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Auto merge of #84299 - lcnr:const-generics-defaults-name-res, r=varkor

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various const parameter defaults improvements

Actually resolve names in const parameter defaults, fixing `struct Foo<const N: usize = { usize::MAX }>`.

---
Split generic parameter ban rib for types and consts, allowing
```rust
#![feature(const_generics_defaults)]
struct Q;
struct Foo<T = Q, const Q: usize = 3>(T);
```

---
Remove the type/const ordering restriction if `const_generics_defaults` is active, even if `const_generics` is not. allowing us to stabilize and test const param defaults separately.

---
Check well formedness of const parameter defaults, eagerly emitting an error for `struct Foo<const N: usize = { 0 - 1 }>`

---
Do not forbid const parameters in param defaults, allowing `struct Foo<const N: usize, T = [u8; N]>(T)` and `struct Foo<const N: usize, const M: usize = N>`. Note that this should not change anything which is stabilized, as on stable, type parameters must be in front of const parameters, which means that type parameter defaults are only allowed if no const parameters exist.

We still forbid generic parameters inside of const param types.

r? `@varkor` `@petrochenkov`
This commit is contained in:
bors 2021-04-25 14:00:49 +00:00
commit 58bdb08947
45 changed files with 385 additions and 217 deletions
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11
compiler/rustc_resolve/src/diagnostics.rs
View file

@ -472,17 +472,6 @@ impl<'a> Resolver<'a> {
);
err
}
ResolutionError::ParamInAnonConstInTyDefault(name) => {
let mut err = self.session.struct_span_err(
span,
"constant values inside of type parameter defaults must not depend on generic parameters",
);
err.span_label(
span,
format!("the anonymous constant must not depend on the parameter `{}`", name),
);
err
}
ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
let mut err = self.session.struct_span_err(
span,

69
compiler/rustc_resolve/src/late.rs
View file

@ -555,18 +555,23 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
// provide previous type parameters as they're built. We
// put all the parameters on the ban list and then remove
// them one by one as they are processed and become available.
let mut default_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
let mut found_default = false;
default_ban_rib.bindings.extend(generics.params.iter().filter_map(
|param| match param.kind {
GenericParamKind::Type { default: Some(_), .. }
| GenericParamKind::Const { default: Some(_), .. } => {
found_default = true;
Some((Ident::with_dummy_span(param.ident.name), Res::Err))
let mut forward_ty_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
let mut forward_const_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
for param in generics.params.iter() {
match param.kind {
GenericParamKind::Type { .. } => {
forward_ty_ban_rib
.bindings
.insert(Ident::with_dummy_span(param.ident.name), Res::Err);
}
_ => None,
},
));
GenericParamKind::Const { .. } => {
forward_const_ban_rib
.bindings
.insert(Ident::with_dummy_span(param.ident.name), Res::Err);
}
GenericParamKind::Lifetime => {}
}
}
// rust-lang/rust#61631: The type `Self` is essentially
// another type parameter. For ADTs, we consider it
@ -579,7 +584,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
// such as in the case of `trait Add<Rhs = Self>`.)
if self.diagnostic_metadata.current_self_item.is_some() {
// (`Some` if + only if we are in ADT's generics.)
default_ban_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), Res::Err);
forward_ty_ban_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), Res::Err);
}
for param in &generics.params {
@ -591,32 +596,38 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
}
if let Some(ref ty) = default {
self.ribs[TypeNS].push(default_ban_rib);
self.with_rib(ValueNS, ForwardGenericParamBanRibKind, |this| {
// HACK: We use an empty `ForwardGenericParamBanRibKind` here which
// is only used to forbid the use of const parameters inside of
// type defaults.
//
// While the rib name doesn't really fit here, it does allow us to use the same
// code for both const and type parameters.
this.visit_ty(ty);
});
default_ban_rib = self.ribs[TypeNS].pop().unwrap();
self.ribs[TypeNS].push(forward_ty_ban_rib);
self.ribs[ValueNS].push(forward_const_ban_rib);
self.visit_ty(ty);
forward_const_ban_rib = self.ribs[ValueNS].pop().unwrap();
forward_ty_ban_rib = self.ribs[TypeNS].pop().unwrap();
}
// Allow all following defaults to refer to this type parameter.
default_ban_rib.bindings.remove(&Ident::with_dummy_span(param.ident.name));
forward_ty_ban_rib.bindings.remove(&Ident::with_dummy_span(param.ident.name));
}
GenericParamKind::Const { ref ty, kw_span: _, default: _ } => {
// FIXME(const_generics_defaults): handle `default` value here
for bound in &param.bounds {
self.visit_param_bound(bound);
}
GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
// Const parameters can't have param bounds.
assert!(param.bounds.is_empty());
self.ribs[TypeNS].push(Rib::new(ConstParamTyRibKind));
self.ribs[ValueNS].push(Rib::new(ConstParamTyRibKind));
self.visit_ty(ty);
self.ribs[TypeNS].pop().unwrap();
self.ribs[ValueNS].pop().unwrap();
if let Some(ref expr) = default {
self.ribs[TypeNS].push(forward_ty_ban_rib);
self.ribs[ValueNS].push(forward_const_ban_rib);
self.visit_anon_const(expr);
forward_const_ban_rib = self.ribs[ValueNS].pop().unwrap();
forward_ty_ban_rib = self.ribs[TypeNS].pop().unwrap();
}
// Allow all following defaults to refer to this const parameter.
forward_const_ban_rib
.bindings
.remove(&Ident::with_dummy_span(param.ident.name));
}
}
}

56
compiler/rustc_resolve/src/lib.rs
View file

@ -239,8 +239,6 @@ enum ResolutionError<'a> {
ForwardDeclaredTyParam, // FIXME(const_generics_defaults)
/// ERROR E0770: the type of const parameters must not depend on other generic parameters.
ParamInTyOfConstParam(Symbol),
/// constant values inside of type parameter defaults must not depend on generic parameters.
ParamInAnonConstInTyDefault(Symbol),
/// generic parameters must not be used inside const evaluations.
///
/// This error is only emitted when using `min_const_generics`.
@ -2672,26 +2670,18 @@ impl<'a> Resolver<'a> {
}
}
Res::Def(DefKind::TyParam, _) | Res::SelfTy(..) => {
let mut in_ty_param_default = false;
for rib in ribs {
let has_generic_params = match rib.kind {
let has_generic_params: HasGenericParams = match rib.kind {
NormalRibKind
| ClosureOrAsyncRibKind
| AssocItemRibKind
| ModuleRibKind(..)
| MacroDefinition(..) => {
| MacroDefinition(..)
| ForwardGenericParamBanRibKind => {
// Nothing to do. Continue.
continue;
}
// We only forbid constant items if we are inside of type defaults,
// for example `struct Foo<T, U = [u8; std::mem::size_of::<T>()]>`
ForwardGenericParamBanRibKind => {
// FIXME(const_generic_defaults): we may need to distinguish between
// being in type parameter defaults and const parameter defaults
in_ty_param_default = true;
continue;
}
ConstantItemRibKind(trivial, _) => {
let features = self.session.features_untracked();
// HACK(min_const_generics): We currently only allow `N` or `{ N }`.
@ -2720,19 +2710,7 @@ impl<'a> Resolver<'a> {
}
}
if in_ty_param_default {
if record_used {
self.report_error(
span,
ResolutionError::ParamInAnonConstInTyDefault(
rib_ident.name,
),
);
}
return Res::Err;
} else {
continue;
}
continue;
}
// This was an attempt to use a type parameter outside its scope.
@ -2770,23 +2748,15 @@ impl<'a> Resolver<'a> {
ribs.next();
}
let mut in_ty_param_default = false;
for rib in ribs {
let has_generic_params = match rib.kind {
NormalRibKind
| ClosureOrAsyncRibKind
| AssocItemRibKind
| ModuleRibKind(..)
| MacroDefinition(..) => continue,
| MacroDefinition(..)
| ForwardGenericParamBanRibKind => continue,
// We only forbid constant items if we are inside of type defaults,
// for example `struct Foo<T, U = [u8; std::mem::size_of::<T>()]>`
ForwardGenericParamBanRibKind => {
// FIXME(const_generic_defaults): we may need to distinguish between
// being in type parameter defaults and const parameter defaults
in_ty_param_default = true;
continue;
}
ConstantItemRibKind(trivial, _) => {
let features = self.session.features_untracked();
// HACK(min_const_generics): We currently only allow `N` or `{ N }`.
@ -2808,19 +2778,7 @@ impl<'a> Resolver<'a> {
return Res::Err;
}
if in_ty_param_default {
if record_used {
self.report_error(
span,
ResolutionError::ParamInAnonConstInTyDefault(
rib_ident.name,
),
);
}
return Res::Err;
} else {
continue;
}
continue;
}
ItemRibKind(has_generic_params) => has_generic_params,