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Rollup merge of #118608 - fee1-dead-contrib:backdoor-in-askconv, r=compiler-errors

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Use default params until effects in desugaring

See the comment and [this section](https://fee1-dead.github.io/devlog001/#effects-desugaring-with-default-type-params) from my blog post

r? ``@compiler-errors``
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Matthias Krüger 2023-12-05 16:08:37 +01:00 • committed by GitHub
commit c6c0c658df
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4 changed files with 44 additions and 6 deletions
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25
compiler/rustc_hir_analysis/src/astconv/generics.rs
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@ -243,6 +243,31 @@ pub fn create_args_for_parent_generic_args<'tcx, 'a>(
match (args_iter.peek(), params.peek()) {
(Some(&arg), Some(&param)) => {
match (arg, &param.kind, arg_count.explicit_late_bound) {
(
GenericArg::Const(hir::ConstArg {
is_desugared_from_effects: true,
..
}),
GenericParamDefKind::Const { is_host_effect: false, .. }
| GenericParamDefKind::Type { .. }
| GenericParamDefKind::Lifetime,
_,
) => {
// SPECIAL CASE FOR DESUGARED EFFECT PARAMS
// This comes from the following example:
//
// ```
// #[const_trait]
// pub trait PartialEq<Rhs: ?Sized = Self> {}
// impl const PartialEq for () {}
// ```
//
// Since this is a const impl, we need to insert `<false>` at the end of
// `PartialEq`'s generics, but this errors since `Rhs` isn't specified.
// To work around this, we infer all arguments until we reach the host param.
args.push(ctx.inferred_kind(Some(&args), param, infer_args));
params.next();
}
(GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
| (
GenericArg::Type(_) | GenericArg::Infer(_),