stat: reject a % directive with flags or a precision

src/uu/stat/src/stat.rs

@@ -804,7 +804,7 @@ impl Stater {
             j += offset;
 
             // Reject directives like `%<NUMBER>` by checking if width has been parsed.
-            if j >= bound || chars[j] == '%' {
+            if j >= bound {
                 let end = j.min(bound - 1);
                 let invalid_directive: String = chars[old..=end].iter().collect();
                 return Err(DirectiveError::new(
@@ -834,6 +834,18 @@ impl Stater {
             check_bound(format_str, bound, old, j)?;
         }
 
+        // A `%` after flags, a width or a precision (`%0%`, `%-%`, `%.3%`) is
+        // not the `%%` escape; GNU rejects it as an invalid directive.
+        if chars[j] == '%' {
+            let invalid_directive: String = chars[old..=j].iter().collect();
+            return Err(DirectiveError::new(
+                format_str,
+                &invalid_directive,
+                old,
+                j + 1,
+            ));
+        }
+
         *i = j;
 
         // Check for multi-character specifiers (e.g., `%Hd`, `%Lr`)

tests/by-util/test_stat.rs

@@ -774,6 +774,31 @@ fn test_printf_invalid_directive() {
         .stderr_contains("'%9%': invalid directive");
 }
 
+#[test]
+fn test_percent_after_flags_is_an_invalid_directive() {
+    let ts = TestScenario::new(util_name!());
+    // Only a bare `%%` is the escape. With flags or a precision in between,
+    // GNU stops at the directive, after printing what came before it.
+    for (fmt, before, directive) in [
+        ("%0%", "", "%0%"),
+        ("%-%s1212x", "", "%-%"),
+        ("%++-+%1212x", "", "%++-+%"),
+        ("%#%d", "", "%#%"),
+        ("%.3%", "", "%.3%"),
+        ("x%+-%%ss", "x", "%+-%"),
+    ] {
+        ts.ucmd()
+            .args(&["-c", fmt, "."])
+            .fails_with_code(1)
+            .stdout_is(before)
+            .stderr_is(format!("stat: '{directive}': invalid directive\n"));
+    }
+    ts.ucmd()
+        .args(&["--printf=100%%\n", "."])
+        .succeeds()
+        .stdout_only("100%\n");
+}
+
 #[test]
 fn test_invalid_directive_after_multibyte_char() {
     let ts = TestScenario::new(util_name!());