Lint unused #[non_exhaustive]

compiler/rustc_passes/src/check_attr.rs

@@ -200,7 +200,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             }
             AttributeKind::Naked(..) => self.check_naked(hir_id, target),
             AttributeKind::NonExhaustive(attr_span) => {
-                self.check_non_exhaustive(*attr_span, span, target, item)
+                self.check_non_exhaustive(hir_id, *attr_span, span, target, item)
             }
             AttributeKind::MayDangle(attr_span) => self.check_may_dangle(hir_id, *attr_span),
             AttributeKind::Link(_, attr_span) => self.check_link(hir_id, *attr_span, target),
@@ -802,30 +802,60 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid.
+    /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid and effective.
     fn check_non_exhaustive(
         &self,
+        hir_id: HirId,
         attr_span: Span,
         span: Span,
         target: Target,
         item: Option<&'tcx Item<'tcx>>,
     ) {
-        match target {
-            Target::Struct => {
-                if let hir::Item {
-                    kind: hir::ItemKind::Struct(_, _, hir::VariantData::Struct { fields, .. }),
-                    ..
-                } = item.unwrap()
-                    && !fields.is_empty()
-                    && fields.iter().any(|f| f.default.is_some())
-                {
-                    self.dcx().emit_err(diagnostics::NonExhaustiveWithDefaultFieldValues {
-                        attr_span,
-                        defn_span: span,
-                    });
+        if matches!(target, Target::Enum | Target::Variant)
+            && !self.tcx.effective_visibilities(()).is_reachable(hir_id.owner.def_id)
+        {
+            self.tcx.emit_node_span_lint(
+                UNUSED_ATTRIBUTES,
+                hir_id,
+                attr_span,
+                diagnostics::UnusedNonExhaustive::Unreachable,
+            );
+        } else if target == Target::Struct {
+            let (_, _, data) = item.unwrap().expect_struct();
+            let fields = data.fields();
+
+            if !fields.is_empty() && fields.iter().any(|f| f.default.is_some()) {
+                self.dcx().emit_err(diagnostics::NonExhaustiveWithDefaultFieldValues {
+                    attr_span,
+                    defn_span: span,
+                });
+            }
+
+            if !self.tcx.effective_visibilities(()).is_reachable(hir_id.owner.def_id) {
+                self.tcx.emit_node_span_lint(
+                    UNUSED_ATTRIBUTES,
+                    hir_id,
+                    attr_span,
+                    diagnostics::UnusedNonExhaustive::Unreachable,
+                );
+                return;
+            }
+
+            let mut spans = MultiSpan::from_span(attr_span);
+            for field in fields.iter() {
+                if !self.tcx.visibility(field.def_id).is_public() {
+                    spans.push_primary_span(field.span);
                 }
             }
-            _ => {}
+
+            if spans.primary_spans().len() > 1 {
+                self.tcx.emit_node_span_lint(
+                    UNUSED_ATTRIBUTES,
+                    hir_id,
+                    spans,
+                    diagnostics::UnusedNonExhaustive::StructWithNonPublicField,
+                );
+            }
         }
     }
 

compiler/rustc_passes/src/diagnostics.rs

@@ -56,6 +56,17 @@ pub(crate) struct NonExhaustiveWithDefaultFieldValues {
     pub defn_span: Span,
 }
 
+#[derive(Diagnostic)]
+pub(crate) enum UnusedNonExhaustive {
+    #[diag("`#[non_exhaustive]` has no effect on an unreachable item")]
+    Unreachable,
+    #[diag("`#[non_exhaustive]` has no effect on a struct with non-public fields")]
+    #[note(
+        "non-public fields already prevent the struct from being constructed or exhaustively matched by downstream crates"
+    )]
+    StructWithNonPublicField,
+}
+
 #[derive(Diagnostic)]
 #[diag("`#[doc(alias = \"...\")]` isn't allowed on {$location}")]
 pub(crate) struct DocAliasBadLocation<'a> {

library/core/src/escape.rs

@@ -167,13 +167,11 @@ union MaybeEscapedCharacter<const N: usize> {
 /// Marker type to indicate that the character is always escaped,
 /// used to optimize the iterator implementation.
 #[derive(Clone, Copy)]
-#[non_exhaustive]
 pub(crate) struct AlwaysEscaped;
 
 /// Marker type to indicate that the character may be escaped,
 /// used to optimize the iterator implementation.
 #[derive(Clone, Copy)]
-#[non_exhaustive]
 pub(crate) struct MaybeEscaped;
 
 /// An iterator over a possibly escaped character.

library/core/src/mem/type_info.rs

@@ -20,7 +20,6 @@ pub struct Type {
 /// Info of a trait implementation, you can retrieve the vtable with [Self::get_vtable]
 #[derive(Debug, PartialEq, Eq)]
 #[unstable(feature = "type_info", issue = "146922")]
-#[non_exhaustive]
 pub struct TraitImpl<T: PointeeSized> {
     pub(crate) vtable: DynMetadata<T>,
 }

library/coretests/tests/mem/type_info.rs

@@ -123,6 +123,7 @@ fn test_structs() {
     }
 
     const {
+        #[expect(unused_attributes)]
         #[non_exhaustive]
         struct NonExhaustive {
             a: u8,
@@ -224,6 +225,7 @@ fn test_enums() {
         enum E {
             Some(u32),
             None,
+            #[expect(unused_attributes)]
             #[non_exhaustive]
             Foomp {
                 a: (),

library/proc_macro/src/lib.rs

@@ -245,7 +245,6 @@ impl !Sync for TokenStream {}
 /// The contained error message is explicitly not guaranteed to be stable in any way,
 /// and may change between Rust versions or across compilations.
 #[stable(feature = "proc_macro_lib", since = "1.15.0")]
-#[non_exhaustive]
 #[derive(Debug)]
 pub struct LexError(String);
 

library/std/src/sys/process/unsupported.rs

@@ -199,7 +199,6 @@ impl fmt::Debug for Command {
 }
 
 #[derive(PartialEq, Eq, Clone, Copy, Debug, Default)]
-#[non_exhaustive]
 pub struct ExitStatus();
 
 impl ExitStatus {

src/tools/miri/tests/fail/match/single_variant.rs

@@ -2,7 +2,7 @@
 // at least the semantics don't depend on the crate you're in.
 //
 // See: rust-lang/rust#147722
-#![allow(dead_code)]
+#![allow(dead_code, unused_attributes)]
 
 #[repr(u8)]
 enum Exhaustive {

src/tools/miri/tests/fail/match/single_variant_uninit.rs

@@ -2,7 +2,7 @@
 // at least the semantics don't depend on the crate you're in.
 //
 // See: rust-lang/rust#147722
-#![allow(dead_code)]
+#![allow(dead_code, unused_attributes)]
 #![allow(unreachable_patterns)]
 
 #[repr(u8)]

tests/ui/attributes/malformed-attrs.rs

@@ -198,6 +198,7 @@ mod yooo {
 
 #[non_exhaustive = 1]
 //~^ ERROR malformed
+//~^^ WARN `#[non_exhaustive]` has no effect on an unreachable item
 enum Slenum {
 
 }

tests/ui/attributes/malformed-attrs.stderr

@@ -23,7 +23,7 @@ LL | #[cfg_attr(predicate, attr1, attr2, ...)]
    |           ++++++++++++++++++++++++++++++
 
 error[E0463]: can't find crate for `wloop`
-  --> $DIR/malformed-attrs.rs:213:1
+  --> $DIR/malformed-attrs.rs:214:1
    |
 LL | extern crate wloop;
    | ^^^^^^^^^^^^^^^^^^^ can't find crate
@@ -755,7 +755,7 @@ LL + #[non_exhaustive]
    |
 
 error[E0565]: malformed `thread_local` attribute input
-  --> $DIR/malformed-attrs.rs:205:3
+  --> $DIR/malformed-attrs.rs:206:3
    |
 LL | #[thread_local()]
    |   ^^^^^^^^^^^^--
@@ -769,7 +769,7 @@ LL + #[thread_local]
    |
 
 error[E0565]: malformed `no_link` attribute input
-  --> $DIR/malformed-attrs.rs:209:3
+  --> $DIR/malformed-attrs.rs:210:3
    |
 LL | #[no_link()]
    |   ^^^^^^^--
@@ -783,7 +783,7 @@ LL + #[no_link]
    |
 
 error[E0539]: malformed `macro_use` attribute input
-  --> $DIR/malformed-attrs.rs:211:3
+  --> $DIR/malformed-attrs.rs:212:3
    |
 LL | #[macro_use = 1]
    |   ^^^^^^^^^^---
@@ -801,7 +801,7 @@ LL + #[macro_use(name1, name2, ...)]
    |
 
 error[E0539]: malformed `macro_export` attribute input
-  --> $DIR/malformed-attrs.rs:216:3
+  --> $DIR/malformed-attrs.rs:217:3
    |
 LL | #[macro_export = 18]
    |   ^^^^^^^^^^^^^----
@@ -818,7 +818,7 @@ LL + #[macro_export(local_inner_macros)]
    |
 
 error[E0658]: the `allow_internal_unsafe` attribute side-steps the `unsafe_code` lint
-  --> $DIR/malformed-attrs.rs:218:3
+  --> $DIR/malformed-attrs.rs:219:3
    |
 LL | #[allow_internal_unsafe = 1]
    |   ^^^^^^^^^^^^^^^^^^^^^
@@ -827,7 +827,7 @@ LL | #[allow_internal_unsafe = 1]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0565]: malformed `allow_internal_unsafe` attribute input
-  --> $DIR/malformed-attrs.rs:218:3
+  --> $DIR/malformed-attrs.rs:219:3
    |
 LL | #[allow_internal_unsafe = 1]
    |   ^^^^^^^^^^^^^^^^^^^^^^---
@@ -852,6 +852,14 @@ LL | |     #[coroutine = 63] || {}
 LL | | }
    | |_- not a `const fn`
 
+warning: `#[non_exhaustive]` has no effect on an unreachable item
+  --> $DIR/malformed-attrs.rs:199:1
+   |
+LL | #[non_exhaustive = 1]
+   | ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: requested on the command line with `-W unused-attributes`
+
 error: valid forms for the attribute are `doc = "string"`, `doc(alias)`, `doc(attribute)`, `doc(auto_cfg)`, `doc(cfg)`, `doc(fake_variadic)`, `doc(hidden)`, `doc(html_favicon_url)`, `doc(html_logo_url)`, `doc(html_no_source)`, `doc(html_playground_url)`, `doc(html_root_url)`, `doc(include)`, `doc(inline)`, `doc(issue_tracker_base_url)`, `doc(keyword)`, `doc(masked)`, `doc(no_default_passes)`, `doc(no_inline)`, `doc(notable_trait)`, `doc(passes)`, `doc(plugins)`, `doc(rust_logo)`, `doc(search_unbox)`, `doc(spotlight)`, and `doc(test)`
   --> $DIR/malformed-attrs.rs:41:3
    |
@@ -888,7 +896,6 @@ LL | |     #[coroutine = 63] || {}
 ...  |
 LL | | }
    | |_^
-   = note: requested on the command line with `-W unused-attributes`
 
 error: valid forms for the attribute are `doc = "string"`, `doc(alias)`, `doc(attribute)`, `doc(auto_cfg)`, `doc(cfg)`, `doc(fake_variadic)`, `doc(hidden)`, `doc(html_favicon_url)`, `doc(html_logo_url)`, `doc(html_no_source)`, `doc(html_playground_url)`, `doc(html_root_url)`, `doc(include)`, `doc(inline)`, `doc(issue_tracker_base_url)`, `doc(keyword)`, `doc(masked)`, `doc(no_default_passes)`, `doc(no_inline)`, `doc(notable_trait)`, `doc(passes)`, `doc(plugins)`, `doc(rust_logo)`, `doc(search_unbox)`, `doc(spotlight)`, and `doc(test)`
   --> $DIR/malformed-attrs.rs:79:3
@@ -965,7 +972,7 @@ LL | #[automatically_derived = 18]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 error: valid forms for the attribute are `ignore` and `ignore = "reason"`
-  --> $DIR/malformed-attrs.rs:225:3
+  --> $DIR/malformed-attrs.rs:226:3
    |
 LL | #[ignore = 1]
    |   ^^^^^^^^^^
@@ -984,7 +991,7 @@ LL |     #[coroutine = 63] || {}
    = note: expected unit type `()`
               found coroutine `{coroutine@$DIR/malformed-attrs.rs:118:23: 118:25}`
 
-error: aborting due to 74 previous errors; 8 warnings emitted
+error: aborting due to 74 previous errors; 9 warnings emitted
 
 Some errors have detailed explanations: E0308, E0463, E0539, E0565, E0658, E0805.
 For more information about an error, try `rustc --explain E0308`.
@@ -1012,7 +1019,7 @@ LL | #[ignore()]
 
 Future breakage diagnostic:
 error: valid forms for the attribute are `ignore` and `ignore = "reason"`
-  --> $DIR/malformed-attrs.rs:225:3
+  --> $DIR/malformed-attrs.rs:226:3
    |
 LL | #[ignore = 1]
    |   ^^^^^^^^^^

tests/ui/closures/2229_closure_analysis/match/non-exhaustive-match.rs

@@ -8,9 +8,11 @@
  */
 
 // Ignore non_exhaustive in the same crate
+#[expect(unused_attributes)]
 #[non_exhaustive]
 enum L1 { A, B }
 
+#[expect(unused_attributes)]
 #[non_exhaustive]
 enum L2 { C }
 

tests/ui/closures/2229_closure_analysis/match/non-exhaustive-match.stderr

@@ -1,11 +1,11 @@
 error[E0004]: non-exhaustive patterns: `L1::B` not covered
-  --> $DIR/non-exhaustive-match.rs:28:25
+  --> $DIR/non-exhaustive-match.rs:30:25
    |
 LL |     let _b = || { match l1 { L1::A => () } };
    |                         ^^ pattern `L1::B` not covered
    |
 note: `L1` defined here
-  --> $DIR/non-exhaustive-match.rs:12:6
+  --> $DIR/non-exhaustive-match.rs:13:6
    |
 LL | enum L1 { A, B }
    |      ^^      - not covered
@@ -16,7 +16,7 @@ LL |     let _b = || { match l1 { L1::A => (), L1::B => todo!() } };
    |                                         ++++++++++++++++++
 
 error[E0004]: non-exhaustive patterns: type `E1` is non-empty
-  --> $DIR/non-exhaustive-match.rs:33:25
+  --> $DIR/non-exhaustive-match.rs:35:25
    |
 LL |     let _d = || { match e1 {} };
    |                         ^^
@@ -35,7 +35,7 @@ LL ~     } };
    |
 
 error[E0004]: non-exhaustive patterns: `_` not covered
-  --> $DIR/non-exhaustive-match.rs:35:25
+  --> $DIR/non-exhaustive-match.rs:37:25
    |
 LL |     let _e = || { match e2 { E2::A => (), E2::B => () } };
    |                         ^^ pattern `_` not covered
@@ -53,7 +53,7 @@ LL |     let _e = || { match e2 { E2::A => (), E2::B => (), _ => todo!() } };
    |                                                      ++++++++++++++
 
 error[E0505]: cannot move out of `l2` because it is borrowed
-  --> $DIR/non-exhaustive-match.rs:42:22
+  --> $DIR/non-exhaustive-match.rs:44:22
    |
 LL |     let _c = || { match l2 { L2::C => (), _ => () }  };
    |              --         -- borrow occurs due to use in closure
@@ -66,7 +66,7 @@ LL |     _c();
    |     -- borrow later used here
 
 error[E0505]: cannot move out of `e3` because it is borrowed
-  --> $DIR/non-exhaustive-match.rs:48:22
+  --> $DIR/non-exhaustive-match.rs:50:22
    |
 LL |     let _g = || { match e3 { E3::C => (), _ => () }  };
    |              --         -- borrow occurs due to use in closure

tests/ui/feature-gates/feature-gate-cfg-target-compact.rs

@@ -2,6 +2,7 @@
 struct Foo(u64, u64);
 
 #[cfg_attr(target(os = "linux"), non_exhaustive)] //~ ERROR compact `cfg(target(..))` is experimental
+//~^ WARN `#[non_exhaustive]` has no effect on an unreachable item
 struct Bar(u64, u64);
 
 #[cfg(not(any(all(target(os = "linux")))))] //~ ERROR compact `cfg(target(..))` is experimental

tests/ui/feature-gates/feature-gate-cfg-target-compact.stderr

@@ -19,7 +19,7 @@ LL | #[cfg_attr(target(os = "linux"), non_exhaustive)]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: compact `cfg(target(..))` is experimental and subject to change
-  --> $DIR/feature-gate-cfg-target-compact.rs:7:19
+  --> $DIR/feature-gate-cfg-target-compact.rs:8:19
    |
 LL | #[cfg(not(any(all(target(os = "linux")))))]
    |                   ^^^^^^^^^^^^^^^^^^^^
@@ -29,7 +29,7 @@ LL | #[cfg(not(any(all(target(os = "linux")))))]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: compact `cfg(target(..))` is experimental and subject to change
-  --> $DIR/feature-gate-cfg-target-compact.rs:11:10
+  --> $DIR/feature-gate-cfg-target-compact.rs:12:10
    |
 LL |     cfg!(target(os = "linux"));
    |          ^^^^^^^^^^^^^^^^^^^^
@@ -38,6 +38,14 @@ LL |     cfg!(target(os = "linux"));
    = help: add `#![feature(cfg_target_compact)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 4 previous errors
+warning: `#[non_exhaustive]` has no effect on an unreachable item
+  --> $DIR/feature-gate-cfg-target-compact.rs:4:34
+   |
+LL | #[cfg_attr(target(os = "linux"), non_exhaustive)]
+   |                                  ^^^^^^^^^^^^^^
+   |
+   = note: requested on the command line with `-W unused-attributes`
+
+error: aborting due to 4 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0658`.