Optimize Regex match check (#3779)

* Initial optimization

* Fix sticky flag

* Apply review

* Update regress to 0.9.1

* Add spec deviation comments

---------

Co-authored-by: raskad <32105367+raskad@users.noreply.github.com>

Cargo.lock

@@ -3074,9 +3074,9 @@ dependencies = [
 
 [[package]]
 name = "regress"
-version = "0.9.0"
+version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d06f9a1f7cd8473611ba1a480cf35f9c5cffc2954336ba90a982fdb7e7d7f51e"
+checksum = "0eae2a1ebfecc58aff952ef8ccd364329abe627762f5bf09ff42eb9d98522479"
 dependencies = [
  "hashbrown 0.14.3",
  "memchr",

Cargo.toml

@@ -64,7 +64,7 @@ once_cell = { version = "1.19.0", default-features = false }
 phf = { version = "0.11.2", default-features = false }
 pollster = "0.3.0"
 regex = "1.10.4"
-regress = { version="0.9.0", features = ["utf16"]}
+regress = { version="0.9.1", features = ["utf16"]}
 rustc-hash = { version = "1.1.0", default-features = false }
 serde_json = "1.0.115"
 serde = "1.0.197"

core/engine/src/builtins/regexp/mod.rs

@@ -940,13 +940,14 @@ impl RegExp {
         // 9. If flags contains "u" or flags contains "v", let fullUnicode be true; else let fullUnicode be false.
         let full_unicode = flags.contains(&('u' as u16)) || flags.contains(&('v' as u16));
 
-        // 11. If fullUnicode is true, let input be StringToCodePoints(S). Otherwise, let input be a List whose elements are the code units that are the elements of S.
-        // 12. NOTE: Each element of input is considered to be a character.
+        // NOTE: The following steps are take care of by regress:
+        //
+        // SKIP: 10. Let matchSucceeded be false.
+        // SKIP: 11. If fullUnicode is true, let input be StringToCodePoints(S). Otherwise, let input be a List whose elements are the code units that are the elements of S.
+        // SKIP: 12. NOTE: Each element of input is considered to be a character.
+        // SKIP: 13. Repeat, while matchSucceeded is false,
 
-        // 10. Let matchSucceeded be false.
-        // 13. Repeat, while matchSucceeded is false,
-        let match_value = loop {
-            // a. If lastIndex > length, then
+        // 13.a. If lastIndex > length, then
         if last_index > length {
             // i. If global is true or sticky is true, then
             if global || sticky {
@@ -958,36 +959,40 @@ impl RegExp {
             return Ok(None);
         }
 
-            // b. Let inputIndex be the index into input of the character that was obtained from element lastIndex of S.
-            // c. Let r be matcher(input, inputIndex).
+        // 13.b. Let inputIndex be the index into input of the character that was obtained from element lastIndex of S.
+        // 13.c. Let r be matcher(input, inputIndex).
         let r: Option<regress::Match> = if full_unicode {
             matcher.find_from_utf16(input, last_index as usize).next()
         } else {
             matcher.find_from_ucs2(input, last_index as usize).next()
         };
 
-            match r {
+        let Some(match_value) = r else {
             // d. If r is failure, then
-                None => {
-                    // i. If sticky is true, then
-                    if sticky {
+            //
+            // NOTE: Merged the following steps (since we no longer have a loop):
+            //       13.d.i. If sticky is true, then
+            //       13.a.i. If global is true or sticky is true, then
+            if global || sticky {
                 // 1. Perform ? Set(R, "lastIndex", +0𝔽, true).
                 this.set(utf16!("lastIndex"), 0, true, context)?;
+            }
 
-                        // 2. Return null.
+            // MOVE: ii. Set lastIndex to AdvanceStringIndex(S, lastIndex, fullUnicode).
+            // NOTE: Handled within the regress matches iterator, see below for last_index assignment.
+
+            // NOTE: Merged  and  steps:
+            //       13.a.ii.  Return null.
+            //       13.d.i.2. Return null.
             return Ok(None);
-                    }
+        };
 
-                    // ii. Set lastIndex to AdvanceStringIndex(S, lastIndex, fullUnicode).
-                    last_index = advance_string_index(input, last_index, full_unicode);
-                }
+        // e. Else
+        // SKIP: i. Assert: r is a MatchState.
+        // SKIP: ii. Set matchSucceeded to true.
 
-                Some(m) => {
-                    // d. If r is failure, then
-                    #[allow(clippy::if_not_else)]
-                    if m.start() as u64 != last_index {
-                        // i. If sticky is true, then
-                        if sticky {
+        // NOTE: regress currently doesn't support the sticky flag so we have to emulate it.
+        if sticky && match_value.start() != last_index as usize {
             // 1. Perform ? Set(R, "lastIndex", +0𝔽, true).
             this.set(utf16!("lastIndex"), 0, true, context)?;
 
@@ -995,27 +1000,14 @@ impl RegExp {
             return Ok(None);
         }
 
-                        // ii. Set lastIndex to AdvanceStringIndex(S, lastIndex, fullUnicode).
-                        last_index = advance_string_index(input, last_index, full_unicode);
-                        // e. Else,
-                    } else {
-                        // i. Assert: r is a State.
-                        // ii. Set matchSucceeded to true.
-                        break m;
-                    }
-                }
-            }
-        };
+        // 13.d.ii. Set lastIndex to AdvanceStringIndex(S, lastIndex, fullUnicode).
+        // NOTE: Calculation of last_index is done in regress.
+        last_index = match_value.start() as u64;
 
         // 14. Let e be r's endIndex value.
-        let e = match_value.end();
-
-        // Note: This is already taken care of be regress.
         // 15. If fullUnicode is true, set e to GetStringIndex(S, e).
-        // e is an index into the Input character list, derived from S, matched by matcher.
-        // Let eUTF be the smallest index into S that corresponds to the character at element e of Input.
-        // If e is greater than or equal to the number of elements in Input, then eUTF is the number of code units in S.
-        // b. Set e to eUTF.
+        // NOTE: Step 15 is already taken care of by regress.
+        let e = match_value.end();
 
         // 16. If global is true or sticky is true, then
         if global || sticky {