library/core/src/panicking.rs

   1 //! Panic support for libcore
   2 //!
   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:
   7 //!
   8 //! ```
   9 //! fn panic_impl(pi: &core::panic::PanicInfo<'_>) -> !
  10 //! # { loop {} }
  11 //! ```
  12 //!
  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.
  17 //!
  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.
  21
  22 #![allow(dead_code, missing_docs)]
  23 #![unstable(
  24     feature = "core_panic",
  25     reason = "internal details of the implementation of the `panic!` and related macros",
  26     issue = "none"
  27 )]
  28
  29 use crate::fmt;
  30 use crate::panic::{Location, PanicInfo};
  31
  32 /// The underlying implementation of libcore's `panic!` macro when no formatting is used.
  33 #[cold]
  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 #[track_caller]
  38 #[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
  39 pub fn panic(expr: &'static str) -> ! {
  40     if cfg!(feature = "panic_immediate_abort") {
  41         super::intrinsics::abort()
  42     }
  43
  44     // Use Arguments::new_v1 instead of format_args!("{}", expr) to potentially
  45     // reduce size overhead. The format_args! macro uses str's Display trait to
  46     // write expr, which calls Formatter::pad, which must accommodate string
  47     // truncation and padding (even though none is used here). Using
  48     // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
  49     // output binary, saving up to a few kilobytes.
  50     panic_fmt(
  51         #[cfg(bootstrap)]
  52         fmt::Arguments::new_v1(&[expr], &[]),
  53         #[cfg(not(bootstrap))]
  54         // SAFETY: Arguments::new_v1 is safe with exactly one str and zero args
  55         unsafe {
  56             fmt::Arguments::new_v1(&[expr], &[])
  57         },
  58     );
  59 }
  60
  61 #[inline]
  62 #[track_caller]
  63 #[lang = "panic_str"] // needed for const-evaluated panics
  64 pub fn panic_str(expr: &str) -> ! {
  65     panic_fmt(format_args!("{}", expr));
  66 }
  67
  68 #[cold]
  69 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
  70 #[track_caller]
  71 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
  72 fn panic_bounds_check(index: usize, len: usize) -> ! {
  73     if cfg!(feature = "panic_immediate_abort") {
  74         super::intrinsics::abort()
  75     }
  76
  77     panic!("index out of bounds: the len is {} but the index is {}", len, index)
  78 }
  79
  80 /// The underlying implementation of libcore's `panic!` macro when formatting is used.
  81 #[cold]
  82 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
  83 #[cfg_attr(feature = "panic_immediate_abort", inline)]
  84 #[track_caller]
  85 #[cfg_attr(not(bootstrap), lang = "panic_fmt")] // needed for const-evaluated panics
  86 pub fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
  87     if cfg!(feature = "panic_immediate_abort") {
  88         super::intrinsics::abort()
  89     }
  90
  91     // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
  92     // that gets resolved to the `#[panic_handler]` function.
  93     extern "Rust" {
  94         #[lang = "panic_impl"]
  95         fn panic_impl(pi: &PanicInfo<'_>) -> !;
  96     }
  97
  98     let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller());
  99
 100     // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
 101     unsafe { panic_impl(&pi) }
 102 }
 103
 104 /// This function is used instead of panic_fmt in const eval.
 105 #[cfg(not(bootstrap))]
 106 #[lang = "const_panic_fmt"]
 107 pub const fn const_panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
 108     if let Some(msg) = fmt.as_str() {
 109         panic_str(msg);
 110     } else {
 111         // SAFETY: This is only evaluated at compile time, which reliably
 112         // handles this UB (in case this branch turns out to be reachable
 113         // somehow).
 114         unsafe { crate::hint::unreachable_unchecked() };
 115     }
 116 }
 117
 118 #[derive(Debug)]
 119 #[doc(hidden)]
 120 pub enum AssertKind {
 121     Eq,
 122     Ne,
 123     Match,
 124 }
 125
 126 /// Internal function for `assert_eq!` and `assert_ne!` macros
 127 #[cold]
 128 #[track_caller]
 129 #[doc(hidden)]
 130 pub fn assert_failed<T, U>(
 131     kind: AssertKind,
 132     left: &T,
 133     right: &U,
 134     args: Option<fmt::Arguments<'_>>,
 135 ) -> !
 136 where
 137     T: fmt::Debug + ?Sized,
 138     U: fmt::Debug + ?Sized,
 139 {
 140     assert_failed_inner(kind, &left, &right, args)
 141 }
 142
 143 /// Internal function for `assert_match!`
 144 #[cold]
 145 #[track_caller]
 146 #[doc(hidden)]
 147 pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
 148     left: &T,
 149     right: &str,
 150     args: Option<fmt::Arguments<'_>>,
 151 ) -> ! {
 152     // Use the Display implementation to display the pattern.
 153     struct Pattern<'a>(&'a str);
 154     impl fmt::Debug for Pattern<'_> {
 155         fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 156             fmt::Display::fmt(self.0, f)
 157         }
 158     }
 159     assert_failed_inner(AssertKind::Match, &left, &Pattern(right), args);
 160 }
 161
 162 /// Non-generic version of the above functions, to avoid code bloat.
 163 #[track_caller]
 164 fn assert_failed_inner(
 165     kind: AssertKind,
 166     left: &dyn fmt::Debug,
 167     right: &dyn fmt::Debug,
 168     args: Option<fmt::Arguments<'_>>,
 169 ) -> ! {
 170     let op = match kind {
 171         AssertKind::Eq => "==",
 172         AssertKind::Ne => "!=",
 173         AssertKind::Match => "matches",
 174     };
 175
 176     match args {
 177         Some(args) => panic!(
 178             r#"assertion failed: `(left {} right)`
 179   left: `{:?}`,
 180  right: `{:?}`: {}"#,
 181             op, left, right, args
 182         ),
 183         None => panic!(
 184             r#"assertion failed: `(left {} right)`
 185   left: `{:?}`,
 186  right: `{:?}`"#,
 187             op, left, right,
 188         ),
 189     }
 190 }