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Stable type_eq #2150

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merged 6 commits into from
May 7, 2024
Merged

Stable type_eq #2150

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a830ab9
stable type eq
addisoncrump May 7, 2024
1f0d8d5
whoops, wrong section
addisoncrump May 7, 2024
6e9ec48
satiate clippy
addisoncrump May 7, 2024
f6e3a61
remove extraneous comment
addisoncrump May 7, 2024
8300165
explain
addisoncrump May 7, 2024
a3afb9c
bonus inline
addisoncrump May 7, 2024
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13 changes: 6 additions & 7 deletions libafl_bolts/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@ document-features = ["dep:document-features"]
std = ["serde_json", "serde_json/std", "hostname", "nix", "serde/std", "uuid", "backtrace", "uds", "serial_test", "alloc"]

## Enables all features that allocate in `no_std`
alloc = ["serde/alloc", "hashbrown", "postcard", "erased-serde/alloc", "ahash"]
alloc = ["serde/alloc", "hashbrown", "postcard", "erased-serde/alloc", "ahash"]

## Provide the `#[derive(SerdeAny)]` macro.
derive = ["libafl_derive"]
Expand Down Expand Up @@ -95,25 +95,24 @@ rustversion = "1.0"
libafl_derive = { version = "0.12.0", optional = true, path = "../libafl_derive" }
static_assertions = "1.1.0"

rustversion = "1.0"
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tuple_list = { version = "0.1.3" }
hashbrown = { version = "0.14", features = ["serde", "ahash"], default-features=false, optional = true } # A faster hashmap, nostd compatible
hashbrown = { version = "0.14", features = ["serde", "ahash"], default-features = false, optional = true } # A faster hashmap, nostd compatible
xxhash-rust = { version = "0.8.5", features = ["xxh3"], optional = true } # xxh3 hashing for rust
serde = { version = "1.0", default-features = false, features = ["derive"] } # serialization lib
erased-serde = { version = "0.3.21", default-features = false, optional = true } # erased serde
postcard = { version = "1.0", features = ["alloc"], default-features = false, optional = true } # no_std compatible serde serialization format
num_enum = { version = "0.7", default-features = false }
ahash = { version = "0.8", default-features=false, optional = true } # The hash function already used in hashbrown
backtrace = {version = "0.3", optional = true} # Used to get the stacktrace in StacktraceObserver
ahash = { version = "0.8", default-features = false, optional = true } # The hash function already used in hashbrown
backtrace = { version = "0.3", optional = true } # Used to get the stacktrace in StacktraceObserver

ctor = { optional = true, version = "0.2" }
serde_json = { version = "1.0", optional = true, default-features = false, features = ["alloc"] }
miniz_oxide = { version = "0.7.1", optional = true}
miniz_oxide = { version = "0.7.1", optional = true }
hostname = { version = "^0.3", optional = true } # Is there really no gethostname in the stdlib?
rand_core = { version = "0.6", optional = true }
nix = { version = "0.27", default-features = false, optional = true, features = ["signal", "socket", "poll"] }
uuid = { version = "1.4", optional = true, features = ["serde", "v4"] }
clap = {version = "4.5", features = ["derive", "wrap_help"], optional = true} # CLI parsing, for libafl_bolts::cli / the `cli` feature
clap = { version = "4.5", features = ["derive", "wrap_help"], optional = true } # CLI parsing, for libafl_bolts::cli / the `cli` feature
log = "0.4.20"

pyo3 = { version = "0.18", optional = true, features = ["serde", "macros"] }
Expand Down
62 changes: 28 additions & 34 deletions libafl_bolts/src/tuples.rs
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Expand Up @@ -6,6 +6,7 @@ use alloc::{borrow::Cow, vec::Vec};
use core::ops::{Deref, DerefMut};
use core::{
any::{type_name, TypeId},
cell::Cell,
fmt::{Debug, Formatter},
marker::PhantomData,
mem::transmute,
Expand All @@ -23,40 +24,37 @@ use crate::HasLen;
#[cfg(feature = "alloc")]
use crate::Named;

/// Returns if the type `T` is equal to `U`
/// From <https://stackoverflow.com/a/60138532/7658998>
#[rustversion::nightly]
#[inline]
/// Returns if the type `T` is equal to `U`, ignoring lifetimes.
#[inline] // this entire call gets optimized away :)
#[must_use]
pub const fn type_eq<T: ?Sized, U: ?Sized>() -> bool {
// Helper trait. `VALUE` is false, except for the specialization of the
// case where `T == U`.
trait TypeEq<U: ?Sized> {
const VALUE: bool;
}

// Default implementation.
impl<T: ?Sized, U: ?Sized> TypeEq<U> for T {
default const VALUE: bool = false;
}

// Specialization for `T == U`.
impl<T: ?Sized> TypeEq<T> for T {
const VALUE: bool = true;
pub fn type_eq<T: ?Sized, U: ?Sized>() -> bool {
// decider struct: hold a cell (which we will update if the types are unequal) and some
// phantom data using a function pointer to allow for Copy to be implemented
struct W<'a, T: ?Sized, U: ?Sized>(&'a Cell<bool>, PhantomData<fn() -> (&'a T, &'a U)>);

// default implementation: if the types are unequal, we will use the clone implementation
impl<'a, T: ?Sized, U: ?Sized> Clone for W<'a, T, U> {
#[inline]
fn clone(&self) -> Self {
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// indicate that the types are unequal
// unfortunately, use of interior mutability (Cell) makes this not const-compatible
// not really possible to get around at this time
self.0.set(false);
W(self.0, self.1)
}
}

<T as TypeEq<U>>::VALUE
}
// specialized implementation: Copy is only implemented if the types are the same
#[allow(clippy::mismatching_type_param_order)]
impl<'a, T: ?Sized> Copy for W<'a, T, T> {}

/// Returns if the type `T` is equal to `U`
/// As this relies on [`type_name`](https://doc.rust-lang.org/std/any/fn.type_name.html#note) internally,
/// there is a chance for collisions.
/// Use `nightly` if you need a perfect match at all times.
#[rustversion::not(nightly)]
#[inline]
#[must_use]
pub fn type_eq<T: ?Sized, U: ?Sized>() -> bool {
type_name::<T>() == type_name::<U>()
let detected = Cell::new(true);
// [].clone() is *specialized* in core.
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Any documentation on this?

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Like, anything official/some blog post, forum entry, docstring, ...?

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Sanity check here (implied specialization): https://doc.rust-lang.org/stable/std/clone/trait.Clone.html#how-can-i-implement-clone

You can see the specific specialization here: https://doc.rust-lang.org/stable/src/core/slice/mod.rs.html#4656-4686

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Can we add those to the code?

// Types which implement copy will have their copy implementations used, falling back to clone.
// If the types are the same, then our clone implementation (which sets our Cell to false)
// will never be called, meaning that our Cell's content remains true.
let res = [W::<T, U>(&detected, PhantomData)].clone();
res[0].0.get()
}

/// Borrow each member of the tuple
Expand Down Expand Up @@ -453,10 +451,6 @@ where
}

/// Match for a name and return the value
///
/// # Note
/// This operation may not be 100% accurate with Rust stable, see the notes for [`type_eq`]
/// (in `nightly`, it uses [specialization](https://stackoverflow.com/a/60138532/7658998)).
#[cfg(feature = "alloc")]
pub trait MatchName {
/// Match for a name and return the borrowed value
Expand Down
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