Rollup merge of #136923 - samueltardieu:push-vxxqvqwspssv, r=davidtwco

Lint `#[must_use]` attributes applied to methods in trait impls The `#[must_use]` attribute has no effect when applied to methods in trait implementations. This PR adds it to the unused `#[must_use]` lint, and cleans the extra attributes in portable-simd and Clippy.
2025-05-14 02:49:40 +00:00 · 2025-02-19 21:16:11 +01:00 · 2025-02-19 21:16:11 +01:00 · c29cc600fd
commit c29cc600fd
parent 40379e299c e639e886b2
11 changed files with 56 additions and 63 deletions
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@ -1431,37 +1431,48 @@ impl<'tcx> CheckAttrVisitor<'tcx> {

    /// Warns against some misuses of `#[must_use]`
    fn check_must_use(&self, hir_id: HirId, attr: &Attribute, target: Target) {
-        if !matches!(
+        if matches!(
            target,
            Target::Fn
                | Target::Enum
                | Target::Struct
                | Target::Union
-                | Target::Method(_)
+                | Target::Method(MethodKind::Trait { body: false } | MethodKind::Inherent)
                | Target::ForeignFn
                // `impl Trait` in return position can trip
                // `unused_must_use` if `Trait` is marked as
                // `#[must_use]`
                | Target::Trait
        ) {
-            let article = match target {
-                Target::ExternCrate
-                | Target::Enum
-                | Target::Impl
-                | Target::Expression
-                | Target::Arm
-                | Target::AssocConst
-                | Target::AssocTy => "an",
-                _ => "a",
-            };
-
-            self.tcx.emit_node_span_lint(
-                UNUSED_ATTRIBUTES,
-                hir_id,
-                attr.span,
-                errors::MustUseNoEffect { article, target },
-            );
+            return;
        }
+
+        // `#[must_use]` can be applied to a trait method definition with a default body
+        if let Target::Method(MethodKind::Trait { body: true }) = target
+            && let parent_def_id = self.tcx.hir().get_parent_item(hir_id).def_id
+            && let containing_item = self.tcx.hir().expect_item(parent_def_id)
+            && let hir::ItemKind::Trait(..) = containing_item.kind
+        {
+            return;
+        }
+
+        let article = match target {
+            Target::ExternCrate
+            | Target::Enum
+            | Target::Impl
+            | Target::Expression
+            | Target::Arm
+            | Target::AssocConst
+            | Target::AssocTy => "an",
+            _ => "a",
+        };
+
+        self.tcx.emit_node_span_lint(
+            UNUSED_ATTRIBUTES,
+            hir_id,
+            attr.span,
+            errors::MustUseNoEffect { article, target },
+        );
    }

    /// Checks if `#[must_not_suspend]` is applied to a struct, enum, union, or trait.
--- a/library/portable-simd/crates/core_simd/src/masks.rs
+++ b/library/portable-simd/crates/core_simd/src/masks.rs
@ -401,7 +401,6 @@ where
    LaneCount<N>: SupportedLaneCount,
 {
    #[inline]
-    #[must_use = "method returns a defaulted mask with all elements set to false (0)"]
    fn default() -> Self {
        Self::splat(false)
    }
@ -413,7 +412,6 @@ where
    LaneCount<N>: SupportedLaneCount,
 {
    #[inline]
-    #[must_use = "method returns a new bool and does not mutate the original value"]
    fn eq(&self, other: &Self) -> bool {
        self.0 == other.0
    }
@ -425,7 +423,6 @@ where
    LaneCount<N>: SupportedLaneCount,
 {
    #[inline]
-    #[must_use = "method returns a new Ordering and does not mutate the original value"]
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.0.partial_cmp(&other.0)
    }
@ -451,7 +448,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitand(self, rhs: Self) -> Self {
        Self(self.0 & rhs.0)
    }
@ -464,7 +460,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitand(self, rhs: bool) -> Self {
        self & Self::splat(rhs)
    }
@ -477,7 +472,6 @@ where
 {
    type Output = Mask<T, N>;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitand(self, rhs: Mask<T, N>) -> Mask<T, N> {
        Mask::splat(self) & rhs
    }
@ -490,7 +484,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitor(self, rhs: Self) -> Self {
        Self(self.0 | rhs.0)
    }
@ -503,7 +496,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitor(self, rhs: bool) -> Self {
        self | Self::splat(rhs)
    }
@ -516,7 +508,6 @@ where
 {
    type Output = Mask<T, N>;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitor(self, rhs: Mask<T, N>) -> Mask<T, N> {
        Mask::splat(self) | rhs
    }
@ -529,7 +520,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitxor(self, rhs: Self) -> Self::Output {
        Self(self.0 ^ rhs.0)
    }
@ -542,7 +532,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitxor(self, rhs: bool) -> Self::Output {
        self ^ Self::splat(rhs)
    }
@ -555,7 +544,6 @@ where
 {
    type Output = Mask<T, N>;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitxor(self, rhs: Mask<T, N>) -> Self::Output {
        Mask::splat(self) ^ rhs
    }
@ -568,7 +556,6 @@ where
 {
    type Output = Mask<T, N>;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn not(self) -> Self::Output {
        Self(!self.0)
    }
--- a/library/portable-simd/crates/core_simd/src/masks/full_masks.rs
+++ b/library/portable-simd/crates/core_simd/src/masks/full_masks.rs
@ -21,7 +21,6 @@ where
    LaneCount<N>: SupportedLaneCount,
 {
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn clone(&self) -> Self {
        *self
    }
@ -252,7 +251,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitand(self, rhs: Self) -> Self {
        // Safety: `self` is an integer vector
        unsafe { Self(core::intrinsics::simd::simd_and(self.0, rhs.0)) }
@ -266,7 +264,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitor(self, rhs: Self) -> Self {
        // Safety: `self` is an integer vector
        unsafe { Self(core::intrinsics::simd::simd_or(self.0, rhs.0)) }
@ -280,7 +277,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn bitxor(self, rhs: Self) -> Self {
        // Safety: `self` is an integer vector
        unsafe { Self(core::intrinsics::simd::simd_xor(self.0, rhs.0)) }
@ -294,7 +290,6 @@ where
 {
    type Output = Self;
    #[inline]
-    #[must_use = "method returns a new mask and does not mutate the original value"]
    fn not(self) -> Self::Output {
        Self::splat(true) ^ self
    }
--- a/library/portable-simd/crates/core_simd/src/ops.rs
+++ b/library/portable-simd/crates/core_simd/src/ops.rs
@ -135,7 +135,6 @@ macro_rules! for_base_types {
                    type Output = $out;

                    #[inline]
-                    #[must_use = "operator returns a new vector without mutating the inputs"]
                    // TODO: only useful for int Div::div, but we hope that this
                    // will essentially always get inlined anyway.
                    #[track_caller]
--- a/library/portable-simd/crates/core_simd/src/ops/deref.rs
+++ b/library/portable-simd/crates/core_simd/src/ops/deref.rs
@ -18,7 +18,6 @@ macro_rules! deref_lhs {
            type Output = Simd<T, N>;

            #[inline]
-            #[must_use = "operator returns a new vector without mutating the inputs"]
            fn $call(self, rhs: $simd) -> Self::Output {
                (*self).$call(rhs)
            }
@ -39,7 +38,6 @@ macro_rules! deref_rhs {
            type Output = Simd<T, N>;

            #[inline]
-            #[must_use = "operator returns a new vector without mutating the inputs"]
            fn $call(self, rhs: &$simd) -> Self::Output {
                self.$call(*rhs)
            }
@ -71,7 +69,6 @@ macro_rules! deref_ops {
                type Output = $simd;

                #[inline]
-                #[must_use = "operator returns a new vector without mutating the inputs"]
                fn $call(self, rhs: &'rhs $simd) -> Self::Output {
                    (*self).$call(*rhs)
                }
--- a/library/portable-simd/crates/core_simd/src/ops/unary.rs
+++ b/library/portable-simd/crates/core_simd/src/ops/unary.rs
@ -11,7 +11,6 @@ macro_rules! neg {
            type Output = Self;

            #[inline]
-            #[must_use = "operator returns a new vector without mutating the input"]
            fn neg(self) -> Self::Output {
                // Safety: `self` is a signed vector
                unsafe { core::intrinsics::simd::simd_neg(self) }
@ -46,7 +45,6 @@ macro_rules! not {
            type Output = Self;

            #[inline]
-            #[must_use = "operator returns a new vector without mutating the input"]
            fn not(self) -> Self::Output {
                self ^ (Simd::splat(!(0 as $scalar)))
            }
--- a/library/portable-simd/crates/core_simd/src/simd/num/float.rs
+++ b/library/portable-simd/crates/core_simd/src/simd/num/float.rs
@ -371,7 +371,6 @@ macro_rules! impl_trait {
            }

            #[inline]
-            #[must_use = "method returns a new mask and does not mutate the original value"]
            fn is_normal(self) -> Self::Mask {
                !(self.abs().simd_eq(Self::splat(0.0)) | self.is_nan() | self.is_subnormal() | self.is_infinite())
            }
--- a/src/tools/clippy/clippy_lints/src/infinite_iter.rs
+++ b/src/tools/clippy/clippy_lints/src/infinite_iter.rs
@ -94,7 +94,6 @@ impl Finiteness {
 }

 impl From<bool> for Finiteness {
-    #[must_use]
    fn from(b: bool) -> Self {
        if b { Infinite } else { Finite }
    }
--- a/src/tools/clippy/clippy_utils/src/consts.rs
+++ b/src/tools/clippy/clippy_utils/src/consts.rs
@ -351,21 +351,18 @@ pub enum FullInt {
 }

 impl PartialEq for FullInt {
-    #[must_use]
    fn eq(&self, other: &Self) -> bool {
        self.cmp(other) == Ordering::Equal
    }
 }

 impl PartialOrd for FullInt {
-    #[must_use]
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
 }

 impl Ord for FullInt {
-    #[must_use]
    fn cmp(&self, other: &Self) -> Ordering {
        use FullInt::{S, U};

--- a/tests/ui/lint/unused/unused_attributes-must_use.rs
+++ b/tests/ui/lint/unused/unused_attributes-must_use.rs
@ -79,6 +79,11 @@ trait Use {
 #[must_use] //~ ERROR `#[must_use]` has no effect
 impl Use for () {
    type AssocTy = ();
+
+    #[must_use] //~ ERROR `#[must_use]` has no effect
+    fn get_four(&self) -> usize {
+        4
+    }
 }

 #[must_use] //~ ERROR `#[must_use]` has no effect
--- a/tests/ui/lint/unused/unused_attributes-must_use.stderr
+++ b/tests/ui/lint/unused/unused_attributes-must_use.stderr
@ -76,43 +76,43 @@ LL | #[must_use]
   | ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to a trait alias
-  --> $DIR/unused_attributes-must_use.rs:84:1
+  --> $DIR/unused_attributes-must_use.rs:89:1
   |
 LL | #[must_use]
   | ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to a macro def
-  --> $DIR/unused_attributes-must_use.rs:87:1
+  --> $DIR/unused_attributes-must_use.rs:92:1
   |
 LL | #[must_use]
   | ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to a statement
-  --> $DIR/unused_attributes-must_use.rs:95:5
+  --> $DIR/unused_attributes-must_use.rs:100:5
   |
 LL |     #[must_use]
   |     ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to a closure
-  --> $DIR/unused_attributes-must_use.rs:99:13
+  --> $DIR/unused_attributes-must_use.rs:104:13
   |
 LL |     let x = #[must_use]
   |             ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to an match arm
-  --> $DIR/unused_attributes-must_use.rs:121:9
+  --> $DIR/unused_attributes-must_use.rs:126:9
   |
 LL |         #[must_use]
   |         ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to a struct field
-  --> $DIR/unused_attributes-must_use.rs:129:28
+  --> $DIR/unused_attributes-must_use.rs:134:28
   |
 LL |     let s = PatternField { #[must_use]  foo: 123 };
   |                            ^^^^^^^^^^^

 error: `#[must_use]` has no effect when applied to a pattern field
-  --> $DIR/unused_attributes-must_use.rs:130:24
+  --> $DIR/unused_attributes-must_use.rs:135:24
   |
 LL |     let PatternField { #[must_use] foo } = s;
   |                        ^^^^^^^^^^^
@ -129,6 +129,12 @@ error: `#[must_use]` has no effect when applied to an associated type
 LL |     #[must_use]
   |     ^^^^^^^^^^^

+error: `#[must_use]` has no effect when applied to a provided trait method
+  --> $DIR/unused_attributes-must_use.rs:83:5
+   |
+LL |     #[must_use]
+   |     ^^^^^^^^^^^
+
 error: `#[must_use]` has no effect when applied to a foreign static item
  --> $DIR/unused_attributes-must_use.rs:50:5
   |
@ -136,7 +142,7 @@ LL |     #[must_use]
   |     ^^^^^^^^^^^

 error: unused `X` that must be used
-  --> $DIR/unused_attributes-must_use.rs:103:5
+  --> $DIR/unused_attributes-must_use.rs:108:5
   |
 LL |     X;
   |     ^
@ -152,7 +158,7 @@ LL |     let _ = X;
   |     +++++++

 error: unused `Y` that must be used
-  --> $DIR/unused_attributes-must_use.rs:104:5
+  --> $DIR/unused_attributes-must_use.rs:109:5
   |
 LL |     Y::Z;
   |     ^^^^
@ -163,7 +169,7 @@ LL |     let _ = Y::Z;
   |     +++++++

 error: unused `U` that must be used
-  --> $DIR/unused_attributes-must_use.rs:105:5
+  --> $DIR/unused_attributes-must_use.rs:110:5
   |
 LL |     U { unit: () };
   |     ^^^^^^^^^^^^^^
@ -174,7 +180,7 @@ LL |     let _ = U { unit: () };
   |     +++++++

 error: unused return value of `U::method` that must be used
-  --> $DIR/unused_attributes-must_use.rs:106:5
+  --> $DIR/unused_attributes-must_use.rs:111:5
   |
 LL |     U::method();
   |     ^^^^^^^^^^^
@ -185,7 +191,7 @@ LL |     let _ = U::method();
   |     +++++++

 error: unused return value of `foo` that must be used
-  --> $DIR/unused_attributes-must_use.rs:107:5
+  --> $DIR/unused_attributes-must_use.rs:112:5
   |
 LL |     foo();
   |     ^^^^^
@ -196,7 +202,7 @@ LL |     let _ = foo();
   |     +++++++

 error: unused return value of `foreign_foo` that must be used
-  --> $DIR/unused_attributes-must_use.rs:110:9
+  --> $DIR/unused_attributes-must_use.rs:115:9
   |
 LL |         foreign_foo();
   |         ^^^^^^^^^^^^^
@ -207,7 +213,7 @@ LL |         let _ = foreign_foo();
   |         +++++++

 error: unused return value of `Use::get_four` that must be used
-  --> $DIR/unused_attributes-must_use.rs:118:5
+  --> $DIR/unused_attributes-must_use.rs:123:5
   |
 LL |     ().get_four();
   |     ^^^^^^^^^^^^^
@ -217,5 +223,5 @@ help: use `let _ = ...` to ignore the resulting value
 LL |     let _ = ().get_four();
   |     +++++++

-error: aborting due to 28 previous errors
+error: aborting due to 29 previous errors