Fix pruning predicate for LIKE expressions with escape sequences (#22375)

## Which issue does this PR close?

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- Closes #22374.

## Rationale for this change

See #22374.

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## What changes are included in this PR?

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This change includes a fix for the issue and a test that fails without
this fix. The fix is straightforward: when splitting on the wildcard, we
also unescape any escape sequences in the prefix.

## Are these changes tested?

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I added a test that fails without this fix.

## Are there any user-facing changes?

No
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Author: masonh22

datafusion/pruning/src/pruning_predicate.rs

@@ -1822,8 +1822,10 @@ fn extract_string_literal(expr: &Arc<dyn PhysicalExpr>) -> Option<&str> {
 fn build_like_match(
     expr_builder: &mut PruningExpressionBuilder,
 ) -> Option<Arc<dyn PhysicalExpr>> {
-    // column LIKE literal => (min, max) LIKE literal split at % => min <= split literal && split literal <= max
+    // column LIKE literal => (min, max) LIKE literal split at unescaped % => min <= split literal && split literal <= max
     // column LIKE 'foo%' => min <= 'foo' && 'foo' <= max
+    // column LIKE 'foo\_%' => min <= 'foo_' && 'foo_' <= max (the _ is escaped)
+    // column LIKE 'foo\%%' => min <= 'foo%' && 'foo%' <= max (the % is escaped)
     // column LIKE '%foo' => min <= '' && '' <= max => true
     // column LIKE '%foo%' => min <= '' && '' <= max => true
     // column LIKE 'foo' => min <= 'foo' && 'foo' <= max
@@ -1836,24 +1838,25 @@ fn build_like_match(
     // check that the scalar is a string literal
     let s = extract_string_literal(scalar_expr)?;
     // ANSI SQL specifies two wildcards: % and _. % matches zero or more characters, _ matches exactly one character.
-    let first_wildcard_index = s.find(['%', '_']);
-    if first_wildcard_index == Some(0) {
-        // there's no filtering we could possibly do, return an error and have this be handled by the unhandled hook
+    let (decoded_prefix, rest) = split_constant_prefix(s);
+    let has_wildcard = !rest.is_empty();
+    if has_wildcard && decoded_prefix.is_empty() {
+        // there's no filtering we could possibly do, return None and have this be handled by the unhandled hook
         return None;
     }
-    let (lower_bound, upper_bound) = if let Some(wildcard_index) = first_wildcard_index {
-        let prefix = &s[..wildcard_index];
+    let (lower_bound, upper_bound) = if has_wildcard {
+        let incremented_prefix = increment_utf8(&decoded_prefix)?;
         let lower_bound_lit = Arc::new(phys_expr::Literal::new(ScalarValue::Utf8(Some(
-            prefix.to_string(),
+            decoded_prefix,
         ))));
         let upper_bound_lit = Arc::new(phys_expr::Literal::new(ScalarValue::Utf8(Some(
-            increment_utf8(prefix)?,
+            incremented_prefix,
         ))));
         (lower_bound_lit, upper_bound_lit)
     } else {
         // the like expression is a literal and can be converted into a comparison
         let bound = Arc::new(phys_expr::Literal::new(ScalarValue::Utf8(Some(
-            s.to_string(),
+            decoded_prefix,
         ))));
         (Arc::clone(&bound), bound)
     };
@@ -1934,19 +1937,20 @@ fn build_not_like_match(
 }
 
 /// Returns unescaped constant prefix of a LIKE pattern (possibly empty) and the remaining pattern (possibly empty)
-fn split_constant_prefix(pattern: &str) -> (&str, &str) {
-    let char_indices = pattern.char_indices().collect::<Vec<_>>();
-    for i in 0..char_indices.len() {
-        let (idx, char) = char_indices[i];
-        if char == '%' || char == '_' {
-            if i != 0 && char_indices[i - 1].1 == '\\' {
-                // ecsaped by `\`
-                continue;
-            }
-            return (&pattern[..idx], &pattern[idx..]);
+fn split_constant_prefix(pattern: &str) -> (String, &str) {
+    let mut prefix = String::with_capacity(pattern.len());
+    let mut iter = pattern.char_indices();
+    while let Some((idx, c)) = iter.next() {
+        match c {
+            '%' | '_' => return (prefix, &pattern[idx..]),
+            '\\' => match iter.next() {
+                Some((_, escaped)) => prefix.push(escaped),
+                None => prefix.push('\\'),
+            },
+            _ => prefix.push(c),
         }
     }
-    (pattern, "")
+    (prefix, "")
 }
 
 /// Increment a UTF8 string by one, returning `None` if it can't be incremented.
@@ -4816,6 +4820,174 @@ mod tests {
         prune_with_expr(expr, &schema, &statistics, expected_ret);
     }
 
+    // `build_like_match()` must honor `\` escapes when scanning the pattern for
+    // wildcards.
+    #[test]
+    fn prune_utf8_like_escaped_chars() {
+        let schema = Arc::new(Schema::new(vec![Field::new("s1", DataType::Utf8, true)]));
+        let statistics = TestStatistics::new().with(
+            "s1",
+            ContainerStats::new_utf8(
+                vec![
+                    Some("foo_aaa"),
+                    Some(r#"foo\aaa"#),
+                    Some("foo"),
+                    Some("bar"),
+                    Some("foo%aaa"),
+                    Some("%foo_aaa"),
+                ], // min
+                vec![
+                    Some("foo_zzz"),
+                    Some(r#"foo\zzz"#),
+                    Some("foozzz"),
+                    Some("baz"),
+                    Some("foo%zzz"),
+                    Some("%foo_zzz"),
+                ], // max
+            ),
+        );
+
+        let expr = col("s1").like(lit(r#"foo\_%"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => every value starts with literal
+            // "foo_" and matches the pattern; must keep.
+            true,
+            // s1 ["foo\aaa", "foo\zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo", "foozzz"] => stats don't prove "foo_" is or isn't in
+            // range; must conservatively keep.
+            true,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["%foo_aaa", "%foo_zzz"] => no rows can pass (not keep)
+            false,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+
+        let expr = col("s1").like(lit(r#"foo\\%"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo\aaa", "foo\zzz"] => every value starts with literal
+            // "foo\" and matches the pattern; must keep.
+            true,
+            // s1 ["foo", "foozzz"] => stats don't prove "foo\" is or isn't in
+            // range; must conservatively keep.
+            true,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["%foo_aaa", "%foo_zzz"] => no rows can pass (not keep)
+            false,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+
+        let expr = col("s1").like(lit(r#"foo\%%"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo\aaa", "foo\zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo", "foozzz"] => range straddles "foo%"; must keep.
+            true,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => every value starts with literal
+            // "foo%" and matches the pattern; must keep.
+            true,
+            // s1 ["%foo_aaa", "%foo_zzz"] => no rows can pass (not keep)
+            false,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+
+        // No wildcard after escapes: pattern reduces to an equality check on
+        // the literal "foo_".
+        let expr = col("s1").like(lit(r#"foo\_"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo\aaa", "foo\zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo", "foozzz"] => "foo_" is within the range; must keep.
+            true,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["%foo_aaa", "%foo_zzz"] => no rows can pass (not keep)
+            false,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+
+        // Leading escaped `%`: prefix is "%foo" (non-empty), so the guard
+        // for "all wildcards" must NOT bail out here.
+        let expr = col("s1").like(lit(r#"\%foo%"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo\aaa", "foo\zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo", "foozzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["%foo_aaa", "%foo_zzz"] => every value starts with literal
+            // "%foo" and matches the pattern; must keep.
+            true,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+
+        // Two escaped wildcards, no real wildcard: equality on "foo%_".
+        let expr = col("s1").like(lit(r#"foo\%\_"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo\aaa", "foo\zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo", "foozzz"] => "foo%_" is within the range; must keep.
+            true,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["%foo_aaa", "%foo_zzz"] => no rows can pass (not keep)
+            false,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+
+        // Escaped backslash followed by more literal chars before the
+        // wildcard: prefix is "foo\bar".
+        let expr = col("s1").like(lit(r#"foo\\bar%"#));
+        #[rustfmt::skip]
+        let expected_ret = &[
+            // s1 ["foo_aaa", "foo_zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo\aaa", "foo\zzz"] => range straddles "foo\bar"; must
+            // keep.
+            true,
+            // s1 ["foo", "foozzz"] => range straddles "foo\bar"; must keep.
+            true,
+            // s1 ["bar", "baz"] => no rows can pass (not keep)
+            false,
+            // s1 ["foo%aaa", "foo%zzz"] => no rows can pass (not keep)
+            false,
+            // s1 ["%foo_aaa", "%foo_zzz"] => no rows can pass (not keep)
+            false,
+        ];
+        prune_with_expr(expr, &schema, &statistics, expected_ret);
+    }
+
     #[test]
     fn prune_utf8_not_like_one() {
         let (schema, statistics) = utf8_setup();