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forbid generic params in complex consts

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This commit is contained in:
Bastian Kauschke 2020-07-28 15:55:42 +02:00
parent 375bccb8b3
commit 289e5fca7e
8 changed files with 194 additions and 18 deletions
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24
src/librustc_ast/ast.rs
View File

@ -1052,6 +1052,30 @@ impl Expr {
}
}
/// Is this expr either `N`, or `{ N }`.
///
/// If this is not the case, name resolution does not resolve `N` when using
/// `feature(min_const_generics)` as more complex expressions are not supported.
pub fn is_potential_trivial_const_param(&self) -> bool {
let this = if let ExprKind::Block(ref block, None) = self.kind {
if block.stmts.len() == 1 {
if let StmtKind::Expr(ref expr) = block.stmts[0].kind { expr } else { self }
} else {
self
}
} else {
self
};
if let ExprKind::Path(None, ref path) = this.kind {
if path.segments.len() == 1 && path.segments[0].args.is_none() {
return true;
}
}
false
}
pub fn to_bound(&self) -> Option<GenericBound> {
match &self.kind {
ExprKind::Path(None, path) => Some(GenericBound::Trait(

17
src/librustc_resolve/diagnostics.rs
View File

@ -466,6 +466,23 @@ impl<'a> Resolver<'a> {
);
err
}
ResolutionError::ParamInNonTrivialAnonConst(name) => {
let mut err = self.session.struct_span_err(
span,
"generic parameters must not be used inside of non trivial constant values",
);
err.span_label(
span,
&format!(
"non-trivial anonymous constants must not depend on the parameter `{}`",
name
),
);
err.help(
&format!("it is currently only allowed to use either `{0}` or `{{ {0} }}` as generic constants", name)
);
err
}
ResolutionError::SelfInTyParamDefault => {
let mut err = struct_span_err!(
self.session,

44
src/librustc_resolve/late.rs
View File

@ -111,7 +111,7 @@ crate enum RibKind<'a> {
ItemRibKind(HasGenericParams),
/// We're in a constant item. Can't refer to dynamic stuff.
ConstantItemRibKind,
ConstantItemRibKind(bool),
/// We passed through a module.
ModuleRibKind(Module<'a>),
@ -137,7 +137,7 @@ impl RibKind<'_> {
NormalRibKind
| ClosureOrAsyncRibKind
| FnItemRibKind
| ConstantItemRibKind
| ConstantItemRibKind(_)
| ModuleRibKind(_)
| MacroDefinition(_)
| ConstParamTyRibKind => false,
@ -426,7 +426,7 @@ impl<'a, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
}
fn visit_anon_const(&mut self, constant: &'ast AnonConst) {
debug!("visit_anon_const {:?}", constant);
self.with_constant_rib(|this| {
self.with_constant_rib(constant.value.is_potential_trivial_const_param(), |this| {
visit::walk_anon_const(this, constant);
});
}
@ -628,7 +628,7 @@ impl<'a, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
if !check_ns(TypeNS) && check_ns(ValueNS) {
// This must be equivalent to `visit_anon_const`, but we cannot call it
// directly due to visitor lifetimes so we have to copy-paste some code.
self.with_constant_rib(|this| {
self.with_constant_rib(true, |this| {
this.smart_resolve_path(
ty.id,
qself.as_ref(),
@ -829,7 +829,7 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
| ClosureOrAsyncRibKind
| FnItemRibKind
| ItemRibKind(..)
| ConstantItemRibKind
| ConstantItemRibKind(_)
| ModuleRibKind(..)
| ForwardTyParamBanRibKind
| ConstParamTyRibKind => {
@ -948,7 +948,10 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
// Only impose the restrictions of `ConstRibKind` for an
// actual constant expression in a provided default.
if let Some(expr) = default {
this.with_constant_rib(|this| this.visit_expr(expr));
this.with_constant_rib(
expr.is_potential_trivial_const_param(),
|this| this.visit_expr(expr),
);
}
}
AssocItemKind::Fn(_, _, generics, _) => {
@ -989,7 +992,9 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
self.with_item_rib(HasGenericParams::No, |this| {
this.visit_ty(ty);
if let Some(expr) = expr {
this.with_constant_rib(|this| this.visit_expr(expr));
this.with_constant_rib(expr.is_potential_trivial_const_param(), |this| {
this.visit_expr(expr)
});
}
});
}
@ -1086,11 +1091,11 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
self.with_rib(ValueNS, kind, |this| this.with_rib(TypeNS, kind, f))
}
fn with_constant_rib(&mut self, f: impl FnOnce(&mut Self)) {
fn with_constant_rib(&mut self, trivial: bool, f: impl FnOnce(&mut Self)) {
debug!("with_constant_rib");
self.with_rib(ValueNS, ConstantItemRibKind, |this| {
this.with_rib(TypeNS, ConstantItemRibKind, |this| {
this.with_label_rib(ConstantItemRibKind, f);
self.with_rib(ValueNS, ConstantItemRibKind(trivial), |this| {
this.with_rib(TypeNS, ConstantItemRibKind(trivial), |this| {
this.with_label_rib(ConstantItemRibKind(trivial), f);
})
});
}
@ -1220,7 +1225,7 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
for item in impl_items {
use crate::ResolutionError::*;
match &item.kind {
AssocItemKind::Const(..) => {
AssocItemKind::Const(_default, _ty, expr) => {
debug!("resolve_implementation AssocItemKind::Const",);
// If this is a trait impl, ensure the const
// exists in trait
@ -1231,9 +1236,18 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
|n, s| ConstNotMemberOfTrait(n, s),
);
this.with_constant_rib(|this| {
visit::walk_assoc_item(this, item, AssocCtxt::Impl)
});
this.with_constant_rib(
expr.as_ref().map_or(false, |e| {
e.is_potential_trivial_const_param()
}),
|this| {
visit::walk_assoc_item(
this,
item,
AssocCtxt::Impl,
)
},
);
}
AssocItemKind::Fn(_, _, generics, _) => {
// We also need a new scope for the impl item type parameters.

32
src/librustc_resolve/lib.rs
View File

@ -218,6 +218,10 @@ enum ResolutionError<'a> {
ParamInTyOfConstParam(Symbol),
/// constant values inside of type parameter defaults must not depend on generic parameters.
ParamInAnonConstInTyDefault(Symbol),
/// generic parameters must not be used inside of non trivial constant values.
///
/// This error is only emitted when using `min_const_generics`.
ParamInNonTrivialAnonConst(Symbol),
/// Error E0735: type parameters with a default cannot use `Self`
SelfInTyParamDefault,
/// Error E0767: use of unreachable label
@ -2507,7 +2511,7 @@ impl<'a> Resolver<'a> {
res_err = Some(CannotCaptureDynamicEnvironmentInFnItem);
}
}
ConstantItemRibKind => {
ConstantItemRibKind(_) => {
// Still doesn't deal with upvars
if record_used {
self.report_error(span, AttemptToUseNonConstantValueInConstant);
@ -2546,7 +2550,18 @@ impl<'a> Resolver<'a> {
in_ty_param_default = true;
continue;
}
ConstantItemRibKind => {
ConstantItemRibKind(trivial) => {
// HACK(min_const_generics): We currently only allow `N` or `{ N }`.
if !trivial && self.session.features_untracked().min_const_generics {
if record_used {
self.report_error(
span,
ResolutionError::ParamInNonTrivialAnonConst(rib_ident.name),
);
}
return Res::Err;
}
if in_ty_param_default {
if record_used {
self.report_error(
@ -2612,7 +2627,18 @@ impl<'a> Resolver<'a> {
in_ty_param_default = true;
continue;
}
ConstantItemRibKind => {
ConstantItemRibKind(trivial) => {
// HACK(min_const_generics): We currently only allow `N` or `{ N }`.
if !trivial && self.session.features_untracked().min_const_generics {
if record_used {
self.report_error(
span,
ResolutionError::ParamInNonTrivialAnonConst(rib_ident.name),
);
}
return Res::Err;
}
if in_ty_param_default {
if record_used {
self.report_error(

37
src/test/ui/const-generics/min_const_generics/complex-expression.rs Normal file
View File

@ -0,0 +1,37 @@
#![feature(min_const_generics)]
fn test<const N: usize>() {}
fn ok<const M: usize>() -> [u8; M] {
[0; { M }]
}
struct Break0<const N: usize>([u8; { N + 1 }]);
//~^ ERROR generic parameters must not be used inside of non trivial constant values
struct Break1<const N: usize>([u8; { { N } }]);
//~^ ERROR generic parameters must not be used inside of non trivial constant values
fn break2<const N: usize>() {
let _: [u8; N + 1];
//~^ ERROR generic parameters must not be used inside of non trivial constant values
}
fn break3<const N: usize>() {
let _ = [0; N + 1];
//~^ ERROR generic parameters must not be used inside of non trivial constant values
}
trait Foo {
const ASSOC: usize;
}
impl<const N: usize> Foo for [u8; N] {
const ASSOC: usize = N + 1;
//~^ ERROR generic parameters must not be used inside of non trivial constant values
// FIXME(min_const_generics): We probably have to allow this as we can
// already allow referencing type parameters here on stable.
}
fn main() {}

42
src/test/ui/const-generics/min_const_generics/complex-expression.stderr Normal file
View File

@ -0,0 +1,42 @@
error: generic parameters must not be used inside of non trivial constant values
--> $DIR/complex-expression.rs:9:38
|
LL | struct Break0<const N: usize>([u8; { N + 1 }]);
| ^ non-trivial anonymous constants must not depend on the parameter `N`
|
= help: it is currently only allowed to use either `N` or `{ N }` as generic constants
error: generic parameters must not be used inside of non trivial constant values
--> $DIR/complex-expression.rs:12:40
|
LL | struct Break1<const N: usize>([u8; { { N } }]);
| ^ non-trivial anonymous constants must not depend on the parameter `N`
|
= help: it is currently only allowed to use either `N` or `{ N }` as generic constants
error: generic parameters must not be used inside of non trivial constant values
--> $DIR/complex-expression.rs:16:17
|
LL | let _: [u8; N + 1];
| ^ non-trivial anonymous constants must not depend on the parameter `N`
|
= help: it is currently only allowed to use either `N` or `{ N }` as generic constants
error: generic parameters must not be used inside of non trivial constant values
--> $DIR/complex-expression.rs:21:17
|
LL | let _ = [0; N + 1];
| ^ non-trivial anonymous constants must not depend on the parameter `N`
|
= help: it is currently only allowed to use either `N` or `{ N }` as generic constants
error: generic parameters must not be used inside of non trivial constant values
--> $DIR/complex-expression.rs:30:26
|
LL | const ASSOC: usize = N + 1;
| ^ non-trivial anonymous constants must not depend on the parameter `N`
|
= help: it is currently only allowed to use either `N` or `{ N }` as generic constants
error: aborting due to 5 previous errors

4
src/test/ui/const-generics/min_const_generics/feature-gate-min_const_generics.rs Normal file
View File

@ -0,0 +1,4 @@
fn test<const N: usize>() {}
//~^ ERROR const generics are unstable
fn main() {}

12
src/test/ui/const-generics/min_const_generics/feature-gate-min_const_generics.stderr Normal file
View File

@ -0,0 +1,12 @@
error[E0658]: const generics are unstable
--> $DIR/feature-gate-min_const_generics.rs:1:15
|
LL | fn test<const N: usize>() {}
| ^
|
= note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
= help: add `#![feature(const_generics)]` to the crate attributes to enable
error: aborting due to previous error
For more information about this error, try `rustc --explain E0658`.