du: honor LC_NUMERIC for decimal separator (#12357)

* du: honor LC_NUMERIC for decimal separator

Route the fractional digit in `uucore::format::human::format_prefixed`
through `locale_decimal_separator()`, the same helper #11941 added for
`numfmt`. Fixes #11956.

* du: spell-check: ignore `replacen`

Matches the directive in `src/uu/numfmt/src/format.rs` for the same
helper introduced by #11941.

src/uu/du/Cargo.toml

@@ -25,6 +25,7 @@ clap = { workspace = true }
 uucore = { workspace = true, features = [
   "format",
   "fsext",
+  "i18n-decimal",
   "parser-size",
   "parser-glob",
   "time",

src/uucore/src/lib/features/format/human.rs

@@ -3,7 +3,7 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore gnulibs sfmt
+// spell-checker:ignore gnulibs sfmt replacen
 
 //! `human`-size formatting
 //!
@@ -24,6 +24,7 @@ pub enum SizeFormat {
 /// 3. The human-readable format uses powers for 1024, but does not display the "i"
 ///    that is commonly used to denote Kibi, Mebi, etc.
 /// 4. Kibi and Kilo are denoted differently ("k" and "K", respectively)
+/// 5. The decimal separator follows LC_NUMERIC ("1.3M" in C, "1,3M" in fr_FR)
 fn format_prefixed(prefixed: &NumberPrefix<f64>) -> String {
     match prefixed {
         NumberPrefix::Standalone(bytes) => bytes.to_string(),
@@ -36,12 +37,29 @@ fn format_prefixed(prefixed: &NumberPrefix<f64>) -> String {
             if (10.0 * bytes).ceil() >= 100.0 {
                 format!("{:.0}{prefix_str}", bytes.ceil())
             } else {
-                format!("{:.1}{prefix_str}", (10.0 * bytes).ceil() / 10.0)
+                let number = format!("{:.1}", (10.0 * bytes).ceil() / 10.0);
+                format!("{}{prefix_str}", localize_decimal(number))
             }
         }
     }
 }
 
+fn localize_decimal(s: String) -> String {
+    #[cfg(feature = "i18n-decimal")]
+    {
+        let sep = crate::i18n::decimal::locale_decimal_separator();
+        if sep == "." {
+            s
+        } else {
+            s.replacen('.', sep, 1)
+        }
+    }
+    #[cfg(not(feature = "i18n-decimal"))]
+    {
+        s
+    }
+}
+
 pub fn human_readable(size: u64, sfmt: SizeFormat) -> String {
     match sfmt {
         SizeFormat::Binary => format_prefixed(&NumberPrefix::binary(size as f64)),

tests/by-util/test_du.rs

@@ -948,6 +948,26 @@ fn test_du_h_precision() {
     }
 }
 
+#[test]
+#[cfg_attr(wasi_runner, ignore = "WASI: locale env vars not propagated")]
+fn test_du_h_locale_decimal_separator() {
+    for (locale, expected) in [("fr_FR.UTF-8", "8,4K"), ("C", "8.4K")] {
+        let (at, mut ucmd) = at_and_ucmd!();
+
+        let fpath = at.plus("test.txt");
+        std::fs::File::create(&fpath)
+            .expect("cannot create test file")
+            .set_len(8500)
+            .expect("cannot truncate test len to size");
+        ucmd.env("LC_ALL", locale)
+            .arg("-h")
+            .arg("--apparent-size")
+            .arg(&fpath)
+            .succeeds()
+            .stdout_only(format!("{expected}\t{}\n", fpath.to_string_lossy()));
+    }
+}
+
 #[allow(clippy::too_many_lines)]
 #[cfg(feature = "touch")]
 #[test]