Fix invalid special casing of the unreachable! macro

compiler/rustc_builtin_macros/src/assert.rs

@@ -1,4 +1,4 @@
-use crate::panic::use_panic_2021;
+use crate::edition_panic::use_panic_2021;
 use rustc_ast::ptr::P;
 use rustc_ast::token;
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};

compiler/rustc_builtin_macros/src/edition_panic.rs

@@ -20,8 +20,29 @@ pub fn expand_panic<'cx>(
     sp: Span,
     tts: TokenStream,
 ) -> Box<dyn MacResult + 'cx> {
-    let panic = if use_panic_2021(sp) { sym::panic_2021 } else { sym::panic_2015 };
+    let mac = if use_panic_2021(sp) { sym::panic_2021 } else { sym::panic_2015 };
+    expand(mac, cx, sp, tts)
+}
 
+// This expands to either
+// - `$crate::panic::unreachable_2015!(...)` or
+// - `$crate::panic::unreachable_2021!(...)`
+// depending on the edition.
+pub fn expand_unreachable<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn MacResult + 'cx> {
+    let mac = if use_panic_2021(sp) { sym::unreachable_2021 } else { sym::unreachable_2015 };
+    expand(mac, cx, sp, tts)
+}
+
+fn expand<'cx>(
+    mac: rustc_span::Symbol,
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn MacResult + 'cx> {
     let sp = cx.with_call_site_ctxt(sp);
 
     MacEager::expr(
@@ -31,7 +52,7 @@ pub fn expand_panic<'cx>(
                 path: Path {
                     span: sp,
                     segments: cx
-                        .std_path(&[sym::panic, panic])
+                        .std_path(&[sym::panic, mac])
                         .into_iter()
                         .map(|ident| PathSegment::from_ident(ident))
                         .collect(),

compiler/rustc_builtin_macros/src/lib.rs

@@ -31,12 +31,12 @@ mod concat_bytes;
 mod concat_idents;
 mod derive;
 mod deriving;
+mod edition_panic;
 mod env;
 mod format;
 mod format_foreign;
 mod global_allocator;
 mod log_syntax;
-mod panic;
 mod source_util;
 mod test;
 mod trace_macros;
@@ -82,8 +82,9 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
         log_syntax: log_syntax::expand_log_syntax,
         module_path: source_util::expand_mod,
         option_env: env::expand_option_env,
-        core_panic: panic::expand_panic,
-        std_panic: panic::expand_panic,
+        core_panic: edition_panic::expand_panic,
+        std_panic: edition_panic::expand_panic,
+        unreachable: edition_panic::expand_unreachable,
         stringify: source_util::expand_stringify,
         trace_macros: trace_macros::expand_trace_macros,
     }

compiler/rustc_span/src/symbol.rs

@@ -1437,7 +1437,12 @@ symbols! {
         unmarked_api,
         unpin,
         unreachable,
+        unreachable_2015,
+        unreachable_2015_macro,
+        unreachable_2021,
+        unreachable_2021_macro,
         unreachable_code,
+        unreachable_display,
         unreachable_macro,
         unrestricted_attribute_tokens,
         unsafe_block_in_unsafe_fn,

library/core/src/macros/mod.rs

@@ -594,6 +594,22 @@ macro_rules! writeln {
 ///     unreachable!("The loop should always return");
 /// }
 /// ```
+#[cfg(not(bootstrap))]
+#[macro_export]
+#[rustc_builtin_macro(unreachable)]
+#[allow_internal_unstable(edition_panic)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "unreachable_macro")]
+macro_rules! unreachable {
+    // Expands to either `$crate::panic::unreachable_2015` or `$crate::panic::unreachable_2021`
+    // depending on the edition of the caller.
+    ($($arg:tt)*) => {
+        /* compiler built-in */
+    };
+}
+
+/// unreachable!() macro
+#[cfg(bootstrap)]
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "unreachable_macro")]

library/core/src/panic.rs

@@ -58,6 +58,39 @@ pub macro panic_2021 {
     ),
 }
 
+#[doc(hidden)]
+#[unstable(feature = "edition_panic", issue = "none", reason = "use unreachable!() instead")]
+#[allow_internal_unstable(core_panic)]
+#[rustc_diagnostic_item = "unreachable_2015_macro"]
+#[rustc_macro_transparency = "semitransparent"]
+pub macro unreachable_2015 {
+    () => (
+        $crate::panicking::panic("internal error: entered unreachable code")
+    ),
+    // Use of `unreachable_display` for non_fmt_panic lint.
+    // NOTE: the message ("internal error ...") is embeded directly in unreachable_display
+    ($msg:expr $(,)?) => (
+        $crate::panicking::unreachable_display(&$msg)
+    ),
+    ($fmt:expr, $($arg:tt)*) => (
+        $crate::panic!($crate::concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
+    ),
+}
+
+#[doc(hidden)]
+#[unstable(feature = "edition_panic", issue = "none", reason = "use unreachable!() instead")]
+#[allow_internal_unstable(core_panic)]
+#[rustc_diagnostic_item = "unreachable_2021_macro"]
+#[rustc_macro_transparency = "semitransparent"]
+pub macro unreachable_2021 {
+    () => (
+        $crate::panicking::panic("internal error: entered unreachable code")
+    ),
+    ($($t:tt)+) => (
+        $crate::panic!("internal error: entered unreachable code: {}", $crate::format_args!($($t)+))
+    ),
+}
+
 /// An internal trait used by libstd to pass data from libstd to `panic_unwind`
 /// and other panic runtimes. Not intended to be stabilized any time soon, do
 /// not use.

library/core/src/panicking.rs

@@ -56,6 +56,14 @@ pub const fn panic_str(expr: &str) -> ! {
     panic_display(&expr);
 }
 
+#[cfg(not(bootstrap))]
+#[inline]
+#[track_caller]
+#[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
+pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
+    panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
+}
+
 #[inline]
 #[track_caller]
 #[lang = "panic_display"] // needed for const-evaluated panics

src/test/mir-opt/issue_76432.test.SimplifyComparisonIntegral.diff

@@ -21,7 +21,7 @@
       let mut _19: *const T;               // in scope 0 at $DIR/issue_76432.rs:9:54: 9:68
       let mut _20: *const T;               // in scope 0 at $DIR/issue_76432.rs:9:70: 9:84
       let mut _21: *const T;               // in scope 0 at $DIR/issue_76432.rs:9:70: 9:84
-      let mut _22: !;                      // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+      let mut _22: !;                      // in scope 0 at $SRC_DIR/core/src/panic.rs:LL:COL
       let mut _23: &[T; 3];                // in scope 0 at $DIR/issue_76432.rs:7:19: 7:29
       scope 1 {
           debug v => _2;                   // in scope 1 at $DIR/issue_76432.rs:7:9: 7:10
@@ -66,16 +66,16 @@
       }
   
       bb1: {
-          StorageLive(_22);                // scope 1 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-          core::panicking::panic(const "internal error: entered unreachable code"); // scope 1 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+          StorageLive(_22);                // scope 1 at $SRC_DIR/core/src/panic.rs:LL:COL
+          core::panicking::panic(const "internal error: entered unreachable code"); // scope 1 at $SRC_DIR/core/src/panic.rs:LL:COL
                                            // mir::Constant
-                                           // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                                           // + span: $SRC_DIR/core/src/panic.rs:LL:COL
                                            // + literal: Const { ty: fn(&'static str) -> ! {core::panicking::panic}, val: Value(Scalar(<ZST>)) }
                                            // ty::Const
                                            // + ty: &str
                                            // + val: Value(Slice { data: Allocation { bytes: [105, 110, 116, 101, 114, 110, 97, 108, 32, 101, 114, 114, 111, 114, 58, 32, 101, 110, 116, 101, 114, 101, 100, 32, 117, 110, 114, 101, 97, 99, 104, 97, 98, 108, 101, 32, 99, 111, 100, 101], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1099511627775], len: Size { raw: 40 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 40 })
                                            // mir::Constant
-                                           // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                                           // + span: $SRC_DIR/core/src/panic.rs:LL:COL
                                            // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [105, 110, 116, 101, 114, 110, 97, 108, 32, 101, 114, 114, 111, 114, 58, 32, 101, 110, 116, 101, 114, 101, 100, 32, 117, 110, 114, 101, 97, 99, 104, 97, 98, 108, 101, 32, 99, 111, 100, 101], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1099511627775], len: Size { raw: 40 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 40 }) }
       }
   

src/test/ui/consts/const-eval/const_panic.stderr

@@ -20,7 +20,7 @@ error[E0080]: evaluation of constant value failed
 LL | const Y: () = std::unreachable!();
    |               ^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:12:15
    |
-   = note: this error originates in the macro `std::unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::panic::unreachable_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:15:15
@@ -68,7 +68,7 @@ error[E0080]: evaluation of constant value failed
 LL | const Y_CORE: () = core::unreachable!();
    |                    ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:30:20
    |
-   = note: this error originates in the macro `core::unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::panic::unreachable_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic.rs:33:20

src/test/ui/consts/const-eval/const_panic_2021.stderr

@@ -20,7 +20,7 @@ error[E0080]: evaluation of constant value failed
 LL | const C: () = std::unreachable!();
    |               ^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_2021.rs:12:15
    |
-   = note: this error originates in the macro `std::unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::panic::unreachable_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic_2021.rs:15:15
@@ -60,7 +60,7 @@ error[E0080]: evaluation of constant value failed
 LL | const C_CORE: () = core::unreachable!();
    |                    ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_2021.rs:27:20
    |
-   = note: this error originates in the macro `core::unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::panic::unreachable_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic_2021.rs:30:20

src/test/ui/consts/const-eval/const_panic_libcore_bin.stderr

@@ -12,7 +12,7 @@ error[E0080]: evaluation of constant value failed
 LL | const Y: () = unreachable!();
    |               ^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_libcore_bin.rs:11:15
    |
-   = note: this error originates in the macro `unreachable` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::panic::unreachable_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/const_panic_libcore_bin.rs:14:15

src/test/ui/macros/unreachable-format-arg.rs

@@ -0,0 +1,13 @@
+// run-fail
+// ignore-emscripten no processes
+
+// revisions: edition_2015 edition_2021
+// [edition_2015]edition:2015
+// [edition_2021]edition:2021
+// [edition_2015]error-pattern:internal error: entered unreachable code: x is {x}
+// [edition_2021]error-pattern:internal error: entered unreachable code: x is 5
+
+fn main() {
+    let x = 5;
+    unreachable!("x is {x}");
+}

src/test/ui/macros/unreachable-format-args.edition_2015.stderr

@@ -0,0 +1,12 @@
+error: there is no argument named `x`
+  --> $DIR/unreachable-format-args.rs:13:5
+   |
+LL |     unreachable!("x is {x} and y is {y}", y = 0);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: did you intend to capture a variable `x` from the surrounding scope?
+   = note: to avoid ambiguity, `format_args!` cannot capture variables when the format string is expanded from a macro
+   = note: this error originates in the macro `$crate::concat` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+

src/test/ui/macros/unreachable-format-args.rs

@@ -0,0 +1,14 @@
+// ignore-emscripten no processes
+
+// revisions: edition_2015 edition_2021
+// [edition_2015]edition:2015
+// [edition_2021]edition:2021
+// [edition_2015]check-fail
+// [edition_2021]run-fail
+// [edition_2015]error-pattern:there is no argument named `x`
+// [edition_2021]error-pattern:internal error: entered unreachable code: x is 5 and y is 0
+
+fn main() {
+    let x = 5;
+    unreachable!("x is {x} and y is {y}", y = 0);
+}

src/test/ui/proc-macro/quote-debug.stdout

@@ -33,9 +33,7 @@ fn main() {
                                             lit.set_span(crate::Span::recover_proc_macro_span(2));
                                             lit
                                         } else {
-                                           {
-                                               ::core::panicking::panic("internal error: entered unreachable code")
-                                           }
+                                           ::core::panicking::panic("internal error: entered unreachable code")
                                        }
                                 })),
                         crate::TokenStream::from(crate::TokenTree::Punct(crate::Punct::new('\u{3b}',