uucore: readlink: introduce IS_POSIXLY_CORRECT static

Author: xtqqczze

src/uu/df/src/blocks.rs

@@ -367,12 +367,4 @@ mod tests {
         assert_eq!(format!("{}", BlockSize::Bytes(1000 * 1024)), "1.1MB");
         assert_eq!(format!("{}", BlockSize::Bytes(1_000_000_000_000)), "1.0TB");
     }
-
-    #[test]
-    fn test_default_block_size() {
-        assert_eq!(BlockSize::Bytes(1024), BlockSize::default());
-        unsafe { env::set_var("POSIXLY_CORRECT", "1") };
-        assert_eq!(BlockSize::Bytes(512), BlockSize::default());
-        unsafe { env::remove_var("POSIXLY_CORRECT") };
-    }
 }

src/uucore/src/lib/features/parser/parse_block_size.rs

@@ -9,6 +9,8 @@
 //! for resolving block sizes from environment variables and defaults.
 //! This module centralizes that logic.
 
+use std::sync::LazyLock;
+
 use super::parse_size::parse_size_non_zero_u64;
 
 /// Result of looking up a block size from environment variables.
@@ -66,13 +68,12 @@ pub fn block_size_from_env(vars: &[&str]) -> BlockSizeEnv {
 ///
 /// Returns 512 if `POSIXLY_CORRECT` is set, 1024 otherwise.
 pub fn default_block_size() -> u64 {
-    if std::env::var("POSIXLY_CORRECT").is_ok() {
-        512
-    } else {
-        1024
-    }
+    if *IS_POSIXLY_CORRECT { 512 } else { 1024 }
 }
 
+static IS_POSIXLY_CORRECT: LazyLock<bool> =
+    LazyLock::new(|| std::env::var_os("POSIXLY_CORRECT").is_some());
+
 #[cfg(test)]
 mod tests {
     use super::*;