Rollup of 10 pull requests

compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

@@ -1,4 +1,6 @@
-use rustc_hir::attrs::{CoverageAttrKind, OptimizeAttr, RtsanSetting, SanitizerSet, UsedBy};
+use rustc_hir::attrs::{
+    CoverageAttrKind, ExportVisibilityAttrValue, OptimizeAttr, RtsanSetting, SanitizerSet, UsedBy,
+};
 use rustc_session::parse::feature_err;
 
 use super::prelude::*;
@@ -153,6 +155,43 @@ impl<S: Stage> SingleAttributeParser<S> for ExportNameParser {
     }
 }
 
+pub(crate) struct ExportVisibilityParser;
+
+impl<S: Stage> SingleAttributeParser<S> for ExportVisibilityParser {
+    const PATH: &[rustc_span::Symbol] = &[sym::export_visibility];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Fn), Allow(Target::Static)]);
+    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "visibility");
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser) -> Option<AttributeKind> {
+        let Some(nv) = args.name_value() else {
+            cx.expected_name_value(cx.attr_span, None);
+            return None;
+        };
+        let Some(sv) = nv.value_as_str() else {
+            cx.expected_string_literal(nv.value_span, Some(nv.value_as_lit()));
+            return None;
+        };
+
+        let str_to_visibility = [("target_default", ExportVisibilityAttrValue::TargetDefault)];
+        for &(s, visibility) in str_to_visibility.iter() {
+            if s == sv.as_str() {
+                return Some(AttributeKind::ExportVisibility { visibility, span: cx.attr_span });
+            }
+        }
+
+        let allowed_str_values = str_to_visibility
+            .into_iter()
+            .map(|(s, _visibility)| s)
+            .map(Symbol::intern)
+            .collect::<Vec<_>>();
+        cx.expected_specific_argument_strings(nv.value_span, &allowed_str_values);
+        None
+    }
+}
+
 pub(crate) struct RustcObjcClassParser;
 
 impl<S: Stage> SingleAttributeParser<S> for RustcObjcClassParser {

compiler/rustc_attr_parsing/src/context.rs

@@ -184,6 +184,7 @@ attribute_parsers!(
         Single<DeprecatedParser>,
         Single<DoNotRecommendParser>,
         Single<ExportNameParser>,
+        Single<ExportVisibilityParser>,
         Single<IgnoreParser>,
         Single<InlineParser>,
         Single<InstructionSetParser>,

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -1,6 +1,7 @@
 use rustc_abi::{Align, ExternAbi};
 use rustc_hir::attrs::{
-    AttributeKind, EiiImplResolution, InlineAttr, Linkage, RtsanSetting, UsedBy,
+    AttributeKind, EiiImplResolution, ExportVisibilityAttrValue, InlineAttr, Linkage, RtsanSetting,
+    UsedBy,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -70,6 +71,13 @@ fn process_builtin_attrs(
         match attr {
             AttributeKind::Cold(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
             AttributeKind::ExportName { name, .. } => codegen_fn_attrs.symbol_name = Some(*name),
+            AttributeKind::ExportVisibility { visibility, .. } => {
+                codegen_fn_attrs.export_visibility = Some(match visibility {
+                    ExportVisibilityAttrValue::TargetDefault => {
+                        tcx.sess.default_visibility().into()
+                    }
+                });
+            }
             AttributeKind::Inline(inline, span) => {
                 codegen_fn_attrs.inline = *inline;
                 interesting_spans.inline = Some(*span);
@@ -533,6 +541,16 @@ fn handle_lang_items(
         }
         err.emit();
     }
+
+    if codegen_fn_attrs.export_visibility.is_some() {
+        let span = find_attr!(attrs, ExportVisibility{span, ..} => *span).unwrap_or_default();
+        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
+            tcx.dcx().emit_err(errors::ExportVisibilityWithRustcStdInternalSymbol { span });
+        }
+        if !codegen_fn_attrs.contains_extern_indicator() {
+            tcx.dcx().emit_err(errors::ExportVisibilityWithoutNoMangleNorExportName { span });
+        }
+    }
 }
 
 /// Generate the [`CodegenFnAttrs`] for an item (identified by the [`LocalDefId`]).

compiler/rustc_codegen_ssa/src/errors.rs

@@ -1268,3 +1268,20 @@ pub(crate) struct LtoProcMacro;
 #[diag("cannot prefer dynamic linking when performing LTO")]
 #[note("only 'staticlib', 'bin', and 'cdylib' outputs are supported with LTO")]
 pub(crate) struct DynamicLinkingWithLTO;
+
+#[derive(Diagnostic)]
+#[diag("`#[export_visibility = ...]` cannot be used on internal language items")]
+pub(crate) struct ExportVisibilityWithRustcStdInternalSymbol {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(
+    "`#[export_visibility = ...]` will be ignored \
+     without `export_name`, `no_mangle`, or similar attribute"
+)]
+pub(crate) struct ExportVisibilityWithoutNoMangleNorExportName {
+    #[primary_span]
+    pub span: Span,
+}

compiler/rustc_feature/src/builtin_attrs.rs

@@ -649,6 +649,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         template!(NameValueStr: "name", "https://doc.rust-lang.org/reference/abi.html#the-export_name-attribute"),
         FutureWarnPreceding, EncodeCrossCrate::No
     ),
+    gated!(export_visibility, Normal, template!(NameValueStr: "visibility"), ErrorPreceding, EncodeCrossCrate::No, experimental!(export_visibility)),
     ungated!(
         unsafe(Edition2024) link_section, Normal,
         template!(NameValueStr: "name", "https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute"),

compiler/rustc_feature/src/unstable.rs

@@ -474,6 +474,8 @@ declare_features! (
     (incomplete, explicit_tail_calls, "1.72.0", Some(112788)),
     /// Allows using `#[export_stable]` which indicates that an item is exportable.
     (incomplete, export_stable, "1.88.0", Some(139939)),
+    /// Allows `#[export_visibility]` on definitions of statics and/or functions.
+    (unstable, export_visibility, "CURRENT_RUSTC_VERSION", Some(151425)),
     /// Externally implementable items
     (unstable, extern_item_impls, "1.94.0", Some(125418)),
     /// Allows defining `extern type`s.

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -251,6 +251,15 @@ impl Deprecation {
     }
 }
 
+/// Pre-parsed value of `#[export_visibility = ...]` attribute.
+///
+/// In a future RFC we may consider adding support for `Hidden`, `Protected`, and/or
+/// `Interposable`.
+#[derive(Clone, Copy, Debug, HashStable_Generic, Encodable, Decodable, PrintAttribute)]
+pub enum ExportVisibilityAttrValue {
+    TargetDefault,
+}
+
 /// There are three valid forms of the attribute:
 /// `#[used]`, which is equivalent to `#[used(linker)]` on targets that support it, but `#[used(compiler)]` if not.
 /// `#[used(compiler)]`
@@ -1045,6 +1054,12 @@ pub enum AttributeKind {
     /// Represents `#[export_stable]`.
     ExportStable,
 
+    /// Represents [`#[export_visibility = ...]`](https://github.com/rust-lang/rust/issues/151425)
+    ExportVisibility {
+        visibility: ExportVisibilityAttrValue,
+        span: Span,
+    },
+
     /// Represents `#[feature(...)]`
     Feature(ThinVec<Ident>, Span),
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -43,6 +43,7 @@ impl AttributeKind {
             EiiImpls(..) => No,
             ExportName { .. } => Yes,
             ExportStable => No,
+            ExportVisibility { .. } => Yes,
             Feature(..) => No,
             FfiConst(..) => No,
             FfiPure(..) => No,

compiler/rustc_infer/src/infer/lexical_region_resolve/indexed_edges.rs

@@ -0,0 +1,68 @@
+use rustc_index::IndexVec;
+use rustc_type_ir::RegionVid;
+
+use crate::infer::SubregionOrigin;
+use crate::infer::region_constraints::{Constraint, ConstraintKind, RegionConstraintData};
+
+/// Selects either out-edges or in-edges for [`IndexedConstraintEdges::adjacent_edges`].
+#[derive(Clone, Copy, Debug)]
+pub(super) enum EdgeDirection {
+    Out,
+    In,
+}
+
+/// Type alias for the pairs stored in [`RegionConstraintData::constraints`],
+/// which we are indexing.
+type ConstraintPair<'tcx> = (Constraint<'tcx>, SubregionOrigin<'tcx>);
+
+/// An index from region variables to their corresponding constraint edges,
+/// used on some error paths.
+pub(super) struct IndexedConstraintEdges<'data, 'tcx> {
+    out_edges: IndexVec<RegionVid, Vec<&'data ConstraintPair<'tcx>>>,
+    in_edges: IndexVec<RegionVid, Vec<&'data ConstraintPair<'tcx>>>,
+}
+
+impl<'data, 'tcx> IndexedConstraintEdges<'data, 'tcx> {
+    pub(super) fn build_index(num_vars: usize, data: &'data RegionConstraintData<'tcx>) -> Self {
+        let mut out_edges = IndexVec::from_fn_n(|_| vec![], num_vars);
+        let mut in_edges = IndexVec::from_fn_n(|_| vec![], num_vars);
+
+        for pair @ (c, _) in &data.constraints {
+            // Only push a var out-edge for `VarSub...` constraints.
+            match c.kind {
+                ConstraintKind::VarSubVar | ConstraintKind::VarSubReg => {
+                    out_edges[c.sub.as_var()].push(pair)
+                }
+                ConstraintKind::RegSubVar | ConstraintKind::RegSubReg => {}
+            }
+        }
+
+        // Index in-edges in reverse order, to match what current tests expect.
+        // (It's unclear whether this is important or not.)
+        for pair @ (c, _) in data.constraints.iter().rev() {
+            // Only push a var in-edge for `...SubVar` constraints.
+            match c.kind {
+                ConstraintKind::VarSubVar | ConstraintKind::RegSubVar => {
+                    in_edges[c.sup.as_var()].push(pair)
+                }
+                ConstraintKind::VarSubReg | ConstraintKind::RegSubReg => {}
+            }
+        }
+
+        IndexedConstraintEdges { out_edges, in_edges }
+    }
+
+    /// Returns either the out-edges or in-edges of the specified region var,
+    /// as selected by `dir`.
+    pub(super) fn adjacent_edges(
+        &self,
+        region_vid: RegionVid,
+        dir: EdgeDirection,
+    ) -> &[&'data ConstraintPair<'tcx>] {
+        let edges = match dir {
+            EdgeDirection::Out => &self.out_edges,
+            EdgeDirection::In => &self.in_edges,
+        };
+        &edges[region_vid]
+    }
+}