Simplify all the code

This also fixes TheLarkInn#2, except I went with LazyLock here, as it's more fitting.

Also use conditional compilation instead of OS constants, to ensure that
on non linux targets the crate *definitely* never compiles to any code and never
allocates static storage.

Cargo.toml

@@ -9,6 +9,5 @@ categories = ["command-line-utilities"]
 
 [dependencies]
 is-docker = "0.2.0"
-once_cell = "1.17.0"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

src/lib.rs

@@ -1,65 +1,25 @@
-extern crate is_docker;
-extern crate once_cell;
-
-use once_cell::sync::OnceCell;
-use std::{fs::File, io::Read};
+use std::sync::LazyLock;
 
+#[cfg(target_os = "linux")]
 pub fn is_wsl() -> bool {
-    static CACHED_RESULT: OnceCell<bool> = OnceCell::new();
+    static CACHED_RESULT: LazyLock<bool> = LazyLock::new(|| {
+        let is_microsoft = file_includes_microsoft("/proc/version")
+            || file_includes_microsoft("/proc/sys/kernel/osrelease");
 
-    *CACHED_RESULT.get_or_init(|| {
-        if std::env::consts::OS != "linux" {
-            return false;
-        }
+        is_microsoft && !is_docker::is_docker()
+    });
 
-        if let Ok(os_release) = get_os_release() {
-            if os_release.to_lowercase().contains("microsoft") {
-                return !is_docker::is_docker();
-            }
-        }
+    *CACHED_RESULT
+}
 
-        if proc_version_includes_microsoft() {
-            !is_docker::is_docker()
-        } else {
-            false
-        }
-    })
+#[cfg(not(target_os = "linux"))]
+pub fn is_wsl() -> bool {
+    false
 }
 
-fn proc_version_includes_microsoft() -> bool {
-    match std::fs::read_to_string("/proc/version") {
+fn file_includes_microsoft(filename: &str) -> bool {
+    match std::fs::read_to_string(filename) {
         Ok(file_contents) => file_contents.to_lowercase().contains("microsoft"),
         Err(_) => false,
     }
 }
-
-// This function is copied from the sys-info crate to avoid taking a dependency on all of sys-info
-// https://docs.rs/sys-info/0.9.1/src/sys_info/lib.rs.html#426-433
-//
-// The MIT License (MIT)
-//
-// Copyright (c) 2015 Siyu Wang
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-fn get_os_release() -> Result<String, std::io::Error> {
-    let mut s = String::new();
-    File::open("/proc/sys/kernel/osrelease")?.read_to_string(&mut s)?;
-    s.pop(); // pop '\n'
-    Ok(s)
-}