From 6be47a6d92d136d121b911d2cd3f15ccb4096c49 Mon Sep 17 00:00:00 2001
From: oech3 <79379754+oech3@users.noreply.github.com>
Date: Tue, 16 Jun 2026 23:27:51 +0900
Subject: [PATCH] cmp: remove unsafe & don't open unnecessary /dev/null

---
 Cargo.lock      |  1 +
 Cargo.toml      |  1 +
 fuzz/Cargo.lock | 36 ++++++++++++++++++++++++++++++++++++
 src/cmp.rs      | 26 ++++----------------------
 4 files changed, 42 insertions(+), 22 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 4d1bf647..1a99af50 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -273,6 +273,7 @@ dependencies = [
  "pretty_assertions",
  "rand",
  "regex",
+ "rustix",
  "same-file",
  "tempfile",
  "unicode-width",
diff --git a/Cargo.toml b/Cargo.toml
index 16738396..2dd8a101 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,6 +19,7 @@ chrono = "0.4.38"
 diff = "0.1.13"
 itoa = "1.0.11"
 regex = "1.10.4"
+rustix = { version = "1.1.4", features = ["fs"] }
 same-file = "1.0.6"
 unicode-width = "0.2.0"
 
diff --git a/fuzz/Cargo.lock b/fuzz/Cargo.lock
index 47a03af4..0d4c7a29 100644
--- a/fuzz/Cargo.lock
+++ b/fuzz/Cargo.lock
@@ -32,6 +32,12 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
+[[package]]
+name = "bitflags"
+version = "2.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
+
 [[package]]
 name = "bumpalo"
 version = "3.20.2"
@@ -89,10 +95,21 @@ dependencies = [
  "diff",
  "itoa",
  "regex",
+ "rustix",
  "same-file",
  "unicode-width",
 ]
 
+[[package]]
+name = "errno"
+version = "0.3.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
 [[package]]
 name = "find-msvc-tools"
 version = "0.1.9"
@@ -177,6 +194,12 @@ dependencies = [
  "cc",
 ]
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"
+
 [[package]]
 name = "log"
 version = "0.4.29"
@@ -257,6 +280,19 @@ version = "0.8.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
 
+[[package]]
+name = "rustix"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
 [[package]]
 name = "rustversion"
 version = "1.0.22"
diff --git a/src/cmp.rs b/src/cmp.rs
index 0175466e..9939604e 100644
--- a/src/cmp.rs
+++ b/src/cmp.rs
@@ -11,12 +11,6 @@ use std::iter::Peekable;
 use std::process::ExitCode;
 use std::{cmp, fs, io};
 
-#[cfg(unix)]
-use std::os::fd::{AsRawFd, FromRawFd};
-
-#[cfg(unix)]
-use std::os::unix::fs::MetadataExt;
-
 #[cfg(target_os = "windows")]
 use std::os::windows::fs::MetadataExt;
 
@@ -45,24 +39,12 @@ fn usage_string(executable: &str) -> String {
 
 #[cfg(unix)]
 fn is_stdout_dev_null() -> bool {
-    let Ok(dev_null) = fs::metadata("/dev/null") else {
+    let stdout = io::stdout();
+    let Ok(stat) = rustix::fs::fstat(stdout) else {
         return false;
     };
-
-    let stdout_fd = io::stdout().lock().as_raw_fd();
-
-    // SAFETY: we have exclusive access to stdout right now.
-    let stdout_file = unsafe { fs::File::from_raw_fd(stdout_fd) };
-    let Ok(stdout) = stdout_file.metadata() else {
-        return false;
-    };
-
-    let is_dev_null = stdout.dev() == dev_null.dev() && stdout.ino() == dev_null.ino();
-
-    // Don't let File close the fd. It's unfortunate that File doesn't have a leak_fd().
-    std::mem::forget(stdout_file);
-
-    is_dev_null
+    let dev = stat.st_rdev;
+    rustix::fs::major(dev) == 1 && rustix::fs::minor(dev) == 3
 }
 
 #[cfg(not(any(unix, target_os = "windows")))]