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Experiment: mark derived Clone impls as const #93255

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Experiment: mark derived Clone impls as const #93255

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1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/bounds.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ pub fn expand_deriving_copy(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: true,
methods: Vec::new(),
associated_types: Vec::new(),
Expand Down
21 changes: 19 additions & 2 deletions compiler/rustc_builtin_macros/src/deriving/clone.rs
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Expand Up @@ -15,7 +15,7 @@ pub fn expand_deriving_clone(
item: &Annotatable,
push: &mut dyn FnMut(Annotatable),
) {
// check if we can use a short form
// check if we can use a short form, and if the impl can be const
//
// the short form is `fn clone(&self) -> Self { *self }`
//
Expand All @@ -29,6 +29,9 @@ pub fn expand_deriving_clone(
// Unions with generic parameters still can derive Clone because they require Copy
// for deriving, Clone alone is not enough.
// Whever Clone is implemented for fields is irrelevant so we don't assert it.
//
// for now, the impl is only able to be marked as const if we can use the short form;
// in the future, this may be expanded
let bounds;
let substructure;
let is_shallow;
Expand Down Expand Up @@ -73,15 +76,29 @@ pub fn expand_deriving_clone(
_ => cx.span_bug(span, "`#[derive(Clone)]` on trait item or impl item"),
}

let features = cx.sess.features_untracked();
let inline = cx.meta_word(span, sym::inline);
let attrs = vec![cx.attribute(inline)];
let is_const = is_shallow && features.const_trait_impl;
let trait_def = TraitDef {
span,
attributes: Vec::new(),
attributes: if is_const && features.staged_api {
vec![cx.attribute(cx.meta_list(
span,
sym::rustc_const_unstable,
vec![
cx.meta_name_value(span, sym::feature, Symbol::intern("const_clone")),
cx.meta_name_value(span, sym::issue, Symbol::intern("none")),
],
))]
} else {
Vec::new()
},
path: path_std!(clone::Clone),
additional_bounds: bounds,
generics: Bounds::empty(),
is_unsafe: false,
is_const,
supports_unions: true,
methods: vec![MethodDef {
name: sym::clone,
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
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Expand Up @@ -28,6 +28,7 @@ pub fn expand_deriving_eq(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: true,
methods: vec![MethodDef {
name: sym::assert_receiver_is_total_eq,
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
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Expand Up @@ -24,6 +24,7 @@ pub fn expand_deriving_ord(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![MethodDef {
name: sym::cmp,
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
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Expand Up @@ -104,6 +104,7 @@ pub fn expand_deriving_partial_eq(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods,
associated_types: Vec::new(),
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
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Expand Up @@ -47,6 +47,7 @@ pub fn expand_deriving_partial_ord(
additional_bounds: vec![],
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![partial_cmp_def],
associated_types: Vec::new(),
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/debug.rs
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Expand Up @@ -30,6 +30,7 @@ pub fn expand_deriving_debug(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![MethodDef {
name: sym::fmt,
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/decodable.rs
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Expand Up @@ -27,6 +27,7 @@ pub fn expand_deriving_rustc_decodable(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![MethodDef {
name: sym::decode,
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/default.rs
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Expand Up @@ -31,6 +31,7 @@ pub fn expand_deriving_default(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![MethodDef {
name: kw::Default,
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/encodable.rs
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Expand Up @@ -112,6 +112,7 @@ pub fn expand_deriving_rustc_encodable(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![MethodDef {
name: sym::encode,
Expand Down
49 changes: 42 additions & 7 deletions compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
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Expand Up @@ -215,6 +215,9 @@ pub struct TraitDef<'a> {
/// Is it an `unsafe` trait?
pub is_unsafe: bool,

/// Is it a `const` impl?
pub is_const: bool,

/// Can this trait be derived for unions?
pub supports_unions: bool,

Expand Down Expand Up @@ -568,7 +571,7 @@ impl<'a> TraitDef<'a> {
});

let Generics { mut params, mut where_clause, .. } =
self.generics.to_generics(cx, self.span, type_ident, generics);
self.generics.to_generics(cx, self.span, type_ident, generics, self.is_const);
where_clause.span = generics.where_clause.span;
let ctxt = self.span.ctxt();
let span = generics.span.with_ctxt(ctxt);
Expand All @@ -583,10 +586,24 @@ impl<'a> TraitDef<'a> {
// 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))
cx.trait_bound(
p.to_path(cx, self.span, type_ident, generics),
if self.is_const {
ast::TraitBoundModifier::MaybeConst
} else {
ast::TraitBoundModifier::None
},
)
}).chain(
// require the current trait
iter::once(cx.trait_bound(trait_path.clone()))
iter::once(cx.trait_bound(
trait_path.clone(),
if self.is_const {
ast::TraitBoundModifier::MaybeConst
} else {
ast::TraitBoundModifier::None
}
))
).chain(
// also add in any bounds from the declaration
param.bounds.iter().cloned()
Expand Down Expand Up @@ -663,11 +680,27 @@ impl<'a> TraitDef<'a> {
let mut bounds: Vec<_> = self
.additional_bounds
.iter()
.map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
.map(|p| {
cx.trait_bound(
p.to_path(cx, self.span, type_ident, generics),
if self.is_const {
ast::TraitBoundModifier::MaybeConst
} else {
ast::TraitBoundModifier::None
},
)
})
.collect();

// require the current trait
bounds.push(cx.trait_bound(trait_path.clone()));
bounds.push(cx.trait_bound(
trait_path.clone(),
if self.is_const {
ast::TraitBoundModifier::MaybeConst
} else {
ast::TraitBoundModifier::None
},
));

let predicate = ast::WhereBoundPredicate {
span: self.span,
Expand Down Expand Up @@ -723,6 +756,7 @@ impl<'a> TraitDef<'a> {
a.extend(self.attributes.iter().cloned());

let unsafety = if self.is_unsafe { ast::Unsafe::Yes(self.span) } else { ast::Unsafe::No };
let constness = if self.is_const { ast::Const::Yes(self.span) } else { ast::Const::No };

cx.item(
self.span,
Expand All @@ -732,7 +766,7 @@ impl<'a> TraitDef<'a> {
unsafety,
polarity: ast::ImplPolarity::Positive,
defaultness: ast::Defaultness::Final,
constness: ast::Const::No,
constness,
generics: trait_generics,
of_trait: opt_trait_ref,
self_ty: self_type,
Expand Down Expand Up @@ -933,7 +967,8 @@ impl<'a> MethodDef<'a> {
) -> 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 fn_generics =
self.generics.to_generics(cx, span, type_ident, generics, trait_.is_const);

let args = {
let self_args = explicit_self.map(|explicit_self| {
Expand Down
17 changes: 13 additions & 4 deletions compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
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Expand Up @@ -200,12 +200,20 @@ fn mk_ty_param(
bounds: &[Path],
self_ident: Ident,
self_generics: &Generics,
is_const: bool,
) -> ast::GenericParam {
let bounds = bounds
.iter()
.map(|b| {
let path = b.to_path(cx, span, self_ident, self_generics);
cx.trait_bound(path)
.map(|path| {
let path = path.to_path(cx, span, self_ident, self_generics);
cx.trait_bound(
path,
if is_const {
ast::TraitBoundModifier::MaybeConst
} else {
ast::TraitBoundModifier::None
},
)
})
.collect();
cx.typaram(span, Ident::new(name, span), attrs.to_owned(), bounds, None)
Expand All @@ -227,13 +235,14 @@ impl Bounds {
span: Span,
self_ty: Ident,
self_generics: &Generics,
is_const: bool,
) -> Generics {
let params = self
.bounds
.iter()
.map(|t| {
let (name, ref bounds) = *t;
mk_ty_param(cx, span, name, &[], &bounds, self_ty, self_generics)
mk_ty_param(cx, span, name, &[], &bounds, self_ty, self_generics, is_const)
})
.collect();

Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_builtin_macros/src/deriving/hash.rs
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Expand Up @@ -27,6 +27,7 @@ pub fn expand_deriving_hash(
additional_bounds: Vec::new(),
generics: Bounds::empty(),
is_unsafe: false,
is_const: false,
supports_unions: false,
methods: vec![MethodDef {
name: sym::hash,
Expand Down
19 changes: 14 additions & 5 deletions compiler/rustc_expand/src/build.rs
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Expand Up @@ -128,11 +128,12 @@ impl<'a> ExtCtxt<'a> {
}
}

pub fn trait_bound(&self, path: ast::Path) -> ast::GenericBound {
ast::GenericBound::Trait(
self.poly_trait_ref(path.span, path),
ast::TraitBoundModifier::None,
)
pub fn trait_bound(
&self,
path: ast::Path,
modif: ast::TraitBoundModifier,
) -> ast::GenericBound {
ast::GenericBound::Trait(self.poly_trait_ref(path.span, path), modif)
}

pub fn lifetime(&self, span: Span, ident: Ident) -> ast::Lifetime {
Expand Down Expand Up @@ -567,4 +568,12 @@ impl<'a> ExtCtxt<'a> {
pub fn meta_word(&self, sp: Span, w: Symbol) -> ast::MetaItem {
attr::mk_word_item(Ident::new(w, sp))
}

pub fn meta_name_value(&self, sp: Span, n: Symbol, v: Symbol) -> ast::NestedMetaItem {
ast::NestedMetaItem::MetaItem(attr::mk_name_value_item_str(Ident::new(n, sp), v, sp))
}

pub fn meta_list(&self, sp: Span, w: Symbol, items: Vec<ast::NestedMetaItem>) -> ast::MetaItem {
attr::mk_list_item(Ident::new(w, sp), items)
}
}
21 changes: 15 additions & 6 deletions library/core/src/clone.rs
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Expand Up @@ -127,7 +127,11 @@ pub trait Clone: Sized {
/// allocations.
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn clone_from(&mut self, source: &Self) {
#[default_method_body_is_const]
fn clone_from(&mut self, source: &Self)
where
Self: ~const Clone + ~const Drop,
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does this show up in rustdoc?

{
*self = source.clone()
}
}
Expand Down Expand Up @@ -178,7 +182,8 @@ mod impls {
($($t:ty)*) => {
$(
#[stable(feature = "rust1", since = "1.0.0")]
impl Clone for $t {
#[rustc_const_unstable(feature = "const_clone", issue = "none")]
impl const Clone for $t {
#[inline]
fn clone(&self) -> Self {
*self
Expand All @@ -196,23 +201,26 @@ mod impls {
}

#[unstable(feature = "never_type", issue = "35121")]
impl Clone for ! {
#[rustc_const_unstable(feature = "const_clone", issue = "none")]
impl const Clone for ! {
#[inline]
fn clone(&self) -> Self {
*self
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Clone for *const T {
#[rustc_const_unstable(feature = "const_clone", issue = "none")]
impl<T: ?Sized> const Clone for *const T {
#[inline]
fn clone(&self) -> Self {
*self
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Clone for *mut T {
#[rustc_const_unstable(feature = "const_clone", issue = "none")]
impl<T: ?Sized> const Clone for *mut T {
#[inline]
fn clone(&self) -> Self {
*self
Expand All @@ -221,7 +229,8 @@ mod impls {

/// Shared references can be cloned, but mutable references *cannot*!
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Clone for &T {
#[rustc_const_unstable(feature = "const_clone", issue = "none")]
impl<T: ?Sized> const Clone for &T {
#[inline]
#[rustc_diagnostic_item = "noop_method_clone"]
fn clone(&self) -> Self {
Expand Down
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