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#![doc = include_str!("../README.md")]
#![no_std]
#![cfg_attr(feature = "polonius",
forbid(unsafe_code),
)]
/// ACT I SCENE I. Elsinore. A platform before the castle.
pub
mod prelude {
pub use crate::{
polonius,
polonius_return,
polonius_break,
};
}
/// See the [top-level docs][crate] for more info.
pub
trait WithLifetime<'lt, Bound = &'lt Self> {
type T;
}
/// See the [top-level docs][crate] for more info.
pub
trait HKT
where
Self : for<'any> WithLifetime<'any>,
{}
impl<T : ?Sized> HKT for T
where
Self : for<'any> WithLifetime<'any>,
{}
/// See the [top-level docs][crate] for more info.
pub
fn polonius<Ret : HKT, State : ?Sized, Err, F> (
state: &mut State,
branch: F,
) -> Result<
<Ret as WithLifetime<'_>>::T,
(&'_ mut State, Err),
>
where
F : FnOnce(&'_ mut State)
-> Result<
<Ret as WithLifetime<'_>>::T,
Err,
>,
{
let err = {
#[cfg(not(feature = "polonius"))]
let state = unsafe {
// SAFETY:
// > Though this be `unsafe`, there is soundness in 't.
//
// More seriously, read the docs, I've detailed the reasoning there
// in great length. And/or check the `tests/soundness.rs` test,
// which `cargo check`s this very snippet without this `unsafe`.
&mut *(state as *mut _)
};
match branch(state) {
| Ok(ret) => return Ok(ret),
| Err(err) => err,
}
};
Err((state, err))
}
/// Convenient entry-point to this crate's logic.
///
/// ## Usage
///
/** ```rust
use ::polonius_the_crab::prelude::*;
# fn foo (arg: &mut ()) -> &mut () {
let mut a_mut_binding: &mut _ = // …
# arg;
# type SomeRetType<'__> = &'__ mut ();
# let some_cond = || true;
# let some_other_cond = || true;
# use ::core::convert::identity as stuff;
// the lifetime placeholder has to be
// named `'polonius` !!
// vvvvvvvvv
let x = polonius!(|a_mut_binding| -> SomeRetType<'polonius> {
let some_dependent_type = stuff(a_mut_binding);
if some_cond() {
polonius_return!(some_dependent_type);
}
if some_other_cond() {
polonius_break!(42);
unreachable!();
}
42
});
assert_eq!(x, 42);
stuff(a_mut_binding) // macro gave it back
// …
# }
``` */
///
/// ### Generic parameters
///
/// Sometimes, the return value of that `polonius!` closure may need to refer to
/// generic parameters. When that's the case, you'll need to tell the macro
/// about those, using `<generics…>` syntax before the `|…| ->` part of the
/// macro input:
///
/** ```rust
use ::polonius_the_crab::prelude::*;
fn get_or_insert<'map, 'v, K, V : ?Sized> (
mut map: &'map mut ::std::collections::HashMap<K, &'v V>,
key: &'_ K,
fallback_value: &'v V,
) -> &'map &'v V
where
K : ::core::hash::Hash + Eq + Clone,
V : ::core::fmt::Debug,
{
// No need to provide `K`, since not part of the return type;
// nor to provide the bounds for `V`, except for:
// - nested borrows (if ever),
// - `?Sized` (every now and then)
// - or to be able to name a bound-provided associated type (super rare!)
polonius!(<'v, V : 'v + ?Sized> |map| -> &'polonius &'v V {
if let Some(v) = map.get(key) {
dbg!(v); // Even though `Debug` is not provided to the signature, it is available to the body.
polonius_return!(v);
}
});
map.insert(key.clone(), fallback_value);
&map[key]
}
``` */
#[macro_export]
macro_rules! polonius {(
$(
<
$( $(
$lt:lifetime
),+ $(,)? )?
$( $(
$T:ident $(:
$( $super:lifetime + )?
$( ?$Sized:ident )?
$( + )?
$( $Bound:path )?
)?
),+ $(,)? )?
>
)?
|$var:ident| -> $Ret:ty $body:block
) => ({
#[allow(nonstandard_style)]
struct __polonius_the_crab_Ret <$(
$($(
$lt
,)+)?
$($(
$T $(:
$( $super + )?
$( ?$Sized + )?
$( $Bound )?
)?
,)+)?
)?> (
*mut Self,
);
impl<
'polonius,
$(
$($(
$lt
,)+)?
$($(
$T $(:
$( $super + )?
$( ?$Sized + )?
$( $Bound )?
)?
,)+)?
)?
>
$crate::WithLifetime<'polonius>
for
__polonius_the_crab_Ret<$(
$($($lt ,)+)?
$($($T ,)+)?
)?>
{
type T = $Ret;
}
match
$crate::polonius::<
__polonius_the_crab_Ret<$(
$($($T ,)+)?
)?>,
_,
_,
_,
>(
$var,
|mut $var: &mut _| {
$var = $var;
$crate::ඞ::core::result::Result::Err(
if true
$body
else {
// avoid a dead-code warning
$crate::ඞ::core::option::Option::None.unwrap()
}
)
},
)
{
| $crate::ඞ::core::result::Result::Ok(ret) => return ret,
| $crate::ඞ::core::result::Result::Err((give_input_back, bail_value)) => {
$var = give_input_back;
bail_value
},
}
})}
/// See [`polonius!`] for more info.
#[macro_export]
macro_rules! polonius_return {( $e:expr $(,)? ) => (
return $crate::ඞ::core::result::Result::Ok($e)
)}
/// See [`polonius!`] for more info.
#[macro_export]
macro_rules! polonius_break {( $($e:expr $(,)?)? ) => (
return $crate::ඞ::core::result::Result::Err(($($e)?))
)}
// macro internals
#[doc(hidden)] /** Not part of the public API */ pub
mod ඞ {
pub use ::core; // or `std`
}
#[cfg_attr(feature = "ui-tests",
cfg_attr(all(), doc = include_str!("compile_fail_tests.md")),
)]
mod _compile_fail_tests {}