feat: no delimiter bonus for delimiter chars

Previously, we would give a bonus for delimiter characters if they came
after a delimiter character. But this caused  cases such as
`nvim__buf_debug` matching against `nvim_buf` to win out against
the `nvim_buf_*` options.

Related to saghen/blink.cmp#1530

Author: saghen

src/incremental/matcher.rs

@@ -192,8 +192,13 @@ mod tests {
         assert_eq!(get_score("b", "a--b"), CHAR_SCORE + DELIMITER_BONUS);
         assert_eq!(get_score("c", "a--bc"), CHAR_SCORE);
         assert_eq!(get_score("a", "-a--bc"), CHAR_SCORE);
+    }
+
+    #[test]
+    fn test_score_no_delimiter_for_delimiter_chars() {
         assert_eq!(get_score("-", "a-bc"), CHAR_SCORE);
-        assert_eq!(get_score("-", "a--bc"), CHAR_SCORE + DELIMITER_BONUS);
+        assert_eq!(get_score("-", "a--bc"), CHAR_SCORE);
+        assert!(get_score("a_b", "a_bb") > get_score("a_b", "a__b"));
     }
 
     #[test]

src/smith_waterman/reference.rs

@@ -25,7 +25,7 @@ pub fn smith_waterman<const W: usize>(needle: &str, haystack: &str) -> (u16, u16
 
         let mut left_gap_penalty_mask = true;
         let mut delimiter_bonus_enabled_mask = false;
-        let mut is_delimiter_mask = false;
+        let mut prev_is_delimiter_mask = false;
 
         for j in 0..haystack.len() {
             let is_prefix = j == 0;
@@ -35,6 +35,7 @@ pub fn smith_waterman<const W: usize>(needle: &str, haystack: &str) -> (u16, u16
             let capital_mask = cased_haystack_simd.is_ascii_uppercase();
             let haystack_simd = cased_haystack_simd.to_ascii_lowercase();
 
+            let is_delimiter_mask = [b' ', b'/', b',', b'_', b'-', b':'].contains(&haystack_simd);
             let matched_casing_mask = needle_cased_mask == capital_mask;
 
             // Give a bonus for prefix matches
@@ -49,7 +50,7 @@ pub fn smith_waterman<const W: usize>(needle: &str, haystack: &str) -> (u16, u16
             let match_mask = needle_char == haystack_simd;
             let diag_score = if match_mask {
                 diag + match_score
-                    + if is_delimiter_mask && delimiter_bonus_enabled_mask { DELIMITER_BONUS } else { 0 }
+                    + if prev_is_delimiter_mask && delimiter_bonus_enabled_mask && !is_delimiter_mask { DELIMITER_BONUS } else { 0 }
                     // ignore capitalization on the prefix
                     + if !is_prefix && capital_mask { CAPITALIZATION_BONUS } else { 0 }
                     + if matched_casing_mask { MATCHING_CASE_BONUS } else { 0 }
@@ -83,9 +84,9 @@ pub fn smith_waterman<const W: usize>(needle: &str, haystack: &str) -> (u16, u16
             left_gap_penalty_mask = max_score != left_score || diag_mask;
 
             // Update delimiter mask
-            is_delimiter_mask = [b' ', b'/', b',', b'_', b'-', b':'].contains(&haystack_simd);
+            prev_is_delimiter_mask = is_delimiter_mask;
             // Only enable delimiter bonus if we've seen a non-delimiter char
-            delimiter_bonus_enabled_mask |= !is_delimiter_mask;
+            delimiter_bonus_enabled_mask |= !prev_is_delimiter_mask;
 
             // Store the scores for the next iterations
             up_score_simd = max_score;
@@ -235,8 +236,13 @@ mod tests {
         assert_eq!(get_score("b", "a--b"), CHAR_SCORE + DELIMITER_BONUS);
         assert_eq!(get_score("c", "a--bc"), CHAR_SCORE);
         assert_eq!(get_score("a", "-a--bc"), CHAR_SCORE);
+    }
+
+    #[test]
+    fn test_score_no_delimiter_for_delimiter_chars() {
         assert_eq!(get_score("-", "a-bc"), CHAR_SCORE);
-        assert_eq!(get_score("-", "a--bc"), CHAR_SCORE + DELIMITER_BONUS);
+        assert_eq!(get_score("-", "a--bc"), CHAR_SCORE);
+        assert!(get_score("a_b", "a_bb") > get_score("a_b", "a__b"));
     }
 
     #[test]

src/smith_waterman/simd.rs

@@ -267,8 +267,10 @@ pub(crate) fn smith_waterman_inner<N, const L: usize>(
                     let capitalization_bonus =
                         capitalization_bonus_mask.select(N::CAPITALIZATION_BONUS, N::ZERO_VEC);
 
-                    let delimiter_bonus_mask: Mask<N::Mask, L> =
-                        prev_haystack_char.is_delimiter_mask & delimiter_bonus_enabled_mask;
+                    let delimiter_bonus_mask: Mask<N::Mask, L> = prev_haystack_char
+                        .is_delimiter_mask
+                        & delimiter_bonus_enabled_mask
+                        & !haystack_char.is_delimiter_mask;
                     let delimiter_bonus =
                         delimiter_bonus_mask.select(N::DELIMITER_BONUS, N::ZERO_VEC);
 
@@ -500,8 +502,13 @@ mod tests {
         assert_eq!(get_score("b", "a--b"), CHAR_SCORE + DELIMITER_BONUS);
         assert_eq!(get_score("c", "a--bc"), CHAR_SCORE);
         assert_eq!(get_score("a", "-a--bc"), CHAR_SCORE);
+    }
+
+    #[test]
+    fn test_score_no_delimiter_for_delimiter_chars() {
         assert_eq!(get_score("-", "a-bc"), CHAR_SCORE);
-        assert_eq!(get_score("-", "a--bc"), CHAR_SCORE + DELIMITER_BONUS);
+        assert_eq!(get_score("-", "a--bc"), CHAR_SCORE);
+        assert!(get_score("a_b", "a_bb") > get_score("a_b", "a__b"));
     }
 
     #[test]