rust/alloc/lib.rs

   1 // SPDX-License-Identifier: Apache-2.0 OR MIT
   2
   3 //! # The Rust core allocation and collections library
   4 //!
   5 //! This library provides smart pointers and collections for managing
   6 //! heap-allocated values.
   7 //!
   8 //! This library, like core, normally doesn’t need to be used directly
   9 //! since its contents are re-exported in the [`std` crate](../std/index.html).
  10 //! Crates that use the `#![no_std]` attribute however will typically
  11 //! not depend on `std`, so they’d use this crate instead.
  12 //!
  13 //! ## Boxed values
  14 //!
  15 //! The [`Box`] type is a smart pointer type. There can only be one owner of a
  16 //! [`Box`], and the owner can decide to mutate the contents, which live on the
  17 //! heap.
  18 //!
  19 //! This type can be sent among threads efficiently as the size of a `Box` value
  20 //! is the same as that of a pointer. Tree-like data structures are often built
  21 //! with boxes because each node often has only one owner, the parent.
  22 //!
  23 //! ## Reference counted pointers
  24 //!
  25 //! The [`Rc`] type is a non-threadsafe reference-counted pointer type intended
  26 //! for sharing memory within a thread. An [`Rc`] pointer wraps a type, `T`, and
  27 //! only allows access to `&T`, a shared reference.
  28 //!
  29 //! This type is useful when inherited mutability (such as using [`Box`]) is too
  30 //! constraining for an application, and is often paired with the [`Cell`] or
  31 //! [`RefCell`] types in order to allow mutation.
  32 //!
  33 //! ## Atomically reference counted pointers
  34 //!
  35 //! The [`Arc`] type is the threadsafe equivalent of the [`Rc`] type. It
  36 //! provides all the same functionality of [`Rc`], except it requires that the
  37 //! contained type `T` is shareable. Additionally, [`Arc<T>`][`Arc`] is itself
  38 //! sendable while [`Rc<T>`][`Rc`] is not.
  39 //!
  40 //! This type allows for shared access to the contained data, and is often
  41 //! paired with synchronization primitives such as mutexes to allow mutation of
  42 //! shared resources.
  43 //!
  44 //! ## Collections
  45 //!
  46 //! Implementations of the most common general purpose data structures are
  47 //! defined in this library. They are re-exported through the
  48 //! [standard collections library](../std/collections/index.html).
  49 //!
  50 //! ## Heap interfaces
  51 //!
  52 //! The [`alloc`](alloc/index.html) module defines the low-level interface to the
  53 //! default global allocator. It is not compatible with the libc allocator API.
  54 //!
  55 //! [`Arc`]: sync
  56 //! [`Box`]: boxed
  57 //! [`Cell`]: core::cell
  58 //! [`Rc`]: rc
  59 //! [`RefCell`]: core::cell
  60
  61 // To run alloc tests without x.py without ending up with two copies of alloc, Miri needs to be
  62 // able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
  63 // rustc itself never sets the feature, so this line has no effect there.
  64 #![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
  65 //
  66 #![allow(unused_attributes)]
  67 #![stable(feature = "alloc", since = "1.36.0")]
  68 #![doc(
  69     html_playground_url = "https://play.rust-lang.org/",
  70     issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
  71     test(no_crate_inject, attr(allow(unused_variables), deny(warnings)))
  72 )]
  73 #![doc(cfg_hide(
  74     not(test),
  75     not(any(test, bootstrap)),
  76     any(not(feature = "miri-test-libstd"), test, doctest),
  77     no_global_oom_handling,
  78     not(no_global_oom_handling),
  79     not(no_rc),
  80     not(no_sync),
  81     target_has_atomic = "ptr"
  82 ))]
  83 #![no_std]
  84 #![needs_allocator]
  85 // Lints:
  86 #![deny(unsafe_op_in_unsafe_fn)]
  87 #![deny(fuzzy_provenance_casts)]
  88 #![warn(deprecated_in_future)]
  89 #![warn(missing_debug_implementations)]
  90 #![warn(missing_docs)]
  91 #![allow(explicit_outlives_requirements)]
  92 #![warn(multiple_supertrait_upcastable)]
  93 #![cfg_attr(not(bootstrap), allow(internal_features))]
  94 #![cfg_attr(not(bootstrap), allow(rustdoc::redundant_explicit_links))]
  95 //
  96 // Library features:
  97 // tidy-alphabetical-start
  98 #![cfg_attr(not(no_global_oom_handling), feature(const_alloc_error))]
  99 #![cfg_attr(not(no_global_oom_handling), feature(const_btree_len))]
 100 #![cfg_attr(test, feature(is_sorted))]
 101 #![cfg_attr(test, feature(new_uninit))]
 102 #![feature(alloc_layout_extra)]
 103 #![feature(allocator_api)]
 104 #![feature(array_chunks)]
 105 #![feature(array_into_iter_constructors)]
 106 #![feature(array_methods)]
 107 #![feature(array_windows)]
 108 #![feature(ascii_char)]
 109 #![feature(assert_matches)]
 110 #![feature(async_iterator)]
 111 #![feature(coerce_unsized)]
 112 #![feature(const_align_of_val)]
 113 #![feature(const_box)]
 114 #![cfg_attr(not(no_borrow), feature(const_cow_is_borrowed))]
 115 #![feature(const_eval_select)]
 116 #![feature(const_maybe_uninit_as_mut_ptr)]
 117 #![feature(const_maybe_uninit_write)]
 118 #![feature(const_maybe_uninit_zeroed)]
 119 #![feature(const_pin)]
 120 #![feature(const_refs_to_cell)]
 121 #![feature(const_size_of_val)]
 122 #![feature(const_waker)]
 123 #![feature(core_intrinsics)]
 124 #![feature(core_panic)]
 125 #![feature(dispatch_from_dyn)]
 126 #![feature(error_generic_member_access)]
 127 #![feature(error_in_core)]
 128 #![feature(exact_size_is_empty)]
 129 #![feature(extend_one)]
 130 #![feature(fmt_internals)]
 131 #![feature(fn_traits)]
 132 #![feature(hasher_prefixfree_extras)]
 133 #![feature(inline_const)]
 134 #![feature(inplace_iteration)]
 135 #![feature(iter_advance_by)]
 136 #![feature(iter_next_chunk)]
 137 #![feature(iter_repeat_n)]
 138 #![feature(layout_for_ptr)]
 139 #![feature(maybe_uninit_slice)]
 140 #![feature(maybe_uninit_uninit_array)]
 141 #![feature(maybe_uninit_uninit_array_transpose)]
 142 #![feature(pattern)]
 143 #![feature(pointer_byte_offsets)]
 144 #![feature(ptr_internals)]
 145 #![feature(ptr_metadata)]
 146 #![feature(ptr_sub_ptr)]
 147 #![feature(receiver_trait)]
 148 #![feature(saturating_int_impl)]
 149 #![feature(set_ptr_value)]
 150 #![feature(sized_type_properties)]
 151 #![feature(slice_from_ptr_range)]
 152 #![feature(slice_group_by)]
 153 #![feature(slice_ptr_get)]
 154 #![feature(slice_ptr_len)]
 155 #![feature(slice_range)]
 156 #![feature(std_internals)]
 157 #![feature(str_internals)]
 158 #![feature(strict_provenance)]
 159 #![feature(trusted_len)]
 160 #![feature(trusted_random_access)]
 161 #![feature(try_trait_v2)]
 162 #![feature(tuple_trait)]
 163 #![feature(unchecked_math)]
 164 #![feature(unicode_internals)]
 165 #![feature(unsize)]
 166 #![feature(utf8_chunks)]
 167 // tidy-alphabetical-end
 168 //
 169 // Language features:
 170 // tidy-alphabetical-start
 171 #![cfg_attr(not(test), feature(generator_trait))]
 172 #![cfg_attr(test, feature(panic_update_hook))]
 173 #![cfg_attr(test, feature(test))]
 174 #![feature(allocator_internals)]
 175 #![feature(allow_internal_unstable)]
 176 #![feature(associated_type_bounds)]
 177 #![feature(c_unwind)]
 178 #![feature(cfg_sanitize)]
 179 #![feature(const_mut_refs)]
 180 #![feature(const_precise_live_drops)]
 181 #![feature(const_ptr_write)]
 182 #![feature(const_trait_impl)]
 183 #![feature(const_try)]
 184 #![feature(dropck_eyepatch)]
 185 #![feature(exclusive_range_pattern)]
 186 #![feature(fundamental)]
 187 #![feature(hashmap_internals)]
 188 #![feature(lang_items)]
 189 #![feature(min_specialization)]
 190 #![feature(multiple_supertrait_upcastable)]
 191 #![feature(negative_impls)]
 192 #![feature(never_type)]
 193 #![feature(pointer_is_aligned)]
 194 #![feature(rustc_allow_const_fn_unstable)]
 195 #![feature(rustc_attrs)]
 196 #![feature(slice_internals)]
 197 #![feature(staged_api)]
 198 #![feature(stmt_expr_attributes)]
 199 #![feature(unboxed_closures)]
 200 #![feature(unsized_fn_params)]
 201 #![feature(with_negative_coherence)]
 202 // tidy-alphabetical-end
 203 //
 204 // Rustdoc features:
 205 #![feature(doc_cfg)]
 206 #![feature(doc_cfg_hide)]
 207 // Technically, this is a bug in rustdoc: rustdoc sees the documentation on `#[lang = slice_alloc]`
 208 // blocks is for `&[T]`, which also has documentation using this feature in `core`, and gets mad
 209 // that the feature-gate isn't enabled. Ideally, it wouldn't check for the feature gate for docs
 210 // from other crates, but since this can only appear for lang items, it doesn't seem worth fixing.
 211 #![feature(intra_doc_pointers)]
 212
 213 // Allow testing this library
 214 #[cfg(test)]
 215 #[macro_use]
 216 extern crate std;
 217 #[cfg(test)]
 218 extern crate test;
 219 #[cfg(test)]
 220 mod testing;
 221
 222 // Module with internal macros used by other modules (needs to be included before other modules).
 223 #[cfg(not(no_macros))]
 224 #[macro_use]
 225 mod macros;
 226
 227 mod raw_vec;
 228
 229 // Heaps provided for low-level allocation strategies
 230
 231 pub mod alloc;
 232
 233 // Primitive types using the heaps above
 234
 235 // Need to conditionally define the mod from `boxed.rs` to avoid
 236 // duplicating the lang-items when building in test cfg; but also need
 237 // to allow code to have `use boxed::Box;` declarations.
 238 #[cfg(not(test))]
 239 pub mod boxed;
 240 #[cfg(test)]
 241 mod boxed {
 242     pub use std::boxed::Box;
 243 }
 244 #[cfg(not(no_borrow))]
 245 pub mod borrow;
 246 pub mod collections;
 247 #[cfg(all(not(no_rc), not(no_sync), not(no_global_oom_handling)))]
 248 pub mod ffi;
 249 #[cfg(not(no_fmt))]
 250 pub mod fmt;
 251 #[cfg(not(no_rc))]
 252 pub mod rc;
 253 pub mod slice;
 254 #[cfg(not(no_str))]
 255 pub mod str;
 256 #[cfg(not(no_string))]
 257 pub mod string;
 258 #[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
 259 pub mod sync;
 260 #[cfg(all(not(no_global_oom_handling), not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
 261 pub mod task;
 262 #[cfg(test)]
 263 mod tests;
 264 pub mod vec;
 265
 266 #[doc(hidden)]
 267 #[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
 268 pub mod __export {
 269     pub use core::format_args;
 270 }
 271
 272 #[cfg(test)]
 273 #[allow(dead_code)] // Not used in all configurations
 274 pub(crate) mod test_helpers {
 275     /// Copied from `std::test_helpers::test_rng`, since these tests rely on the
 276     /// seed not being the same for every RNG invocation too.
 277     pub(crate) fn test_rng() -> rand_xorshift::XorShiftRng {
 278         use std::hash::{BuildHasher, Hash, Hasher};
 279         let mut hasher = std::collections::hash_map::RandomState::new().build_hasher();
 280         std::panic::Location::caller().hash(&mut hasher);
 281         let hc64 = hasher.finish();
 282         let seed_vec =
 283             hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<crate::vec::Vec<u8>>();
 284         let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
 285         rand::SeedableRng::from_seed(seed)
 286     }
 287 }