panic.rs.html -- source
Description: Source to the Rust file `src/libcore/panic.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Panic support in the standard library.

    #![unstable(feature = "core_panic_info",
                reason = "newly available in libcore",
                issue = "44489")]

    use any::Any;
    use fmt;

    /// A struct providing information about a panic.
    ///
    /// `PanicInfo` structure is passed to a panic hook set by the [`set_hook`]
    /// function.
    ///
    /// [`set_hook`]: ../../std/panic/fn.set_hook.html
    ///
    /// # Examples
    ///
    /// ```should_panic
    /// use std::panic;
    ///
    /// panic::set_hook(Box::new(|panic_info| {
    ///     if let Some(s) = panic_info.payload().downcast_ref::<&str>() {
    ///         println!("panic occurred: {:?}", s);
    ///     } else {
    ///         println!("panic occurred");
    ///     }
    /// }));
    ///
    /// panic!("Normal panic");
    /// ```
    #[lang = "panic_info"]
    #[stable(feature = "panic_hooks", since = "1.10.0")]
    #[derive(Debug)]
    pub struct PanicInfo<'a> {
        payload: &'a (dyn Any + Send),
        message: Option<&'a fmt::Arguments<'a>>,
        location: Location<'a>,
    }

    impl<'a> PanicInfo<'a> {
        #![unstable(feature = "panic_internals",
                    reason = "internal details of the implementation of the `panic!` \
                              and related macros",
                    issue = "0")]
        #[doc(hidden)]
        #[inline]
        pub fn internal_constructor(message: Option<&'a fmt::Arguments<'a>>,
                                    location: Location<'a>)
                                    -> Self {
            struct NoPayload;
            PanicInfo { payload: &NoPayload, location, message }
        }

        #[doc(hidden)]
        #[inline]
        pub fn set_payload(&mut self, info: &'a (dyn Any + Send)) {
            self.payload = info;
        }

        /// Returns the payload associated with the panic.
        ///
        /// This will commonly, but not always, be a `&'static str` or [`String`].
        ///
        /// [`String`]: ../../std/string/struct.String.html
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::panic;
        ///
        /// panic::set_hook(Box::new(|panic_info| {
        ///     println!("panic occurred: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
        /// }));
        ///
        /// panic!("Normal panic");
        /// ```
        #[stable(feature = "panic_hooks", since = "1.10.0")]
        pub fn payload(&self) -> &(dyn Any + Send) {
            self.payload
        }

        /// If the `panic!` macro from the `core` crate (not from `std`)
        /// was used with a formatting string and some additional arguments,
        /// returns that message ready to be used for example with [`fmt::write`]
        ///
        /// [`fmt::write`]: ../fmt/fn.write.html
        #[unstable(feature = "panic_info_message", issue = "44489")]
        pub fn message(&self) -> Option<&fmt::Arguments> {
            self.message
        }

        /// Returns information about the location from which the panic originated,
        /// if available.
        ///
        /// This method will currently always return [`Some`], but this may change
        /// in future versions.
        ///
        /// [`Some`]: ../../std/option/enum.Option.html#variant.Some
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::panic;
        ///
        /// panic::set_hook(Box::new(|panic_info| {
        ///     if let Some(location) = panic_info.location() {
        ///         println!("panic occurred in file '{}' at line {}", location.file(),
        ///             location.line());
        ///     } else {
        ///         println!("panic occurred but can't get location information...");
        ///     }
        /// }));
        ///
        /// panic!("Normal panic");
        /// ```
        #[stable(feature = "panic_hooks", since = "1.10.0")]
        pub fn location(&self) -> Option<&Location> {
            // NOTE: If this is changed to sometimes return None,
            // deal with that case in std::panicking::default_hook and std::panicking::begin_panic_fmt.
            Some(&self.location)
        }
    }

    #[stable(feature = "panic_hook_display", since = "1.26.0")]
    impl fmt::Display for PanicInfo<'_> {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("panicked at ")?;
            if let Some(message) = self.message {
                write!(formatter, "'{}', ", message)?
            } else if let Some(payload) = self.payload.downcast_ref::<&'static str>() {
                write!(formatter, "'{}', ", payload)?
            }
            // NOTE: we cannot use downcast_ref::<String>() here
            // since String is not available in libcore!
            // The payload is a String when `std::panic!` is called with multiple arguments,
            // but in that case the message is also available.

            self.location.fmt(formatter)
        }
    }

    /// A struct containing information about the location of a panic.
    ///
    /// This structure is created by the [`location`] method of [`PanicInfo`].
    ///
    /// [`location`]: ../../std/panic/struct.PanicInfo.html#method.location
    /// [`PanicInfo`]: ../../std/panic/struct.PanicInfo.html
    ///
    /// # Examples
    ///
    /// ```should_panic
    /// use std::panic;
    ///
    /// panic::set_hook(Box::new(|panic_info| {
    ///     if let Some(location) = panic_info.location() {
    ///         println!("panic occurred in file '{}' at line {}", location.file(), location.line());
    ///     } else {
    ///         println!("panic occurred but can't get location information...");
    ///     }
    /// }));
    ///
    /// panic!("Normal panic");
    /// ```
    #[derive(Debug)]
    #[stable(feature = "panic_hooks", since = "1.10.0")]
    pub struct Location<'a> {
        file: &'a str,
        line: u32,
        col: u32,
    }

    impl<'a> Location<'a> {
        #![unstable(feature = "panic_internals",
                    reason = "internal details of the implementation of the `panic!` \
                              and related macros",
                    issue = "0")]
        #[doc(hidden)]
        pub fn internal_constructor(file: &'a str, line: u32, col: u32) -> Self {
            Location { file, line, col }
        }

        /// Returns the name of the source file from which the panic originated.
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::panic;
        ///
        /// panic::set_hook(Box::new(|panic_info| {
        ///     if let Some(location) = panic_info.location() {
        ///         println!("panic occurred in file '{}'", location.file());
        ///     } else {
        ///         println!("panic occurred but can't get location information...");
        ///     }
        /// }));
        ///
        /// panic!("Normal panic");
        /// ```
        #[stable(feature = "panic_hooks", since = "1.10.0")]
        pub fn file(&self) -> &str {
            self.file
        }

        /// Returns the line number from which the panic originated.
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::panic;
        ///
        /// panic::set_hook(Box::new(|panic_info| {
        ///     if let Some(location) = panic_info.location() {
        ///         println!("panic occurred at line {}", location.line());
        ///     } else {
        ///         println!("panic occurred but can't get location information...");
        ///     }
        /// }));
        ///
        /// panic!("Normal panic");
        /// ```
        #[stable(feature = "panic_hooks", since = "1.10.0")]
        pub fn line(&self) -> u32 {
            self.line
        }

        /// Returns the column from which the panic originated.
        ///
        /// # Examples
        ///
        /// ```should_panic
        /// use std::panic;
        ///
        /// panic::set_hook(Box::new(|panic_info| {
        ///     if let Some(location) = panic_info.location() {
        ///         println!("panic occurred at column {}", location.column());
        ///     } else {
        ///         println!("panic occurred but can't get location information...");
        ///     }
        /// }));
        ///
        /// panic!("Normal panic");
        /// ```
        #[stable(feature = "panic_col", since = "1.25.0")]
        pub fn column(&self) -> u32 {
            self.col
        }
    }

    #[stable(feature = "panic_hook_display", since = "1.26.0")]
    impl fmt::Display for Location<'_> {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            write!(formatter, "{}:{}:{}", self.file, self.line, self.col)
        }
    }

    /// An internal trait used by libstd to pass data from libstd to `panic_unwind`
    /// and other panic runtimes. Not intended to be stabilized any time soon, do
    /// not use.
    #[unstable(feature = "std_internals", issue = "0")]
    #[doc(hidden)]
    pub unsafe trait BoxMeUp {
        fn box_me_up(&mut self) -> *mut (dyn Any + Send);
        fn get(&mut self) -> &(dyn Any + Send);
    }

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