Constify assert_eq! and assert_ne!

library/core/src/macros/mod.rs

@@ -42,7 +42,7 @@ 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::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
+                    $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None, $crate::concat!("assertion failed: `", $crate::stringify!($left), " == ", $crate::stringify!($right), "`"));
                 }
             }
         }
@@ -55,7 +55,7 @@ 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::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
+                    $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)), $crate::concat!("assertion failed: `", $crate::stringify!($left), " == ", $crate::stringify!($right), "`"));
                 }
             }
         }
@@ -92,7 +92,7 @@ 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::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
+                    $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None, $crate::concat!("assertion failed: `", $crate::stringify!($left), " != ", $crate::stringify!($right), "`"));
                 }
             }
         }
@@ -105,7 +105,7 @@ 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::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
+                    $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)), $crate::concat!("assertion failed: `", $crate::stringify!($left), " != ", $crate::stringify!($right), "`"));
                 }
             }
         }

library/core/src/panicking.rs

@@ -199,17 +199,53 @@ pub enum AssertKind {
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
 #[track_caller]
 #[doc(hidden)]
-pub fn assert_failed<T, U>(
+#[rustc_const_unstable(feature = "const_assert_eq", issue = "none")]
+pub const fn assert_failed<T, U>(
     kind: AssertKind,
     left: &T,
     right: &U,
     args: Option<fmt::Arguments<'_>>,
+    string_for_const_msg: &str,
 ) -> !
 where
     T: fmt::Debug + ?Sized,
     U: fmt::Debug + ?Sized,
 {
-    assert_failed_inner(kind, &left, &right, args)
+    #[track_caller]
+    const fn assert_failed_const_impl<T: ?Sized, U: ?Sized>(
+        _: AssertKind,
+        _: &T,
+        _: &U,
+        _: Option<fmt::Arguments<'_>>,
+        msg: &str,
+    ) -> ! {
+        panic_str(msg)
+    }
+
+    #[track_caller]
+    #[inline]
+    fn assert_failed_runtime_impl<T, U>(
+        kind: AssertKind,
+        left: &T,
+        right: &U,
+        args: Option<fmt::Arguments<'_>>,
+        _: &str,
+    ) -> !
+    where
+        T: fmt::Debug + ?Sized,
+        U: fmt::Debug + ?Sized,
+    {
+        assert_failed_inner(kind, &left, &right, args)
+    }
+
+    // SAFETY: we are panicking in both branches, so this is consistent.
+    unsafe {
+        crate::intrinsics::const_eval_select(
+            (kind, left, right, args, string_for_const_msg),
+            assert_failed_const_impl,
+            assert_failed_runtime_impl,
+        )
+    }
 }
 
 /// Internal function for `assert_match!`

tests/mir-opt/retag.array_casts.SimplifyCfg-elaborate-drops.after.mir

@@ -30,6 +30,8 @@ fn array_casts() -> () {
     let mut _32: &usize;                 // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let _33: &usize;                     // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let mut _34: std::option::Option<std::fmt::Arguments<'_>>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+    let mut _35: &str;                   // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+    let _36: &str;                       // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     scope 1 {
         debug x => _1;                   // in scope 1 at $DIR/retag.rs:+1:9: +1:14
         let _2: *mut usize;              // in scope 1 at $DIR/retag.rs:+2:9: +2:10
@@ -45,7 +47,7 @@ fn array_casts() -> () {
                     debug p => _9;       // in scope 5 at $DIR/retag.rs:+6:9: +6:10
                     let _20: &usize;     // in scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
                     let _21: &usize;     // in scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-                    let mut _35: &usize; // in scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                    let mut _37: &usize; // in scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
                     scope 6 {
                     }
                     scope 7 {
@@ -116,12 +118,12 @@ fn array_casts() -> () {
         _15 = (*_16);                    // scope 6 at $DIR/retag.rs:+7:25: +7:34
         _14 = &_15;                      // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         StorageLive(_18);                // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-        _35 = const _;                   // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _37 = const _;                   // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
                                          // mir::Constant
                                          // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
                                          // + literal: Const { ty: &usize, val: Unevaluated(array_casts, [], Some(promoted[0])) }
-        Retag(_35);                      // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-        _18 = &(*_35);                   // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        Retag(_37);                      // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _18 = &(*_37);                   // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         Deinit(_13);                     // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         (_13.0: &usize) = move _14;      // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         (_13.1: &usize) = move _18;      // scope 5 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
@@ -167,10 +169,18 @@ fn array_casts() -> () {
         Deinit(_34);                     // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         discriminant(_34) = 0;           // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         Retag(_34);                      // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-        _28 = core::panicking::assert_failed::<usize, usize>(move _29, move _30, move _32, move _34); // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        StorageLive(_35);                // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        StorageLive(_36);                // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _36 = const "assertion failed: `unsafe { *p.add(1) } == 1`"; // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
                                          // mir::Constant
                                          // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
-                                         // + literal: Const { ty: for<'a, 'b, 'c> fn(core::panicking::AssertKind, &'a usize, &'b usize, Option<Arguments<'c>>) -> ! {core::panicking::assert_failed::<usize, usize>}, val: Value(<ZST>) }
+                                         // + literal: Const { ty: &str, val: Value(Slice(..)) }
+        Retag(_36);                      // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _35 = &(*_36);                   // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _28 = core::panicking::assert_failed::<usize, usize>(move _29, move _30, move _32, move _34, move _35); // scope 8 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                                         // mir::Constant
+                                         // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                                         // + literal: Const { ty: for<'a, 'b, 'c, 'd> fn(core::panicking::AssertKind, &'a usize, &'b usize, Option<Arguments<'c>>, &'d str) -> ! {core::panicking::assert_failed::<usize, usize>}, val: Value(<ZST>) }
     }
 
     bb4: {

tests/ui/consts/assert_eq_gate.rs

@@ -0,0 +1,5 @@
+const _: () = assert_eq!(1, 1);
+//~^ ERROR `core::panicking::assert_failed` is not yet stable as a const fn
+//~| HELP add `#![feature(const_assert_eq)]` to the crate attributes to enable
+
+fn main() {}

tests/ui/consts/assert_eq_gate.stderr

@@ -0,0 +1,11 @@
+error: `core::panicking::assert_failed` is not yet stable as a const fn
+  --> $DIR/assert_eq_gate.rs:1:15
+   |
+LL | const _: () = assert_eq!(1, 1);
+   |               ^^^^^^^^^^^^^^^^
+   |
+   = help: add `#![feature(const_assert_eq)]` to the crate attributes to enable
+   = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+

tests/ui/consts/assertions.rs

@@ -0,0 +1,15 @@
+#![feature(const_assert_eq)]
+
+const _BAD1: () = {
+    assert_eq!(1, 2)
+}; //~^ ERROR: evaluation of constant value failed
+
+const _BAD2: () = {
+    assert_ne!(1, 1)
+}; //~^ ERROR: evaluation of constant value failed
+
+const _BAD3: () = {
+    assert!(false)
+}; //~^ ERROR: evaluation of constant value failed
+
+fn main() {}

tests/ui/consts/assertions.stderr

@@ -0,0 +1,27 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/assertions.rs:4:5
+   |
+LL |     assert_eq!(1, 2)
+   |     ^^^^^^^^^^^^^^^^ the evaluated program panicked at 'assertion failed: `1 == 2`', $DIR/assertions.rs:4:5
+   |
+   = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/assertions.rs:8:5
+   |
+LL |     assert_ne!(1, 1)
+   |     ^^^^^^^^^^^^^^^^ the evaluated program panicked at 'assertion failed: `1 != 1`', $DIR/assertions.rs:8:5
+   |
+   = note: this error originates in the macro `assert_ne` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/assertions.rs:12:5
+   |
+LL |     assert!(false)
+   |     ^^^^^^^^^^^^^^ the evaluated program panicked at 'assertion failed: false', $DIR/assertions.rs:12:5
+   |
+   = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0080`.