Auto merge of rust-lang#80851 - m-ou-se:panic-2021, r=petrochenkov

Implement Rust 2021 panic

This implements the Rust 2021 versions of `panic!()`. See rust-lang#80162 and rust-lang/rfcs#3007.

It does so by replacing `{std, core}::panic!()` by a bulitin macro that expands to either `$crate::panic::panic_2015!(..)` or `$crate::panic::panic_2021!(..)` depending on the edition of the caller.

This does not yet make std's panic an alias for core's panic on Rust 2021 as the RFC proposes. That will be a separate change: rust-lang@c5273bd That change is blocked on figuring out what to do with rust-lang#80846 first.

tests/ui/panicking_macros.stderr

@@ -11,16 +11,12 @@ error: `panic` should not be present in production code
    |
 LL |     panic!("message");
    |     ^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `panic` should not be present in production code
   --> $DIR/panicking_macros.rs:10:5
    |
 LL |     panic!("{} {}", "panic with", "multiple arguments");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `todo` should not be present in production code
   --> $DIR/panicking_macros.rs:16:5
@@ -29,18 +25,23 @@ LL |     todo!();
    |     ^^^^^^^^
    |
    = note: `-D clippy::todo` implied by `-D warnings`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `todo` should not be present in production code
   --> $DIR/panicking_macros.rs:17:5
    |
 LL |     todo!("message");
    |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `todo` should not be present in production code
   --> $DIR/panicking_macros.rs:18:5
    |
 LL |     todo!("{} {}", "panic with", "multiple arguments");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `unimplemented` should not be present in production code
   --> $DIR/panicking_macros.rs:24:5
@@ -49,18 +50,23 @@ LL |     unimplemented!();
    |     ^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::unimplemented` implied by `-D warnings`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `unimplemented` should not be present in production code
   --> $DIR/panicking_macros.rs:25:5
    |
 LL |     unimplemented!("message");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `unimplemented` should not be present in production code
   --> $DIR/panicking_macros.rs:26:5
    |
 LL |     unimplemented!("{} {}", "panic with", "multiple arguments");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: usage of the `unreachable!` macro
   --> $DIR/panicking_macros.rs:32:5
@@ -69,6 +75,7 @@ LL |     unreachable!();
    |     ^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::unreachable` implied by `-D warnings`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: usage of the `unreachable!` macro
   --> $DIR/panicking_macros.rs:33:5
@@ -83,6 +90,8 @@ error: usage of the `unreachable!` macro
    |
 LL |     unreachable!("{} {}", "panic with", "multiple arguments");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `panic` should not be present in production code
   --> $DIR/panicking_macros.rs:40:5
@@ -95,18 +104,24 @@ error: `todo` should not be present in production code
    |
 LL |     todo!();
    |     ^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `unimplemented` should not be present in production code
   --> $DIR/panicking_macros.rs:42:5
    |
 LL |     unimplemented!();
    |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: usage of the `unreachable!` macro
   --> $DIR/panicking_macros.rs:43:5
    |
 LL |     unreachable!();
    |     ^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 16 previous errors