Switch to rustix from libc

This commit replaces the code using libc with equivalent code using
rustix. In addition to safety, this move also removes the dependency on
C code and replaces it with a syscall, which is much faster.

This PR also adds `forbid(unsafe_code)`, so that this crate shows up as
unsafe-free when processed in `cargo-geiger`.

Signed-off-by: John Nunley <dev@notgull.net>

Cargo.toml

@@ -14,13 +14,14 @@ keywords = ["which", "which-rs", "unix", "command"]
 [dependencies]
 dirs = "5.0.1"
 either = "1.6.1"
-libc = "0.2.121"
 regex = { version = "1.5.5", optional = true }
+rustix = { version = "0.38.10", default-features = false, features = ["fs", "std"] }
 
 [target.'cfg(windows)'.dependencies]
 once_cell = "1"
 
 [dev-dependencies]
+libc = "0.2.147"
 tempfile = "3.3.0"
 
 [package.metadata.docs.rs]

src/checker.rs

@@ -1,11 +1,5 @@
 use crate::finder::Checker;
-#[cfg(any(unix, target_os = "wasi"))]
-use std::ffi::CString;
 use std::fs;
-#[cfg(unix)]
-use std::os::unix::ffi::OsStrExt;
-#[cfg(target_os = "wasi")]
-use std::os::wasi::ffi::OsStrExt;
 use std::path::Path;
 
 pub struct ExecutableChecker;
@@ -19,9 +13,8 @@ impl ExecutableChecker {
 impl Checker for ExecutableChecker {
     #[cfg(any(unix, target_os = "wasi"))]
     fn is_valid(&self, path: &Path) -> bool {
-        CString::new(path.as_os_str().as_bytes())
-            .map(|c| unsafe { libc::access(c.as_ptr(), libc::X_OK) == 0 })
-            .unwrap_or(false)
+        use rustix::fs as rfs;
+        rfs::access(path, rfs::Access::EXEC_OK).is_ok()
     }
 
     #[cfg(windows)]

src/lib.rs

@@ -14,6 +14,8 @@
 //!
 //! ```
 
+#![forbid(unsafe_code)]
+
 mod checker;
 mod error;
 mod finder;