Rollup merge of #127054 - compiler-errors:bound-ordering, r=fmease
Reorder trait bound modifiers *after* `for<...>` binder in trait bounds This PR suggests changing the grammar of trait bounds from: ``` [CONSTNESS] [ASYNCNESS] [?] [BINDER] [TRAIT_PATH] const async ? for<'a> Sized ``` to ``` ([BINDER] [CONSTNESS] [ASYNCNESS] | [?]) [TRAIT_PATH] ``` i.e., either ``` ? Sized ``` or ``` for<'a> const async Sized ``` (but not both) ### Why? I think it's strange that the binder applies "more tightly" than the `?` trait polarity. This becomes even weirder when considering that we (or at least, I) want to have `async` trait bounds expressed like: ``` where T: for<'a> async Fn(&'a ()) -> i32, ``` and not: ``` where T: async for<'a> Fn(&'a ()) -> i32, ``` ### Fallout No crates on crater use this syntax, presumably because it's literally useless. This will require modifying the reference grammar, though. ### Alternatives If this is not desirable, then we can alternatively keep parsing `for<'a>` after the `?` but deprecate it with either an FCW (or an immediate hard error), and begin parsing `for<'a>` *before* the `?`.
This commit is contained in:
Matthias Krüger
GitHub
commit
cfc5f25b3d
@ -155,8 +155,6 @@ ast_passes_impl_trait_path = `impl Trait` is not allowed in path parameters
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ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
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.help = remove one of these features
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ast_passes_incompatible_trait_bound_modifiers = `{$left}` and `{$right}` are mutually exclusive
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ast_passes_inherent_cannot_be = inherent impls cannot be {$annotation}
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.because = {$annotation} because of this
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.type = inherent impl for this type
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@ -1366,17 +1366,6 @@ fn visit_param_bound(&mut self, bound: &'a GenericBound, ctxt: BoundKind) {
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{
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self.dcx().emit_err(errors::TildeConstDisallowed { span, reason });
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}
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(
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_,
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BoundConstness::Always(_) | BoundConstness::Maybe(_),
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BoundPolarity::Negative(_) | BoundPolarity::Maybe(_),
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) => {
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self.dcx().emit_err(errors::IncompatibleTraitBoundModifiers {
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span: bound.span(),
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left: modifiers.constness.as_str(),
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right: modifiers.polarity.as_str(),
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});
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}
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_ => {}
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}
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@ -656,15 +656,6 @@ pub enum TildeConstReason {
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Item,
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}
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#[derive(Diagnostic)]
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#[diag(ast_passes_incompatible_trait_bound_modifiers)]
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pub struct IncompatibleTraitBoundModifiers {
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#[primary_span]
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pub span: Span,
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pub left: &'static str,
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pub right: &'static str,
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}
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#[derive(Diagnostic)]
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#[diag(ast_passes_const_and_async)]
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pub struct ConstAndAsync {
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@ -53,6 +53,12 @@ parse_bare_cr = {$double_quotes ->
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parse_bare_cr_in_raw_string = bare CR not allowed in raw string
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parse_binder_and_polarity = `for<...>` binder not allowed with `{$polarity}` trait polarity modifier
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.label = there is not a well-defined meaning for a higher-ranked `{$polarity}` trait
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parse_binder_before_modifiers = `for<...>` binder should be placed before trait bound modifiers
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.label = place the `for<...>` binder before any modifiers
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parse_bounds_not_allowed_on_trait_aliases = bounds are not allowed on trait aliases
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parse_box_not_pat = expected pattern, found {$descr}
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@ -577,6 +583,9 @@ parse_missing_trait_in_trait_impl = missing trait in a trait impl
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parse_modifier_lifetime = `{$modifier}` may only modify trait bounds, not lifetime bounds
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.suggestion = remove the `{$modifier}`
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parse_modifiers_and_polarity = `{$modifiers_concatenated}` trait not allowed with `{$polarity}` trait polarity modifier
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.label = there is not a well-defined meaning for a `{$modifiers_concatenated} {$polarity}` trait
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parse_more_than_one_char = character literal may only contain one codepoint
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.followed_by = this `{$chr}` is followed by the combining {$len ->
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[one] mark
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@ -3212,3 +3212,33 @@ pub struct UnsafeAttrOutsideUnsafeSuggestion {
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#[suggestion_part(code = ")")]
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pub right: Span,
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}
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#[derive(Diagnostic)]
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#[diag(parse_binder_before_modifiers)]
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pub struct BinderBeforeModifiers {
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#[primary_span]
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pub binder_span: Span,
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#[label]
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pub modifiers_span: Span,
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}
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#[derive(Diagnostic)]
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#[diag(parse_binder_and_polarity)]
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pub struct BinderAndPolarity {
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#[primary_span]
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pub polarity_span: Span,
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#[label]
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pub binder_span: Span,
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pub polarity: &'static str,
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}
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#[derive(Diagnostic)]
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#[diag(parse_modifiers_and_polarity)]
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pub struct PolarityAndModifiers {
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#[primary_span]
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pub polarity_span: Span,
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#[label]
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pub modifiers_span: Span,
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pub polarity: &'static str,
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pub modifiers_concatenated: String,
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}
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@ -935,9 +935,14 @@ fn recover_paren_lifetime(&mut self, lo: Span) -> PResult<'a, ()> {
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/// If no modifiers are present, this does not consume any tokens.
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///
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/// ```ebnf
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/// TRAIT_BOUND_MODIFIERS = [["~"] "const"] ["async"] ["?" | "!"]
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/// CONSTNESS = [["~"] "const"]
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/// ASYNCNESS = ["async"]
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/// POLARITY = ["?" | "!"]
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/// ```
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///
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/// See `parse_generic_ty_bound` for the complete grammar of trait bound modifiers.
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fn parse_trait_bound_modifiers(&mut self) -> PResult<'a, TraitBoundModifiers> {
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let modifier_lo = self.token.span;
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let constness = if self.eat(&token::Tilde) {
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let tilde = self.prev_token.span;
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self.expect_keyword(kw::Const)?;
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@ -970,6 +975,7 @@ fn parse_trait_bound_modifiers(&mut self) -> PResult<'a, TraitBoundModifiers> {
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} else {
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BoundAsyncness::Normal
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};
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let modifier_hi = self.prev_token.span;
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let polarity = if self.eat(&token::Question) {
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BoundPolarity::Maybe(self.prev_token.span)
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@ -980,13 +986,40 @@ fn parse_trait_bound_modifiers(&mut self) -> PResult<'a, TraitBoundModifiers> {
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BoundPolarity::Positive
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};
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// Enforce the mutual-exclusivity of `const`/`async` and `?`/`!`.
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match polarity {
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BoundPolarity::Positive => {
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// All trait bound modifiers allowed to combine with positive polarity
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}
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BoundPolarity::Maybe(polarity_span) | BoundPolarity::Negative(polarity_span) => {
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match (asyncness, constness) {
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(BoundAsyncness::Normal, BoundConstness::Never) => {
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// Ok, no modifiers.
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}
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(_, _) => {
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let constness = constness.as_str();
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let asyncness = asyncness.as_str();
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let glue =
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if !constness.is_empty() && !asyncness.is_empty() { " " } else { "" };
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let modifiers_concatenated = format!("{constness}{glue}{asyncness}");
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self.dcx().emit_err(errors::PolarityAndModifiers {
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polarity_span,
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polarity: polarity.as_str(),
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modifiers_span: modifier_lo.to(modifier_hi),
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modifiers_concatenated,
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});
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}
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}
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}
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}
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Ok(TraitBoundModifiers { constness, asyncness, polarity })
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}
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/// Parses a type bound according to:
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/// ```ebnf
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/// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
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/// TY_BOUND_NOPAREN = [TRAIT_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
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/// TY_BOUND_NOPAREN = [for<GENERIC_PARAMS> CONSTNESS ASYNCNESS | POLARITY] SIMPLE_PATH
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/// ```
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///
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/// For example, this grammar accepts `for<'a: 'b> ~const ?m::Trait<'a>`.
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@ -996,9 +1029,25 @@ fn parse_generic_ty_bound(
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has_parens: bool,
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leading_token: &Token,
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) -> PResult<'a, GenericBound> {
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let modifiers = self.parse_trait_bound_modifiers()?;
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let (mut lifetime_defs, binder_span) = self.parse_late_bound_lifetime_defs()?;
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let modifiers_lo = self.token.span;
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let modifiers = self.parse_trait_bound_modifiers()?;
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let modifiers_span = modifiers_lo.to(self.prev_token.span);
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if let Some(binder_span) = binder_span {
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match modifiers.polarity {
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BoundPolarity::Negative(polarity_span) | BoundPolarity::Maybe(polarity_span) => {
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self.dcx().emit_err(errors::BinderAndPolarity {
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binder_span,
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polarity_span,
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polarity: modifiers.polarity.as_str(),
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});
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}
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BoundPolarity::Positive => {}
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}
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}
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// Recover erroneous lifetime bound with modifiers or binder.
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// e.g. `T: for<'a> 'a` or `T: ~const 'a`.
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if self.token.is_lifetime() {
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@ -1006,6 +1055,11 @@ fn parse_generic_ty_bound(
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return self.parse_generic_lt_bound(lo, has_parens);
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}
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if let (more_lifetime_defs, Some(binder_span)) = self.parse_late_bound_lifetime_defs()? {
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lifetime_defs.extend(more_lifetime_defs);
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self.dcx().emit_err(errors::BinderBeforeModifiers { binder_span, modifiers_span });
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}
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let mut path = if self.token.is_keyword(kw::Fn)
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&& self.look_ahead(1, |tok| tok.kind == TokenKind::OpenDelim(Delimiter::Parenthesis))
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&& let Some(path) = self.recover_path_from_fn()
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@ -146,8 +146,6 @@ trait T: ~ const Super {}
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const fn not_quite_const<S: ~ const T>() -> i32 { <S as T>::CONST }
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struct S<T:~ const ? Sized>(std::marker::PhantomData<T>);
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impl ~ const T {}
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fn apit(_: impl ~ const T) {}
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@ -3,9 +3,3 @@ fn negative()
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i32: !Copy,
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{
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}
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fn maybe_const_negative()
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where
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i32: ~const !Copy,
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{
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}
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@ -153,8 +153,6 @@ const fn not_quite_const<S: ~const T>() -> i32 {
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<S as T>::CONST
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}
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struct S<T: ~const ?Sized>(std::marker::PhantomData<T>);
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impl ~const T {}
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fn apit(_: impl ~const T) {}
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@ -16,7 +16,7 @@
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const ENTRY_LIMIT: u32 = 901;
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// FIXME: The following limits should be reduced eventually.
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const ISSUES_ENTRY_LIMIT: u32 = 1672;
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const ISSUES_ENTRY_LIMIT: u32 = 1673;
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const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
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"rs", // test source files
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@ -15,7 +15,7 @@ async fn f(arg: &i32) {}
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async fn func<F>(f: F)
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where
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F: async for<'a> Fn(&'a i32),
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F: for<'a> async Fn(&'a i32),
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{
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let x: i32 = 0;
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f(&x).await;
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@ -24,7 +24,7 @@ pub const fn filter_positive<'a>() -> &'a Alias<'a> {
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}
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use foo::*;
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const fn with_positive<F: ~const for<'a> Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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const fn with_positive<F: for<'a> ~const Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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fun(filter_positive());
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}
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@ -1,13 +1,13 @@
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error: `~const` can only be applied to `#[const_trait]` traits
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--> $DIR/normalize-tait-in-const.rs:27:42
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LL | const fn with_positive<F: ~const for<'a> Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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LL | const fn with_positive<F: for<'a> ~const Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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| ^^^^^^^^^^^^^^^^^
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error: `~const` can only be applied to `#[const_trait]` traits
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--> $DIR/normalize-tait-in-const.rs:27:69
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|
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LL | const fn with_positive<F: ~const for<'a> Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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LL | const fn with_positive<F: for<'a> ~const Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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| ^^^^^^^^
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error[E0015]: cannot call non-const closure in constant functions
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@ -19,7 +19,7 @@ LL | fun(filter_positive());
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= note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
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help: consider further restricting this bound
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|
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LL | const fn with_positive<F: ~const for<'a> Fn(&'a Alias<'a>) + ~const Destruct + ~const Fn(&foo::Alias<'_>)>(fun: F) {
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LL | const fn with_positive<F: for<'a> ~const Fn(&'a Alias<'a>) + ~const Destruct + ~const Fn(&foo::Alias<'_>)>(fun: F) {
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| ++++++++++++++++++++++++++++
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help: add `#![feature(effects)]` to the crate attributes to enable
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|
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@ -29,7 +29,7 @@ LL + #![feature(effects)]
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error[E0493]: destructor of `F` cannot be evaluated at compile-time
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--> $DIR/normalize-tait-in-const.rs:27:79
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|
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LL | const fn with_positive<F: ~const for<'a> Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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LL | const fn with_positive<F: for<'a> ~const Fn(&'a Alias<'a>) + ~const Destruct>(fun: F) {
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| ^^^ the destructor for this type cannot be evaluated in constant functions
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LL | fun(filter_positive());
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LL | }
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@ -1,5 +1,4 @@
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//@ check-pass
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#![allow(dead_code)]
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fn f<T: ?for<'a> Sized>() {}
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//~^ ERROR `for<...>` binder should be placed before trait bound modifiers
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fn main() {}
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10
tests/ui/issues/issue-39089.stderr
Normal file
10
tests/ui/issues/issue-39089.stderr
Normal file
@ -0,0 +1,10 @@
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error: `for<...>` binder should be placed before trait bound modifiers
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--> $DIR/issue-39089.rs:1:13
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|
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LL | fn f<T: ?for<'a> Sized>() {}
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| - ^^^^
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| |
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| place the `for<...>` binder before any modifiers
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error: aborting due to 1 previous error
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@ -1,19 +1,30 @@
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//@ compile-flags: -Z parse-only
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//@ edition: 2021
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struct S<
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T: 'a + Tr, // OK
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T: Tr + 'a, // OK
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T: 'a, // OK
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T:, // OK
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T: ?for<'a> Trait, // OK
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T: for<'a> ?Trait, //~ ERROR `for<...>` binder not allowed with `?` trait polarity modifier
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T: Tr +, // OK
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T: ?'a, //~ ERROR `?` may only modify trait bounds, not lifetime bounds
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T: ~const Tr, // OK
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T: ~const ?Tr, // OK
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T: ~const ?Tr, //~ ERROR `~const` trait not allowed with `?` trait polarity modifier
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T: ~const Tr + 'a, // OK
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T: ~const 'a, //~ ERROR `~const` may only modify trait bounds, not lifetime bounds
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T: const 'a, //~ ERROR `const` may only modify trait bounds, not lifetime bounds
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T: async Tr, // OK
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T: async ?Tr, //~ ERROR `async` trait not allowed with `?` trait polarity modifier
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T: async Tr + 'a, // OK
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T: async 'a, //~ ERROR `async` may only modify trait bounds, not lifetime bounds
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T: const async Tr, // OK
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T: const async ?Tr, //~ ERROR `const async` trait not allowed with `?` trait polarity modifier
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T: const async Tr + 'a, // OK
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T: const async 'a, //~ ERROR `const` may only modify trait bounds, not lifetime bounds
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>;
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fn main() {}
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@ -1,20 +1,64 @@
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error: `for<...>` binder not allowed with `?` trait polarity modifier
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--> $DIR/bounds-type.rs:9:16
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|
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LL | T: for<'a> ?Trait,
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| ---- ^
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| |
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| there is not a well-defined meaning for a higher-ranked `?` trait
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error: `?` may only modify trait bounds, not lifetime bounds
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--> $DIR/bounds-type.rs:10:8
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--> $DIR/bounds-type.rs:11:8
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|
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LL | T: ?'a,
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| ^
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error: `~const` trait not allowed with `?` trait polarity modifier
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--> $DIR/bounds-type.rs:14:15
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|
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LL | T: ~const ?Tr,
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| ------ ^
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| |
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||||
| there is not a well-defined meaning for a `~const ?` trait
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error: `~const` may only modify trait bounds, not lifetime bounds
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--> $DIR/bounds-type.rs:15:8
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--> $DIR/bounds-type.rs:16:8
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|
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LL | T: ~const 'a,
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| ^^^^^^
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error: `const` may only modify trait bounds, not lifetime bounds
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--> $DIR/bounds-type.rs:16:8
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--> $DIR/bounds-type.rs:17:8
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|
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LL | T: const 'a,
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| ^^^^^
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||||
|
||||
error: aborting due to 3 previous errors
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error: `async` trait not allowed with `?` trait polarity modifier
|
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--> $DIR/bounds-type.rs:20:14
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||||
|
|
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LL | T: async ?Tr,
|
||||
| ----- ^
|
||||
| |
|
||||
| there is not a well-defined meaning for a `async ?` trait
|
||||
|
||||
error: `async` may only modify trait bounds, not lifetime bounds
|
||||
--> $DIR/bounds-type.rs:22:8
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|
|
||||
LL | T: async 'a,
|
||||
| ^^^^^
|
||||
|
||||
error: `const async` trait not allowed with `?` trait polarity modifier
|
||||
--> $DIR/bounds-type.rs:25:20
|
||||
|
|
||||
LL | T: const async ?Tr,
|
||||
| ----------- ^
|
||||
| |
|
||||
| there is not a well-defined meaning for a `const async ?` trait
|
||||
|
||||
error: `const` may only modify trait bounds, not lifetime bounds
|
||||
--> $DIR/bounds-type.rs:27:8
|
||||
|
|
||||
LL | T: const async 'a,
|
||||
| ^^^^^
|
||||
|
||||
error: aborting due to 9 previous errors
|
||||
|
||||
|
||||
@ -1,17 +1,17 @@
|
||||
#![feature(const_trait_impl)]
|
||||
|
||||
const fn maybe_const_maybe<T: ~const ?Sized>() {}
|
||||
//~^ ERROR `~const` and `?` are mutually exclusive
|
||||
//~^ ERROR `~const` trait not allowed with `?` trait polarity modifier
|
||||
|
||||
fn const_maybe<T: const ?Sized>() {}
|
||||
//~^ ERROR `const` and `?` are mutually exclusive
|
||||
//~^ ERROR `const` trait not allowed with `?` trait polarity modifier
|
||||
|
||||
const fn maybe_const_negative<T: ~const !Trait>() {}
|
||||
//~^ ERROR `~const` and `!` are mutually exclusive
|
||||
//~^ ERROR `~const` trait not allowed with `!` trait polarity modifier
|
||||
//~| ERROR negative bounds are not supported
|
||||
|
||||
fn const_negative<T: const !Trait>() {}
|
||||
//~^ ERROR `const` and `!` are mutually exclusive
|
||||
//~^ ERROR `const` trait not allowed with `!` trait polarity modifier
|
||||
//~| ERROR negative bounds are not supported
|
||||
|
||||
#[const_trait]
|
||||
|
||||
@ -1,26 +1,34 @@
|
||||
error: `~const` and `?` are mutually exclusive
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:3:31
|
||||
error: `~const` trait not allowed with `?` trait polarity modifier
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:3:38
|
||||
|
|
||||
LL | const fn maybe_const_maybe<T: ~const ?Sized>() {}
|
||||
| ^^^^^^^^^^^^^
|
||||
| ------ ^
|
||||
| |
|
||||
| there is not a well-defined meaning for a `~const ?` trait
|
||||
|
||||
error: `const` and `?` are mutually exclusive
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:6:19
|
||||
error: `const` trait not allowed with `?` trait polarity modifier
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:6:25
|
||||
|
|
||||
LL | fn const_maybe<T: const ?Sized>() {}
|
||||
| ^^^^^^^^^^^^
|
||||
| ----- ^
|
||||
| |
|
||||
| there is not a well-defined meaning for a `const ?` trait
|
||||
|
||||
error: `~const` and `!` are mutually exclusive
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:9:34
|
||||
error: `~const` trait not allowed with `!` trait polarity modifier
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:9:41
|
||||
|
|
||||
LL | const fn maybe_const_negative<T: ~const !Trait>() {}
|
||||
| ^^^^^^^^^^^^^
|
||||
| ------ ^
|
||||
| |
|
||||
| there is not a well-defined meaning for a `~const !` trait
|
||||
|
||||
error: `const` and `!` are mutually exclusive
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:13:22
|
||||
error: `const` trait not allowed with `!` trait polarity modifier
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:13:28
|
||||
|
|
||||
LL | fn const_negative<T: const !Trait>() {}
|
||||
| ^^^^^^^^^^^^
|
||||
| ----- ^
|
||||
| |
|
||||
| there is not a well-defined meaning for a `const !` trait
|
||||
|
||||
error: negative bounds are not supported
|
||||
--> $DIR/mutually-exclusive-trait-bound-modifiers.rs:9:41
|
||||
|
||||
@ -4,6 +4,6 @@
|
||||
#![feature(const_trait_impl)]
|
||||
|
||||
struct S<
|
||||
T: ~const ?for<'a> Tr<'a> + 'static + ~const std::ops::Add,
|
||||
T: ~const ?for<'a: 'b> m::Trait<'a>,
|
||||
T: for<'a> ~const Tr<'a> + 'static + ~const std::ops::Add,
|
||||
T: for<'a: 'b> ~const m::Trait<'a>,
|
||||
>;
|
||||
|
||||
Loading…
Reference in New Issue
Block a user