du: Add support for reading time-style from environment

Similar as what ls does, but du has an extra compatibility layer
described in the GNU manual (and that upstream dev helped me
understand: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=79113 ).

Author: drinkcat

src/uu/du/src/du.rs

@@ -666,7 +666,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     };
 
     let time_format = if time.is_some() {
-        parse_time_style(matches.get_one::<String>("time-style").map(|s| s.as_str()))?.to_string()
+        parse_time_style(matches.get_one::<String>("time-style"))?
     } else {
         format::LONG_ISO.to_string()
     };
@@ -755,18 +755,40 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     Ok(())
 }
 
-fn parse_time_style(s: Option<&str>) -> UResult<&str> {
+// Parse --time-style argument, falling back to environment variable if necessary.
+fn parse_time_style(s: Option<&String>) -> UResult<String> {
+    let s = match s {
+        Some(s) => Some(s.into()),
+        None => {
+            match env::var("TIME_STYLE") {
+                // Per GNU manual, strip `posix-` if present, ignore anything after a newline if
+                // the string starts with +, and ignore "locale".
+                Ok(s) => {
+                    let s = s.strip_prefix("posix-").unwrap_or(s.as_str());
+                    let s = match s.chars().next().unwrap() {
+                        '+' => s.split('\n').next().unwrap(),
+                        _ => s,
+                    };
+                    match s {
+                        "locale" => None,
+                        _ => Some(s.to_string()),
+                    }
+                }
+                Err(_) => None,
+            }
+        }
+    };
     match s {
-        Some(s) => match s {
-            "full-iso" => Ok(format::FULL_ISO),
-            "long-iso" => Ok(format::LONG_ISO),
-            "iso" => Ok(format::ISO),
+        Some(s) => match s.as_ref() {
+            "full-iso" => Ok(format::FULL_ISO.to_string()),
+            "long-iso" => Ok(format::LONG_ISO.to_string()),
+            "iso" => Ok(format::ISO.to_string()),
             _ => match s.chars().next().unwrap() {
-                '+' => Ok(&s[1..]),
-                _ => Err(DuError::InvalidTimeStyleArg(s.into()).into()),
+                '+' => Ok(s[1..].to_string()),
+                _ => Err(DuError::InvalidTimeStyleArg(s).into()),
             },
         },
-        None => Ok(format::LONG_ISO),
+        None => Ok(format::LONG_ISO.to_string()),
     }
 }
 

tests/by-util/test_du.rs

@@ -591,6 +591,7 @@ fn test_du_h_precision() {
     }
 }
 
+#[allow(clippy::too_many_lines)]
 #[cfg(feature = "touch")]
 #[test]
 fn test_du_time() {
@@ -676,6 +677,57 @@ fn test_du_time() {
         .succeeds();
     result.stdout_only("0\t2016_\n_00\tdate_test\n");
 
+    // Time style can also be setup from environment
+    let result = ts
+        .ucmd()
+        .env("TZ", "UTC")
+        .env("TIME_STYLE", "full-iso")
+        .arg("--time")
+        .arg("date_test")
+        .succeeds();
+    result.stdout_only("0\t2016-06-16 00:00:00.000000000 +0000\tdate_test\n");
+
+    // For compatibility reason, we also allow posix- prefix.
+    let result = ts
+        .ucmd()
+        .env("TZ", "UTC")
+        .env("TIME_STYLE", "posix-full-iso")
+        .arg("--time")
+        .arg("date_test")
+        .succeeds();
+    result.stdout_only("0\t2016-06-16 00:00:00.000000000 +0000\tdate_test\n");
+
+    // ... and we strip content after a new line
+    let result = ts
+        .ucmd()
+        .env("TZ", "UTC")
+        .env("TIME_STYLE", "+XXX\nYYY")
+        .arg("--time")
+        .arg("date_test")
+        .succeeds();
+    result.stdout_only("0\tXXX\tdate_test\n");
+
+    // ... and we ignore "locale", fall back to full-iso.
+    let result = ts
+        .ucmd()
+        .env("TZ", "UTC")
+        .env("TIME_STYLE", "locale")
+        .arg("--time")
+        .arg("date_test")
+        .succeeds();
+    result.stdout_only("0\t2016-06-16 00:00\tdate_test\n");
+
+    // Command line option takes precedence
+    let result = ts
+        .ucmd()
+        .env("TZ", "UTC")
+        .env("TIME_STYLE", "full-iso")
+        .arg("--time")
+        .arg("--time-style=iso")
+        .arg("date_test")
+        .succeeds();
+    result.stdout_only("0\t2016-06-16\tdate_test\n");
+
     for argument in ["--time=atime", "--time=atim", "--time=a"] {
         let result = ts
             .ucmd()