format: support whitespace padding in str formatting

fish-rust/src/wutil/format/format.rs

@@ -478,7 +478,7 @@ impl Printf for &wstr {
 impl Printf for &str {
     fn format(&self, spec: &ConversionSpecifier) -> Result<WString> {
         if spec.conversion_type == ConversionType::String {
-            Ok((*self).into())
+            add_padding((*self).into(), spec)
         } else {
             Err(PrintfError::WrongType)
         }
@@ -514,3 +514,19 @@ impl Printf for &WString {
         self.as_utfstr().format(spec)
     }
 }
+
+fn add_padding(mut s: WString, spec: &ConversionSpecifier) -> Result<WString> {
+    let width: usize = match spec.width {
+        NumericParam::Literal(w) => w,
+        _ => {
+            return Err(PrintfError::Unknown); // should not happen at this point!!
+        }
+    }
+    .try_into()
+    .unwrap_or_default();
+    if s.len() < width {
+        let padding = L!(" ").repeat(width - s.len());
+        s.insert_utfstr(0, &padding);
+    };
+    Ok(s)
+}

fish-rust/src/wutil/format/tests.rs

@@ -29,6 +29,12 @@ fn check_fmt<T: Printf>(nfmt: &str, arg: T, expected: &str) {
     assert_eq!(our_result, expected);
 }
 
+fn check_fmt_2<T: Printf, T2: Printf>(nfmt: &str, arg: T, arg2: T2, expected: &str) {
+    let fmt: WString = nfmt.into();
+    let our_result = sprintf!(&fmt, arg, arg2);
+    assert_eq!(our_result, expected);
+}
+
 #[test]
 fn test_int() {
     check_fmt("%d", 12, "12");
@@ -89,6 +95,7 @@ fn test_str() {
         "test % with string: FOO yay\n",
     );
     check_fmt("test char %c", '~', "test char ~");
+    check_fmt_2("%*ls", 5, "^", "    ^");
 }
 
 #[test]