library/alloc/src/lib.rs

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