Revert "Partially outline code inside the panic! macro".

Without any tests/benchmarks that show some improvement, it's hard to
know whether the change had any positive effect at all. (And if it did,
whether that effect is still achieved today.)

Author: m-ou-se

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -827,7 +827,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
                 // At this point, we are calling a function, `callee`, whose `DefId` is known...
 
-                // `begin_panic` and `#[rustc_const_panic_str]` functions accept generic
+                // `begin_panic` and `panic_display` functions accept generic
                 // types other than str. Check to enforce that only str can be used in
                 // const-eval.
 
@@ -841,8 +841,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     return;
                 }
 
-                // const-eval of `#[rustc_const_panic_str]` functions assumes the argument is `&&str`
-                if tcx.has_attr(callee, sym::rustc_const_panic_str) {
+                // const-eval of `panic_display` assumes the argument is `&&str`
+                if tcx.is_lang_item(callee, LangItem::PanicDisplay) {
                     match args[0].node.ty(&self.ccx.body.local_decls, tcx).kind() {
                         ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) =>
                             {}

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -237,7 +237,7 @@ impl<'tcx> CompileTimeInterpCx<'tcx> {
     ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
         let def_id = instance.def_id();
 
-        if self.tcx.has_attr(def_id, sym::rustc_const_panic_str)
+        if self.tcx.is_lang_item(def_id, LangItem::PanicDisplay)
             || self.tcx.is_lang_item(def_id, LangItem::BeginPanic)
         {
             let args = self.copy_fn_args(args);

compiler/rustc_feature/src/builtin_attrs.rs

@@ -929,10 +929,6 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_do_not_const_check, Normal, template!(Word), WarnFollowing,
         EncodeCrossCrate::Yes, "`#[rustc_do_not_const_check]` skips const-check for this function's body",
     ),
-    rustc_attr!(
-        rustc_const_panic_str, Normal, template!(Word), WarnFollowing,
-        EncodeCrossCrate::Yes, "`#[rustc_const_panic_str]` ensures the argument to this function is &&str during const-check",
-    ),
     rustc_attr!(
         rustc_const_stable_indirect, Normal,
         template!(Word),

compiler/rustc_hir/src/lang_items.rs

@@ -286,6 +286,7 @@ language_item_table! {
     Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::Exact(0);
     PanicNounwind,           sym::panic_nounwind,      panic_nounwind,             Target::Fn,             GenericRequirement::Exact(0);
     PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
+    PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
     ConstPanicFmt,           sym::const_panic_fmt,     const_panic_fmt,            Target::Fn,             GenericRequirement::None;
     PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::Exact(0);
     PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);

compiler/rustc_span/src/symbol.rs

@@ -1583,6 +1583,7 @@ symbols! {
         panic_const_shl_overflow,
         panic_const_shr_overflow,
         panic_const_sub_overflow,
+        panic_display,
         panic_fmt,
         panic_handler,
         panic_impl,
@@ -1828,7 +1829,6 @@ symbols! {
         rustc_coherence_is_core,
         rustc_coinductive,
         rustc_confusables,
-        rustc_const_panic_str,
         rustc_const_stable,
         rustc_const_stable_indirect,
         rustc_const_unstable,

library/core/src/panic.rs

@@ -48,7 +48,6 @@ pub macro panic_2015 {
 #[allow_internal_unstable(panic_internals, const_format_args)]
 #[rustc_diagnostic_item = "core_panic_2021_macro"]
 #[rustc_macro_transparency = "semitransparent"]
-#[cfg(feature = "panic_immediate_abort")]
 pub macro panic_2021 {
     () => (
         $crate::panicking::panic("explicit panic")
@@ -64,50 +63,6 @@ pub macro panic_2021 {
     }),
 }
 
-#[doc(hidden)]
-#[unstable(feature = "edition_panic", issue = "none", reason = "use panic!() instead")]
-#[allow_internal_unstable(
-    panic_internals,
-    core_intrinsics,
-    const_dispatch,
-    const_eval_select,
-    const_format_args,
-    rustc_attrs
-)]
-#[rustc_diagnostic_item = "core_panic_2021_macro"]
-#[rustc_macro_transparency = "semitransparent"]
-#[cfg(not(feature = "panic_immediate_abort"))]
-pub macro panic_2021 {
-    () => ({
-        // Create a function so that the argument for `track_caller`
-        // can be moved inside if possible.
-        #[cold]
-        #[track_caller]
-        #[inline(never)]
-        const fn panic_cold_explicit() -> ! {
-            $crate::panicking::panic_explicit()
-        }
-        panic_cold_explicit();
-    }),
-    // Special-case the single-argument case for const_panic.
-    ("{}", $arg:expr $(,)?) => ({
-        #[cold]
-        #[track_caller]
-        #[inline(never)]
-        #[rustc_const_panic_str] // enforce a &&str argument in const-check and hook this by const-eval
-        #[rustc_do_not_const_check] // hooked by const-eval
-        const fn panic_cold_display<T: $crate::fmt::Display>(arg: &T) -> ! {
-            $crate::panicking::panic_display(arg)
-        }
-        panic_cold_display(&$arg);
-    }),
-    ($($t:tt)+) => ({
-        // Semicolon to prevent temporaries inside the formatting machinery from
-        // being considered alive in the caller after the panic_fmt call.
-        $crate::panicking::panic_fmt($crate::const_format_args!($($t)+));
-    }),
-}
-
 #[doc(hidden)]
 #[unstable(feature = "edition_panic", issue = "none", reason = "use unreachable!() instead")]
 #[allow_internal_unstable(panic_internals)]

library/core/src/panicking.rs

@@ -233,14 +233,6 @@ pub fn panic_nounwind_nobacktrace(expr: &'static str) -> ! {
     panic_nounwind_fmt(fmt::Arguments::new_const(&[expr]), /* force_no_backtrace */ true);
 }
 
-#[track_caller]
-#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
-#[cfg_attr(feature = "panic_immediate_abort", inline)]
-#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
-pub const fn panic_explicit() -> ! {
-    panic_display(&"explicit panic");
-}
-
 #[inline]
 #[track_caller]
 #[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
@@ -260,9 +252,8 @@ pub const fn panic_str_2015(expr: &str) -> ! {
 
 #[inline]
 #[track_caller]
+#[lang = "panic_display"] // needed for const-evaluated panics
 #[rustc_do_not_const_check] // hooked by const-eval
-// enforce a &&str argument in const-check and hook this by const-eval
-#[rustc_const_panic_str]
 #[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
 pub const fn panic_display<T: fmt::Display>(x: &T) -> ! {
     panic_fmt(format_args!("{}", *x));

src/tools/clippy/clippy_utils/src/macros.rs

@@ -250,18 +250,13 @@ impl<'a> PanicExpn<'a> {
         };
         let name = path.segments.last().unwrap().ident.name;
 
-        // This has no argument
-        if name == sym::panic_cold_explicit {
-            return Some(Self::Empty);
-        }
-
         let [arg, rest @ ..] = args else {
             return None;
         };
         let result = match name {
             sym::panic if arg.span.eq_ctxt(expr.span) => Self::Empty,
             sym::panic | sym::panic_str => Self::Str(arg),
-            sym::panic_display | sym::panic_cold_display => {
+            sym::panic_display => {
                 let ExprKind::AddrOf(_, _, e) = &arg.kind else {
                     return None;
                 };

src/tools/clippy/clippy_utils/src/sym.rs

@@ -241,9 +241,6 @@ generate! {
     or_insert,
     or_insert_with,
     outer_expn,
-    panic_cold_display,
-    panic_cold_explicit,
-    panic_display,
     panic_str,
     parse,
     partition,