etseidl commented on code in PR #6870:
URL: https://github.com/apache/arrow-rs/pull/6870#discussion_r1885127784
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parquet/src/column/writer/mod.rs:
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@@ -3192,6 +3262,40 @@ mod tests {
// One multi-byte code point, and a length shorter than it, so we
can't slice it
let r = truncate_utf8("\u{0836}", 1);
assert!(r.is_none());
+
+ // Test truncate and increment for max bounds on UTF-8 statistics
+ // 7-bit (i.e. ASCII)
+ let r = truncate_and_increment_utf8("yyyyyyyyy", 8).unwrap();
+ assert_eq!(&r, "yyyyyyyz".as_bytes());
+
+ // 2-byte without overflow
+ let r = truncate_and_increment_utf8("ééééé", 8).unwrap();
+ assert_eq!(&r, "éééê".as_bytes());
+
+ // 2-byte that overflows lowest byte
+ let r = truncate_and_increment_utf8("\u{ff}\u{ff}\u{ff}\u{ff}\u{ff}",
8).unwrap();
+ assert_eq!(&r, "\u{ff}\u{ff}\u{ff}\u{100}".as_bytes());
+
+ // max 2-byte should not truncate as it would need 3-byte code points
+ let r = truncate_and_increment_utf8("߿߿߿߿߿", 8);
+ assert!(r.is_none());
+
+ // 3-byte without overflow [U+800, U+800, U+800] -> [U+800, U+801]
(note that these
+ // characters should render right to left).
+ let r = truncate_and_increment_utf8("ࠀࠀࠀ", 8).unwrap();
+ assert_eq!(&r, "ࠀࠁ".as_bytes());
+
+ // max 3-byte should not truncate as it would need 4-byte code points
+ let r = truncate_and_increment_utf8("\u{ffff}\u{ffff}\u{ffff}", 8);
+ assert!(r.is_none());
+
+ // 4-byte without overflow
+ let r = truncate_and_increment_utf8("𐀀𐀀𐀀", 8).unwrap();
+ assert_eq!(&r, "𐀀𐀁".as_bytes());
Review Comment:
Hmm, no, I don't think there is a test like that. There is a truncation test
that does, but not followed by increment. I'll modify some as you suggest.
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