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rename rustc_legacy_const_generics to make it more clear that it is (soft) deprecated #146577

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rename rustc_legacy_const_generics to make it more clear that it is (soft) deprecated #146577

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189a27b
rename rustc_legacy_const_generics to make it more clear that it is (…
RalfJung Sep 15, 2025
760afcc
adjust tests and library
RalfJung Sep 15, 2025
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2 changes: 1 addition & 1 deletion compiler/rustc_feature/src/builtin_attrs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1162,7 +1162,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
rustc_promotable, Normal, template!(Word), WarnFollowing,
EncodeCrossCrate::No, ),
rustc_attr!(
rustc_legacy_const_generics, Normal, template!(List: &["N"]), ErrorFollowing,
rustc_deprecated_legacy_const_generics, Normal, template!(List: &["N"]), ErrorFollowing,
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Perhaps it'd be worth adding a comment here to the effect that this should not be newly applied anywhere.

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I doubt anyone who might be tempted to apply it would see a comment deep inside the rustc sources.

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Ha, just an hour ago I was thinking to name it legacy_const_generics_do_not_use just to avoid any and all ambiguity

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Yeah I considered that name but it seemed a bit too cheesy ;)

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I also considered rustc_legacy_const_generics_deprecated (instead of rustc_deprecated_legacy_const_generics), not sure which order makes more sense.

EncodeCrossCrate::Yes,
),
// Do not const-check this function's body. It will always get replaced during CTFE via `hook_special_const_fn`.
Expand Down
12 changes: 6 additions & 6 deletions compiler/rustc_passes/messages.ftl
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Expand Up @@ -521,11 +521,11 @@ passes_rustc_force_inline_coro =
attribute cannot be applied to a `async`, `gen` or `async gen` function
.label = `async`, `gen` or `async gen` function

passes_rustc_legacy_const_generics_index =
#[rustc_legacy_const_generics] must have one index for each generic parameter
passes_rustc_deprecated_legacy_const_generics_index =
#[rustc_deprecated_legacy_const_generics] must have one index for each generic parameter
.label = generic parameters

passes_rustc_legacy_const_generics_index_exceed =
passes_rustc_deprecated_legacy_const_generics_index_exceed =
index exceeds number of arguments
.label = there {$arg_count ->
[one] is
Expand All @@ -535,11 +535,11 @@ passes_rustc_legacy_const_generics_index_exceed =
*[other] arguments
}

passes_rustc_legacy_const_generics_index_negative =
passes_rustc_deprecated_legacy_const_generics_index_negative =
arguments should be non-negative integers

passes_rustc_legacy_const_generics_only =
#[rustc_legacy_const_generics] functions must only have const generics
passes_rustc_deprecated_legacy_const_generics_only =
#[rustc_deprecated_legacy_const_generics] functions must only have const generics
.label = non-const generic parameter

passes_rustc_lint_opt_deny_field_access =
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_passes/src/check_attr.rs
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Expand Up @@ -303,8 +303,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
[sym::rustc_never_returns_null_ptr, ..] => {
self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
}
[sym::rustc_legacy_const_generics, ..] => {
self.check_rustc_legacy_const_generics(hir_id, attr, span, target, item)
[sym::rustc_deprecated_legacy_const_generics, ..] => {
self.check_rustc_deprecated_legacy_const_generics(hir_id, attr, span, target, item)
}
[sym::rustc_lint_query_instability, ..] => {
self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
Expand Down Expand Up @@ -1423,8 +1423,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
}
}

/// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.
fn check_rustc_legacy_const_generics(
/// Checks if `#[rustc_deprecated_legacy_const_generics]` is applied to a function and has a valid argument.
fn check_rustc_deprecated_legacy_const_generics(
&self,
hir_id: HirId,
attr: &Attribute,
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_passes/src/errors.rs
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Expand Up @@ -406,7 +406,7 @@ pub(crate) struct NoLink {
}

#[derive(Diagnostic)]
#[diag(passes_rustc_legacy_const_generics_only)]
#[diag(passes_rustc_deprecated_legacy_const_generics_only)]
pub(crate) struct RustcLegacyConstGenericsOnly {
#[primary_span]
pub attr_span: Span,
Expand All @@ -415,7 +415,7 @@ pub(crate) struct RustcLegacyConstGenericsOnly {
}

#[derive(Diagnostic)]
#[diag(passes_rustc_legacy_const_generics_index)]
#[diag(passes_rustc_deprecated_legacy_const_generics_index)]
pub(crate) struct RustcLegacyConstGenericsIndex {
#[primary_span]
pub attr_span: Span,
Expand All @@ -424,7 +424,7 @@ pub(crate) struct RustcLegacyConstGenericsIndex {
}

#[derive(Diagnostic)]
#[diag(passes_rustc_legacy_const_generics_index_exceed)]
#[diag(passes_rustc_deprecated_legacy_const_generics_index_exceed)]
pub(crate) struct RustcLegacyConstGenericsIndexExceed {
#[primary_span]
#[label]
Expand All @@ -433,7 +433,7 @@ pub(crate) struct RustcLegacyConstGenericsIndexExceed {
}

#[derive(Diagnostic)]
#[diag(passes_rustc_legacy_const_generics_index_negative)]
#[diag(passes_rustc_deprecated_legacy_const_generics_index_negative)]
pub(crate) struct RustcLegacyConstGenericsIndexNegative {
#[primary_span]
pub invalid_args: Vec<Span>,
Expand Down
5 changes: 3 additions & 2 deletions compiler/rustc_resolve/src/lib.rs
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Expand Up @@ -2352,7 +2352,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
}

/// Checks if an expression refers to a function marked with
/// `#[rustc_legacy_const_generics]` and returns the argument index list
/// `#[rustc_deprecated_legacy_const_generics]` and returns the argument index list
/// from the attribute.
fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<usize>> {
if let ExprKind::Path(None, path) = &expr.kind {
Expand All @@ -2375,7 +2375,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
return v.clone();
}

let attr = self.tcx.get_attr(def_id, sym::rustc_legacy_const_generics)?;
let attr =
self.tcx.get_attr(def_id, sym::rustc_deprecated_legacy_const_generics)?;
let mut ret = Vec::new();
for meta in attr.meta_item_list()? {
match meta.lit()?.kind {
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_span/src/symbol.rs
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Expand Up @@ -1872,6 +1872,7 @@ symbols! {
rustc_default_body_unstable,
rustc_delayed_bug_from_inside_query,
rustc_deny_explicit_impl,
rustc_deprecated_legacy_const_generics,
rustc_deprecated_safe_2024,
rustc_diagnostic_item,
rustc_diagnostic_macros,
Expand Down Expand Up @@ -1900,7 +1901,6 @@ symbols! {
rustc_layout,
rustc_layout_scalar_valid_range_end,
rustc_layout_scalar_valid_range_start,
rustc_legacy_const_generics,
rustc_lint_diagnostics,
rustc_lint_opt_deny_field_access,
rustc_lint_opt_ty,
Expand Down
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