src/libcore/panic.rs

   1 //! Panic support in the standard library.
   2
   3 #![stable(feature = "core_panic_info", since = "1.41.0")]
   4
   5 use crate::any::Any;
   6 use crate::fmt;
   7
   8 /// A struct providing information about a panic.
   9 ///
  10 /// `PanicInfo` structure is passed to a panic hook set by the [`set_hook`]
  11 /// function.
  12 ///
  13 /// [`set_hook`]: ../../std/panic/fn.set_hook.html
  14 ///
  15 /// # Examples
  16 ///
  17 /// ```should_panic
  18 /// use std::panic;
  19 ///
  20 /// panic::set_hook(Box::new(|panic_info| {
  21 ///     if let Some(s) = panic_info.payload().downcast_ref::<&str>() {
  22 ///         println!("panic occurred: {:?}", s);
  23 ///     } else {
  24 ///         println!("panic occurred");
  25 ///     }
  26 /// }));
  27 ///
  28 /// panic!("Normal panic");
  29 /// ```
  30 #[lang = "panic_info"]
  31 #[stable(feature = "panic_hooks", since = "1.10.0")]
  32 #[derive(Debug)]
  33 pub struct PanicInfo<'a> {
  34     payload: &'a (dyn Any + Send),
  35     message: Option<&'a fmt::Arguments<'a>>,
  36     location: &'a Location<'a>,
  37 }
  38
  39 impl<'a> PanicInfo<'a> {
  40     #[unstable(feature = "panic_internals",
  41                reason = "internal details of the implementation of the `panic!` \
  42                          and related macros",
  43                issue = "0")]
  44     #[doc(hidden)]
  45     #[inline]
  46     pub fn internal_constructor(
  47         message: Option<&'a fmt::Arguments<'a>>,
  48         location: &'a Location<'a>,
  49     ) -> Self {
  50         struct NoPayload;
  51         PanicInfo {
  52             location,
  53             message,
  54             payload: &NoPayload,
  55         }
  56     }
  57
  58     #[unstable(feature = "panic_internals",
  59                reason = "internal details of the implementation of the `panic!` \
  60                          and related macros",
  61                issue = "0")]
  62     #[doc(hidden)]
  63     #[inline]
  64     pub fn set_payload(&mut self, info: &'a (dyn Any + Send)) {
  65         self.payload = info;
  66     }
  67
  68     /// Returns the payload associated with the panic.
  69     ///
  70     /// This will commonly, but not always, be a `&'static str` or [`String`].
  71     ///
  72     /// [`String`]: ../../std/string/struct.String.html
  73     ///
  74     /// # Examples
  75     ///
  76     /// ```should_panic
  77     /// use std::panic;
  78     ///
  79     /// panic::set_hook(Box::new(|panic_info| {
  80     ///     println!("panic occurred: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
  81     /// }));
  82     ///
  83     /// panic!("Normal panic");
  84     /// ```
  85     #[stable(feature = "panic_hooks", since = "1.10.0")]
  86     pub fn payload(&self) -> &(dyn Any + Send) {
  87         self.payload
  88     }
  89
  90     /// If the `panic!` macro from the `core` crate (not from `std`)
  91     /// was used with a formatting string and some additional arguments,
  92     /// returns that message ready to be used for example with [`fmt::write`]
  93     ///
  94     /// [`fmt::write`]: ../fmt/fn.write.html
  95     #[unstable(feature = "panic_info_message", issue = "66745")]
  96     pub fn message(&self) -> Option<&fmt::Arguments<'_>> {
  97         self.message
  98     }
  99
 100     /// Returns information about the location from which the panic originated,
 101     /// if available.
 102     ///
 103     /// This method will currently always return [`Some`], but this may change
 104     /// in future versions.
 105     ///
 106     /// [`Some`]: ../../std/option/enum.Option.html#variant.Some
 107     ///
 108     /// # Examples
 109     ///
 110     /// ```should_panic
 111     /// use std::panic;
 112     ///
 113     /// panic::set_hook(Box::new(|panic_info| {
 114     ///     if let Some(location) = panic_info.location() {
 115     ///         println!("panic occurred in file '{}' at line {}", location.file(),
 116     ///             location.line());
 117     ///     } else {
 118     ///         println!("panic occurred but can't get location information...");
 119     ///     }
 120     /// }));
 121     ///
 122     /// panic!("Normal panic");
 123     /// ```
 124     #[stable(feature = "panic_hooks", since = "1.10.0")]
 125     pub fn location(&self) -> Option<&Location<'_>> {
 126         // NOTE: If this is changed to sometimes return None,
 127         // deal with that case in std::panicking::default_hook and std::panicking::begin_panic_fmt.
 128         Some(&self.location)
 129     }
 130 }
 131
 132 #[stable(feature = "panic_hook_display", since = "1.26.0")]
 133 impl fmt::Display for PanicInfo<'_> {
 134     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
 135         formatter.write_str("panicked at ")?;
 136         if let Some(message) = self.message {
 137             write!(formatter, "'{}', ", message)?
 138         } else if let Some(payload) = self.payload.downcast_ref::<&'static str>() {
 139             write!(formatter, "'{}', ", payload)?
 140         }
 141         // NOTE: we cannot use downcast_ref::<String>() here
 142         // since String is not available in libcore!
 143         // The payload is a String when `std::panic!` is called with multiple arguments,
 144         // but in that case the message is also available.
 145
 146         self.location.fmt(formatter)
 147     }
 148 }
 149
 150 /// A struct containing information about the location of a panic.
 151 ///
 152 /// This structure is created by the [`location`] method of [`PanicInfo`].
 153 ///
 154 /// [`location`]: ../../std/panic/struct.PanicInfo.html#method.location
 155 /// [`PanicInfo`]: ../../std/panic/struct.PanicInfo.html
 156 ///
 157 /// # Examples
 158 ///
 159 /// ```should_panic
 160 /// use std::panic;
 161 ///
 162 /// panic::set_hook(Box::new(|panic_info| {
 163 ///     if let Some(location) = panic_info.location() {
 164 ///         println!("panic occurred in file '{}' at line {}", location.file(), location.line());
 165 ///     } else {
 166 ///         println!("panic occurred but can't get location information...");
 167 ///     }
 168 /// }));
 169 ///
 170 /// panic!("Normal panic");
 171 /// ```
 172 #[lang = "panic_location"]
 173 #[derive(Debug)]
 174 #[stable(feature = "panic_hooks", since = "1.10.0")]
 175 pub struct Location<'a> {
 176     file: &'a str,
 177     line: u32,
 178     col: u32,
 179 }
 180
 181 impl<'a> Location<'a> {
 182     /// Returns the source location of the caller of this function. If that function's caller is
 183     /// annotated then its call location will be returned, and so on up the stack to the first call
 184     /// within a non-tracked function body.
 185     ///
 186     /// # Examples
 187     ///
 188     /// ```
 189     /// #![feature(track_caller)]
 190     /// use core::panic::Location;
 191     ///
 192     /// /// Returns the [`Location`] at which it is called.
 193     /// #[track_caller]
 194     /// fn get_caller_location() -> &'static Location<'static> {
 195     ///     Location::caller()
 196     /// }
 197     ///
 198     /// /// Returns a [`Location`] from within this function's definition.
 199     /// fn get_just_one_location() -> &'static Location<'static> {
 200     ///     get_caller_location()
 201     /// }
 202     ///
 203     /// let fixed_location = get_just_one_location();
 204     /// assert_eq!(fixed_location.file(), file!());
 205     /// assert_eq!(fixed_location.line(), 15);
 206     /// assert_eq!(fixed_location.column(), 5);
 207     ///
 208     /// // running the same untracked function in a different location gives us the same result
 209     /// let second_fixed_location = get_just_one_location();
 210     /// assert_eq!(fixed_location.file(), second_fixed_location.file());
 211     /// assert_eq!(fixed_location.line(), second_fixed_location.line());
 212     /// assert_eq!(fixed_location.column(), second_fixed_location.column());
 213     ///
 214     /// let this_location = get_caller_location();
 215     /// assert_eq!(this_location.file(), file!());
 216     /// assert_eq!(this_location.line(), 29);
 217     /// assert_eq!(this_location.column(), 21);
 218     ///
 219     /// // running the tracked function in a different location produces a different value
 220     /// let another_location = get_caller_location();
 221     /// assert_eq!(this_location.file(), another_location.file());
 222     /// assert_ne!(this_location.line(), another_location.line());
 223     /// assert_ne!(this_location.column(), another_location.column());
 224     /// ```
 225     #[cfg(not(bootstrap))]
 226     #[unstable(feature = "track_caller",
 227                reason = "uses #[track_caller] which is not yet stable",
 228                issue = "47809")]
 229     #[track_caller]
 230     pub const fn caller() -> &'static Location<'static> {
 231         crate::intrinsics::caller_location()
 232     }
 233 }
 234
 235 impl<'a> Location<'a> {
 236     #![unstable(feature = "panic_internals",
 237                 reason = "internal details of the implementation of the `panic!` \
 238                           and related macros",
 239                 issue = "0")]
 240     #[doc(hidden)]
 241     pub const fn internal_constructor(file: &'a str, line: u32, col: u32) -> Self {
 242         Location { file, line, col }
 243     }
 244
 245     /// Returns the name of the source file from which the panic originated.
 246     ///
 247     /// # Examples
 248     ///
 249     /// ```should_panic
 250     /// use std::panic;
 251     ///
 252     /// panic::set_hook(Box::new(|panic_info| {
 253     ///     if let Some(location) = panic_info.location() {
 254     ///         println!("panic occurred in file '{}'", location.file());
 255     ///     } else {
 256     ///         println!("panic occurred but can't get location information...");
 257     ///     }
 258     /// }));
 259     ///
 260     /// panic!("Normal panic");
 261     /// ```
 262     #[stable(feature = "panic_hooks", since = "1.10.0")]
 263     pub fn file(&self) -> &str {
 264         self.file
 265     }
 266
 267     /// Returns the line number from which the panic originated.
 268     ///
 269     /// # Examples
 270     ///
 271     /// ```should_panic
 272     /// use std::panic;
 273     ///
 274     /// panic::set_hook(Box::new(|panic_info| {
 275     ///     if let Some(location) = panic_info.location() {
 276     ///         println!("panic occurred at line {}", location.line());
 277     ///     } else {
 278     ///         println!("panic occurred but can't get location information...");
 279     ///     }
 280     /// }));
 281     ///
 282     /// panic!("Normal panic");
 283     /// ```
 284     #[stable(feature = "panic_hooks", since = "1.10.0")]
 285     pub fn line(&self) -> u32 {
 286         self.line
 287     }
 288
 289     /// Returns the column from which the panic originated.
 290     ///
 291     /// # Examples
 292     ///
 293     /// ```should_panic
 294     /// use std::panic;
 295     ///
 296     /// panic::set_hook(Box::new(|panic_info| {
 297     ///     if let Some(location) = panic_info.location() {
 298     ///         println!("panic occurred at column {}", location.column());
 299     ///     } else {
 300     ///         println!("panic occurred but can't get location information...");
 301     ///     }
 302     /// }));
 303     ///
 304     /// panic!("Normal panic");
 305     /// ```
 306     #[stable(feature = "panic_col", since = "1.25.0")]
 307     pub fn column(&self) -> u32 {
 308         self.col
 309     }
 310 }
 311
 312 #[stable(feature = "panic_hook_display", since = "1.26.0")]
 313 impl fmt::Display for Location<'_> {
 314     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
 315         write!(formatter, "{}:{}:{}", self.file, self.line, self.col)
 316     }
 317 }
 318
 319 /// An internal trait used by libstd to pass data from libstd to `panic_unwind`
 320 /// and other panic runtimes. Not intended to be stabilized any time soon, do
 321 /// not use.
 322 #[unstable(feature = "std_internals", issue = "0")]
 323 #[doc(hidden)]
 324 pub unsafe trait BoxMeUp {
 325     /// Take full ownership of the contents.
 326     /// The return type is actually `Box<dyn Any + Send>`, but we cannot use `Box` in libcore.
 327     ///
 328     /// After this method got called, only some dummy default value is left in `self`.
 329     /// Calling this method twice, or calling `get` after calling this method, is an error.
 330     ///
 331     /// The argument is borrowed because the panic runtime (`__rust_start_panic`) only
 332     /// gets a borrowed `dyn BoxMeUp`.
 333     fn take_box(&mut self) -> *mut (dyn Any + Send);
 334
 335     /// Just borrow the contents.
 336     fn get(&mut self) -> &(dyn Any + Send);
 337 }