Improve assert_eq! and assert_ne!

It should improve compile times and reduce instruction cache use by moving the
panic formatting to a monomorphised function

library/core/src/lib.rs

@@ -173,6 +173,13 @@ mod macros;
 
 #[macro_use]
 mod internal_macros;
+#[doc(hidden)]
+#[unstable(
+    feature = "macros_internals",
+    reason = "macros implementation detail",
+    issue = "none"
+)]
+pub use macros::internals as macros_internals;
 
 #[path = "num/shells/int_macros.rs"]
 #[macro_use]

library/core/src/macros/internals.rs

@@ -0,0 +1,85 @@
+use crate::{fmt, panic};
+
+#[cold]
+#[doc(hidden)]
+#[unstable(feature = "macros_internals", reason = "macros implementation detail", issue = "none")]
+#[track_caller]
+pub fn assert_eq_failed<T, U>(left: &T, right: &U) -> !
+where
+    T: fmt::Debug + ?Sized,
+    U: fmt::Debug + ?Sized,
+{
+    #[track_caller]
+    fn inner(left: &dyn fmt::Debug, right: &dyn fmt::Debug) -> ! {
+        panic!(
+            r#"assertion failed: `(left == right)`
+left: `{:?}`,
+right: `{:?}`"#,
+            left, right
+        )
+    }
+    inner(&left, &right)
+}
+
+#[cold]
+#[doc(hidden)]
+#[unstable(feature = "macros_internals", reason = "macros implementation detail", issue = "none")]
+#[track_caller]
+pub fn assert_eq_failed_args<T, U>(left: &T, right: &U, args: fmt::Arguments<'_>) -> !
+where
+    T: fmt::Debug + ?Sized,
+    U: fmt::Debug + ?Sized,
+{
+    #[track_caller]
+    fn inner(left: &dyn fmt::Debug, right: &dyn fmt::Debug, args: fmt::Arguments<'_>) -> ! {
+        panic!(
+            r#"assertion failed: `(left == right)`
+left: `{:?}`,
+right: `{:?}: {}`"#,
+            left, right, args
+        )
+    }
+    inner(&left, &right, args)
+}
+
+#[cold]
+#[doc(hidden)]
+#[unstable(feature = "macros_internals", reason = "macros implementation detail", issue = "none")]
+#[track_caller]
+pub fn assert_ne_failed<T, U>(left: &T, right: &U) -> !
+where
+    T: fmt::Debug + ?Sized,
+    U: fmt::Debug + ?Sized,
+{
+    #[track_caller]
+    fn inner(left: &dyn fmt::Debug, right: &dyn fmt::Debug) -> ! {
+        panic!(
+            r#"assertion failed: `(left != right)`
+left: `{:?}`,
+right: `{:?}`"#,
+            left, right
+        )
+    }
+    inner(&left, &right)
+}
+
+#[cold]
+#[doc(hidden)]
+#[unstable(feature = "macros_internals", reason = "macros implementation detail", issue = "none")]
+#[track_caller]
+pub fn assert_ne_failed_args<T, U>(left: &T, right: &U, args: fmt::Arguments<'_>) -> !
+where
+    T: fmt::Debug + ?Sized,
+    U: fmt::Debug + ?Sized,
+{
+    #[track_caller]
+    fn inner(left: &dyn fmt::Debug, right: &dyn fmt::Debug, args: fmt::Arguments<'_>) -> ! {
+        panic!(
+            r#"assertion failed: `(left != right)`
+left: `{:?}`,
+right: `{:?}: {}`"#,
+            left, right, args
+        )
+    }
+    inner(&left, &right, args)
+}

library/core/src/macros/mod.rs

@@ -1,3 +1,7 @@
+#[unstable(feature = "macros_internals", reason = "macros implementation detail", issue = "none")]
+#[doc(hidden)]
+pub mod internals;
+
 #[cfg(bootstrap)]
 #[doc(include = "panic.md")]
 #[macro_export]
@@ -53,6 +57,7 @@ macro_rules! panic {
 /// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable(macros_internals)]
 macro_rules! assert_eq {
     ($left:expr, $right:expr $(,)?) => ({
         match (&$left, &$right) {
@@ -61,24 +66,19 @@ macro_rules! assert_eq {
                     // The reborrows below are intentional. Without them, the stack slot for the
                     // borrow is initialized even before the values are compared, leading to a
                     // noticeable slow down.
-                    $crate::panic!(r#"assertion failed: `(left == right)`
+                    $crate::macros_internals::assert_eq_failed(&*left_val, &*right_val);
-  left: `{:?}`,
- right: `{:?}`"#, &*left_val, &*right_val)
                 }
             }
         }
     });
     ($left:expr, $right:expr, $($arg:tt)+) => ({
-        match (&($left), &($right)) {
+        match (&$left, &$right) {
             (left_val, right_val) => {
                 if !(*left_val == *right_val) {
                     // The reborrows below are intentional. Without them, the stack slot for the
                     // borrow is initialized even before the values are compared, leading to a
                     // noticeable slow down.
-                    $crate::panic!(r#"assertion failed: `(left == right)`
+                    $crate::macros_internals::assert_eq_failed_args(&*left_val, &*right_val, $crate::format_args!($($arg)+));
-  left: `{:?}`,
- right: `{:?}`: {}"#, &*left_val, &*right_val,
-                           $crate::format_args!($($arg)+))
                 }
             }
         }
@@ -104,6 +104,7 @@ macro_rules! assert_eq {
 /// ```
 #[macro_export]
 #[stable(feature = "assert_ne", since = "1.13.0")]
+#[allow_internal_unstable(macros_internals)]
 macro_rules! assert_ne {
     ($left:expr, $right:expr $(,)?) => ({
         match (&$left, &$right) {
@@ -112,9 +113,7 @@ macro_rules! assert_ne {
                     // The reborrows below are intentional. Without them, the stack slot for the
                     // borrow is initialized even before the values are compared, leading to a
                     // noticeable slow down.
-                    $crate::panic!(r#"assertion failed: `(left != right)`
+                    $crate::macros_internals::assert_eq_failed(&*left_val, &*right_val);
-  left: `{:?}`,
- right: `{:?}`"#, &*left_val, &*right_val)
                 }
             }
         }
@@ -126,10 +125,7 @@ macro_rules! assert_ne {
                     // The reborrows below are intentional. Without them, the stack slot for the
                     // borrow is initialized even before the values are compared, leading to a
                     // noticeable slow down.
-                    $crate::panic!(r#"assertion failed: `(left != right)`
+                    $crate::macros_internals::assert_ne_failed_args(&*left_val, &*right_val, $crate::format_args!($($arg)+));
-  left: `{:?}`,
- right: `{:?}`: {}"#, &*left_val, &*right_val,
-                           $crate::format_args!($($arg)+))
                 }
             }
         }