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(fmt::Arguments::new_v1(&[expr], &[]));
  51 }
  52
  53 #[inline]
  54 #[track_caller]
  55 #[lang = "panic_str"] // needed for const-evaluated panics
  56 pub fn panic_str(expr: &str) -> ! {
  57     panic_fmt(format_args!("{}", expr));
  58 }
  59
  60 #[cold]
  61 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
  62 #[track_caller]
  63 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
  64 fn panic_bounds_check(index: usize, len: usize) -> ! {
  65     if cfg!(feature = "panic_immediate_abort") {
  66         super::intrinsics::abort()
  67     }
  68
  69     panic!("index out of bounds: the len is {} but the index is {}", len, index)
  70 }
  71
  72 /// The underlying implementation of libcore's `panic!` macro when formatting is used.
  73 #[cold]
  74 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
  75 #[cfg_attr(feature = "panic_immediate_abort", inline)]
  76 #[track_caller]
  77 pub fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
  78     if cfg!(feature = "panic_immediate_abort") {
  79         super::intrinsics::abort()
  80     }
  81
  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.
  84     extern "Rust" {
  85         #[lang = "panic_impl"]
  86         fn panic_impl(pi: &PanicInfo<'_>) -> !;
  87     }
  88
  89     let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller());
  90
  91     // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
  92     unsafe { panic_impl(&pi) }
  93 }
  94
  95 #[derive(Debug)]
  96 #[doc(hidden)]
  97 pub enum AssertKind {
  98     Eq,
  99     Ne,
 100     Match,
 101 }
 102
 103 /// Internal function for `assert_eq!` and `assert_ne!` macros
 104 #[cold]
 105 #[track_caller]
 106 #[doc(hidden)]
 107 pub fn assert_failed<T, U>(
 108     kind: AssertKind,
 109     left: &T,
 110     right: &U,
 111     args: Option<fmt::Arguments<'_>>,
 112 ) -> !
 113 where
 114     T: fmt::Debug + ?Sized,
 115     U: fmt::Debug + ?Sized,
 116 {
 117     assert_failed_inner(kind, &left, &right, args)
 118 }
 119
 120 /// Internal function for `assert_match!`
 121 #[cold]
 122 #[track_caller]
 123 #[doc(hidden)]
 124 pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
 125     left: &T,
 126     right: &str,
 127     args: Option<fmt::Arguments<'_>>,
 128 ) -> ! {
 129     // Use the Display implementation to display the pattern.
 130     struct Pattern<'a>(&'a str);
 131     impl fmt::Debug for Pattern<'_> {
 132         fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 133             fmt::Display::fmt(self.0, f)
 134         }
 135     }
 136     assert_failed_inner(AssertKind::Match, &left, &Pattern(right), args);
 137 }
 138
 139 /// Non-generic version of the above functions, to avoid code bloat.
 140 #[track_caller]
 141 fn assert_failed_inner(
 142     kind: AssertKind,
 143     left: &dyn fmt::Debug,
 144     right: &dyn fmt::Debug,
 145     args: Option<fmt::Arguments<'_>>,
 146 ) -> ! {
 147     let op = match kind {
 148         AssertKind::Eq => "==",
 149         AssertKind::Ne => "!=",
 150         AssertKind::Match => "matches",
 151     };
 152
 153     match args {
 154         Some(args) => panic!(
 155             r#"assertion failed: `(left {} right)`
 156   left: `{:?}`,
 157  right: `{:?}`: {}"#,
 158             op, left, right, args
 159         ),
 160         None => panic!(
 161             r#"assertion failed: `(left {} right)`
 162   left: `{:?}`,
 163  right: `{:?}`"#,
 164             op, left, right,
 165         ),
 166     }
 167 }