Mark some macros with must_use hint

rust-lang · Jul 9, 2024 · 2ab317b · 2ab317b
1 parent 99b7134
commit 2ab317b
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Showing 51 changed files with 269 additions and 999 deletions.
diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs
@@ -38,21 +38,21 @@
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "vec_macro"]
-#[allow_internal_unstable(rustc_attrs, liballoc_internals)]
+#[allow_internal_unstable(rustc_attrs, liballoc_internals, hint_must_use)]
 macro_rules! vec {
     () => (
-        $crate::vec::Vec::new()
+        $crate::__export::must_use($crate::vec::Vec::new())
     );
     ($elem:expr; $n:expr) => (
-        $crate::vec::from_elem($elem, $n)
+        $crate::__export::must_use($crate::vec::from_elem($elem, $n))
     );
     ($($x:expr),+ $(,)?) => (
-        <[_]>::into_vec(
+        $crate::__export::must_use(<[_]>::into_vec(
             // This rustc_box is not required, but it produces a dramatic improvement in compile
             // time when constructing arrays with many elements.
             #[rustc_box]
             $crate::boxed::Box::new([$($x),+])
-        )
+        ))
     );
 }
 

diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs
@@ -451,13 +451,16 @@ pub macro debug_assert_matches($($arg:tt)*) {
 /// ```
 #[macro_export]
 #[stable(feature = "matches_macro", since = "1.42.0")]
+#[allow_internal_unstable(hint_must_use)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "matches_macro")]
 macro_rules! matches {
     ($expression:expr, $pattern:pat $(if $guard:expr)? $(,)?) => {
-        match $expression {
-            $pattern $(if $guard)? => true,
-            _ => false
-        }
+        $crate::hint::must_use({
+            match $expression {
+                $pattern $(if $guard)? => true,
+                _ => false
+            }
+        })
     };
 }
 
@@ -1010,8 +1013,12 @@ pub(crate) mod builtin {
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! format_args {
-        ($fmt:expr) => {{ /* compiler built-in */ }};
-        ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
+        ($fmt:expr) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
+        ($fmt:expr, $($args:tt)*) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Same as [`format_args`], but can be used in some const contexts.
@@ -1081,8 +1088,12 @@ pub(crate) mod builtin {
     #[macro_export]
     #[rustc_diagnostic_item = "env_macro"] // useful for external lints
     macro_rules! env {
-        ($name:expr $(,)?) => {{ /* compiler built-in */ }};
-        ($name:expr, $error_msg:expr $(,)?) => {{ /* compiler built-in */ }};
+        ($name:expr $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
+        ($name:expr, $error_msg:expr $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Optionally inspects an environment variable at compile time.
@@ -1112,7 +1123,9 @@ pub(crate) mod builtin {
     #[macro_export]
     #[rustc_diagnostic_item = "option_env_macro"] // useful for external lints
     macro_rules! option_env {
-        ($name:expr $(,)?) => {{ /* compiler built-in */ }};
+        ($name:expr $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Concatenates identifiers into one identifier.
@@ -1174,7 +1187,9 @@ pub(crate) mod builtin {
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! concat_bytes {
-        ($($e:literal),+ $(,)?) => {{ /* compiler built-in */ }};
+        ($($e:literal),+ $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Concatenates literals into a static string slice.
@@ -1193,10 +1208,13 @@ pub(crate) mod builtin {
     /// assert_eq!(s, "test10btrue");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[allow_internal_unstable(hint_must_use)]
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! concat {
-        ($($e:expr),* $(,)?) => {{ /* compiler built-in */ }};
+        ($($e:expr),* $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Expands to the line number on which it was invoked.
@@ -1218,11 +1236,12 @@ pub(crate) mod builtin {
     /// println!("defined on line: {current_line}");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[allow_internal_unstable(hint_must_use)]
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! line {
         () => {
-            /* compiler built-in */
+            $crate::hint::must_use({ /* compiler built-in */ })
         };
     }
 
@@ -1257,11 +1276,12 @@ pub(crate) mod builtin {
     /// assert_ne!(b, c);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[allow_internal_unstable(hint_must_use)]
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! column {
         () => {
-            /* compiler built-in */
+            $crate::hint::must_use(/* compiler built-in */)
         };
     }
 
@@ -1282,11 +1302,12 @@ pub(crate) mod builtin {
     /// println!("defined in file: {this_file}");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[allow_internal_unstable(hint_must_use)]
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! file {
         () => {
-            /* compiler built-in */
+            $crate::hint::must_use(/* compiler built-in */)
         };
     }
 
@@ -1306,11 +1327,12 @@ pub(crate) mod builtin {
     /// assert_eq!(one_plus_one, "1 + 1");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[allow_internal_unstable(hint_must_use)]
     #[rustc_builtin_macro]
     #[macro_export]
     macro_rules! stringify {
         ($($t:tt)*) => {
-            /* compiler built-in */
+            $crate::hint::must_use(/* compiler built-in */)
         };
     }
 
@@ -1351,7 +1373,9 @@ pub(crate) mod builtin {
     #[macro_export]
     #[cfg_attr(not(test), rustc_diagnostic_item = "include_str_macro")]
     macro_rules! include_str {
-        ($file:expr $(,)?) => {{ /* compiler built-in */ }};
+        ($file:expr $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Includes a file as a reference to a byte array.
@@ -1391,7 +1415,9 @@ pub(crate) mod builtin {
     #[macro_export]
     #[cfg_attr(not(test), rustc_diagnostic_item = "include_bytes_macro")]
     macro_rules! include_bytes {
-        ($file:expr $(,)?) => {{ /* compiler built-in */ }};
+        ($file:expr $(,)?) => {
+            $crate::hint::must_use({ /* compiler built-in */ })
+        };
     }
 
     /// Expands to a string that represents the current module path.
@@ -1449,7 +1475,7 @@ pub(crate) mod builtin {
     #[macro_export]
     macro_rules! cfg {
         ($($cfg:tt)*) => {
-            /* compiler built-in */
+            $crate::hint::must_use(/* compiler built-in */)
         };
     }
 

diff --git a/library/core/tests/macros.rs b/library/core/tests/macros.rs
@@ -39,7 +39,7 @@ fn assert_ne_trailing_comma() {
 #[rustfmt::skip]
 #[test]
 fn matches_leading_pipe() {
-    matches!(1, | 1 | 2 | 3);
+    let _ = matches!(1, | 1 | 2 | 3);
 }
 
 #[test]

diff --git a/src/tools/clippy/tests/ui/box_default.fixed b/src/tools/clippy/tests/ui/box_default.fixed
@@ -36,7 +36,7 @@ fn main() {
     let impl1: Box<ImplementsDefault> = Box::default();
     let vec: Box<Vec<u8>> = Box::default();
     let byte: Box<u8> = Box::default();
-    let vec2: Box<Vec<ImplementsDefault>> = Box::default();
+    let vec2: Box<Vec<ImplementsDefault>> = Box::new(vec![]);
     let vec3: Box<Vec<bool>> = Box::default();
 
     let plain_default = Box::default();

diff --git a/src/tools/clippy/tests/ui/box_default.stderr b/src/tools/clippy/tests/ui/box_default.stderr
@@ -31,12 +31,6 @@ error: `Box::new(_)` of default value
 LL |     let byte: Box<u8> = Box::new(u8::default());
    |                         ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
 
-error: `Box::new(_)` of default value
-  --> tests/ui/box_default.rs:39:45
-   |
-LL |     let vec2: Box<Vec<ImplementsDefault>> = Box::new(vec![]);
-   |                                             ^^^^^^^^^^^^^^^^ help: try: `Box::default()`
-
 error: `Box::new(_)` of default value
   --> tests/ui/box_default.rs:40:32
    |
@@ -61,5 +55,5 @@ error: `Box::new(_)` of default value
 LL |         Self::x(Box::new(T::default()));
    |                 ^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
 
-error: aborting due to 10 previous errors
+error: aborting due to 9 previous errors
 
diff --git a/src/tools/clippy/tests/ui/derivable_impls.fixed b/src/tools/clippy/tests/ui/derivable_impls.fixed
@@ -2,7 +2,6 @@
 
 use std::collections::HashMap;
 
-#[derive(Default)]
 struct FooDefault<'a> {
     a: bool,
     b: i32,
@@ -18,6 +17,24 @@ struct FooDefault<'a> {
     l: &'a [i32],
 }
 
+impl std::default::Default for FooDefault<'_> {
+    fn default() -> Self {
+        Self {
+            a: false,
+            b: 0,
+            c: 0u64,
+            d: vec![],
+            e: Default::default(),
+            f: FooND2::default(),
+            g: HashMap::new(),
+            h: (0, vec![]),
+            i: [vec![], vec![], vec![]],
+            j: [0; 5],
+            k: None,
+            l: &[],
+        }
+    }
+}
 
 #[derive(Default)]
 struct TupleDefault(bool, i32, u64);

diff --git a/src/tools/clippy/tests/ui/derivable_impls.stderr b/src/tools/clippy/tests/ui/derivable_impls.stderr
@@ -1,24 +1,3 @@
-error: this `impl` can be derived
-  --> tests/ui/derivable_impls.rs:20:1
-   |
-LL | / impl std::default::Default for FooDefault<'_> {
-LL | |     fn default() -> Self {
-LL | |         Self {
-LL | |             a: false,
-...  |
-LL | |     }
-LL | | }
-   | |_^
-   |
-   = note: `-D clippy::derivable-impls` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::derivable_impls)]`
-   = help: remove the manual implementation...
-help: ...and instead derive it
-   |
-LL + #[derive(Default)]
-LL | struct FooDefault<'a> {
-   |
-
 error: this `impl` can be derived
   --> tests/ui/derivable_impls.rs:41:1
    |
@@ -29,6 +8,8 @@ LL | |     }
 LL | | }
    | |_^
    |
+   = note: `-D clippy::derivable-impls` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::derivable_impls)]`
    = help: remove the manual implementation...
 help: ...and instead derive it
    |
@@ -143,5 +124,5 @@ LL ~     #[default]
 LL ~     Bar,
    |
 
-error: aborting due to 8 previous errors
+error: aborting due to 7 previous errors
 
diff --git a/src/tools/clippy/tests/ui/eta.fixed b/src/tools/clippy/tests/ui/eta.fixed
@@ -30,7 +30,7 @@ fn main() {
     let c = Some(1u8).map(|a| {1+2; foo}(a));
     true.then(|| mac!()); // don't lint function in macro expansion
     Some(1).map(closure_mac!()); // don't lint closure in macro expansion
-    let _: Option<Vec<u8>> = true.then(std::vec::Vec::new); // special case vec!
+    let _: Option<Vec<u8>> = true.then(|| vec![]); // special case vec!
     let d = Some(1u8).map(|a| foo(foo2(a))); //is adjusted?
     all(&[1, 2, 3], &&2, below); //is adjusted
     unsafe {

diff --git a/src/tools/clippy/tests/ui/eta.stderr b/src/tools/clippy/tests/ui/eta.stderr
@@ -7,12 +7,6 @@ LL |     let a = Some(1u8).map(|a| foo(a));
    = note: `-D clippy::redundant-closure` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::redundant_closure)]`
 
-error: redundant closure
-  --> tests/ui/eta.rs:33:40
-   |
-LL |     let _: Option<Vec<u8>> = true.then(|| vec![]); // special case vec!
-   |                                        ^^^^^^^^^ help: replace the closure with `Vec::new`: `std::vec::Vec::new`
-
 error: redundant closure
   --> tests/ui/eta.rs:34:35
    |
@@ -202,5 +196,5 @@ error: redundant closure
 LL |         let x = Box::new(|| None.map(|x| f(x)));
    |                                      ^^^^^^^^ help: replace the closure with the function itself: `f`
 
-error: aborting due to 33 previous errors
+error: aborting due to 32 previous errors
 
diff --git a/src/tools/clippy/tests/ui/iter_out_of_bounds.rs b/src/tools/clippy/tests/ui/iter_out_of_bounds.rs
@@ -32,10 +32,8 @@ fn main() {
     for _ in opaque_empty_iter().skip(1) {}
 
     for _ in vec![1, 2, 3].iter().skip(4) {}
-    //~^ ERROR: this `.skip()` call skips more items than the iterator will produce
 
     for _ in vec![1; 3].iter().skip(4) {}
-    //~^ ERROR: this `.skip()` call skips more items than the iterator will produce
 
     let x = [1, 2, 3];
     for _ in x.iter().skip(4) {}