1 //! Panic support for core
3 //! The core library cannot define panicking, but it does *declare* panicking. This
4 //! means that the functions inside of core are allowed to panic, but to be
5 //! useful an upstream crate must define panicking for core 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 core 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 // First we define the two main entry points that all panics go through.
33 // In the end both are just convenience wrappers around `panic_impl`.
35 /// The entry point for panicking with a formatted message.
37 /// This is designed to reduce the amount of code required at the call
38 /// site as much as possible (so that `panic!()` has as low an impact
39 /// on (e.g.) the inlining of other functions as possible), by moving
40 /// the actual formatting into this shared place.
41 // If panic_immediate_abort, inline the abort call,
42 // otherwise avoid inlining because of it is cold path.
43 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
44 #[cfg_attr(feature = "panic_immediate_abort", inline)]
46 #[lang = "panic_fmt"] // needed for const-evaluated panics
47 #[rustc_do_not_const_check] // hooked by const-eval
48 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
49 pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
50 if cfg!(feature = "panic_immediate_abort") {
51 super::intrinsics::abort()
54 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
55 // that gets resolved to the `#[panic_handler]` function.
57 #[lang = "panic_impl"]
58 fn panic_impl(pi: &PanicInfo<'_>) -> !;
61 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
63 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
64 unsafe { panic_impl(&pi) }
67 /// Like `panic_fmt`, but for non-unwinding panics.
69 /// Has to be a separate function so that it can carry the `rustc_nounwind` attribute.
70 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
71 #[cfg_attr(feature = "panic_immediate_abort", inline)]
73 // This attribute has the key side-effect that if the panic handler ignores `can_unwind`
74 // and unwinds anyway, we will hit the "unwinding out of nounwind function" guard,
75 // which causes a "panic in a function that cannot unwind".
77 pub fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>) -> ! {
78 if cfg!(feature = "panic_immediate_abort") {
79 super::intrinsics::abort()
82 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
83 // that gets resolved to the `#[panic_handler]` function.
85 #[lang = "panic_impl"]
86 fn panic_impl(pi: &PanicInfo<'_>) -> !;
89 // PanicInfo with the `can_unwind` flag set to false forces an abort.
90 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
92 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
93 unsafe { panic_impl(&pi) }
96 // Next we define a bunch of higher-level wrappers that all bottom out in the two core functions
99 /// The underlying implementation of core's `panic!` macro when no formatting is used.
100 // never inline unless panic_immediate_abort to avoid code
101 // bloat at the call sites as much as possible
102 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
103 #[cfg_attr(feature = "panic_immediate_abort", inline)]
105 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
106 #[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
107 pub const fn panic(expr: &'static str) -> ! {
108 // Use Arguments::new_v1 instead of format_args!("{expr}") to potentially
109 // reduce size overhead. The format_args! macro uses str's Display trait to
110 // write expr, which calls Formatter::pad, which must accommodate string
111 // truncation and padding (even though none is used here). Using
112 // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
113 // output binary, saving up to a few kilobytes.
114 panic_fmt(fmt::Arguments::new_v1(&[expr], &[]));
117 /// Like `panic`, but without unwinding and track_caller to reduce the impact on codesize.
118 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
119 #[cfg_attr(feature = "panic_immediate_abort", inline)]
120 #[lang = "panic_nounwind"] // needed by codegen for non-unwinding panics
122 pub fn panic_nounwind(expr: &'static str) -> ! {
123 panic_nounwind_fmt(fmt::Arguments::new_v1(&[expr], &[]));
128 #[rustc_diagnostic_item = "panic_str"]
129 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
130 pub const fn panic_str(expr: &str) -> ! {
131 panic_display(&expr);
136 #[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
137 pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
138 panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
143 #[lang = "panic_display"] // needed for const-evaluated panics
144 #[rustc_do_not_const_check] // hooked by const-eval
145 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
146 pub const fn panic_display<T: fmt::Display>(x: &T) -> ! {
147 panic_fmt(format_args!("{}", *x));
150 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
151 #[cfg_attr(feature = "panic_immediate_abort", inline)]
153 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
154 fn panic_bounds_check(index: usize, len: usize) -> ! {
155 if cfg!(feature = "panic_immediate_abort") {
156 super::intrinsics::abort()
159 panic!("index out of bounds: the len is {len} but the index is {index}")
162 /// Panic because we cannot unwind out of a function.
164 /// This function is called directly by the codegen backend, and must not have
165 /// any extra arguments (including those synthesized by track_caller).
166 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
167 #[cfg_attr(feature = "panic_immediate_abort", inline)]
168 #[lang = "panic_cannot_unwind"] // needed by codegen for panic in nounwind function
170 fn panic_cannot_unwind() -> ! {
171 panic_nounwind("panic in a function that cannot unwind")
174 /// This function is used instead of panic_fmt in const eval.
175 #[lang = "const_panic_fmt"]
176 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
177 pub const fn const_panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
178 if let Some(msg) = fmt.as_str() {
181 // SAFETY: This is only evaluated at compile time, which reliably
182 // handles this UB (in case this branch turns out to be reachable
184 unsafe { crate::hint::unreachable_unchecked() };
190 pub enum AssertKind {
196 /// Internal function for `assert_eq!` and `assert_ne!` macros
197 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
198 #[cfg_attr(feature = "panic_immediate_abort", inline)]
201 pub fn assert_failed<T, U>(
205 args: Option<fmt::Arguments<'_>>,
208 T: fmt::Debug + ?Sized,
209 U: fmt::Debug + ?Sized,
211 assert_failed_inner(kind, &left, &right, args)
214 /// Internal function for `assert_match!`
215 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
216 #[cfg_attr(feature = "panic_immediate_abort", inline)]
219 pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
222 args: Option<fmt::Arguments<'_>>,
224 // The pattern is a string so it can be displayed directly.
225 struct Pattern<'a>(&'a str);
226 impl fmt::Debug for Pattern<'_> {
227 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
231 assert_failed_inner(AssertKind::Match, &left, &Pattern(right), args);
234 /// Non-generic version of the above functions, to avoid code bloat.
235 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
236 #[cfg_attr(feature = "panic_immediate_abort", inline)]
238 fn assert_failed_inner(
240 left: &dyn fmt::Debug,
241 right: &dyn fmt::Debug,
242 args: Option<fmt::Arguments<'_>>,
244 let op = match kind {
245 AssertKind::Eq => "==",
246 AssertKind::Ne => "!=",
247 AssertKind::Match => "matches",
251 Some(args) => panic!(
252 r#"assertion failed: `(left {} right)`
255 op, left, right, args
258 r#"assertion failed: `(left {} right)`