Port #[used] to new attribute parsing infrastructure

JonathanBrouwer · JonathanBrouwer · commit 44fa5f0de4ea · 2025-06-21T10:55:44.000+02:00
Signed-off-by: Jonathan Brouwer &lt;jonathantbrouwer@gmail.com&gt;
diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -131,6 +131,17 @@ impl Deprecation {
     }
 }
 
+/// There are three valid forms of the attribute:
+/// `#[used]`, which is semantically equivalent to `#[used(compiler)]` except that the latter is currently unstable.
+/// `#[used(compiler)]`
+/// `#[used(linker)]`
+#[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(HashStable_Generic, PrintAttribute)]
+pub enum UsedBy {
+    Compiler,
+    Linker,
+}
+
 /// Represents parsed *built-in* inert attributes.
 ///
 /// ## Overview
@@ -244,5 +255,8 @@ pub enum AttributeKind {
         /// Span of the attribute.
         span: Span,
     },
+
+    /// Represents `#[used]`
+    Used { used_by: UsedBy, span: Span },
     // tidy-alphabetical-end
 }
diff --git a/compiler/rustc_attr_parsing/messages.ftl b/compiler/rustc_attr_parsing/messages.ftl
@@ -142,3 +142,6 @@ attr_parsing_unused_multiple =
 
 -attr_parsing_perviously_accepted =
     this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+attr_parsing_used_compiler_linker =
+    `used(compiler)` and `used(linker)` can't be used together
diff --git a/compiler/rustc_attr_parsing/src/attributes/mod.rs b/compiler/rustc_attr_parsing/src/attributes/mod.rs
@@ -36,6 +36,7 @@ pub(crate) mod lint_helpers;
 pub(crate) mod repr;
 pub(crate) mod stability;
 pub(crate) mod transparency;
+pub(crate) mod used;
 pub(crate) mod util;
 
 type AcceptFn<T, S> = for<'sess> fn(&mut T, &mut AcceptContext<'_, 'sess, S>, &ArgParser<'_>);
diff --git a/compiler/rustc_attr_parsing/src/attributes/used.rs b/compiler/rustc_attr_parsing/src/attributes/used.rs
@@ -0,0 +1,111 @@
+use rustc_attr_data_structures::lints::AttributeLintKind;
+use rustc_attr_data_structures::{AttributeKind, UsedBy};
+use rustc_feature::template;
+use rustc_macros::Diagnostic;
+use rustc_session::parse::feature_err;
+use rustc_span::{Span, sym};
+
+use crate::attributes::{AcceptMapping, AttributeParser};
+use crate::context::{FinalizeContext, Stage};
+use crate::parser::ArgParser;
+
+#[derive(Diagnostic)]
+#[diag(attr_parsing_used_compiler_linker)]
+pub(crate) struct UsedCompilerLinker {
+    #[primary_span]
+    pub spans: Vec<Span>,
+}
+
+#[derive(Default)]
+pub(crate) struct UsedParser {
+    first_compiler: Option<Span>,
+    first_linker: Option<Span>,
+    result: Option<(UsedBy, Span)>,
+}
+
+// A custom `AttributeParser` is used rather than a Simple attribute parser because
+// - Specifying two `#[used]` attributes is a warning (but will be an error in the future)
+// - But specifying two conflicting attributes: `#[used(compiler)]` and `#[used(linker)]` is already an error today
+// We can change this to a Simple parser once the warning becomes an error
+impl<S: Stage> AttributeParser<S> for UsedParser {
+    const ATTRIBUTES: AcceptMapping<Self, S> = &[(
+        &[sym::used],
+        template!(Word, List: "compiler|linker"),
+        |group: &mut Self, cx, args| {
+            let used_by = match args {
+                ArgParser::NoArgs => UsedBy::Compiler,
+                ArgParser::List(list) => {
+                    let Some(l) = list.single() else {
+                        cx.expected_single_argument(list.span);
+                        return;
+                    };
+
+                    match l.meta_item().and_then(|i| i.path().word_sym()) {
+                        Some(sym::compiler) => {
+                            if !cx.features().used_with_arg() {
+                                feature_err(
+                                    &cx.sess(),
+                                    sym::used_with_arg,
+                                    cx.attr_span,
+                                    "`#[used(compiler)]` is currently unstable",
+                                )
+                                .emit();
+                            }
+                            UsedBy::Compiler
+                        }
+                        Some(sym::linker) => {
+                            if !cx.features().used_with_arg() {
+                                feature_err(
+                                    &cx.sess(),
+                                    sym::used_with_arg,
+                                    cx.attr_span,
+                                    "`#[used(linker)]` is currently unstable",
+                                )
+                                .emit();
+                            }
+                            UsedBy::Linker
+                        }
+                        _ => {
+                            cx.expected_specific_argument(l.span(), vec!["compiler", "linker"]);
+                            return;
+                        }
+                    }
+                }
+                ArgParser::NameValue(_) => return,
+            };
+
+            match used_by {
+                UsedBy::Compiler { .. } => {
+                    if group.first_compiler.is_none() {
+                        group.first_compiler = Some(cx.attr_span);
+                    }
+                }
+                UsedBy::Linker => {
+                    if group.first_linker.is_none() {
+                        group.first_linker = Some(cx.attr_span);
+                    }
+                }
+            }
+
+            if let Some(prev) = &group.result {
+                cx.emit_lint(
+                    AttributeLintKind::UnusedDuplicate {
+                        this: cx.attr_span,
+                        other: prev.1,
+                        warning: true,
+                    },
+                    cx.attr_span,
+                );
+            } else {
+                group.result = Some((used_by, cx.attr_span))
+            }
+        },
+    )];
+
+    fn finalize(self, cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
+        if let (Some(linker_span), Some(compiler_span)) = (self.first_linker, self.first_compiler) {
+            cx.dcx().emit_err(UsedCompilerLinker { spans: vec![linker_span, compiler_span] });
+        }
+        self.result.map(|(used_by, span)| AttributeKind::Used { used_by, span })
+    }
+}
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
@@ -25,6 +25,7 @@ use crate::attributes::stability::{
     BodyStabilityParser, ConstStabilityIndirectParser, ConstStabilityParser, StabilityParser,
 };
 use crate::attributes::transparency::TransparencyParser;
+use crate::attributes::used::UsedParser;
 use crate::attributes::{AttributeParser as _, Combine, Single};
 use crate::parser::{ArgParser, MetaItemParser};
 use crate::session_diagnostics::{AttributeParseError, AttributeParseErrorReason, UnknownMetaItem};
@@ -96,6 +97,7 @@ attribute_parsers!(
         ConfusablesParser,
         ConstStabilityParser,
         StabilityParser,
+        UsedParser,
         // tidy-alphabetical-end
 
         // tidy-alphabetical-start
diff --git a/compiler/rustc_codegen_ssa/messages.ftl b/compiler/rustc_codegen_ssa/messages.ftl
@@ -48,8 +48,6 @@ codegen_ssa_error_writing_def_file =
 
 codegen_ssa_expected_name_value_pair = expected name value pair
 
-codegen_ssa_expected_used_symbol = expected `used`, `used(compiler)` or `used(linker)`
-
 codegen_ssa_extern_funcs_not_found = some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
 
 codegen_ssa_extract_bundled_libs_archive_member = failed to get data from archive member '{$rlib}': {$error}
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -4,7 +4,7 @@ use rustc_abi::ExternAbi;
 use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode};
 use rustc_ast::{LitKind, MetaItem, MetaItemInner, attr};
 use rustc_attr_data_structures::{
-    AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, ReprAttr, find_attr,
+    AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, ReprAttr, UsedBy, find_attr,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -122,6 +122,10 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                 }
                 AttributeKind::Cold(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
                 AttributeKind::Align { align, .. } => codegen_fn_attrs.alignment = Some(*align),
+                AttributeKind::Used { used_by, .. } => match used_by {
+                    UsedBy::Compiler => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_COMPILER,
+                    UsedBy::Linker => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER,
+                },
                 _ => {}
             }
         }
@@ -166,44 +170,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
             sym::rustc_std_internal_symbol => {
                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL
             }
-            sym::used => {
-                let inner = attr.meta_item_list();
-                match inner.as_deref() {
-                    Some([item]) if item.has_name(sym::linker) => {
-                        if !tcx.features().used_with_arg() {
-                            feature_err(
-                                &tcx.sess,
-                                sym::used_with_arg,
-                                attr.span(),
-                                "`#[used(linker)]` is currently unstable",
-                            )
-                            .emit();
-                        }
-                        codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER;
-                    }
-                    Some([item]) if item.has_name(sym::compiler) => {
-                        if !tcx.features().used_with_arg() {
-                            feature_err(
-                                &tcx.sess,
-                                sym::used_with_arg,
-                                attr.span(),
-                                "`#[used(compiler)]` is currently unstable",
-                            )
-                            .emit();
-                        }
-                        codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_COMPILER;
-                    }
-                    Some(_) => {
-                        tcx.dcx().emit_err(errors::ExpectedUsedSymbol { span: attr.span() });
-                    }
-                    None => {
-                        // Unconditionally using `llvm.used` causes issues in handling
-                        // `.init_array` with the gold linker. Luckily gold has been
-                        // deprecated with GCC 15 and rustc now warns about using gold.
-                        codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER
-                    }
-                }
-            }
             sym::thread_local => codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL,
             sym::track_caller => {
                 let is_closure = tcx.is_closure_like(did.to_def_id());
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -733,13 +733,6 @@ pub struct UnknownArchiveKind<'a> {
     pub kind: &'a str,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_expected_used_symbol)]
-pub(crate) struct ExpectedUsedSymbol {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_multiple_main_functions)]
 #[help]
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
@@ -809,9 +809,6 @@ passes_unused_variable_try_prefix = unused variable: `{$name}`
     .suggestion = if this is intentional, prefix it with an underscore
 
 
-passes_used_compiler_linker =
-    `used(compiler)` and `used(linker)` can't be used together
-
 passes_used_static =
     attribute must be applied to a `static` variable
     .label = but this is a {$target}
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
@@ -163,6 +163,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Attribute::Parsed(AttributeKind::AsPtr(attr_span)) => {
                     self.check_applied_to_fn_or_method(hir_id, *attr_span, span, target)
                 }
+                Attribute::Parsed(AttributeKind::Used { span: attr_span, .. }) => {
+                    self.check_used(*attr_span, target, span);
+                }
                 Attribute::Unparsed(_) => {
                     match attr.path().as_slice() {
                         [sym::diagnostic, sym::do_not_recommend, ..] => {
@@ -303,7 +306,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             | sym::cfi_encoding // FIXME(cfi_encoding)
                             | sym::pointee // FIXME(derive_coerce_pointee)
                             | sym::omit_gdb_pretty_printer_section // FIXME(omit_gdb_pretty_printer_section)
-                            | sym::used // handled elsewhere to restrict to static items
                             | sym::instruction_set // broken on stable!!!
                             | sym::windows_subsystem // broken on stable!!!
                             | sym::patchable_function_entry // FIXME(patchable_function_entry)
@@ -373,7 +375,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
 
         self.check_repr(attrs, span, target, item, hir_id);
-        self.check_used(attrs, target, span);
         self.check_rustc_force_inline(hir_id, attrs, span, target);
     }
 
@@ -2189,44 +2190,13 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_used(&self, attrs: &[Attribute], target: Target, target_span: Span) {
-        let mut used_linker_span = None;
-        let mut used_compiler_span = None;
-        for attr in attrs.iter().filter(|attr| attr.has_name(sym::used)) {
-            if target != Target::Static {
-                self.dcx().emit_err(errors::UsedStatic {
-                    attr_span: attr.span(),
-                    span: target_span,
-                    target: target.name(),
-                });
-            }
-            let inner = attr.meta_item_list();
-            match inner.as_deref() {
-                Some([item]) if item.has_name(sym::linker) => {
-                    if used_linker_span.is_none() {
-                        used_linker_span = Some(attr.span());
-                    }
-                }
-                Some([item]) if item.has_name(sym::compiler) => {
-                    if used_compiler_span.is_none() {
-                        used_compiler_span = Some(attr.span());
-                    }
-                }
-                Some(_) => {
-                    // This error case is handled in rustc_hir_analysis::collect.
-                }
-                None => {
-                    // Default case (compiler) when arg isn't defined.
-                    if used_compiler_span.is_none() {
-                        used_compiler_span = Some(attr.span());
-                    }
-                }
-            }
-        }
-        if let (Some(linker_span), Some(compiler_span)) = (used_linker_span, used_compiler_span) {
-            self.tcx
-                .dcx()
-                .emit_err(errors::UsedCompilerLinker { spans: vec![linker_span, compiler_span] });
+    fn check_used(&self, attr_span: Span, target: Target, target_span: Span) {
+        if target != Target::Static {
+            self.dcx().emit_err(errors::UsedStatic {
+                attr_span,
+                span: target_span,
+                target: target.name(),
+            });
         }
     }
 
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
@@ -611,13 +611,6 @@ pub(crate) struct UsedStatic {
     pub target: &'static str,
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_used_compiler_linker)]
-pub(crate) struct UsedCompilerLinker {
-    #[primary_span]
-    pub spans: Vec<Span>,
-}
-
 #[derive(Diagnostic)]
 #[diag(passes_allow_internal_unstable)]
 pub(crate) struct AllowInternalUnstable {
diff --git a/tests/ui/attributes/used_with_multi_args.rs b/tests/ui/attributes/used_with_multi_args.rs
@@ -1,6 +1,6 @@
 #![feature(used_with_arg)]
 
-#[used(compiler, linker)] //~ ERROR expected `used`, `used(compiler)` or `used(linker)`
+#[used(compiler, linker)] //~ ERROR malformed `used` attribute input
 static mut USED_COMPILER_LINKER: [usize; 1] = [0];
 
 fn main() {}
diff --git a/tests/ui/attributes/used_with_multi_args.stderr b/tests/ui/attributes/used_with_multi_args.stderr
@@ -1,8 +1,20 @@
-error: expected `used`, `used(compiler)` or `used(linker)`
+error[E0805]: malformed `used` attribute input
   --> $DIR/used_with_multi_args.rs:3:1
    |
 LL | #[used(compiler, linker)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^------------------^
+   |       |
+   |       expected a single argument here
+   |
+help: try changing it to one of the following valid forms of the attribute
+   |
+LL - #[used(compiler, linker)]
+LL + #[used(compiler|linker)]
+   |
+LL - #[used(compiler, linker)]
+LL + #[used]
+   |
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0805`.
diff --git a/tests/ui/lint/unused/unused-attr-duplicate.rs b/tests/ui/lint/unused/unused-attr-duplicate.rs
@@ -100,6 +100,7 @@ pub fn no_mangle_test() {}
 
 #[used]
 #[used] //~ ERROR unused attribute
+//~^ WARN this was previously accepted
 static FOO: u32 = 0;
 
 fn main() {}
diff --git a/tests/ui/lint/unused/unused-attr-duplicate.stderr b/tests/ui/lint/unused/unused-attr-duplicate.stderr
