bjoernager/rust
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Improve "~const is not allowed here" message

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This commit is contained in:
Deadbeef 2022-10-20 19:32:16 +00:00
parent 542febd2d3
commit ebf5028574
6 changed files with 85 additions and 25 deletions
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63
compiler/rustc_ast_passes/src/ast_validation.rs
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@ -38,6 +38,13 @@ enum SelfSemantic {
No,
}
/// What is the context that prevents using `~const`?
enum DisallowTildeConstContext<'a> {
TraitObject,
ImplTrait,
Fn(FnKind<'a>),
}
struct AstValidator<'a> {
session: &'a Session,
@ -56,7 +63,7 @@ struct AstValidator<'a> {
/// e.g., `impl Iterator<Item = impl Debug>`.
outer_impl_trait: Option<Span>,
is_tilde_const_allowed: bool,
disallow_tilde_const: Option<DisallowTildeConstContext<'a>>,
/// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
/// or `Foo::Bar<impl Trait>`
@ -93,18 +100,26 @@ impl<'a> AstValidator<'a> {
self.is_impl_trait_banned = old;
}
fn with_tilde_const(&mut self, allowed: bool, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.is_tilde_const_allowed, allowed);
fn with_tilde_const(
&mut self,
disallowed: Option<DisallowTildeConstContext<'a>>,
f: impl FnOnce(&mut Self),
) {
let old = mem::replace(&mut self.disallow_tilde_const, disallowed);
f(self);
self.is_tilde_const_allowed = old;
self.disallow_tilde_const = old;
}
fn with_tilde_const_allowed(&mut self, f: impl FnOnce(&mut Self)) {
self.with_tilde_const(true, f)
self.with_tilde_const(None, f)
}
fn with_banned_tilde_const(&mut self, f: impl FnOnce(&mut Self)) {
self.with_tilde_const(false, f)
fn with_banned_tilde_const(
&mut self,
ctx: DisallowTildeConstContext<'a>,
f: impl FnOnce(&mut Self),
) {
self.with_tilde_const(Some(ctx), f)
}
fn with_let_management(
@ -172,7 +187,7 @@ 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_banned_tilde_const(f);
self.with_banned_tilde_const(DisallowTildeConstContext::ImplTrait, f);
} else {
f(self);
}
@ -197,7 +212,10 @@ impl<'a> AstValidator<'a> {
TyKind::ImplTrait(..) => {
self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
}
TyKind::TraitObject(..) => self.with_banned_tilde_const(|this| visit::walk_ty(this, t)),
TyKind::TraitObject(..) => self
.with_banned_tilde_const(DisallowTildeConstContext::TraitObject, |this| {
visit::walk_ty(this, t)
}),
TyKind::Path(ref qself, ref path) => {
// We allow these:
// - `Option<impl Trait>`
@ -1411,13 +1429,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
);
err.emit();
}
(_, TraitBoundModifier::MaybeConst) => {
if !self.is_tilde_const_allowed {
self.err_handler()
.struct_span_err(bound.span(), "`~const` is not allowed here")
.note("only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions")
.emit();
}
(_, TraitBoundModifier::MaybeConst) if let Some(reason) = &self.disallow_tilde_const => {
let mut err = self.err_handler().struct_span_err(bound.span(), "`~const` is not allowed here");
match reason {
DisallowTildeConstContext::TraitObject => err.note("trait objects cannot have `~const` trait bounds"),
DisallowTildeConstContext::ImplTrait => err.note("`impl Trait`s cannot have `~const` trait bounds"),
DisallowTildeConstContext::Fn(FnKind::Closure(..)) => err.note("closures cannot have `~const` trait bounds"),
DisallowTildeConstContext::Fn(FnKind::Fn(_, ident, ..)) => err.span_note(ident.span, "this function is not `const`, so it cannot have `~const` trait bounds"),
};
err.emit();
}
(_, TraitBoundModifier::MaybeConstMaybe) => {
self.err_handler()
@ -1523,10 +1543,13 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
});
}
let tilde_const_allowed = matches!(fk.header(), Some(FnHeader { .. }))
|| matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
let tilde_const_allowed =
matches!(fk.header(), Some(FnHeader { constness: ast::Const::Yes(_), .. }))
|| matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
self.with_tilde_const(tilde_const_allowed, |this| visit::walk_fn(this, fk));
let disallowed = (!tilde_const_allowed).then(|| DisallowTildeConstContext::Fn(fk));
self.with_tilde_const(disallowed, |this| visit::walk_fn(this, fk));
}
fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
@ -1770,7 +1793,7 @@ pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) ->
in_const_trait_impl: false,
has_proc_macro_decls: false,
outer_impl_trait: None,
is_tilde_const_allowed: false,
disallow_tilde_const: None,
is_impl_trait_banned: false,
is_assoc_ty_bound_banned: false,
forbidden_let_reason: Some(ForbiddenLetReason::GenericForbidden),