use std::convert::TryInto;
use std::iter;
+use std::lazy::Lazy;
use std::ops::ControlFlow;
/// Helper type of a temporary returned by `.for_item(...)`.
identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
+ // Lazily calculated because it is only needed in case of an error.
+ let explicitly_bounded_params = Lazy::new(|| {
+ let icx = crate::collect::ItemCtxt::new(tcx, item.def_id.to_def_id());
+ hir_generics
+ .where_clause
+ .predicates
+ .iter()
+ .filter_map(|predicate| match predicate {
+ hir::WherePredicate::BoundPredicate(predicate) => {
+ match icx.to_ty(predicate.bounded_ty).kind() {
+ ty::Param(data) => Some(Parameter(data.index)),
+ _ => None,
+ }
+ }
+ _ => None,
+ })
+ .collect::<FxHashSet<_>>()
+ });
+
for (index, _) in variances.iter().enumerate() {
- if constrained_parameters.contains(&Parameter(index as u32)) {
+ let parameter = Parameter(index as u32);
+
+ if constrained_parameters.contains(¶meter) {
continue;
}
match param.name {
hir::ParamName::Error => {}
_ => {
- report_bivariance(tcx, param);
+ let has_explicit_bounds =
+ !param.bounds.is_empty() || explicitly_bounded_params.contains(¶meter);
+ report_bivariance(tcx, param, has_explicit_bounds);
}
}
}
}
-fn report_bivariance(tcx: TyCtxt<'_>, param: &rustc_hir::GenericParam<'_>) -> ErrorReported {
+fn report_bivariance(
+ tcx: TyCtxt<'_>,
+ param: &rustc_hir::GenericParam<'_>,
+ has_explicit_bounds: bool,
+) -> ErrorReported {
let span = param.span;
let param_name = param.name.ident().name;
let mut err = error_392(tcx, span, param_name);
};
err.help(&msg);
- if matches!(param.kind, rustc_hir::GenericParamKind::Type { .. }) {
+ if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds {
err.help(&format!(
"if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
param_name
= help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
= help: if you intended `T` to be a const parameter, use `const T: usize` instead
-error: aborting due to 3 previous errors
+error[E0392]: parameter `T` is never used
+ --> $DIR/variance-unused-type-param.rs:19:19
+ |
+LL | struct WithBounds<T: Sized> {}
+ | ^ unused parameter
+ |
+ = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
+
+error[E0392]: parameter `T` is never used
+ --> $DIR/variance-unused-type-param.rs:22:24
+ |
+LL | struct WithWhereBounds<T> where T: Sized {}
+ | ^ unused parameter
+ |
+ = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
+
+error[E0392]: parameter `T` is never used
+ --> $DIR/variance-unused-type-param.rs:25:27
+ |
+LL | struct WithOutlivesBounds<T: 'static> {}
+ | ^ unused parameter
+ |
+ = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
+
+error: aborting due to 6 previous errors
For more information about this error, try `rustc --explain E0392`.