sptr: The Strict Provenance Polyfill

This library provides a stable polyfill for Rust's [Strict Provenance] experiment.

Mapping to STD APIs:

```rust ,ignore // core::ptr (sptr) pub fn invalid(addr: usize) -> *const T; pub fn invalid_mut(addr: usize) -> *mut T;

// core::pointer (sptr::Strict) pub fn addr(self) -> usize; pub fn withaddr(self, addr: usize) -> Self; pub fn mapaddr(self, f: impl FnOnce(usize) -> usize) -> Self;

// NON-STANDARD EXTENSIONS (feature = uptr) sptr::uptr sptr::iptr

// NON-STANDARD EXTENSIONS (feature = opaque_fn) sptr::OpaqueFn

// DEPRECATED BY THIS MODEL in core::pointer (sptr::Strict) // (disable with default-features = false) pub fn tobits(self) -> usize; pub fn frombits(usize) -> Self; ```

Swapping between the two should be as simple as switching between sptr:: and ptr:: for static functions. For methods, you must import sptr::Strict into your module for the extension trait's methods to overlay std. The compiler will (understandably) complain that you are overlaying std, so you will need to also silence that as seen in the following example:

```rust

![allow(unstablenamecollisions)]

use sptr::Strict;

let ptr = sptr::invalid_mut::(1); println!("{}", ptr.addr()); ```

By default, this crate will also mark methods on pointers as "deprecated" if they are incompatible with strict_provenance. If you don't want this, set default-features = false in your Cargo.toml.

Rust is the canonical source of definitions for these APIs and semantics, but the docs here will vaguely try to mirror the docs checked into Rust.