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Introduce ~const

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- [x] Removed `?const` and change uses of `?const`
 - [x] Added `~const` to the AST. It is gated behind const_trait_impl.
 - [x] Validate `~const` in ast_validation.
 - [ ] Add enum `BoundConstness` to the HIR. (With variants `NotConst` and
 `ConstIfConst` allowing future extensions)
 - [ ] Adjust trait selection and pre-existing code to use `BoundConstness`.
 - [ ] Optional steps (*for this PR, obviously*)
      - [ ] Fix #88155
      - [ ] Do something with constness bounds in chalk
This commit is contained in:
Deadbeef 2021-08-25 11:53:16 +00:00
parent d5cd3205fd
commit 8660832086
No known key found for this signature in database
GPG key ID: 027DF9338862ADDD
16 changed files with 178 additions and 125 deletions
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6
compiler/rustc_ast/src/ast.rs
View file

@ -284,7 +284,7 @@ impl ParenthesizedArgs {
pub use crate::node_id::{NodeId, CRATE_NODE_ID, DUMMY_NODE_ID};
/// A modifier on a bound, e.g., `?Sized` or `?const Trait`.
/// A modifier on a bound, e.g., `?Sized` or `~const Trait`.
///
/// Negative bounds should also be handled here.
#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug)]
@ -295,10 +295,10 @@ pub enum TraitBoundModifier {
/// `?Trait`
Maybe,
/// `?const Trait`
/// `~const Trait`
MaybeConst,
/// `?const ?Trait`
/// `~const ?Trait`
//
// This parses but will be rejected during AST validation.
MaybeConstMaybe,

2
compiler/rustc_ast_lowering/src/lib.rs
View file

@ -1414,7 +1414,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
ref ty,
TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
// `?const ?Bound` will cause an error during AST validation
// `~const ?Bound` will cause an error during AST validation
// anyways, so treat it like `?Bound` as compilation proceeds.
GenericBound::Trait(
_,

152
compiler/rustc_ast_passes/src/ast_validation.rs
View file

@ -17,10 +17,11 @@ use rustc_errors::{error_code, pluralize, struct_span_err, Applicability};
use rustc_parse::validate_attr;
use rustc_session::lint::builtin::PATTERNS_IN_FNS_WITHOUT_BODY;
use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
use rustc_session::Session;
use rustc_session::{DiagnosticMessageId, Session};
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident};
use rustc_span::Span;
use std::convert::TryInto;
use std::mem;
use std::ops::DerefMut;
@ -33,24 +34,6 @@ enum SelfSemantic {
No,
}
/// A syntactic context that disallows certain kinds of bounds (e.g., `?Trait` or `?const Trait`).
#[derive(Clone, Copy)]
enum BoundContext {
ImplTrait,
TraitBounds,
TraitObject,
}
impl BoundContext {
fn description(&self) -> &'static str {
match self {
Self::ImplTrait => "`impl Trait`",
Self::TraitBounds => "supertraits",
Self::TraitObject => "trait objects",
}
}
}
struct AstValidator<'a> {
session: &'a Session,
@ -60,6 +43,8 @@ struct AstValidator<'a> {
/// Are we inside a trait impl?
in_trait_impl: bool,
in_const_trait_impl: bool,
has_proc_macro_decls: bool,
/// Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
@ -67,11 +52,7 @@ struct AstValidator<'a> {
/// e.g., `impl Iterator<Item = impl Debug>`.
outer_impl_trait: Option<Span>,
/// Keeps track of the `BoundContext` as we recurse.
///
/// This is used to forbid `?const Trait` bounds in, e.g.,
/// `impl Iterator<Item = Box<dyn ?const Trait>`.
bound_context: Option<BoundContext>,
is_tilde_const_allowed: bool,
/// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
/// or `Foo::Bar<impl Trait>`
@ -88,10 +69,18 @@ struct AstValidator<'a> {
}
impl<'a> AstValidator<'a> {
fn with_in_trait_impl(&mut self, is_in: bool, f: impl FnOnce(&mut Self)) {
fn with_in_trait_impl(
&mut self,
is_in: bool,
constness: Option<Const>,
f: impl FnOnce(&mut Self),
) {
let old = mem::replace(&mut self.in_trait_impl, is_in);
let old_const =
mem::replace(&mut self.in_const_trait_impl, matches!(constness, Some(Const::Yes(_))));
f(self);
self.in_trait_impl = old;
self.in_const_trait_impl = old_const;
}
fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
@ -100,6 +89,18 @@ impl<'a> AstValidator<'a> {
self.is_impl_trait_banned = old;
}
fn with_tilde_const_allowed(&mut self, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.is_tilde_const_allowed, true);
f(self);
self.is_tilde_const_allowed = old;
}
fn with_banned_tilde_const(&mut self, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.is_tilde_const_allowed, false);
f(self);
self.is_tilde_const_allowed = old;
}
fn with_let_allowed(&mut self, allowed: bool, f: impl FnOnce(&mut Self, bool)) {
let old = mem::replace(&mut self.is_let_allowed, allowed);
f(self, old);
@ -130,19 +131,13 @@ impl<'a> AstValidator<'a> {
fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.outer_impl_trait, outer);
if outer.is_some() {
self.with_bound_context(BoundContext::ImplTrait, |this| f(this));
self.with_banned_tilde_const(f);
} else {
f(self)
f(self);
}
self.outer_impl_trait = old;
}
fn with_bound_context(&mut self, ctx: BoundContext, f: impl FnOnce(&mut Self)) {
let old = self.bound_context.replace(ctx);
f(self);
self.bound_context = old;
}
fn visit_assoc_ty_constraint_from_generic_args(&mut self, constraint: &'a AssocTyConstraint) {
match constraint.kind {
AssocTyConstraintKind::Equality { .. } => {}
@ -164,9 +159,7 @@ impl<'a> AstValidator<'a> {
TyKind::ImplTrait(..) => {
self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
}
TyKind::TraitObject(..) => {
self.with_bound_context(BoundContext::TraitObject, |this| visit::walk_ty(this, t));
}
TyKind::TraitObject(..) => self.with_banned_tilde_const(|this| visit::walk_ty(this, t)),
TyKind::Path(ref qself, ref path) => {
// We allow these:
// - `Option<impl Trait>`
@ -1083,13 +1076,13 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
unsafety,
polarity,
defaultness: _,
constness: _,
generics: _,
constness,
ref generics,
of_trait: Some(ref t),
ref self_ty,
items: _,
ref items,
}) => {
self.with_in_trait_impl(true, |this| {
self.with_in_trait_impl(true, Some(constness), |this| {
this.invalid_visibility(&item.vis, None);
if let TyKind::Err = self_ty.kind {
this.err_handler()
@ -1112,7 +1105,17 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
.emit();
}
visit::walk_item(this, item);
this.visit_vis(&item.vis);
this.visit_ident(item.ident);
if let Const::Yes(_) = constness {
this.with_tilde_const_allowed(|this| this.visit_generics(generics));
} else {
this.visit_generics(generics);
}
this.visit_trait_ref(t);
this.visit_ty(self_ty);
walk_list!(this, visit_assoc_item, items, AssocCtxt::Impl);
});
return; // Avoid visiting again.
}
@ -1157,13 +1160,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
.emit();
}
}
ItemKind::Fn(box FnKind(def, _, _, ref body)) => {
ItemKind::Fn(box FnKind(def, ref sig, ref generics, ref body)) => {
self.check_defaultness(item.span, def);
if body.is_none() {
let msg = "free function without a body";
self.error_item_without_body(item.span, "function", msg, " { <body> }");
}
self.visit_vis(&item.vis);
self.visit_ident(item.ident);
if let Const::Yes(_) = sig.header.constness {
self.with_tilde_const_allowed(|this| this.visit_generics(generics));
} else {
self.visit_generics(generics);
}
let kind = FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, body.as_deref());
self.visit_fn(kind, item.span, item.id);
walk_list!(self, visit_attribute, &item.attrs);
}
ItemKind::ForeignMod(ForeignMod { unsafety, .. }) => {
let old_item = mem::replace(&mut self.extern_mod, Some(item));
@ -1206,9 +1219,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
self.visit_vis(&item.vis);
self.visit_ident(item.ident);
self.visit_generics(generics);
self.with_bound_context(BoundContext::TraitBounds, |this| {
walk_list!(this, visit_param_bound, bounds);
});
self.with_banned_tilde_const(|this| walk_list!(this, visit_param_bound, bounds));
walk_list!(self, visit_assoc_item, trait_items, AssocCtxt::Trait);
walk_list!(self, visit_attribute, &item.attrs);
return;
@ -1281,7 +1292,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
_ => {}
}
visit::walk_item(self, item)
visit::walk_item(self, item);
}
fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
@ -1428,15 +1439,26 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
fn visit_param_bound(&mut self, bound: &'a GenericBound) {
match bound {
GenericBound::Trait(_, TraitBoundModifier::MaybeConst) => {
if let Some(ctx) = self.bound_context {
let msg = format!("`?const` is not permitted in {}", ctx.description());
self.err_handler().span_err(bound.span(), &msg);
if !self.is_tilde_const_allowed {
let msg = "`~const` is not allowed here";
let id_span_msg = (
DiagnosticMessageId::StabilityId(67792.try_into().ok()),
Some(bound.span()),
msg.to_owned(),
);
let fresh = self.session.one_time_diagnostics.borrow_mut().insert(id_span_msg);
if fresh {
self.err_handler()
.struct_span_err(bound.span(), msg)
.note("only allowed on bounds on traits' associated types, const fns, const impls and its associated functions")
.emit();
}
}
}
GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
self.err_handler()
.span_err(bound.span(), "`?const` and `?` are mutually exclusive");
.span_err(bound.span(), "`~const` and `?` are mutually exclusive");
}
_ => {}
@ -1589,7 +1611,32 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
self.check_item_named(item.ident, "const");
}
self.with_in_trait_impl(false, |this| visit::walk_assoc_item(this, item, ctxt));
match item.kind {
AssocItemKind::TyAlias(box TyAliasKind(_, ref generics, ref bounds, ref ty))
if ctxt == AssocCtxt::Trait =>
{
self.visit_vis(&item.vis);
self.visit_ident(item.ident);
walk_list!(self, visit_attribute, &item.attrs);
self.with_tilde_const_allowed(|this| {
this.visit_generics(generics);
walk_list!(this, visit_param_bound, bounds);
});
walk_list!(self, visit_ty, ty);
}
AssocItemKind::Fn(box FnKind(_, ref sig, ref generics, ref body))
if self.in_const_trait_impl =>
{
self.visit_vis(&item.vis);
self.visit_ident(item.ident);
self.with_tilde_const_allowed(|this| this.visit_generics(generics));
let kind =
FnKind::Fn(FnCtxt::Assoc(ctxt), item.ident, sig, &item.vis, body.as_deref());
self.visit_fn(kind, item.span, item.id);
}
_ => self
.with_in_trait_impl(false, None, |this| visit::walk_assoc_item(this, item, ctxt)),
}
}
}
@ -1683,9 +1730,10 @@ pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) ->
session,
extern_mod: None,
in_trait_impl: false,
in_const_trait_impl: false,
has_proc_macro_decls: false,
outer_impl_trait: None,
bound_context: None,
is_tilde_const_allowed: false,
is_impl_trait_banned: false,
is_assoc_ty_bound_banned: false,
is_let_allowed: false,

1
compiler/rustc_ast_passes/src/feature_gate.rs
View file

@ -656,7 +656,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
gate_all!(generators, "yield syntax is experimental");
gate_all!(raw_ref_op, "raw address of syntax is experimental");
gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");
gate_all!(const_trait_impl, "const trait impls are experimental");
gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
gate_all!(inline_const, "inline-const is experimental");

3
compiler/rustc_feature/src/active.rs
View file

@ -515,9 +515,6 @@ declare_features! (
/// Allows `impl const Trait for T` syntax.
(active, const_trait_impl, "1.42.0", Some(67792), None),
/// Allows `T: ?const Trait` syntax in bounds.
(incomplete, const_trait_bound_opt_out, "1.42.0", Some(67794), None),
/// Allows the use of `no_sanitize` attribute.
(active, no_sanitize, "1.42.0", Some(39699), None),

3
compiler/rustc_feature/src/removed.rs
View file

@ -123,6 +123,9 @@ declare_features! (
/// Allows overlapping impls of marker traits.
(removed, overlapping_marker_traits, "1.42.0", Some(29864), None,
Some("removed in favor of `#![feature(marker_trait_attr)]`")),
/// Allows `T: ?const Trait` syntax in bounds.
(removed, const_trait_bound_opt_out, "1.42.0", Some(67794), None,
Some("Removed in favor of `~const` bound in #![feature(const_trait_impl)]")),
/// Allows `#[no_debug]`.
(removed, no_debug, "1.43.0", Some(29721), None, Some("removed due to lack of demand")),
/// Allows comparing raw pointers during const eval.

7
compiler/rustc_middle/src/ty/mod.rs
View file

@ -457,10 +457,6 @@ pub enum PredicateKind<'tcx> {
/// Corresponds to `where Foo: Bar<A, B, C>`. `Foo` here would be
/// the `Self` type of the trait reference and `A`, `B`, and `C`
/// would be the type parameters.
///
/// A trait predicate will have `Constness::Const` if it originates
/// from a bound on a `const fn` without the `?const` opt-out (e.g.,
/// `const fn foobar<Foo: Bar>() {}`).
Trait(TraitPredicate<'tcx>),
/// `where 'a: 'b`
@ -633,8 +629,7 @@ pub struct TraitPredicate<'tcx> {
pub trait_ref: TraitRef<'tcx>,
/// A trait predicate will have `Constness::Const` if it originates
/// from a bound on a `const fn` without the `?const` opt-out (e.g.,
/// `const fn foobar<Foo: Bar>() {}`).
/// from a bound marked with `~const`.
pub constness: hir::Constness,
}

46
compiler/rustc_parse/src/parser/ty.rs
View file

@ -11,12 +11,12 @@ use rustc_errors::{pluralize, struct_span_err, Applicability, PResult};
use rustc_span::source_map::Span;
use rustc_span::symbol::{kw, sym};
/// Any `?` or `?const` modifiers that appear at the start of a bound.
/// Any `?` or `~const` modifiers that appear at the start of a bound.
struct BoundModifiers {
/// `?Trait`.
maybe: Option<Span>,
/// `?const Trait`.
/// `~const Trait`.
maybe_const: Option<Span>,
}
@ -609,6 +609,7 @@ impl<'a> Parser<'a> {
|| self.check_lifetime()
|| self.check(&token::Not) // Used for error reporting only.
|| self.check(&token::Question)
|| self.check(&token::Tilde)
|| self.check_keyword(kw::For)
|| self.check(&token::OpenDelim(token::Paren))
}
@ -655,7 +656,7 @@ impl<'a> Parser<'a> {
let inner_lo = self.token.span;
let is_negative = self.eat(&token::Not);
let modifiers = self.parse_ty_bound_modifiers();
let modifiers = self.parse_ty_bound_modifiers()?;
let bound = if self.token.is_lifetime() {
self.error_lt_bound_with_modifiers(modifiers);
self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
@ -690,7 +691,7 @@ impl<'a> Parser<'a> {
if let Some(span) = modifiers.maybe_const {
self.struct_span_err(
span,
"`?const` may only modify trait bounds, not lifetime bounds",
"`~const` may only modify trait bounds, not lifetime bounds",
)
.emit();
}
@ -721,34 +722,27 @@ impl<'a> Parser<'a> {
Ok(())
}
/// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `?const Trait`.
/// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
///
/// If no modifiers are present, this does not consume any tokens.
///
/// ```
/// TY_BOUND_MODIFIERS = "?" ["const" ["?"]]
/// TY_BOUND_MODIFIERS = ["~const"] ["?"]
/// ```
fn parse_ty_bound_modifiers(&mut self) -> BoundModifiers {
if !self.eat(&token::Question) {
return BoundModifiers { maybe: None, maybe_const: None };
}
fn parse_ty_bound_modifiers(&mut self) -> PResult<'a, BoundModifiers> {
let maybe_const = if self.eat(&token::Tilde) {
let tilde = self.prev_token.span;
self.expect_keyword(kw::Const)?;
let span = tilde.to(self.prev_token.span);
self.sess.gated_spans.gate(sym::const_trait_impl, span);
Some(span)
} else {
None
};
// `? ...`
let first_question = self.prev_token.span;
if !self.eat_keyword(kw::Const) {
return BoundModifiers { maybe: Some(first_question), maybe_const: None };
}
let maybe = if self.eat(&token::Question) { Some(self.prev_token.span) } else { None };
// `?const ...`
let maybe_const = first_question.to(self.prev_token.span);
self.sess.gated_spans.gate(sym::const_trait_bound_opt_out, maybe_const);
if !self.eat(&token::Question) {
return BoundModifiers { maybe: None, maybe_const: Some(maybe_const) };
}
// `?const ? ...`
let second_question = self.prev_token.span;
BoundModifiers { maybe: Some(second_question), maybe_const: Some(maybe_const) }
Ok(BoundModifiers { maybe, maybe_const })
}
/// Parses a type bound according to:
@ -757,7 +751,7 @@ impl<'a> Parser<'a> {
/// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
/// ```
///
/// For example, this grammar accepts `?const ?for<'a: 'b> m::Trait<'a>`.
/// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
fn parse_generic_ty_bound(
&mut self,
lo: Span,

8
compiler/rustc_typeck/src/collect.rs
View file

@ -2227,8 +2227,8 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
match bound {
hir::GenericBound::Trait(poly_trait_ref, modifier) => {
let constness = match modifier {
hir::TraitBoundModifier::MaybeConst => hir::Constness::NotConst,
hir::TraitBoundModifier::None => constness,
hir::TraitBoundModifier::None => hir::Constness::NotConst,
hir::TraitBoundModifier::MaybeConst => constness,
// We ignore `where T: ?Sized`, it is already part of
// type parameter `T`.
hir::TraitBoundModifier::Maybe => continue,
@ -2497,8 +2497,8 @@ fn predicates_from_bound<'tcx>(
hir::GenericBound::Trait(ref tr, modifier) => {
let constness = match modifier {
hir::TraitBoundModifier::Maybe => return vec![],
hir::TraitBoundModifier::MaybeConst => hir::Constness::NotConst,
hir::TraitBoundModifier::None => constness,
hir::TraitBoundModifier::MaybeConst => constness,
hir::TraitBoundModifier::None => hir::Constness::NotConst,
};
let mut bounds = Bounds::default();

2
src/librustdoc/html/format.rs
View file

@ -387,7 +387,7 @@ impl clean::GenericBound {
let modifier_str = match modifier {
hir::TraitBoundModifier::None => "",
hir::TraitBoundModifier::Maybe => "?",
hir::TraitBoundModifier::MaybeConst => "?const",
hir::TraitBoundModifier::MaybeConst => "~const",
};
if f.alternate() {
write!(f, "{}{:#}", modifier_str, ty.print(cx))

13
src/test/ui/consts/const-eval/issue-49296.rs
View file

@ -1,22 +1,13 @@
// issue-49296: Unsafe shenigans in constants can result in missing errors
#![feature(const_fn_trait_bound)]
#![feature(const_trait_bound_opt_out)]
#![allow(incomplete_features)]
const unsafe fn transmute<T: ?const Copy, U: ?const Copy>(t: T) -> U {
#[repr(C)]
union Transmute<T: Copy, U: Copy> {
from: T,
to: U,
}
Transmute { from: t }.to
}
use std::mem::transmute;
const fn wat(x: u64) -> &'static u64 {
unsafe { transmute(&x) }
}
const X: u64 = *wat(42);
//~^ ERROR evaluation of constant value failed

4
src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst-opt-out.rs
View file

@ -13,12 +13,10 @@ impl PartialEq for S {
}
}
const fn equals_self<T: ?const PartialEq>(t: &T) -> bool {
const fn equals_self<T: PartialEq>(t: &T) -> bool {
true
}
pub const EQ: bool = equals_self(&S);
// Calling `equals_self` with a type that only has a non-const impl is fine, because we opted out.
fn main() {}

12
src/test/ui/rfc-2632-const-trait-impl/tilde-const-on-non-const-fn.rs Normal file
View file

@ -0,0 +1,12 @@
#![feature(const_trait_impl)]
fn a<T: ~const From<u8>>() {}
//~^ ERROR: `~const` is not allowed
struct S;
impl S {
fn b<T: ~const From<u8>>() {}
//~^ ERROR: `~const` is not allowed
}
fn main() {}

18
src/test/ui/rfc-2632-const-trait-impl/tilde-const-on-non-const-fn.stderr Normal file
View file

@ -0,0 +1,18 @@
error: `~const` is not allowed here
--> $DIR/tilde-const-on-non-const-fn.rs:2:9
|
LL | fn a<T: ~const From<u8>>() {}
| ^^^^^^^^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
error: `~const` is not allowed here
--> $DIR/tilde-const-on-non-const-fn.rs:8:13
|
LL | fn b<T: ~const From<u8>>() {}
| ^^^^^^^^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
error: aborting due to 2 previous errors

4
src/tools/rustfmt/src/types.rs
View file

@ -537,10 +537,10 @@ impl Rewrite for ast::GenericBound {
.map(|s| format!("?{}", s)),
ast::TraitBoundModifier::MaybeConst => poly_trait_ref
.rewrite(context, shape.offset_left(7)?)
.map(|s| format!("?const {}", s)),
.map(|s| format!("~const {}", s)),
ast::TraitBoundModifier::MaybeConstMaybe => poly_trait_ref
.rewrite(context, shape.offset_left(8)?)
.map(|s| format!("?const ?{}", s)),
.map(|s| format!("~const ?{}", s)),
};
rewrite.map(|s| if has_paren { format!("({})", s) } else { s })
}

22
src/tools/rustfmt/tests/target/type.rs
View file

@ -145,35 +145,33 @@ type MyFn = fn(
b: SomeOtherLongComplexType,
) -> Box<Future<Item = AnotherLongType, Error = ALongErrorType>>;
// Const opt-out
// Const bound
trait T: ?const Super {}
trait T: ~const Super {}
const fn maybe_const<S: ?const T>() -> i32 {
const fn not_quite_const<S: ~const T>() -> i32 {
<S as T>::CONST
}
struct S<T: ?const ?Sized>(std::marker::PhantomData<T>);
struct S<T: ~const ?Sized>(std::marker::PhantomData<T>);
impl ?const T {}
impl ~const T {}
fn trait_object() -> &'static dyn ?const T {
fn trait_object() -> &'static dyn ~const T {
&S
}
fn i(_: impl IntoIterator<Item = Box<dyn ?const T>>) {}
fn i(_: impl IntoIterator<Item = Box<dyn ~const T>>) {}
fn apit(_: impl ?const T) {}
fn apit(_: impl ~const T) {}
fn rpit() -> impl ?const T {
fn rpit() -> impl ~const T {
S
}
pub struct Foo<T: Trait>(T);
impl<T: ?const Trait> Foo<T> {
impl<T: ~const Trait> Foo<T> {
fn new(t: T) -> Self {
// not calling methods on `t`, so we opt out of requiring
// `<T as Trait>` to have const methods via `?const`
Self(t)
}
}