1 //! Panic support for libcore
3 //! The core library cannot define panicking, but it does *declare* panicking. This
4 //! means that the functions inside of libcore are allowed to panic, but to be
5 //! useful an upstream crate must define panicking for libcore to use. The current
6 //! interface for panicking is:
9 //! fn panic_impl(pi: &core::panic::PanicInfo<'_>) -> !
13 //! This definition allows for panicking with any general message, but it does not
14 //! allow for failing with a `Box<Any>` value. (`PanicInfo` just contains a `&(dyn Any + Send)`,
15 //! for which we fill in a dummy value in `PanicInfo::internal_constructor`.)
16 //! The reason for this is that libcore is not allowed to allocate.
18 //! This module contains a few other panicking functions, but these are just the
19 //! necessary lang items for the compiler. All panics are funneled through this
20 //! one function. The actual symbol is declared through the `#[panic_handler]` attribute.
22 #![allow(dead_code, missing_docs)]
24 feature = "core_panic",
25 reason = "internal details of the implementation of the `panic!` and related macros",
30 use crate::panic::{Location, PanicInfo};
32 /// The underlying implementation of libcore's `panic!` macro when no formatting is used.
34 // never inline unless panic_immediate_abort to avoid code
35 // bloat at the call sites as much as possible
36 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
37 #[cfg_attr(feature = "panic_immediate_abort", inline)]
39 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
40 #[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
41 pub const fn panic(expr: &'static str) -> ! {
42 // Use Arguments::new_v1 instead of format_args!("{expr}") to potentially
43 // reduce size overhead. The format_args! macro uses str's Display trait to
44 // write expr, which calls Formatter::pad, which must accommodate string
45 // truncation and padding (even though none is used here). Using
46 // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
47 // output binary, saving up to a few kilobytes.
48 panic_fmt(fmt::Arguments::new_v1(&[expr], &[]));
53 #[rustc_diagnostic_item = "panic_str"]
54 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
55 pub const fn panic_str(expr: &str) -> ! {
61 #[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
62 pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
63 panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
68 #[lang = "panic_display"] // needed for const-evaluated panics
69 #[rustc_do_not_const_check] // hooked by const-eval
70 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
71 pub const fn panic_display<T: fmt::Display>(x: &T) -> ! {
72 panic_fmt(format_args!("{}", *x));
76 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
78 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
79 fn panic_bounds_check(index: usize, len: usize) -> ! {
80 if cfg!(feature = "panic_immediate_abort") {
81 super::intrinsics::abort()
84 panic!("index out of bounds: the len is {len} but the index is {index}")
87 // This function is called directly by the codegen backend, and must not have
88 // any extra arguments (including those synthesized by track_caller).
91 #[lang = "panic_no_unwind"] // needed by codegen for panic in nounwind function
92 fn panic_no_unwind() -> ! {
93 if cfg!(feature = "panic_immediate_abort") {
94 super::intrinsics::abort()
97 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
98 // that gets resolved to the `#[panic_handler]` function.
100 #[lang = "panic_impl"]
101 fn panic_impl(pi: &PanicInfo<'_>) -> !;
104 // PanicInfo with the `can_unwind` flag set to false forces an abort.
105 let fmt = format_args!("panic in a function that cannot unwind");
106 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
108 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
109 unsafe { panic_impl(&pi) }
112 /// The entry point for panicking with a formatted message.
114 /// This is designed to reduce the amount of code required at the call
115 /// site as much as possible (so that `panic!()` has as low an impact
116 /// on (e.g.) the inlining of other functions as possible), by moving
117 /// the actual formatting into this shared place.
119 // If panic_immediate_abort, inline the abort call,
120 // otherwise avoid inlining because of it is cold path.
121 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
122 #[cfg_attr(feature = "panic_immediate_abort", inline)]
124 #[lang = "panic_fmt"] // needed for const-evaluated panics
125 #[rustc_do_not_const_check] // hooked by const-eval
126 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
127 pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
128 if cfg!(feature = "panic_immediate_abort") {
129 super::intrinsics::abort()
132 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
133 // that gets resolved to the `#[panic_handler]` function.
135 #[lang = "panic_impl"]
136 fn panic_impl(pi: &PanicInfo<'_>) -> !;
139 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
141 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
142 unsafe { panic_impl(&pi) }
145 /// This function is used instead of panic_fmt in const eval.
146 #[lang = "const_panic_fmt"]
147 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
148 pub const fn const_panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
149 if let Some(msg) = fmt.as_str() {
152 // SAFETY: This is only evaluated at compile time, which reliably
153 // handles this UB (in case this branch turns out to be reachable
155 unsafe { crate::hint::unreachable_unchecked() };
161 pub enum AssertKind {
167 /// Internal function for `assert_eq!` and `assert_ne!` macros
171 pub fn assert_failed<T, U>(
175 args: Option<fmt::Arguments<'_>>,
178 T: fmt::Debug + ?Sized,
179 U: fmt::Debug + ?Sized,
181 assert_failed_inner(kind, &left, &right, args)
184 /// Internal function for `assert_match!`
188 pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
191 args: Option<fmt::Arguments<'_>>,
193 // Use the Display implementation to display the pattern.
194 struct Pattern<'a>(&'a str);
195 impl fmt::Debug for Pattern<'_> {
196 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
197 fmt::Display::fmt(self.0, f)
200 assert_failed_inner(AssertKind::Match, &left, &Pattern(right), args);
203 /// Non-generic version of the above functions, to avoid code bloat.
205 fn assert_failed_inner(
207 left: &dyn fmt::Debug,
208 right: &dyn fmt::Debug,
209 args: Option<fmt::Arguments<'_>>,
211 let op = match kind {
212 AssertKind::Eq => "==",
213 AssertKind::Ne => "!=",
214 AssertKind::Match => "matches",
218 Some(args) => panic!(
219 r#"assertion failed: `(left {} right)`
222 op, left, right, args
225 r#"assertion failed: `(left {} right)`