Fallback from fsst specialised like expression if there are escape characters in the like string (#8038)

"\\" is the escape character but we might need to specialise it in the future to arbitrary symbols

fix #8027

Signed-off-by: Robert Kruszewski <github@robertk.io>

Author: robert3005

encodings/fsst/src/dfa/mod.rs

@@ -208,6 +208,13 @@ enum LikeKind<'a> {
 
 impl<'a> LikeKind<'a> {
     fn parse(pattern: &'a [u8]) -> Option<Self> {
+        // The fast-path matchers below do not understand SQL LIKE escape sequences (e.g. `\%`
+        // matching a literal `%`). If the pattern contains a backslash we fall back to the
+        // general implementation, which correctly interprets escapes.
+        if pattern.contains(&b'\\') {
+            return None;
+        }
+
         // `prefix%` (including just `%` where prefix is empty)
         if let Some(prefix) = pattern.strip_suffix(b"%")
             && !prefix.contains(&b'%')

encodings/fsst/src/dfa/tests.rs

@@ -64,6 +64,16 @@ fn test_like_kind_parse() {
     // Suffix and underscore patterns are not supported.
     assert!(LikeKind::parse(b"%suffix").is_none());
     assert!(LikeKind::parse(b"a_c").is_none());
+
+    // Patterns containing the SQL LIKE escape character must not be parsed by the fast path,
+    // because that path treats `%` and `_` literally and would misinterpret escapes. For
+    // example, `%\%` (the pattern produced by Spark's `endsWith("%")`) means "ends with `%`",
+    // not "contains `\`". The fast path should bail so the general implementation handles it.
+    assert!(LikeKind::parse(br"%\%").is_none());
+    assert!(LikeKind::parse(br"\%%").is_none());
+    assert!(LikeKind::parse(br"%\_%").is_none());
+    assert!(LikeKind::parse(br"\_%").is_none());
+    assert!(LikeKind::parse(br"%\\%").is_none());
 }
 
 /// No symbols — all bytes escaped. Simplest case to see the two tables.