166 lines
5.0 KiB
Rust
166 lines
5.0 KiB
Rust
// SPDX-License-Identifier: Apache-2.0 OR MIT
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//! The contents of this file come from the Rust standard library, hosted in
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//! the <https://github.com/rust-lang/rust> repository, licensed under
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//! "Apache-2.0 OR MIT" and adapted for kernel use. For copyright details,
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//! see <https://github.com/rust-lang/rust/blob/master/COPYRIGHT>.
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/// [`std::dbg`], but using [`pr_info`] instead of [`eprintln`].
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///
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/// Prints and returns the value of a given expression for quick and dirty
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/// debugging.
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///
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/// An example:
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///
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/// ```rust
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/// let a = 2;
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/// # #[allow(clippy::dbg_macro)]
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/// let b = dbg!(a * 2) + 1;
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/// // ^-- prints: [src/main.rs:2] a * 2 = 4
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/// assert_eq!(b, 5);
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/// ```
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///
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/// The macro works by using the `Debug` implementation of the type of
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/// the given expression to print the value with [`printk`] along with the
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/// source location of the macro invocation as well as the source code
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/// of the expression.
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///
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/// Invoking the macro on an expression moves and takes ownership of it
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/// before returning the evaluated expression unchanged. If the type
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/// of the expression does not implement `Copy` and you don't want
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/// to give up ownership, you can instead borrow with `dbg!(&expr)`
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/// for some expression `expr`.
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///
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/// The `dbg!` macro works exactly the same in release builds.
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/// This is useful when debugging issues that only occur in release
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/// builds or when debugging in release mode is significantly faster.
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///
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/// Note that the macro is intended as a temporary debugging tool to be
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/// used during development. Therefore, avoid committing `dbg!` macro
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/// invocations into the kernel tree.
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///
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/// For debug output that is intended to be kept in the kernel tree,
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/// use [`pr_debug`] and similar facilities instead.
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///
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/// # Stability
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///
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/// The exact output printed by this macro should not be relied upon
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/// and is subject to future changes.
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///
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/// # Further examples
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///
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/// With a method call:
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///
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/// ```rust
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/// # #[allow(clippy::dbg_macro)]
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/// fn foo(n: usize) {
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/// if dbg!(n.checked_sub(4)).is_some() {
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/// // ...
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/// }
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/// }
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///
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/// foo(3)
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/// ```
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///
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/// This prints to the kernel log:
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///
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/// ```text,ignore
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/// [src/main.rs:4] n.checked_sub(4) = None
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/// ```
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///
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/// Naive factorial implementation:
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///
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/// ```rust
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/// # #[allow(clippy::dbg_macro)]
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/// # {
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/// fn factorial(n: u32) -> u32 {
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/// if dbg!(n <= 1) {
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/// dbg!(1)
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/// } else {
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/// dbg!(n * factorial(n - 1))
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/// }
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/// }
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///
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/// dbg!(factorial(4));
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/// # }
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/// ```
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///
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/// This prints to the kernel log:
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///
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/// ```text,ignore
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/// [src/main.rs:3] n <= 1 = false
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/// [src/main.rs:3] n <= 1 = false
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/// [src/main.rs:3] n <= 1 = false
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/// [src/main.rs:3] n <= 1 = true
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/// [src/main.rs:4] 1 = 1
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/// [src/main.rs:5] n * factorial(n - 1) = 2
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/// [src/main.rs:5] n * factorial(n - 1) = 6
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/// [src/main.rs:5] n * factorial(n - 1) = 24
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/// [src/main.rs:11] factorial(4) = 24
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/// ```
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///
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/// The `dbg!(..)` macro moves the input:
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///
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/// ```ignore
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/// /// A wrapper around `usize` which importantly is not Copyable.
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/// #[derive(Debug)]
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/// struct NoCopy(usize);
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///
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/// let a = NoCopy(42);
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/// let _ = dbg!(a); // <-- `a` is moved here.
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/// let _ = dbg!(a); // <-- `a` is moved again; error!
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/// ```
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///
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/// You can also use `dbg!()` without a value to just print the
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/// file and line whenever it's reached.
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///
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/// Finally, if you want to `dbg!(..)` multiple values, it will treat them as
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/// a tuple (and return it, too):
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///
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/// ```
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/// # #[allow(clippy::dbg_macro)]
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/// assert_eq!(dbg!(1usize, 2u32), (1, 2));
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/// ```
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///
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/// However, a single argument with a trailing comma will still not be treated
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/// as a tuple, following the convention of ignoring trailing commas in macro
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/// invocations. You can use a 1-tuple directly if you need one:
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///
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/// ```
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/// # #[allow(clippy::dbg_macro)]
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/// # {
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/// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored
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/// assert_eq!((1,), dbg!((1u32,))); // 1-tuple
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/// # }
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/// ```
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///
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/// [`std::dbg`]: https://doc.rust-lang.org/std/macro.dbg.html
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/// [`eprintln`]: https://doc.rust-lang.org/std/macro.eprintln.html
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/// [`printk`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html
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/// [`pr_info`]: crate::pr_info!
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/// [`pr_debug`]: crate::pr_debug!
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#[macro_export]
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macro_rules! dbg {
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// NOTE: We cannot use `concat!` to make a static string as a format argument
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// of `pr_info!` because `file!` could contain a `{` or
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// `$val` expression could be a block (`{ .. }`), in which case the `pr_info!`
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// will be malformed.
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() => {
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$crate::pr_info!("[{}:{}]\n", ::core::file!(), ::core::line!())
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};
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($val:expr $(,)?) => {
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// Use of `match` here is intentional because it affects the lifetimes
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// of temporaries - https://stackoverflow.com/a/48732525/1063961
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match $val {
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tmp => {
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$crate::pr_info!("[{}:{}] {} = {:#?}\n",
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::core::file!(), ::core::line!(), ::core::stringify!($val), &tmp);
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tmp
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}
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}
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};
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($($val:expr),+ $(,)?) => {
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($($crate::dbg!($val)),+,)
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};
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}
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