Tweak output of const panic diagnostic

[estebank]

Shorten span of panic failures in const context

Previously, we included a redundant prefix on the panic message and a postfix of the location of the panic. The prefix didn't carry any additional information beyond "something failed", and the location of the panic is redundant with the diagnostic's span, which gets printed out even if its code is not shown.

error[E0080]: evaluation of constant value failed
--> $DIR/assert-type-intrinsics.rs:11:9
   |
LL |         MaybeUninit::<!>::uninit().assume_init();
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ panic: aborted execution: attempted to instantiate uninhabited type `!`

error[E0080]: evaluation of `Fail::<i32>::C` failed
--> $DIR/collect-in-dead-closure.rs:9:19
   |
LL |     const C: () = panic!();
   |                   ^^^^^^^^ explicit panic
   |
   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0080]: evaluation of constant value failed
--> $DIR/uninhabited.rs:87:9
   |
LL |         assert!(false);
   |         ^^^^^^^^^^^^^^ assertion failed: false
   |
   = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)

Remove duplicated span from const eval frame list

When the primary span for a const error is the same as the first frame in the const error report, skip it.

error[E0080]: evaluation of constant value failed
  --> $DIR/issue-88434-removal-index-should-be-less.rs:3:24
   |
LL | const _CONST: &[u8] = &f(&[], |_| {});
   |                        ^^^^^^^^^^^^^^ explicit panic
   |
note: inside `f::<{closure@$DIR/issue-88434-removal-index-should-be-less.rs:3:31: 3:34}>`
  --> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
   |
LL |     panic!()
   |     ^^^^^^^^ the failure occurred here
   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)

instead of

error[E0080]: evaluation of constant value failed
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
   |
LL |     panic!()
   |     ^^^^^^^^ explicit panic
   |
note: inside `f::<{closure@$DIR/issue-88434-removal-index-should-be-less.rs:3:31: 3:34}>`
--> $DIR/issue-88434-removal-index-should-be-less.rs:10:5
   |
LL |     panic!()
   |     ^^^^^^^^
note: inside `_CONST`
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:24
   |
LL | const _CONST: &[u8] = &f(&[], |_| {});
   |                        ^^^^^^^^^^^^^^
   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)

note: erroneous constant encountered
--> $DIR/issue-88434-removal-index-should-be-less.rs:3:23
   |
LL | const _CONST: &[u8] = &f(&[], |_| {});
   |                       ^^^^^^^^^^^^^^^

r? @oli-obk

[rustbot]

Some changes occurred to the CTFE machinery

cc @rust-lang/wg-const-eval

The Miri subtree was changed

cc @rust-lang/miri

[rustbot]

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

[estebank]

I reverted the "inside" -> "called from" wording change purely to ease on the review of this PR. I think it'd be nicer on the reviewer if we split off that change to its own PR with fewer moving parts.

[RalfJung]

(not new in your PR) why is this not in the "miri unleashes" folder...?

[bors]

☔ The latest upstream changes (presumably #137446) made this pull request unmergeable. Please resolve the merge conflicts.

[oli-obk]

r? @RalfJung

[RalfJung]

Thanks for the patience, I like the new output! We can keep discussing further changes to the format if you want in some issue, but meanwhile we can land this as a strict improvement. I just have some nits.

@rustbot author

[RalfJung]

Thanks! r=me with the final nit resolved, and the commits squashed.