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Simplify some places that deal with generic parameter defaults

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León Orell Valerian Liehr 2024-11-11 18:41:27 +01:00
parent 143ce0920a
commit d0ddba3d5b
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4 changed files with 39 additions and 115 deletions
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98
compiler/rustc_hir_analysis/src/check/wfcheck.rs
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@ -1427,16 +1427,6 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
let predicates = tcx.predicates_of(def_id.to_def_id());
let generics = tcx.generics_of(def_id);
let is_our_default = |def: &ty::GenericParamDef| match def.kind {
GenericParamDefKind::Type { has_default, .. }
| GenericParamDefKind::Const { has_default, .. } => {
has_default && def.index >= generics.parent_count as u32
}
GenericParamDefKind::Lifetime => {
span_bug!(tcx.def_span(def.def_id), "lifetime params can have no default")
}
};
// Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
// For example, this forbids the declaration:
//
@ -1444,40 +1434,21 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
//
// Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
for param in &generics.own_params {
match param.kind {
GenericParamDefKind::Type { .. } => {
if is_our_default(param) {
let ty = tcx.type_of(param.def_id).instantiate_identity();
// Ignore dependent defaults -- that is, where the default of one type
// parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
// be sure if it will error or not as user might always specify the other.
if !ty.has_param() {
wfcx.register_wf_obligation(
tcx.def_span(param.def_id),
Some(WellFormedLoc::Ty(param.def_id.expect_local())),
ty.into(),
);
}
}
if let Some(default) = param.default_value(tcx).map(ty::EarlyBinder::instantiate_identity) {
// Ignore dependent defaults -- that is, where the default of one type
// parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
// be sure if it will error or not as user might always specify the other.
// FIXME(generic_const_exprs): This is incorrect when dealing with unused const params.
// E.g: `struct Foo<const N: usize, const M: usize = { 1 - 2 }>;`. Here, we should
// eagerly error but we don't as we have `ConstKind::Unevaluated(.., [N, M])`.
if !default.has_param() {
wfcx.register_wf_obligation(
tcx.def_span(param.def_id),
matches!(param.kind, GenericParamDefKind::Type { .. })
.then(|| WellFormedLoc::Ty(param.def_id.expect_local())),
default,
);
}
GenericParamDefKind::Const { .. } => {
if is_our_default(param) {
// FIXME(const_generics_defaults): This
// is incorrect when dealing with unused args, for example
// for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
// we should eagerly error.
let default_ct = tcx.const_param_default(param.def_id).instantiate_identity();
if !default_ct.has_param() {
wfcx.register_wf_obligation(
tcx.def_span(param.def_id),
None,
default_ct.into(),
);
}
}
}
// Doesn't have defaults.
GenericParamDefKind::Lifetime => {}
}
}
@ -1490,39 +1461,16 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
//
// First we build the defaulted generic parameters.
let args = GenericArgs::for_item(tcx, def_id.to_def_id(), |param, _| {
match param.kind {
GenericParamDefKind::Lifetime => {
// All regions are identity.
tcx.mk_param_from_def(param)
}
GenericParamDefKind::Type { .. } => {
// If the param has a default, ...
if is_our_default(param) {
let default_ty = tcx.type_of(param.def_id).instantiate_identity();
// ... and it's not a dependent default, ...
if !default_ty.has_param() {
// ... then instantiate it with the default.
return default_ty.into();
}
}
tcx.mk_param_from_def(param)
}
GenericParamDefKind::Const { .. } => {
// If the param has a default, ...
if is_our_default(param) {
let default_ct = tcx.const_param_default(param.def_id).instantiate_identity();
// ... and it's not a dependent default, ...
if !default_ct.has_param() {
// ... then instantiate it with the default.
return default_ct.into();
}
}
tcx.mk_param_from_def(param)
}
if param.index >= generics.parent_count as u32
// If the param has a default, ...
&& let Some(default) = param.default_value(tcx).map(ty::EarlyBinder::instantiate_identity)
// ... and it's not a dependent default, ...
&& !default.has_param()
{
// ... then instantiate it with the default.
return default;
}
tcx.mk_param_from_def(param)
});
// Now we build the instantiated predicates.