Mark format! with must_use hint

rust-lang · Jul 5, 2024 · 21650b1 · 21650b1
1 parent 51917ba
commit 21650b1
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Showing 16 changed files with 116 additions and 111 deletions.
diff --git a/library/alloc/src/collections/btree/map/tests.rs b/library/alloc/src/collections/btree/map/tests.rs
@@ -1796,18 +1796,18 @@ fn test_ord_absence() {
     }
 
     fn map_debug<K: Debug>(mut map: BTreeMap<K, ()>) {
-        format!("{map:?}");
-        format!("{:?}", map.iter());
-        format!("{:?}", map.iter_mut());
-        format!("{:?}", map.keys());
-        format!("{:?}", map.values());
-        format!("{:?}", map.values_mut());
+        let _ = format!("{map:?}");
+        let _ = format!("{:?}", map.iter());
+        let _ = format!("{:?}", map.iter_mut());
+        let _ = format!("{:?}", map.keys());
+        let _ = format!("{:?}", map.values());
+        let _ = format!("{:?}", map.values_mut());
         if true {
-            format!("{:?}", map.into_iter());
+            let _ = format!("{:?}", map.into_iter());
         } else if true {
-            format!("{:?}", map.into_keys());
+            let _ = format!("{:?}", map.into_keys());
         } else {
-            format!("{:?}", map.into_values());
+            let _ = format!("{:?}", map.into_values());
         }
     }
 

diff --git a/library/alloc/src/collections/btree/set/tests.rs b/library/alloc/src/collections/btree/set/tests.rs
@@ -705,9 +705,9 @@ fn test_ord_absence() {
     }
 
     fn set_debug<K: Debug>(set: BTreeSet<K>) {
-        format!("{set:?}");
-        format!("{:?}", set.iter());
-        format!("{:?}", set.into_iter());
+        let _ = format!("{set:?}");
+        let _ = format!("{:?}", set.iter());
+        let _ = format!("{:?}", set.into_iter());
     }
 
     fn set_clone<K: Clone>(mut set: BTreeSet<K>) {

diff --git a/library/alloc/src/fmt.rs b/library/alloc/src/fmt.rs
@@ -12,19 +12,19 @@
 //! Some examples of the [`format!`] extension are:
 //!
 //! ```
-//! format!("Hello");                 // => "Hello"
-//! format!("Hello, {}!", "world");   // => "Hello, world!"
-//! format!("The number is {}", 1);   // => "The number is 1"
-//! format!("{:?}", (3, 4));          // => "(3, 4)"
-//! format!("{value}", value=4);      // => "4"
+//! let _ = format!("Hello");                 // => "Hello"
+//! let _ = format!("Hello, {}!", "world");   // => "Hello, world!"
+//! let _ = format!("The number is {}", 1);   // => "The number is 1"
+//! let _ = format!("{:?}", (3, 4));          // => "(3, 4)"
+//! let _ = format!("{value}", value=4);      // => "4"
 //! let people = "Rustaceans";
-//! format!("Hello {people}!");       // => "Hello Rustaceans!"
-//! format!("{} {}", 1, 2);           // => "1 2"
-//! format!("{:04}", 42);             // => "0042" with leading zeros
-//! format!("{:#?}", (100, 200));     // => "(
-//!                                   //       100,
-//!                                   //       200,
-//!                                   //     )"
+//! let _ = format!("Hello {people}!");       // => "Hello Rustaceans!"
+//! let _ = format!("{} {}", 1, 2);           // => "1 2"
+//! let _ = format!("{:04}", 42);             // => "0042" with leading zeros
+//! let _ = format!("{:#?}", (100, 200));     // => "(
+//!                                           //       100,
+//!                                           //       200,
+//!                                           //     )"
 //! ```
 //!
 //! From these, you can see that the first argument is a format string. It is
@@ -50,7 +50,7 @@
 //! the iterator advances. This leads to behavior like this:
 //!
 //! ```
-//! format!("{1} {} {0} {}", 1, 2); // => "2 1 1 2"
+//! let _ = format!("{1} {} {0} {}", 1, 2); // => "2 1 1 2"
 //! ```
 //!
 //! The internal iterator over the argument has not been advanced by the time
@@ -77,17 +77,17 @@
 //! For example, the following [`format!`] expressions all use named arguments:
 //!
 //! ```
-//! format!("{argument}", argument = "test");   // => "test"
-//! format!("{name} {}", 1, name = 2);          // => "2 1"
-//! format!("{a} {c} {b}", a="a", b='b', c=3);  // => "a 3 b"
+//! let _ = format!("{argument}", argument = "test");   // => "test"
+//! let _ = format!("{name} {}", 1, name = 2);          // => "2 1"
+//! let _ = format!("{a} {c} {b}", a="a", b='b', c=3);  // => "a 3 b"
 //! ```
 //!
 //! If a named parameter does not appear in the argument list, `format!` will
 //! reference a variable with that name in the current scope.
 //!
 //! ```
 //! let argument = 2 + 2;
-//! format!("{argument}");   // => "4"
+//! let _ = format!("{argument}");   // => "4"
 //!
 //! fn make_string(a: u32, b: &str) -> String {
 //!     format!("{b} {a}")

diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
@@ -256,6 +256,7 @@ pub mod vec;
 #[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
 pub mod __export {
     pub use core::format_args;
+    pub use core::hint::must_use;
 }
 
 #[cfg(test)]

diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs
@@ -111,18 +111,21 @@ macro_rules! vec {
 /// # Examples
 ///
 /// ```
-/// format!("test");                             // => "test"
-/// format!("hello {}", "world!");               // => "hello world!"
-/// format!("x = {}, y = {val}", 10, val = 30);  // => "x = 10, y = 30"
+/// let _ = format!("test");                             // => "test"
+/// let _ = format!("hello {}", "world!");               // => "hello world!"
+/// let _ = format!("x = {}, y = {val}", 10, val = 30);  // => "x = 10, y = 30"
 /// let (x, y) = (1, 2);
-/// format!("{x} + {y} = 3");                    // => "1 + 2 = 3"
+/// let _ = format!("{x} + {y} = 3");                    // => "1 + 2 = 3"
 /// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable(hint_must_use, liballoc_internals)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "format_macro")]
 macro_rules! format {
-    ($($arg:tt)*) => {{
-        let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
-        res
-    }}
+    ($($arg:tt)*) => {
+        $crate::__export::must_use({
+            let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
+            res
+        })
+    }
 }
diff --git a/library/alloc/tests/fmt.rs b/library/alloc/tests/fmt.rs
@@ -217,19 +217,19 @@ fn test_format_macro_interface() {
 
     // make sure that format! doesn't move out of local variables
     let a = Box::new(3);
-    format!("{a}");
-    format!("{a}");
+    let _ = format!("{a}");
+    let _ = format!("{a}");
 
     // make sure that format! doesn't cause spurious unused-unsafe warnings when
     // it's inside of an outer unsafe block
     unsafe {
         let a: isize = ::std::mem::transmute(3_usize);
-        format!("{a}");
+        let _ = format!("{a}");
     }
 
     // test that trailing commas are acceptable
-    format!("{}", "test",);
-    format!("{foo}", foo = "test",);
+    let _ = format!("{}", "test",);
+    let _ = format!("{foo}", foo = "test",);
 }
 
 // Basic test to make sure that we can invoke the `write!` macro with an

diff --git a/library/core/tests/fmt/builders.rs b/library/core/tests/fmt/builders.rs
@@ -441,7 +441,7 @@ mod debug_map {
             }
         }
 
-        format!("{Foo:?}");
+        let _ = format!("{Foo:?}");
     }
 
     #[test]
@@ -455,7 +455,7 @@ mod debug_map {
             }
         }
 
-        format!("{Foo:?}");
+        let _ = format!("{Foo:?}");
     }
 
     #[test]
@@ -469,7 +469,7 @@ mod debug_map {
             }
         }
 
-        format!("{Foo:?}");
+        let _ = format!("{Foo:?}");
     }
 }
 

diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -755,7 +755,7 @@ fn configure_cmake(
     }
 
     if builder.config.llvm_clang_cl.is_some() {
-        cflags.push(&format!(" --target={target}"));
+        cflags.push(format!(" --target={target}"));
     }
     cfg.define("CMAKE_C_FLAGS", cflags);
     let mut cxxflags: OsString = builder
@@ -774,7 +774,7 @@ fn configure_cmake(
         cxxflags.push(s);
     }
     if builder.config.llvm_clang_cl.is_some() {
-        cxxflags.push(&format!(" --target={target}"));
+        cxxflags.push(format!(" --target={target}"));
     }
     cfg.define("CMAKE_CXX_FLAGS", cxxflags);
     if let Some(ar) = builder.ar(target) {
@@ -915,7 +915,7 @@ impl Step for Lld {
                 // Find clang's runtime library directory and push that as a search path to the
                 // cmake linker flags.
                 let clang_rt_dir = get_clang_cl_resource_dir(clang_cl_path);
-                ldflags.push_all(&format!("/libpath:{}", clang_rt_dir.display()));
+                ldflags.push_all(format!("/libpath:{}", clang_rt_dir.display()));
             }
         }
 

diff --git a/src/bootstrap/src/core/builder.rs b/src/bootstrap/src/core/builder.rs
@@ -2527,7 +2527,7 @@ impl Cargo {
 
         if let Some(target_linker) = builder.linker(target) {
             let target = crate::envify(&target.triple);
-            self.command.env(&format!("CARGO_TARGET_{target}_LINKER"), target_linker);
+            self.command.env(format!("CARGO_TARGET_{target}_LINKER"), target_linker);
         }
         // We want to set -Clinker using Cargo, therefore we only call `linker_flags` and not
         // `linker_args` here.

diff --git a/src/tools/clippy/tests/ui/or_fun_call.rs b/src/tools/clippy/tests/ui/or_fun_call.rs
@@ -98,7 +98,7 @@ fn or_fun_call() {
 
     let opt = Some(1);
     let hello = "Hello";
-    let _ = opt.ok_or(format!("{} world.", hello));
+    let _ = opt.ok_or_else(|| format!("{} world.", hello));
 
     // index
     let map = HashMap::<u64, u64>::new();

diff --git a/tests/pretty/issue-4264.pp b/tests/pretty/issue-4264.pp
@@ -29,16 +29,17 @@
 
 
 
-    ({
-        let res =
-            ((::alloc::fmt::format as
-                    for<'a> fn(Arguments<'a>) -> String {format})(((format_arguments::new_const
-                        as
-                        fn(&[&'static str; 1]) -> Arguments<'_> {Arguments::<'_>::new_const::<1>})((&([("test"
-                                    as &str)] as [&str; 1]) as &[&str; 1])) as Arguments<'_>))
-                as String);
-        (res as String)
-    } as String);
+    ((::alloc::__export::must_use as
+            fn(String) -> String {must_use::<String>})(({
+            let res =
+                ((::alloc::fmt::format as
+                        for<'a> fn(Arguments<'a>) -> String {format})(((format_arguments::new_const
+                            as
+                            fn(&[&'static str; 1]) -> Arguments<'_> {Arguments::<'_>::new_const::<1>})((&([("test"
+                                        as &str)] as [&str; 1]) as &[&str; 1])) as Arguments<'_>))
+                    as String);
+            (res as String)
+        } as String)) as String);
 } as ())
 type Foo = [i32; (3 as usize)];
 struct Bar {

diff --git a/tests/ui/deriving/deriving-in-fn.rs b/tests/ui/deriving/deriving-in-fn.rs
@@ -9,5 +9,5 @@ pub fn main() {
     }
 
     let f = Foo { foo: 10 };
-    format!("{:?}", f);
+    let _ = format!("{:?}", f);
 }
diff --git a/tests/ui/fmt/struct-field-as-captured-argument.fixed b/tests/ui/fmt/struct-field-as-captured-argument.fixed
@@ -8,11 +8,11 @@ struct Foo {
 fn main() {
     let foo = Foo { field: 0 };
     let bar = 3;
-    format!("{0}", foo.field); //~ ERROR invalid format string: field access isn't supported
-    format!("{1} {} {bar}", "aa", foo.field); //~ ERROR invalid format string: field access isn't supported
-    format!("{2} {} {1} {bar}", "aa", "bb", foo.field); //~ ERROR invalid format string: field access isn't supported
-    format!("{1} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{1:?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{1:#?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{1:.3} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{0}", foo.field); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1} {} {bar}", "aa", foo.field); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{2} {} {1} {bar}", "aa", "bb", foo.field); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1:?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1:#?} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{1:.3} {} {baz}", "aa", foo.field, baz = 3); //~ ERROR invalid format string: field access isn't supported
 }
diff --git a/tests/ui/fmt/struct-field-as-captured-argument.rs b/tests/ui/fmt/struct-field-as-captured-argument.rs
@@ -8,11 +8,11 @@ struct Foo {
 fn main() {
     let foo = Foo { field: 0 };
     let bar = 3;
-    format!("{foo.field}"); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field} {} {bar}", "aa"); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field} {} {1} {bar}", "aa", "bb"); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field:?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field:#?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
-    format!("{foo.field:.3} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field}"); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field} {} {bar}", "aa"); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field} {} {1} {bar}", "aa", "bb"); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field:?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field:#?} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
+    let _ = format!("{foo.field:.3} {} {baz}", "aa", baz = 3); //~ ERROR invalid format string: field access isn't supported
 }