Replace more type casts with non-cast equivalents (#437)

.clippy.toml

@@ -1 +1 @@
-msrv = "1.56"
+msrv = "1.57"

.github/workflows/tests.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-22.04, windows-2022]
-        toolchain: [nightly, beta, stable, 1.56]
+        toolchain: [nightly, beta, stable, 1.57]
         # Only Test macOS on stable to reduce macOS CI jobs
         include:
           # x86_64-apple-darwin.

Cargo.toml

@@ -1,8 +1,8 @@
 [package]
 name = "getrandom"
 version = "0.2.15" # Also update html_root_url in lib.rs when bumping this
-edition = "2018"
-rust-version = "1.56"
+edition = "2021"
+rust-version = "1.57" # Sync .clippy.toml, tests.yml, and README.md.
 authors = ["The Rand Project Developers"]
 license = "MIT OR Apache-2.0"
 description = "A small cross-platform library for retrieving random data from system source"

README.md

@@ -52,7 +52,7 @@ crate features, WASM support and Custom RNGs see the
 
 ## Minimum Supported Rust Version
 
-This crate requires Rust 1.56.0 or later.
+This crate requires Rust 1.57.0 or later.
 
 ## Platform Support
 

benches/buffer.rs

@@ -8,7 +8,7 @@ use std::mem::MaybeUninit;
 fn bench_getrandom<const N: usize>() {
     let mut buf = [0u8; N];
     getrandom::getrandom(&mut buf).unwrap();
-    test::black_box(&buf as &[u8]);
+    test::black_box(&buf[..]);
 }
 
 // Call getrandom_uninit on an uninitialized stack buffer

src/hermit.rs

@@ -2,11 +2,6 @@
 use crate::Error;
 use core::{mem::MaybeUninit, num::NonZeroU32};
 
-/// Minimum return value which we should get from syscalls in practice,
-/// because Hermit uses positive `i32`s for error codes:
-/// https://github.com/hermitcore/libhermit-rs/blob/main/src/errno.rs
-const MIN_RET_CODE: isize = -(i32::MAX as isize);
-
 extern "C" {
     fn sys_read_entropy(buffer: *mut u8, length: usize, flags: u32) -> isize;
 }
@@ -18,9 +13,13 @@ pub fn getrandom_inner(mut dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
         if res > 0 && (res as usize) <= dest.len() {
             dest = &mut dest[res as usize..];
         } else {
-            let err = match res {
-                MIN_RET_CODE..=-1 => NonZeroU32::new(-res as u32).unwrap().into(),
-                _ => Error::UNEXPECTED,
+            let err = if res < 0 {
+                u32::try_from(res.unsigned_abs())
+                    .ok()
+                    .and_then(NonZeroU32::new)
+                    .map_or(Error::UNEXPECTED, Error::from)
+            } else {
+                Error::UNEXPECTED
             };
             return Err(err);
         }

src/lazy.rs

@@ -55,7 +55,7 @@ impl LazyBool {
     }
 
     pub fn unsync_init(&self, init: impl FnOnce() -> bool) -> bool {
-        self.0.unsync_init(|| init() as usize) != 0
+        self.0.unsync_init(|| usize::from(init())) != 0
     }
 }
 

src/solid.rs

@@ -13,6 +13,6 @@ pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     } else {
         // ITRON error numbers are always negative, so we negate it so that it
         // falls in the dedicated OS error range (1..INTERNAL_START).
-        Err(NonZeroU32::new((-ret) as u32).unwrap().into())
+        Err(NonZeroU32::new(ret.unsigned_abs()).map_or(Error::UNEXPECTED, Error::from))
     }
 }

src/util_libc.rs

@@ -35,12 +35,15 @@ cfg_if! {
 }
 
 pub fn last_os_error() -> Error {
-    let errno = unsafe { get_errno() };
-    if errno > 0 {
-        Error::from(NonZeroU32::new(errno as u32).unwrap())
-    } else {
-        Error::ERRNO_NOT_POSITIVE
-    }
+    let errno: libc::c_int = unsafe { get_errno() };
+
+    // c_int-to-u32 conversion is lossless for nonnegative values if they are the same size.
+    const _: () = assert!(core::mem::size_of::<libc::c_int>() == core::mem::size_of::<u32>());
+
+    u32::try_from(errno)
+        .ok()
+        .and_then(NonZeroU32::new)
+        .map_or(Error::ERRNO_NOT_POSITIVE, Error::from)
 }
 
 // Fill a buffer by repeatedly invoking a system call. The `sys_fill` function: