library/core/src/panic/location.rs

use crate::cmp::Ordering;
use crate::ffi::CStr;
use crate::fmt;
use crate::hash::{Hash, Hasher};
use crate::marker::PhantomData;
use crate::ptr::NonNull;

/// A struct containing information about the location of a panic.
///
/// This structure is created by [`PanicHookInfo::location()`] and [`PanicInfo::location()`].
///
/// [`PanicInfo::location()`]: crate::panic::PanicInfo::location
/// [`PanicHookInfo::location()`]: ../../std/panic/struct.PanicHookInfo.html#method.location
///
/// # 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");
/// ```
///
/// # Comparisons
///
/// Comparisons for equality and ordering are made in file, line, then column priority.
/// Files are compared as strings, not `Path`, which could be unexpected.
/// See [`Location::file`]'s documentation for more discussion.
#[lang = "panic_location"]
#[derive(Copy, Clone)]
#[stable(feature = "panic_hooks", since = "1.10.0")]
pub struct Location<'a> {
    // A raw pointer is used rather than a reference because the pointer is valid for one more byte
    // than the length stored in this pointer; the additional byte is the NUL-terminator used by
    // `Location::file_as_c_str`.
    filename: NonNull<str>,
    line: u32,
    col: u32,
    _filename: PhantomData<&'a str>,
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl PartialEq for Location<'_> {
    fn eq(&self, other: &Self) -> bool {
        // Compare col / line first as they're cheaper to compare and more likely to differ,
        // while not impacting the result.
        self.col == other.col && self.line == other.line && self.file() == other.file()
    }
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl Eq for Location<'_> {}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl Ord for Location<'_> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.file()
            .cmp(other.file())
            .then_with(|| self.line.cmp(&other.line))
            .then_with(|| self.col.cmp(&other.col))
    }
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl PartialOrd for Location<'_> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl Hash for Location<'_> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.file().hash(state);
        self.line.hash(state);
        self.col.hash(state);
    }
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl fmt::Debug for Location<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Location")
            .field("file", &self.file())
            .field("line", &self.line)
            .field("column", &self.col)
            .finish()
    }
}

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
    ///
    /// ```standalone_crate
    /// use std::panic::Location;
    ///
    /// /// ```
    /// ///      |1        |11       |21       |31       |41
    /// ///    +-|---------|---------|---------|---------|--------
    /// /// 15 | #[track_caller]
    /// /// 16 | fn new_location() -> &'static Location<'static> {
    /// /// 17 |     Location::caller()
    /// ///    |     ------------------| the value of this expression depends on the caller,
    /// ///    |                       | since the function is marked #[track_caller]
    /// /// 18 | }
    /// /// ```
    /// #[track_caller]
    /// fn new_location() -> &'static Location<'static> {
    ///     Location::caller()
    /// }
    ///
    /// /// ```
    /// ///      |1  |5    |11       |21       |31       |41       |51
    /// ///    +-|---|-----|---------|---------|---------|---------|---
    /// /// 29 | fn constant_location() -> &'static Location<'static> {
    /// /// 30 |     new_location()
    /// ///    |     ^ any invocation of constant_location() points here,
    /// ///    |       no matter the location it is called from
    /// /// 31 | }
    /// /// ```
    /// fn constant_location() -> &'static Location<'static> {
    ///     new_location()
    /// }
    ///
    /// fn main() {
    ///     //      |1  |5    |11       |21       |31       |41       |51
    ///     //    +-|---|-----|---------|---------|---------|---------|---
    ///     // 29 | fn constant_location() -> &'static Location<'static> {
    ///     // 30 |     new_location()
    ///     //    |     ^ `let constant` points here
    ///     // 31 | }
    ///     let constant = constant_location();
    ///     assert_eq!(constant.file(), file!());
    ///     assert_eq!((constant.line(), constant.column()), (30, 5));
    ///
    ///     let constant_2 = constant_location();
    ///     assert_eq!(
    ///         (constant.file(), constant.line(), constant.column()),
    ///         (constant_2.file(), constant_2.line(), constant_2.column())
    ///     );
    ///
    ///     //      |1        |11  |16  |21       |31
    ///     //    +-|---------|----|----|---------|------
    ///     // 55 |     let here = new_location();
    ///     //    |                ^ `let here` points here, as `new_location()` is the callsite
    ///     // 56 |     assert_eq!(here.file(), file!());
    ///     let here = new_location();
    ///     assert_eq!(here.file(), file!());
    ///     assert_eq!((here.line(), here.column()), (55, 16));
    ///
    ///     //      |1        |11       |21       ||32      |41       |51
    ///     //    +-|---------|---------|---------||--------|---------|------
    ///     // 64 |     let yet_another_location = new_location();
    ///     //    |                                ^ `let yet_another_location` points here
    ///     // 65 |     assert_eq!(here.file(), yet_another_location.file());
    ///     let yet_another_location = new_location();
    ///     assert_eq!(here.file(), yet_another_location.file());
    ///     assert_ne!(
    ///         (here.line(), here.column()),
    ///         (yet_another_location.line(), yet_another_location.column())
    ///     );
    /// }
    /// ```
    #[must_use]
    #[stable(feature = "track_caller", since = "1.46.0")]
    #[rustc_const_stable(feature = "const_caller_location", since = "1.79.0")]
    #[track_caller]
    #[inline]
    pub const fn caller() -> &'static Location<'static> {
        crate::intrinsics::caller_location()
    }

    /// Returns the name of the source file from which the panic originated.
    ///
    /// # `&str`, not `&Path`
    ///
    /// The returned name refers to a source path on the compiling system, but it isn't valid to
    /// represent this directly as a `&Path`. The compiled code may run on a different system with
    /// a different `Path` implementation than the system providing the contents and this library
    /// does not currently have a different "host path" type.
    ///
    /// The most surprising behavior occurs when "the same" file is reachable via multiple paths in
    /// the module system (usually using the `#[path = "..."]` attribute or similar), which can
    /// cause what appears to be identical code to return differing values from this function.
    ///
    /// # Cross-compilation
    ///
    /// This value is not suitable for passing to `Path::new` or similar constructors when the host
    /// platform and target platform differ.
    ///
    /// # 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");
    /// ```
    #[must_use]
    #[stable(feature = "panic_hooks", since = "1.10.0")]
    #[rustc_const_stable(feature = "const_location_fields", since = "1.79.0")]
    pub const fn file(&self) -> &'a str {
        // SAFETY: The filename is valid.
        unsafe { self.filename.as_ref() }
    }

    /// Returns the name of the source file as a nul-terminated `CStr`.
    ///
    /// This is useful for interop with APIs that expect C/C++ `__FILE__` or
    /// `std::source_location::file_name`, both of which return a nul-terminated `const char*`.
    #[must_use]
    #[inline]
    #[stable(feature = "file_with_nul", since = "1.92.0")]
    #[rustc_const_stable(feature = "file_with_nul", since = "1.92.0")]
    pub const fn file_as_c_str(&self) -> &'a CStr {
        let filename = self.filename.as_ptr();

        // SAFETY: The filename is valid for `filename_len+1` bytes, so this addition can't
        // overflow.
        let cstr_len = unsafe { crate::mem::size_of_val_raw(filename).unchecked_add(1) };

        // SAFETY: The filename is valid for `filename_len+1` bytes.
        let slice = unsafe { crate::slice::from_raw_parts(filename.cast(), cstr_len) };

        // SAFETY: The filename is guaranteed to have a trailing nul byte and no interior nul bytes.
        unsafe { CStr::from_bytes_with_nul_unchecked(slice) }
    }

    /// 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");
    /// ```
    #[must_use]
    #[stable(feature = "panic_hooks", since = "1.10.0")]
    #[rustc_const_stable(feature = "const_location_fields", since = "1.79.0")]
    #[inline]
    pub const 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");
    /// ```
    #[must_use]
    #[stable(feature = "panic_col", since = "1.25.0")]
    #[rustc_const_stable(feature = "const_location_fields", since = "1.79.0")]
    #[inline]
    pub const fn column(&self) -> u32 {
        self.col
    }
}

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

#[stable(feature = "panic_hooks", since = "1.10.0")]
unsafe impl Send for Location<'_> {}
#[stable(feature = "panic_hooks", since = "1.10.0")]
unsafe impl Sync for Location<'_> {}