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Rfc 2070 panic implementation deprecated (#467)

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* Make changes to code examples.

* Explain that panic_implementation has been deprecated

* Update attributes in source code.
This commit is contained in:
Ben
2018-10-01 16:38:48 +08:00
committed by Philipp Oppermann
parent 0bd4fcd99e
commit 2a9075d642
10 changed files with 21 additions and 33 deletions
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18
blog/content/second-edition/posts/01-freestanding-rust-binary/index.md
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@@ -134,17 +134,19 @@ This sets the panic strategy to `abort` for both the `dev` profile (used for `ca
### Panic Implementation
The `panic_impl` language item defines the function that the compiler should invoke when a [panic] occurs. Instead of providing the language item directly, we can use the [`panic_implementation`] attribute to create a `panic` function:
The `panic_impl` language item defines the function that the compiler should invoke when a [panic] occurs. Instead of providing the language item directly, we can use the [`panic_handler`] attribute to create a `panic` function. This used to take the for [`panic_implementation`], which has been deprecated and replaced by [`panic_handler`].
[`panic_implementation`]: https://github.com/rust-lang/rfcs/blob/master/text/2070-panic-implementation.md#panic_implementation
Note: [`panic_implementation`] has been deprecated, and we now use [`panic_handler`] instead
```rust
// in main.rs
use core::panic::PanicInfo;
/// This function is called on panic.
#[panic_implementation]
#[panic_handler]
#[no_mangle]
pub fn panic(_info: &PanicInfo) -> ! {
loop {}
@@ -157,11 +159,11 @@ The [`PanicInfo` parameter][PanicInfo] contains the file and line where the pani
[diverging function]: https://doc.rust-lang.org/book/first-edition/functions.html#diverging-functions
[“never” type]: https://doc.rust-lang.org/nightly/std/primitive.never.html
When we try `cargo build` now, we get an error that “#[panic_implementation] is an unstable feature”.
When we try `cargo build` now, we get an error that “#[panic_handler] is an unstable feature”.
#### Enabling Unstable Features
The `panic_implementation` attribute was recently added and is thus still unstable and protected by a so-called _feature gate_. A feature gate is a special attribute that you have to specify at the top of your `main.rs` in order to use the corresponding feature. By doing this you basically say: “I know that this feature is unstable and that it might stop working without any warnings. I want to use it anyway.”
The `panic_handler` attribute was recently added and is thus still unstable and protected by a so-called _feature gate_. A feature gate is a special attribute that you have to specify at the top of your `main.rs` in order to use the corresponding feature. By doing this you basically say: “I know that this feature is unstable and that it might stop working without any warnings. I want to use it anyway.”
Feature gates are not available in the stable or beta Rust compilers, only [nightly Rust] makes it possible to opt-in. This means that you have to use a nightly compiler for OS development for the near future (until all unstable features that we need are added are stabilized).
@@ -171,8 +173,6 @@ To manage Rust installations I highly recommend [rustup]. It allows you to insta
[rustup]: https://www.rustup.rs/
After installing a nightly Rust compiler, you can enable the unstable `panic_implementation` feature by inserting `#![feature(panic_implementation)]` right at the top of `main.rs`.
Now we fixed both language item errors. However, if we try to compile it now, another language item is required:
```
@@ -196,14 +196,13 @@ Our freestanding executable does not have access to the Rust runtime and `crt0`,
To tell the Rust compiler that we don't want to use the normal entry point chain, we add the `#![no_main]` attribute.
```rust
#![feature(panic_implementation)]
#![no_std]
#![no_main]
use core::panic::PanicInfo;
/// This function is called on panic.
#[panic_implementation]
#[panic_handler]
#[no_mangle]
pub fn panic(_info: &PanicInfo) -> ! {
loop {}
@@ -311,14 +310,13 @@ A minimal freestanding Rust binary looks like this:
`src/main.rs`:
```rust
#![feature(panic_implementation)] // required for defining the panic handler
#![no_std] // don't link the Rust standard library
#![no_main] // disable all Rust-level entry points
use core::panic::PanicInfo;
/// This function is called on panic.
#[panic_implementation]
#[panic_handler]
#[no_mangle]
pub fn panic(_info: &PanicInfo) -> ! {
loop {}