Rollup merge of #88954 - nbdd0121:panic3, r=oli-obk

Allow `panic!("{}", computed_str)` in const fn.

Special-case `panic!("{}", arg)` and translate it to `panic_display(&arg)`. `panic_display` will behave like `panic_any` in cosnt eval and behave like `panic!(format_args!("{}", arg))` in runtime.

This should bring Rust 2015 and 2021 to feature parity in terms of `const_panic`; and hopefully would unblock the stabilisation of #51999.

`@rustbot` modify labels: +T-compiler +T-libs +A-const-eval +A-const-fn

r? `@oli-obk`

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -36,12 +36,17 @@ fn hook_panic_fn(
         let def_id = instance.def_id();
         if Some(def_id) == self.tcx.lang_items().panic_fn()
             || Some(def_id) == self.tcx.lang_items().panic_str()
+            || Some(def_id) == self.tcx.lang_items().panic_display()
             || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
         {
-            // &str
+            // &str or &&str
             assert!(args.len() == 1);
 
-            let msg_place = self.deref_operand(&args[0])?;
+            let mut msg_place = self.deref_operand(&args[0])?;
+            while msg_place.layout.ty.is_ref() {
+                msg_place = self.deref_operand(&msg_place.into())?;
+            }
+
             let msg = Symbol::intern(self.read_str(&msg_place)?);
             let span = self.find_closest_untracked_caller_location();
             let (file, line, col) = self.location_triple_for_span(span);

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -888,6 +888,10 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location
                 if is_lang_panic_fn(tcx, callee) {
                     self.check_op(ops::Panic);
 
+                    // `begin_panic` and `panic_display` are generic functions that accept
+                    // types other than str. Check to enforce that only str can be used in
+                    // const-eval.
+
                     // const-eval of the `begin_panic` fn assumes the argument is `&str`
                     if Some(callee) == tcx.lang_items().begin_panic_fn() {
                         match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
@@ -896,6 +900,15 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location
                         }
                     }
 
+                    // const-eval of the `panic_display` fn assumes the argument is `&&str`
+                    if Some(callee) == tcx.lang_items().panic_display() {
+                        match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
+                            ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) =>
+                                {}
+                            _ => self.check_op(ops::PanicNonStr),
+                        }
+                    }
+
                     return;
                 }
 

compiler/rustc_const_eval/src/transform/check_consts/mod.rs

@@ -79,6 +79,7 @@ pub fn is_lang_panic_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
     // Keep in sync with what that function handles!
     Some(def_id) == tcx.lang_items().panic_fn()
         || Some(def_id) == tcx.lang_items().panic_str()
+        || Some(def_id) == tcx.lang_items().panic_display()
         || Some(def_id) == tcx.lang_items().begin_panic_fn()
         || Some(def_id) == tcx.lang_items().panic_fmt()
         || Some(def_id) == tcx.lang_items().begin_panic_fmt()

compiler/rustc_hir/src/lang_items.rs

@@ -283,6 +283,7 @@ pub fn extract<'a, F>(check_name: F, attrs: &'a [ast::Attribute]) -> Option<(Sym
     // a weak lang item, but do not have it defined.
     Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::None;
     PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
+    PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
     PanicStr,                sym::panic_str,           panic_str,                  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::None;

compiler/rustc_span/src/symbol.rs

@@ -923,6 +923,7 @@
         panic_2021,
         panic_abort,
         panic_bounds_check,
+        panic_display,
         panic_fmt,
         panic_handler,
         panic_impl,

library/core/src/panic.rs

@@ -27,9 +27,14 @@
     ($msg:literal $(,)?) => (
         $crate::panicking::panic($msg)
     ),
+    // Use `panic_str` instead of `panic_display::<&str>` for non_fmt_panic lint.
     ($msg:expr $(,)?) => (
         $crate::panicking::panic_str($msg)
     ),
+    // Special-case the single-argument case for const_panic.
+    ("{}", $arg:expr $(,)?) => (
+        $crate::panicking::panic_display(&$arg)
+    ),
     ($fmt:expr, $($arg:tt)+) => (
         $crate::panicking::panic_fmt($crate::const_format_args!($fmt, $($arg)+))
     ),
@@ -44,6 +49,10 @@
     () => (
         $crate::panicking::panic("explicit panic")
     ),
+    // Special-case the single-argument case for const_panic.
+    ("{}", $arg:expr $(,)?) => (
+        $crate::panicking::panic_display(&$arg)
+    ),
     ($($t:tt)+) => (
         $crate::panicking::panic_fmt($crate::const_format_args!($($t)+))
     ),

library/core/src/panicking.rs

@@ -60,6 +60,13 @@ pub fn panic_str(expr: &str) -> ! {
     panic_fmt(format_args!("{}", expr));
 }
 
+#[inline]
+#[track_caller]
+#[cfg_attr(not(bootstrap), lang = "panic_display")] // needed for const-evaluated panics
+pub fn panic_display<T: fmt::Display>(x: &T) -> ! {
+    panic_fmt(format_args!("{}", *x));
+}
+
 #[cold]
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
 #[track_caller]

library/std/src/lib.rs

@@ -258,6 +258,7 @@
 #![feature(const_trait_impl)]
 #![feature(container_error_extra)]
 #![feature(core_intrinsics)]
+#![feature(core_panic)]
 #![feature(custom_test_frameworks)]
 #![feature(decl_macro)]
 #![feature(doc_cfg)]

library/std/src/panic.rs

@@ -10,7 +10,7 @@
 
 #[doc(hidden)]
 #[unstable(feature = "edition_panic", issue = "none", reason = "use panic!() instead")]
-#[allow_internal_unstable(libstd_sys_internals, const_format_args)]
+#[allow_internal_unstable(libstd_sys_internals, const_format_args, core_panic)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "std_panic_2015_macro")]
 #[rustc_macro_transparency = "semitransparent"]
 pub macro panic_2015 {
@@ -20,6 +20,10 @@
     ($msg:expr $(,)?) => ({
         $crate::rt::begin_panic($msg)
     }),
+    // Special-case the single-argument case for const_panic.
+    ("{}", $arg:expr $(,)?) => ({
+        $crate::rt::panic_display(&$arg)
+    }),
     ($fmt:expr, $($arg:tt)+) => ({
         $crate::rt::begin_panic_fmt(&$crate::const_format_args!($fmt, $($arg)+))
     }),

library/std/src/rt.rs

@@ -16,6 +16,7 @@
 
 // Re-export some of our utilities which are expected by other crates.
 pub use crate::panicking::{begin_panic, begin_panic_fmt, panic_count};
+pub use core::panicking::panic_display;
 
 // To reduce the generated code of the new `lang_start`, this function is doing
 // the real work.

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

@@ -15,10 +15,13 @@
 
 const X: () = std::unimplemented!();
 //~^ ERROR evaluation of constant value failed
-//
+
 const W: () = std::panic!(MSG);
 //~^ ERROR evaluation of constant value failed
 
+const W2: () = std::panic!("{}", MSG);
+//~^ ERROR evaluation of constant value failed
+
 const Z_CORE: () = core::panic!("cheese");
 //~^ ERROR evaluation of constant value failed
 
@@ -33,3 +36,6 @@
 
 const W_CORE: () = core::panic!(MSG);
 //~^ ERROR evaluation of constant value failed
+
+const W2_CORE: () = core::panic!("{}", MSG);
+//~^ ERROR evaluation of constant value failed

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

@@ -39,45 +39,61 @@ LL | const W: () = std::panic!(MSG);
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic.rs:22:20
+  --> $DIR/const_panic.rs:22:16
+   |
+LL | const W2: () = std::panic!("{}", MSG);
+   |                ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic.rs:22:16
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const_panic.rs:25:20
    |
 LL | const Z_CORE: () = core::panic!("cheese");
-   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'cheese', $DIR/const_panic.rs:22:20
+   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'cheese', $DIR/const_panic.rs:25:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic.rs:25:21
+  --> $DIR/const_panic.rs:28:21
    |
 LL | const Z2_CORE: () = core::panic!();
-   |                     ^^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:25:21
+   |                     ^^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:28:21
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic.rs:28:20
+  --> $DIR/const_panic.rs:31:20
    |
 LL | const Y_CORE: () = core::unreachable!();
-   |                    ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:28:20
+   |                    ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:31:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic.rs:31:20
+  --> $DIR/const_panic.rs:34:20
    |
 LL | const X_CORE: () = core::unimplemented!();
-   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:31:20
+   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:34:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic.rs:34:20
+  --> $DIR/const_panic.rs:37:20
    |
 LL | const W_CORE: () = core::panic!(MSG);
-   |                    ^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic.rs:34:20
+   |                    ^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic.rs:37:20
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const_panic.rs:40:21
+   |
+LL | const W2_CORE: () = core::panic!("{}", MSG);
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic.rs:40:21
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 10 previous errors
+error: aborting due to 12 previous errors
 
 For more information about this error, try `rustc --explain E0080`.

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

@@ -2,6 +2,8 @@
 #![feature(const_panic)]
 #![crate_type = "lib"]
 
+const MSG: &str = "hello";
+
 const A: () = std::panic!("blåhaj");
 //~^ ERROR evaluation of constant value failed
 
@@ -14,14 +16,20 @@
 const D: () = std::unimplemented!();
 //~^ ERROR evaluation of constant value failed
 
-const E: () = core::panic!("shark");
+const E: () = std::panic!("{}", MSG);
+//~^ ERROR evaluation of constant value failed
+
+const A_CORE: () = core::panic!("shark");
+//~^ ERROR evaluation of constant value failed
+
+const B_CORE: () = core::panic!();
 //~^ ERROR evaluation of constant value failed
 
-const F: () = core::panic!();
+const C_CORE: () = core::unreachable!();
 //~^ ERROR evaluation of constant value failed
 
-const G: () = core::unreachable!();
+const D_CORE: () = core::unimplemented!();
 //~^ ERROR evaluation of constant value failed
 
-const H: () = core::unimplemented!();
+const E_CORE: () = core::panic!("{}", MSG);
 //~^ ERROR evaluation of constant value failed

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

 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:5:15
+  --> $DIR/const_panic_2021.rs:7:15
    |
 LL | const A: () = std::panic!("blåhaj");
-   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'blåhaj', $DIR/const_panic_2021.rs:5:15
+   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'blåhaj', $DIR/const_panic_2021.rs:7:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:8:15
+  --> $DIR/const_panic_2021.rs:10:15
    |
 LL | const B: () = std::panic!();
-   |               ^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic_2021.rs:8:15
+   |               ^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic_2021.rs:10:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:11:15
+  --> $DIR/const_panic_2021.rs:13:15
    |
 LL | const C: () = std::unreachable!();
-   |               ^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_2021.rs:11:15
+   |               ^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_2021.rs:13:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:14:15
+  --> $DIR/const_panic_2021.rs:16:15
    |
 LL | const D: () = std::unimplemented!();
-   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic_2021.rs:14:15
+   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic_2021.rs:16:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:17:15
+  --> $DIR/const_panic_2021.rs:19:15
    |
-LL | const E: () = core::panic!("shark");
-   |               ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'shark', $DIR/const_panic_2021.rs:17:15
+LL | const E: () = std::panic!("{}", MSG);
+   |               ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic_2021.rs:19:15
    |
    = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:20:15
+  --> $DIR/const_panic_2021.rs:22:20
    |
-LL | const F: () = core::panic!();
-   |               ^^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic_2021.rs:20:15
+LL | const A_CORE: () = core::panic!("shark");
+   |                    ^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'shark', $DIR/const_panic_2021.rs:22:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:23:15
+  --> $DIR/const_panic_2021.rs:25:20
    |
-LL | const G: () = core::unreachable!();
-   |               ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_2021.rs:23:15
+LL | const B_CORE: () = core::panic!();
+   |                    ^^^^^^^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/const_panic_2021.rs:25:20
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const_panic_2021.rs:28:20
+   |
+LL | const C_CORE: () = core::unreachable!();
+   |                    ^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_2021.rs:28:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_panic_2021.rs:26:15
+  --> $DIR/const_panic_2021.rs:31:20
    |
-LL | const H: () = core::unimplemented!();
-   |               ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic_2021.rs:26:15
+LL | const D_CORE: () = core::unimplemented!();
+   |                    ^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'not implemented', $DIR/const_panic_2021.rs:31:20
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 8 previous errors
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const_panic_2021.rs:34:20
+   |
+LL | const E_CORE: () = core::panic!("{}", MSG);
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'hello', $DIR/const_panic_2021.rs:34:20
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0080`.