Rollup merge of #152291 - jdonszelmann:port-rustc-insignificant-dtor, r=jonathanbrouwer

Port `rustc_insignificant_dtor`

r? @JonathanBrouwer

Second commit removes it from an impl in std. I looked, and I really think it had no effect in the past. We only look for this attr on ADTs...

compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

@@ -739,6 +739,19 @@ impl<S: Stage> CombineAttributeParser<S> for RustcThenThisWouldNeedParser {
     }
 }
 
+pub(crate) struct RustcInsignificantDtorParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for RustcInsignificantDtorParser {
+    const PATH: &[Symbol] = &[sym::rustc_insignificant_dtor];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Enum),
+        Allow(Target::Struct),
+        Allow(Target::ForeignTy),
+    ]);
+    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcInsignificantDtor;
+}
+
 pub(crate) struct RustcEffectiveVisibilityParser;
 
 impl<S: Stage> NoArgsAttributeParser<S> for RustcEffectiveVisibilityParser {

compiler/rustc_attr_parsing/src/context.rs

@@ -272,6 +272,7 @@ attribute_parsers!(
         Single<WithoutArgs<RustcEvaluateWhereClausesParser>>,
         Single<WithoutArgs<RustcHasIncoherentInherentImplsParser>>,
         Single<WithoutArgs<RustcHiddenTypeOfOpaquesParser>>,
+        Single<WithoutArgs<RustcInsignificantDtorParser>>,
         Single<WithoutArgs<RustcIntrinsicConstStableIndirectParser>>,
         Single<WithoutArgs<RustcIntrinsicParser>>,
         Single<WithoutArgs<RustcLintOptTyParser>>,

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -1126,6 +1126,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_if_this_changed]`
     RustcIfThisChanged(Span, Option<Symbol>),
 
+    /// Represents `#[rustc_insignificant_dtor]`
+    RustcInsignificantDtor,
+
     /// Represents `#[rustc_intrinsic]`
     RustcIntrinsic,
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -120,6 +120,7 @@ impl AttributeKind {
             RustcHasIncoherentInherentImpls => Yes,
             RustcHiddenTypeOfOpaques => No,
             RustcIfThisChanged(..) => No,
+            RustcInsignificantDtor => Yes,
             RustcIntrinsic => Yes,
             RustcIntrinsicConstStableIndirect => No,
             RustcLayout(..) => No,

compiler/rustc_passes/src/check_attr.rs

@@ -315,6 +315,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::RustcHasIncoherentInherentImpls
                     | AttributeKind::RustcHiddenTypeOfOpaques
                     | AttributeKind::RustcIfThisChanged(..)
+                    | AttributeKind::RustcInsignificantDtor
                     | AttributeKind::RustcIntrinsic
                     | AttributeKind::RustcIntrinsicConstStableIndirect
                     | AttributeKind::RustcLayout(..)
@@ -390,7 +391,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             | sym::default_lib_allocator
                             | sym::rustc_diagnostic_item
                             | sym::rustc_no_mir_inline
-                            | sym::rustc_insignificant_dtor
                             | sym::rustc_nonnull_optimization_guaranteed
                             | sym::rustc_inherit_overflow_checks
                             | sym::rustc_trivial_field_reads

compiler/rustc_ty_utils/src/needs_drop.rs

@@ -1,13 +1,14 @@
 //! Check whether a type has (potentially) non-trivial drop glue.
 
 use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::attrs::AttributeKind;
 use rustc_hir::def_id::DefId;
+use rustc_hir::find_attr;
 use rustc_hir::limit::Limit;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::util::{AlwaysRequiresDrop, needs_drop_components};
 use rustc_middle::ty::{self, EarlyBinder, GenericArgsRef, Ty, TyCtxt};
-use rustc_span::sym;
 use tracing::{debug, instrument};
 
 use crate::errors::NeedsDropOverflow;
@@ -396,8 +397,7 @@ fn adt_consider_insignificant_dtor<'tcx>(
     tcx: TyCtxt<'tcx>,
 ) -> impl Fn(ty::AdtDef<'tcx>) -> Option<DtorType> {
     move |adt_def: ty::AdtDef<'tcx>| {
-        let is_marked_insig = tcx.has_attr(adt_def.did(), sym::rustc_insignificant_dtor);
-        if is_marked_insig {
+        if find_attr!(tcx.get_all_attrs(adt_def.did()), AttributeKind::RustcInsignificantDtor) {
             // In some cases like `std::collections::HashMap` where the struct is a wrapper around
             // a type that is a Drop type, and the wrapped type (eg: `hashbrown::HashMap`) lies
             // outside stdlib, we might choose to still annotate the wrapper (std HashMap) with

library/alloc/src/ffi/c_str.rs

@@ -103,6 +103,7 @@ use crate::vec::Vec;
 /// and other memory errors.
 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
 #[rustc_diagnostic_item = "cstring_type"]
+#[rustc_insignificant_dtor]
 #[stable(feature = "alloc_c_string", since = "1.64.0")]
 pub struct CString {
     // Invariant 1: the slice ends with a zero byte and has a length of at least one.
@@ -694,7 +695,6 @@ impl CString {
 // memory-unsafe code from working by accident. Inline
 // to prevent LLVM from optimizing it away in debug builds.
 #[stable(feature = "cstring_drop", since = "1.13.0")]
-#[rustc_insignificant_dtor]
 impl Drop for CString {
     #[inline]
     fn drop(&mut self) {