GenericBound::Trait(
cx.poly_trait_ref(span, sized),
TraitBoundModifiers {
polarity: ast::BoundPolarity::Maybe(span),
constness: ast::BoundConstness::Never,
asyncness: ast::BoundAsyncness::Normal,
},
);
let extra_param = cx.typaram(span, Ident::new(sym::__S, span), vec![bound], None);
impl_generics.params.push(extra_param);
// For some reason, we are not allowed to write `?Sized` bound twice like `__S: ?Sized + ?Sized`.
if !contains_maybe_sized_bound(&self_bounds)
&& !contains_maybe_sized_bound_on_pointee(
&generics.where_clause.predicates,
pointee_ty_ident.name,
)
{
self_bounds.push(GenericBound::Trait(
cx.poly_trait_ref(span, sized),
TraitBoundModifiers {
polarity: ast::BoundPolarity::Maybe(span),
constness: ast::BoundConstness::Never,
asyncness: ast::BoundAsyncness::Normal,
},
));
}
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You never have to add a ?Sized bound because the user must already specify T: ?Sized on the pointee, which results in a __S: ?Sized bound. If they don't, then the generated impls are useless as any type with an unsized type in T is invalid per the struct's trait bounds anyway.

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Applied. So this section is yanked, and assertion has added earlier to require this bound.

{
let mut substitution =
TypeSubstitution { from_name: pointee_ty_ident.name, to_ty: &s_ty, rewritten: false };
for bound in &mut self_bounds {
substitution.visit_param_bound(bound, BoundKind::Bound);
}
}

// # Rewrite `where` clauses
//
// Move on to `where` clauses.
// Example:
// ```
// struct MyPointer<#[pointee] T, ..>
// where
// U: Trait<V> + Trait<T>,
// Companion<T>: Trait<T>,
// T: Trait<T>,
// { .. }
// ```
// ... will have a impl prelude like so
// ```
// impl<..> ..
// where
// U: Trait<V> + Trait<T>,
// U: Trait<__S>,
// Companion<T>: Trait<T>,
// Companion<__S>: Trait<__S>,
// T: Trait<T>,
// __S: Trait<__S>,
// ```
//
// We should also write a few new `where` bounds from `#[pointee] T` to `__S`
// as well as any bound that indirectly involves the `#[pointee] T` type.
for bound in &generics.where_clause.predicates {
if let ast::WherePredicate::BoundPredicate(bound) = bound {
let mut substitution = TypeSubstitution {
from_name: pointee_ty_ident.name,
to_ty: &s_ty,
rewritten: false,
};
let mut predicate = ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
span: bound.span,
bound_generic_params: bound.bound_generic_params.clone(),
bounded_ty: bound.bounded_ty.clone(),
bounds: bound.bounds.clone(),
});
substitution.visit_where_predicate(&mut predicate);
if substitution.rewritten {
impl_generics.where_clause.predicates.push(predicate);
}
}
}

let extra_param = cx.typaram(span, Ident::new(sym::__S, span), self_bounds, None);
impl_generics.params.insert(pointee_param_idx + 1, extra_param);

// Add the impl blocks for `DispatchFromDyn` and `CoerceUnsized`.
let gen_args = vec![GenericArg::Type(alt_self_type.clone())];
add_impl_block(impl_generics.clone(), sym::DispatchFromDyn, gen_args.clone());
add_impl_block(impl_generics.clone(), sym::CoerceUnsized, gen_args.clone());
}

fn contains_maybe_sized_bound_on_pointee(predicates: &[WherePredicate], pointee: Symbol) -> bool {
for bound in predicates {
if let ast::WherePredicate::BoundPredicate(bound) = bound
&& bound.bounded_ty.kind.is_simple_path().is_some_and(|name| name == pointee)
{
for bound in &bound.bounds {
if is_maybe_sized_bound(bound) {
return true;
}
}
}
}
false
}

fn is_maybe_sized_bound(bound: &GenericBound) -> bool {
if let GenericBound::Trait(
trait_ref,
TraitBoundModifiers { polarity: ast::BoundPolarity::Maybe(_), .. },
) = bound
{
is_sized_marker(&trait_ref.trait_ref.path)
} else {
false
}
}

fn contains_maybe_sized_bound(bounds: &[GenericBound]) -> bool {
bounds.iter().any(is_maybe_sized_bound)
}

fn path_segment_is_exact_match(path_segments: &[ast::PathSegment], syms: &[Symbol]) -> bool {
path_segments.iter().zip(syms).all(|(segment, &symbol)| segment.ident.name == symbol)
}

fn is_sized_marker(path: &ast::Path) -> bool {
const CORE_UNSIZE: [Symbol; 3] = [sym::core, sym::marker, sym::Sized];
const STD_UNSIZE: [Symbol; 3] = [sym::std, sym::marker, sym::Sized];
if path.segments.len() == 4 && path.is_global() {
path_segment_is_exact_match(&path.segments[1..], &CORE_UNSIZE)
|| path_segment_is_exact_match(&path.segments[1..], &STD_UNSIZE)
} else if path.segments.len() == 3 {
path_segment_is_exact_match(&path.segments, &CORE_UNSIZE)
|| path_segment_is_exact_match(&path.segments, &STD_UNSIZE)
} else {
*path == sym::Sized
}
}

struct TypeSubstitution<'a> {
from_name: Symbol,
to_ty: &'a ast::Ty,
rewritten: bool,
}

impl<'a> ast::mut_visit::MutVisitor for TypeSubstitution<'a> {
fn visit_ty(&mut self, ty: &mut P<ast::Ty>) {
if let Some(name) = ty.kind.is_simple_path()
&& name == self.from_name
{
**ty = self.to_ty.clone();
self.rewritten = true;
} else {
ast::mut_visit::walk_ty(self, ty);
}
}

fn visit_where_predicate(&mut self, where_predicate: &mut ast::WherePredicate) {
match where_predicate {
rustc_ast::WherePredicate::BoundPredicate(bound) => {
bound
.bound_generic_params
.flat_map_in_place(|param| self.flat_map_generic_param(param));
self.visit_ty(&mut bound.bounded_ty);
for bound in &mut bound.bounds {
self.visit_param_bound(bound, BoundKind::Bound)
}
}
rustc_ast::WherePredicate::RegionPredicate(_)
| rustc_ast::WherePredicate::EqPredicate(_) => {}
}
}
}
22 changes: 22 additions & 0 deletions tests/ui/deriving/deriving-smart-pointer-expanded.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
//@ check-pass
//@ compile-flags: -Zunpretty=expanded
#![feature(derive_smart_pointer)]
use std::marker::SmartPointer;

pub trait MyTrait<T: ?Sized> {}

#[derive(SmartPointer)]
#[repr(transparent)]
struct MyPointer<'a, #[pointee] T: ?Sized> {
ptr: &'a T,
}

#[derive(core::marker::SmartPointer)]
#[repr(transparent)]
pub struct MyPointer2<'a, Y, Z: MyTrait<T>, #[pointee] T: ?Sized + MyTrait<T>, X: MyTrait<T> = ()>
where
Y: MyTrait<T>,
{
data: &'a mut T,
x: core::marker::PhantomData<X>,
}
44 changes: 44 additions & 0 deletions tests/ui/deriving/deriving-smart-pointer-expanded.stdout
Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
#![feature(prelude_import)]
#![no_std]
//@ check-pass
//@ compile-flags: -Zunpretty=expanded
#![feature(derive_smart_pointer)]
#[prelude_import]
use ::std::prelude::rust_2015::*;
#[macro_use]
extern crate std;
use std::marker::SmartPointer;

pub trait MyTrait<T: ?Sized> {}

#[repr(transparent)]
struct MyPointer<'a, #[pointee] T: ?Sized> {
ptr: &'a T,
}
#[automatically_derived]
impl<'a, T: ?Sized + ::core::marker::Unsize<__S>, __S: ?Sized>
::core::ops::DispatchFromDyn<MyPointer<'a, __S>> for MyPointer<'a, T> {
}
#[automatically_derived]
impl<'a, T: ?Sized + ::core::marker::Unsize<__S>, __S: ?Sized>
::core::ops::CoerceUnsized<MyPointer<'a, __S>> for MyPointer<'a, T> {
}

#[repr(transparent)]
pub struct MyPointer2<'a, Y, Z: MyTrait<T>, #[pointee] T: ?Sized + MyTrait<T>,
X: MyTrait<T> = ()> where Y: MyTrait<T> {
data: &'a mut T,
x: core::marker::PhantomData<X>,
}
#[automatically_derived]
impl<'a, Y, Z: MyTrait<T> + MyTrait<__S>, T: ?Sized + MyTrait<T> +
::core::marker::Unsize<__S>, __S: ?Sized + MyTrait<__S>, X: MyTrait<T> +
MyTrait<__S>> ::core::ops::DispatchFromDyn<MyPointer2<'a, Y, Z, __S, X>>
for MyPointer2<'a, Y, Z, T, X> where Y: MyTrait<T>, Y: MyTrait<__S> {
}
#[automatically_derived]
impl<'a, Y, Z: MyTrait<T> + MyTrait<__S>, T: ?Sized + MyTrait<T> +
::core::marker::Unsize<__S>, __S: ?Sized + MyTrait<__S>, X: MyTrait<T> +
MyTrait<__S>> ::core::ops::CoerceUnsized<MyPointer2<'a, Y, Z, __S, X>> for
MyPointer2<'a, Y, Z, T, X> where Y: MyTrait<T>, Y: MyTrait<__S> {
}
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