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 // 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.
42 // If panic_immediate_abort, inline the abort call,
43 // otherwise avoid inlining because of it is cold path.
44 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
45 #[cfg_attr(feature = "panic_immediate_abort", inline)]
47 #[lang = "panic_fmt"] // needed for const-evaluated panics
48 #[rustc_do_not_const_check] // hooked by const-eval
49 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
50 pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
51 if cfg!(feature = "panic_immediate_abort") {
52 super::intrinsics::abort()
55 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
56 // that gets resolved to the `#[panic_handler]` function.
58 #[lang = "panic_impl"]
59 fn panic_impl(pi: &PanicInfo<'_>) -> !;
62 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
64 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
65 unsafe { panic_impl(&pi) }
68 /// Like panic_fmt, but without unwinding and track_caller to reduce the impact on codesize.
69 /// Also just works on `str`, as a `fmt::Arguments` needs more space to be passed.
71 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
72 #[cfg_attr(feature = "panic_immediate_abort", inline)]
74 pub fn panic_str_nounwind(msg: &'static str) -> ! {
75 if cfg!(feature = "panic_immediate_abort") {
76 super::intrinsics::abort()
79 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
80 // that gets resolved to the `#[panic_handler]` function.
82 #[lang = "panic_impl"]
83 fn panic_impl(pi: &PanicInfo<'_>) -> !;
86 // PanicInfo with the `can_unwind` flag set to false forces an abort.
88 let fmt = fmt::Arguments::new_v1(&pieces, &[]);
89 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
91 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
92 unsafe { panic_impl(&pi) }
95 // Next we define a bunch of higher-level wrappers that all bottom out in the two core functions
98 /// The underlying implementation of libcore'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))]
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], &[]));
119 #[rustc_diagnostic_item = "panic_str"]
120 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
121 pub const fn panic_str(expr: &str) -> ! {
122 panic_display(&expr);
127 #[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
128 pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
129 panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
134 #[lang = "panic_display"] // needed for const-evaluated panics
135 #[rustc_do_not_const_check] // hooked by const-eval
136 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
137 pub const fn panic_display<T: fmt::Display>(x: &T) -> ! {
138 panic_fmt(format_args!("{}", *x));
142 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
144 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
145 fn panic_bounds_check(index: usize, len: usize) -> ! {
146 if cfg!(feature = "panic_immediate_abort") {
147 super::intrinsics::abort()
150 panic!("index out of bounds: the len is {len} but the index is {index}")
153 /// Panic because we cannot unwind out of a function.
155 /// This function is called directly by the codegen backend, and must not have
156 /// any extra arguments (including those synthesized by track_caller).
159 #[lang = "panic_no_unwind"] // needed by codegen for panic in nounwind function
161 fn panic_no_unwind() -> ! {
162 panic_str_nounwind("panic in a function that cannot unwind")
165 /// This function is used instead of panic_fmt in const eval.
166 #[lang = "const_panic_fmt"]
167 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
168 pub const fn const_panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
169 if let Some(msg) = fmt.as_str() {
172 // SAFETY: This is only evaluated at compile time, which reliably
173 // handles this UB (in case this branch turns out to be reachable
175 unsafe { crate::hint::unreachable_unchecked() };
181 pub enum AssertKind {
187 /// Internal function for `assert_eq!` and `assert_ne!` macros
191 pub fn assert_failed<T, U>(
195 args: Option<fmt::Arguments<'_>>,
198 T: fmt::Debug + ?Sized,
199 U: fmt::Debug + ?Sized,
201 assert_failed_inner(kind, &left, &right, args)
204 /// Internal function for `assert_match!`
208 pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
211 args: Option<fmt::Arguments<'_>>,
213 // The pattern is a string so it can be displayed directly.
214 struct Pattern<'a>(&'a str);
215 impl fmt::Debug for Pattern<'_> {
216 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
220 assert_failed_inner(AssertKind::Match, &left, &Pattern(right), args);
223 /// Non-generic version of the above functions, to avoid code bloat.
225 fn assert_failed_inner(
227 left: &dyn fmt::Debug,
228 right: &dyn fmt::Debug,
229 args: Option<fmt::Arguments<'_>>,
231 let op = match kind {
232 AssertKind::Eq => "==",
233 AssertKind::Ne => "!=",
234 AssertKind::Match => "matches",
238 Some(args) => panic!(
239 r#"assertion failed: `(left {} right)`
242 op, left, right, args
245 r#"assertion failed: `(left {} right)`