Rollup merge of #142600 - GrigorenkoPV:attributes/rustc_pub_transparent, r=jdonszelmann

Port `#[rustc_pub_transparent]` to the new attribute system

Very similar to #142498.

This is a part of #131229, so
r? ````@jdonszelmann````

---

For reference, the `#[rustc_pub_transparent]` attribute was created by me back in #129487.

As mentioned back in #129487 (comment), this attribute does not check that it is applied to an ADT, because it checks that `#[repr(transparent)]` is also applied to the same item, which, in turn, should check for ADT.

Author: jhpratt

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -240,6 +240,9 @@ pub enum AttributeKind {
     /// Represents `#[optimize(size|speed)]`
     Optimize(OptimizeAttr, Span),
 
+    /// Represents `#[rustc_pub_transparent]` (used by the `repr_transparent_external_private_fields` lint).
+    PubTransparent(Span),
+
     /// Represents [`#[repr]`](https://doc.rust-lang.org/stable/reference/type-layout.html#representations).
     Repr(ThinVec<(ReprAttr, Span)>),
 

compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs

@@ -19,3 +19,16 @@ impl<S: Stage> SingleAttributeParser<S> for AsPtrParser {
         Some(AttributeKind::AsPtr(cx.attr_span))
     }
 }
+
+pub(crate) struct PubTransparentParser;
+impl<S: Stage> SingleAttributeParser<S> for PubTransparentParser {
+    const PATH: &[Symbol] = &[sym::rustc_pub_transparent];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepFirst;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const TEMPLATE: AttributeTemplate = template!(Word);
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, _args: &ArgParser<'_>) -> Option<AttributeKind> {
+        // FIXME: check that there's no args (this is currently checked elsewhere)
+        Some(AttributeKind::PubTransparent(cx.attr_span))
+    }
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -19,7 +19,7 @@ use crate::attributes::codegen_attrs::{ColdParser, OptimizeParser};
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
-use crate::attributes::lint_helpers::AsPtrParser;
+use crate::attributes::lint_helpers::{AsPtrParser, PubTransparentParser};
 use crate::attributes::repr::{AlignParser, ReprParser};
 use crate::attributes::semantics::MayDangleParser;
 use crate::attributes::stability::{
@@ -113,6 +113,7 @@ attribute_parsers!(
         Single<InlineParser>,
         Single<MayDangleParser>,
         Single<OptimizeParser>,
+        Single<PubTransparentParser>,
         Single<RustcForceInlineParser>,
         Single<TransparencyParser>,
         // tidy-alphabetical-end

compiler/rustc_feature/src/builtin_attrs.rs

@@ -710,7 +710,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     rustc_attr!(
         rustc_pub_transparent, Normal, template!(Word),
-        WarnFollowing, EncodeCrossCrate::Yes,
+        ErrorFollowing, EncodeCrossCrate::Yes,
         "used internally to mark types with a `transparent` representation when it is guaranteed by the documentation",
     ),
 

compiler/rustc_hir_analysis/src/check/check.rs

@@ -2,6 +2,7 @@ use std::cell::LazyCell;
 use std::ops::ControlFlow;
 
 use rustc_abi::FieldIdx;
+use rustc_attr_data_structures::AttributeKind;
 use rustc_attr_data_structures::ReprAttr::ReprPacked;
 use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_errors::codes::*;
@@ -1384,7 +1385,11 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>)
                 ty::Tuple(list) => list.iter().try_for_each(|t| check_non_exhaustive(tcx, t)),
                 ty::Array(ty, _) => check_non_exhaustive(tcx, *ty),
                 ty::Adt(def, args) => {
-                    if !def.did().is_local() && !tcx.has_attr(def.did(), sym::rustc_pub_transparent)
+                    if !def.did().is_local()
+                        && !attrs::find_attr!(
+                            tcx.get_all_attrs(def.did()),
+                            AttributeKind::PubTransparent(_)
+                        )
                     {
                         let non_exhaustive = def.is_variant_list_non_exhaustive()
                             || def

compiler/rustc_passes/src/check_attr.rs

@@ -149,6 +149,10 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 }
                 Attribute::Parsed(AttributeKind::Repr(_)) => { /* handled below this loop and elsewhere */
                 }
+
+                &Attribute::Parsed(AttributeKind::PubTransparent(attr_span)) => {
+                    self.check_rustc_pub_transparent(attr_span, span, attrs)
+                }
                 Attribute::Parsed(AttributeKind::Cold(attr_span)) => {
                     self.check_cold(hir_id, *attr_span, span, target)
                 }
@@ -288,7 +292,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             self.check_type_const(hir_id,attr, target);
                         }
                         [sym::linkage, ..] => self.check_linkage(attr, span, target),
-                        [sym::rustc_pub_transparent, ..] => self.check_rustc_pub_transparent(attr.span(), span, attrs),
                         [
                             // ok
                             sym::allow