Rollup merge of rust-lang#128771 - carbotaniuman:stabilize_unsafe_attr, r=nnethercote

Stabilize `unsafe_attributes`

# Stabilization report

## Summary

This is a tracking issue for the RFC 3325: unsafe attributes

We are stabilizing `#![feature(unsafe_attributes)]`,  which makes certain attributes considered 'unsafe', meaning that they must be surrounded by an `unsafe(...)`, as in `#[unsafe(no_mangle)]`.

RFC: rust-lang/rfcs#3325
Tracking issue: rust-lang#123757

## What is stabilized

### Summary of stabilization

Certain attributes will now be designated as unsafe attributes, namely, `no_mangle`, `export_name`, and `link_section` (stable only), and these attributes will need to be called by surrounding them in `unsafe(...)` syntax. On editions prior to 2024, this is simply an edition lint, but it will become a hard error in 2024. This also works in `cfg_attr`, but `unsafe` is not allowed for any other attributes, including proc-macros ones.

```rust
#[unsafe(no_mangle)]
fn a() {}

#[cfg_attr(any(), unsafe(export_name = "c"))]
fn b() {}
```

For a table showing the attributes that were considered to be included in the list to require unsafe, and subsequent reasoning about why each such attribute was or was not included, see [this comment here](rust-lang#124214 (comment))

## Tests

The relevant tests are in `tests/ui/rust-2024/unsafe-attributes` and `tests/ui/attributes/unsafe`.

Author: tgross35

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -887,7 +887,7 @@ fn validate_generic_param_order(dcx: DiagCtxtHandle<'_>, generics: &[GenericPara
 
 impl<'a> Visitor<'a> for AstValidator<'a> {
     fn visit_attribute(&mut self, attr: &Attribute) {
-        validate_attr::check_attr(&self.features, &self.session.psess, attr);
+        validate_attr::check_attr(&self.session.psess, attr);
     }
 
     fn visit_ty(&mut self, ty: &'a Ty) {

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -559,7 +559,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(mut_ref, "mutable by-reference bindings are experimental");
     gate_all!(precise_capturing, "precise captures on `impl Trait` are experimental");
     gate_all!(global_registration, "global registration is experimental");
-    gate_all!(unsafe_attributes, "`#[unsafe()]` markers for attributes are experimental");
     gate_all!(return_type_notation, "return type notation is experimental");
 
     if !visitor.features.never_patterns {

compiler/rustc_builtin_macros/src/cfg_accessible.rs

@@ -47,7 +47,6 @@ impl MultiItemModifier for Expander {
     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
         let template = AttributeTemplate { list: Some("path"), ..Default::default() };
         validate_attr::check_builtin_meta_item(
-            &ecx.ecfg.features,
             &ecx.sess.psess,
             meta_item,
             ast::AttrStyle::Outer,

compiler/rustc_builtin_macros/src/derive.rs

@@ -38,7 +38,6 @@ impl MultiItemModifier for Expander {
                 let template =
                     AttributeTemplate { list: Some("Trait1, Trait2, ..."), ..Default::default() };
                 validate_attr::check_builtin_meta_item(
-                    features,
                     &sess.psess,
                     meta_item,
                     ast::AttrStyle::Outer,

compiler/rustc_builtin_macros/src/util.rs

@@ -17,7 +17,6 @@ pub(crate) fn check_builtin_macro_attribute(ecx: &ExtCtxt<'_>, meta_item: &MetaI
     // All the built-in macro attributes are "words" at the moment.
     let template = AttributeTemplate { word: true, ..Default::default() };
     validate_attr::check_builtin_meta_item(
-        &ecx.ecfg.features,
         &ecx.sess.psess,
         meta_item,
         AttrStyle::Outer,

compiler/rustc_expand/src/config.rs

@@ -265,12 +265,7 @@ impl<'a> StripUnconfigured<'a> {
     /// is in the original source file. Gives a compiler error if the syntax of
     /// the attribute is incorrect.
     pub(crate) fn expand_cfg_attr(&self, cfg_attr: &Attribute, recursive: bool) -> Vec<Attribute> {
-        validate_attr::check_attribute_safety(
-            self.features.unwrap_or(&Features::default()),
-            &self.sess.psess,
-            AttributeSafety::Normal,
-            &cfg_attr,
-        );
+        validate_attr::check_attribute_safety(&self.sess.psess, AttributeSafety::Normal, &cfg_attr);
 
         let Some((cfg_predicate, expanded_attrs)) =
             rustc_parse::parse_cfg_attr(cfg_attr, &self.sess.psess)
@@ -395,11 +390,7 @@ impl<'a> StripUnconfigured<'a> {
             }
         };
 
-        validate_attr::deny_builtin_meta_unsafety(
-            self.features.unwrap_or(&Features::default()),
-            &self.sess.psess,
-            &meta_item,
-        );
+        validate_attr::deny_builtin_meta_unsafety(&self.sess.psess, &meta_item);
 
         (
             parse_cfg(&meta_item, self.sess).map_or(true, |meta_item| {

compiler/rustc_expand/src/expand.rs

@@ -1882,7 +1882,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         let mut span: Option<Span> = None;
         while let Some(attr) = attrs.next() {
             rustc_ast_passes::feature_gate::check_attribute(attr, self.cx.sess, features);
-            validate_attr::check_attr(features, &self.cx.sess.psess, attr);
+            validate_attr::check_attr(&self.cx.sess.psess, attr);
 
             let current_span = if let Some(sp) = span { sp.to(attr.span) } else { attr.span };
             span = Some(current_span);

compiler/rustc_feature/src/accepted.rs

@@ -392,6 +392,8 @@ declare_features! (
     (accepted, universal_impl_trait, "1.26.0", Some(34511)),
     /// Allows arbitrary delimited token streams in non-macro attributes.
     (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208)),
+    /// Allows unsafe attributes.
+    (accepted, unsafe_attributes, "CURRENT_RUSTC_VERSION", Some(123757)),
     /// The `unsafe_op_in_unsafe_fn` lint (allowed by default): no longer treat an unsafe function as an unsafe block.
     (accepted, unsafe_block_in_unsafe_fn, "1.52.0", Some(71668)),
     /// Allows unsafe on extern declarations and safety qualifiers over internal items.

compiler/rustc_feature/src/unstable.rs

@@ -622,8 +622,6 @@ declare_features! (
     (unstable, type_changing_struct_update, "1.58.0", Some(86555)),
     /// Allows unnamed fields of struct and union type
     (incomplete, unnamed_fields, "1.74.0", Some(49804)),
-    /// Allows unsafe attributes.
-    (unstable, unsafe_attributes, "1.80.0", Some(123757)),
     /// Allows const generic parameters to be defined with types that
     /// are not `Sized`, e.g. `fn foo<const N: [u8]>() {`.
     (incomplete, unsized_const_params, "CURRENT_RUSTC_VERSION", Some(95174)),

compiler/rustc_lint_defs/src/builtin.rs

@@ -4971,7 +4971,6 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #![feature(unsafe_attributes)]
     /// #![warn(unsafe_attr_outside_unsafe)]
     ///
     /// #[no_mangle]

compiler/rustc_parse/src/parser/attr.rs

@@ -4,7 +4,7 @@ use rustc_ast::token::{self, Delimiter};
 use rustc_errors::codes::*;
 use rustc_errors::{Diag, PResult};
 use rustc_span::symbol::kw;
-use rustc_span::{sym, BytePos, Span};
+use rustc_span::{BytePos, Span};
 use thin_vec::ThinVec;
 use tracing::debug;
 
@@ -265,7 +265,6 @@ impl<'a> Parser<'a> {
             let is_unsafe = this.eat_keyword(kw::Unsafe);
             let unsafety = if is_unsafe {
                 let unsafe_span = this.prev_token.span;
-                this.psess.gated_spans.gate(sym::unsafe_attributes, unsafe_span);
                 this.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
                 ast::Safety::Unsafe(unsafe_span)
             } else {
@@ -406,7 +405,6 @@ impl<'a> Parser<'a> {
         };
         let unsafety = if is_unsafe {
             let unsafe_span = self.prev_token.span;
-            self.psess.gated_spans.gate(sym::unsafe_attributes, unsafe_span);
             self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
 
             ast::Safety::Unsafe(unsafe_span)

compiler/rustc_parse/src/validate_attr.rs

@@ -7,9 +7,7 @@ use rustc_ast::{
     NestedMetaItem, Safety,
 };
 use rustc_errors::{Applicability, FatalError, PResult};
-use rustc_feature::{
-    AttributeSafety, AttributeTemplate, BuiltinAttribute, Features, BUILTIN_ATTRIBUTE_MAP,
-};
+use rustc_feature::{AttributeSafety, AttributeTemplate, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
 use rustc_session::errors::report_lit_error;
 use rustc_session::lint::builtin::{ILL_FORMED_ATTRIBUTE_INPUT, UNSAFE_ATTR_OUTSIDE_UNSAFE};
 use rustc_session::lint::BuiltinLintDiag;
@@ -18,7 +16,7 @@ use rustc_span::{sym, BytePos, Span, Symbol};
 
 use crate::{errors, parse_in};
 
-pub fn check_attr(features: &Features, psess: &ParseSess, attr: &Attribute) {
+pub fn check_attr(psess: &ParseSess, attr: &Attribute) {
     if attr.is_doc_comment() {
         return;
     }
@@ -28,17 +26,17 @@ pub fn check_attr(features: &Features, psess: &ParseSess, attr: &Attribute) {
 
     // All non-builtin attributes are considered safe
     let safety = attr_info.map(|x| x.safety).unwrap_or(AttributeSafety::Normal);
-    check_attribute_safety(features, psess, safety, attr);
+    check_attribute_safety(psess, safety, attr);
 
     // Check input tokens for built-in and key-value attributes.
     match attr_info {
         // `rustc_dummy` doesn't have any restrictions specific to built-in attributes.
         Some(BuiltinAttribute { name, template, .. }) if *name != sym::rustc_dummy => {
             match parse_meta(psess, attr) {
                 // Don't check safety again, we just did that
-                Ok(meta) => check_builtin_meta_item(
-                    features, psess, &meta, attr.style, *name, *template, false,
-                ),
+                Ok(meta) => {
+                    check_builtin_meta_item(psess, &meta, attr.style, *name, *template, false)
+                }
                 Err(err) => {
                     err.emit();
                 }
@@ -157,16 +155,7 @@ fn is_attr_template_compatible(template: &AttributeTemplate, meta: &ast::MetaIte
     }
 }
 
-pub fn check_attribute_safety(
-    features: &Features,
-    psess: &ParseSess,
-    safety: AttributeSafety,
-    attr: &Attribute,
-) {
-    if !features.unsafe_attributes {
-        return;
-    }
-
+pub fn check_attribute_safety(psess: &ParseSess, safety: AttributeSafety, attr: &Attribute) {
     let attr_item = attr.get_normal_item();
 
     if safety == AttributeSafety::Unsafe {
@@ -215,21 +204,18 @@ pub fn check_attribute_safety(
 
 // Called by `check_builtin_meta_item` and code that manually denies
 // `unsafe(...)` in `cfg`
-pub fn deny_builtin_meta_unsafety(features: &Features, psess: &ParseSess, meta: &MetaItem) {
+pub fn deny_builtin_meta_unsafety(psess: &ParseSess, meta: &MetaItem) {
     // This only supports denying unsafety right now - making builtin attributes
     // support unsafety will requite us to thread the actual `Attribute` through
     // for the nice diagnostics.
-    if features.unsafe_attributes {
-        if let Safety::Unsafe(unsafe_span) = meta.unsafety {
-            psess
-                .dcx()
-                .emit_err(errors::InvalidAttrUnsafe { span: unsafe_span, name: meta.path.clone() });
-        }
+    if let Safety::Unsafe(unsafe_span) = meta.unsafety {
+        psess
+            .dcx()
+            .emit_err(errors::InvalidAttrUnsafe { span: unsafe_span, name: meta.path.clone() });
     }
 }
 
 pub fn check_builtin_meta_item(
-    features: &Features,
     psess: &ParseSess,
     meta: &MetaItem,
     style: ast::AttrStyle,
@@ -246,7 +232,7 @@ pub fn check_builtin_meta_item(
     }
 
     if deny_unsafety {
-        deny_builtin_meta_unsafety(features, psess, meta);
+        deny_builtin_meta_unsafety(psess, meta);
     }
 }
 

src/tools/rustfmt/tests/target/unsafe_attributes.rs

@@ -1,4 +1,3 @@
-#![feature(unsafe_attributes)]
 // https://github.com/rust-lang/rust/issues/123757
 //
 #![simple_ident]

tests/ui/attributes/unsafe/cfg-unsafe-attributes.rs

@@ -1,5 +1,4 @@
 //@ build-pass
-#![feature(unsafe_attributes)]
 
 #[cfg_attr(all(), unsafe(no_mangle))]
 fn a() {}

tests/ui/attributes/unsafe/derive-unsafe-attributes.rs

@@ -1,5 +1,3 @@
-#![feature(unsafe_attributes)]
-
 #[derive(unsafe(Debug))]
 //~^ ERROR: expected identifier, found keyword `unsafe`
 //~| ERROR: traits in `#[derive(...)]` don't accept arguments

tests/ui/attributes/unsafe/derive-unsafe-attributes.stderr

@@ -1,5 +1,5 @@
 error: expected identifier, found keyword `unsafe`
-  --> $DIR/derive-unsafe-attributes.rs:3:10
+  --> $DIR/derive-unsafe-attributes.rs:1:10
    |
 LL | #[derive(unsafe(Debug))]
    |          ^^^^^^ expected identifier, found keyword
@@ -10,21 +10,21 @@ LL | #[derive(r#unsafe(Debug))]
    |          ++
 
 error: traits in `#[derive(...)]` don't accept arguments
-  --> $DIR/derive-unsafe-attributes.rs:3:16
+  --> $DIR/derive-unsafe-attributes.rs:1:16
    |
 LL | #[derive(unsafe(Debug))]
    |                ^^^^^^^ help: remove the arguments
 
 error: `derive` is not an unsafe attribute
-  --> $DIR/derive-unsafe-attributes.rs:12:3
+  --> $DIR/derive-unsafe-attributes.rs:10:3
    |
 LL | #[unsafe(derive(Debug))]
    |   ^^^^^^ this is not an unsafe attribute
    |
    = note: extraneous unsafe is not allowed in attributes
 
 error: expected identifier, found keyword `unsafe`
-  --> $DIR/derive-unsafe-attributes.rs:3:10
+  --> $DIR/derive-unsafe-attributes.rs:1:10
    |
 LL | #[derive(unsafe(Debug))]
    |          ^^^^^^ expected identifier, found keyword
@@ -36,7 +36,7 @@ LL | #[derive(r#unsafe(Debug))]
    |          ++
 
 error: expected identifier, found keyword `unsafe`
-  --> $DIR/derive-unsafe-attributes.rs:3:10
+  --> $DIR/derive-unsafe-attributes.rs:1:10
    |
 LL | #[derive(unsafe(Debug))]
    |          ^^^^^^ expected identifier, found keyword
@@ -48,13 +48,13 @@ LL | #[derive(r#unsafe(Debug))]
    |          ++
 
 error: cannot find derive macro `r#unsafe` in this scope
-  --> $DIR/derive-unsafe-attributes.rs:3:10
+  --> $DIR/derive-unsafe-attributes.rs:1:10
    |
 LL | #[derive(unsafe(Debug))]
    |          ^^^^^^
 
 error: cannot find derive macro `r#unsafe` in this scope
-  --> $DIR/derive-unsafe-attributes.rs:3:10
+  --> $DIR/derive-unsafe-attributes.rs:1:10
    |
 LL | #[derive(unsafe(Debug))]
    |          ^^^^^^

tests/ui/attributes/unsafe/double-unsafe-attributes.rs

@@ -1,5 +1,3 @@
-#![feature(unsafe_attributes)]
-
 #[unsafe(unsafe(no_mangle))]
 //~^ ERROR expected identifier, found keyword `unsafe`
 //~| ERROR cannot find attribute `r#unsafe` in this scope

tests/ui/attributes/unsafe/double-unsafe-attributes.stderr

@@ -1,5 +1,5 @@
 error: expected identifier, found keyword `unsafe`
-  --> $DIR/double-unsafe-attributes.rs:3:10
+  --> $DIR/double-unsafe-attributes.rs:1:10
    |
 LL | #[unsafe(unsafe(no_mangle))]
    |          ^^^^^^ expected identifier, found keyword
@@ -10,15 +10,15 @@ LL | #[unsafe(r#unsafe(no_mangle))]
    |          ++
 
 error: `r#unsafe` is not an unsafe attribute
-  --> $DIR/double-unsafe-attributes.rs:3:3
+  --> $DIR/double-unsafe-attributes.rs:1:3
    |
 LL | #[unsafe(unsafe(no_mangle))]
    |   ^^^^^^ this is not an unsafe attribute
    |
    = note: extraneous unsafe is not allowed in attributes
 
 error: cannot find attribute `r#unsafe` in this scope
-  --> $DIR/double-unsafe-attributes.rs:3:10
+  --> $DIR/double-unsafe-attributes.rs:1:10
    |
 LL | #[unsafe(unsafe(no_mangle))]
    |          ^^^^^^

tests/ui/attributes/unsafe/extraneous-unsafe-attributes.rs

@@ -1,6 +1,5 @@
 //@ edition: 2024
 //@ compile-flags: -Zunstable-options
-#![feature(unsafe_attributes)]
 
 #[unsafe(cfg(any()))] //~ ERROR: is not an unsafe attribute
 fn a() {}