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.

    #![stable(feature = "core_panic_info", since = "1.41.0")]

    use crate::any::Any;
    use crate::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: &'a Location<'a>,
    }

    impl<'a> PanicInfo<'a> {
        #[unstable(
            feature = "panic_internals",
            reason = "internal details of the implementation of the `panic!` \
                             and related macros",
            issue = "none"
        )]
        #[doc(hidden)]
        #[inline]
        pub fn internal_constructor(
            message: Option<&'a fmt::Arguments<'a>>,
            location: &'a Location<'a>,
        ) -> Self {
            struct NoPayload;
            PanicInfo { location, message, payload: &NoPayload }
        }

        #[unstable(
            feature = "panic_internals",
            reason = "internal details of the implementation of the `panic!` \
                             and related macros",
            issue = "none"
        )]
        #[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| {
        ///     if let Some(s) = panic_info.payload().downcast_ref::<&str>() {
        ///         println!("panic occurred: {:?}", s);
        ///     } else {
        ///         println!("panic occurred");
        ///     }
        /// }));
        ///
        /// 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 = "66745")]
        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");
    /// ```
    #[lang = "panic_location"]
    #[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> {
        /// Returns the source location of the caller of this function. If that function's caller is
        /// annotated then its call location will be returned, and so on up the stack to the first call
        /// within a non-tracked function body.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(track_caller)]
        /// use core::panic::Location;
        ///
        /// /// Returns the [`Location`] at which it is called.
        /// #[track_caller]
        /// fn get_caller_location() -> &'static Location<'static> {
        ///     Location::caller()
        /// }
        ///
        /// /// Returns a [`Location`] from within this function's definition.
        /// fn get_just_one_location() -> &'static Location<'static> {
        ///     get_caller_location()
        /// }
        ///
        /// let fixed_location = get_just_one_location();
        /// assert_eq!(fixed_location.file(), file!());
        /// assert_eq!(fixed_location.line(), 15);
        /// assert_eq!(fixed_location.column(), 5);
        ///
        /// // running the same untracked function in a different location gives us the same result
        /// let second_fixed_location = get_just_one_location();
        /// assert_eq!(fixed_location.file(), second_fixed_location.file());
        /// assert_eq!(fixed_location.line(), second_fixed_location.line());
        /// assert_eq!(fixed_location.column(), second_fixed_location.column());
        ///
        /// let this_location = get_caller_location();
        /// assert_eq!(this_location.file(), file!());
        /// assert_eq!(this_location.line(), 29);
        /// assert_eq!(this_location.column(), 21);
        ///
        /// // running the tracked function in a different location produces a different value
        /// let another_location = get_caller_location();
        /// assert_eq!(this_location.file(), another_location.file());
        /// assert_ne!(this_location.line(), another_location.line());
        /// assert_ne!(this_location.column(), another_location.column());
        /// ```
        // FIXME: When stabilizing this method, please also update the documentation
        // of `intrinsics::caller_location`.
        #[unstable(
            feature = "track_caller",
            reason = "uses #[track_caller] which is not yet stable",
            issue = "47809"
        )]
        #[track_caller]
        pub const fn caller() -> &'static Location<'static> {
            crate::intrinsics::caller_location()
        }
    }

    impl<'a> Location<'a> {
        #![unstable(
            feature = "panic_internals",
            reason = "internal details of the implementation of the `panic!` \
                              and related macros",
            issue = "none"
        )]
        #[doc(hidden)]
        pub const 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 = "none")]
    #[doc(hidden)]
    pub unsafe trait BoxMeUp {
        /// Take full ownership of the contents.
        /// The return type is actually `Box<dyn Any + Send>`, but we cannot use `Box` in libcore.
        ///
        /// After this method got called, only some dummy default value is left in `self`.
        /// Calling this method twice, or calling `get` after calling this method, is an error.
        ///
        /// The argument is borrowed because the panic runtime (`__rust_start_panic`) only
        /// gets a borrowed `dyn BoxMeUp`.
        fn take_box(&mut self) -> *mut (dyn Any + Send);

        /// Just borrow the contents.
        fn get(&mut self) -> &(dyn Any + Send);
    }