perf(regex): remove redundant character-class and quantifier checks (#28288)

Character classes cannot contain strings outside Unicode sets mode, and
existing parser invariants already establish the removed class-string
and quantifier checks.

AI-assisted implementation.

crates/oxc_regular_expression/src/parser/pattern_parser/pattern_parser_impl.rs

@@ -782,7 +782,10 @@ impl<'a> PatternParser<'a> {
             let (kind, body) = self.parse_class_contents()?;
 
             if self.reader.eat(']') {
-                let strings = PatternParser::may_contain_strings_in_class_contents(kind, &body);
+                // Without UnicodeSetsMode, ClassContents is empty or NonemptyClassRanges,
+                // whose MayContainStrings is always false.
+                let strings = self.state.unicode_sets_mode
+                    && PatternParser::may_contain_strings_in_class_contents(kind, &body);
 
                 // [SS:EE] CharacterClass :: [^ ClassContents ]
                 // It is a Syntax Error if MayContainStrings of the ClassContents is true.
@@ -1432,10 +1435,6 @@ impl<'a> PatternParser<'a> {
             }
         }
 
-        if body.is_empty() {
-            strings = true;
-        }
-
         Ok((body, strings))
     }
 
@@ -1777,7 +1776,7 @@ impl<'a> PatternParser<'a> {
                                 self.span_factory.create(span_start, self.reader.offset()),
                             ));
                         }
-                        if MAX_QUANTIFIER < min || MAX_QUANTIFIER < max {
+                        if MAX_QUANTIFIER < max {
                             return Err(diagnostics::too_large_number_in_braced_quantifier(
                                 self.span_factory.create(span_start, self.reader.offset()),
                             ));

tasks/coverage/misc/pass/regexp-character-class-strings.js

@@ -0,0 +1,13 @@
+const patterns = [
+  /[]/,
+  /[a-z\d]/,
+  /[a-z\p{Letter}]/u,
+  /[a-z]/v,
+  /[\q{}]/v,
+  /[\q{a|b}]/v,
+  /[\q{ab}]/v,
+  /[\p{Basic_Emoji}]/v,
+  /[[\q{ab}]&&[a-z]]/v,
+  /[[\q{ab}]--[a-z]]/v,
+  /[[a-z]--[\q{ab}]]/v,
+];

tasks/coverage/snapshots/codegen_misc.snap

@@ -1,3 +1,3 @@
 codegen_misc Summary:
-AST Parsed     : 118/118 (100.00%)
-Positive Passed: 118/118 (100.00%)
+AST Parsed     : 119/119 (100.00%)
+Positive Passed: 119/119 (100.00%)

tasks/coverage/snapshots/formatter_misc.snap

@@ -1,3 +1,3 @@
 formatter_misc Summary:
-AST Parsed     : 118/118 (100.00%)
-Positive Passed: 118/118 (100.00%)
+AST Parsed     : 119/119 (100.00%)
+Positive Passed: 119/119 (100.00%)

tasks/coverage/snapshots/lexer_misc.snap

@@ -1,3 +1,3 @@
 lexer_misc Summary:
-AST Parsed     : 373/373 (100.00%)
-Positive Passed: 373/373 (100.00%)
+AST Parsed     : 374/374 (100.00%)
+Positive Passed: 374/374 (100.00%)

tasks/coverage/snapshots/parser_misc.snap

@@ -1,6 +1,6 @@
 parser_misc Summary:
-AST Parsed     : 118/118 (100.00%)
-Positive Passed: 118/118 (100.00%)
+AST Parsed     : 119/119 (100.00%)
+Positive Passed: 119/119 (100.00%)
 Negative Passed: 257/257 (100.00%)
 
   × TS(1275): 'accessor' modifier can only appear on a property declaration.

tasks/coverage/snapshots/semantic_misc.snap

@@ -1,6 +1,6 @@
 semantic_misc Summary:
-AST Parsed     : 118/118 (100.00%)
-Positive Passed: 112/118 (94.92%)
+AST Parsed     : 119/119 (100.00%)
+Positive Passed: 113/119 (94.96%)
 semantic Error: tasks/coverage/misc/pass/declare-let-private.ts
 Bindings mismatch:
 after transform: ScopeId(0): ["private"]

tasks/coverage/snapshots/transformer_misc.snap

@@ -1,3 +1,3 @@
 transformer_misc Summary:
-AST Parsed     : 118/118 (100.00%)
-Positive Passed: 118/118 (100.00%)
+AST Parsed     : 119/119 (100.00%)
+Positive Passed: 119/119 (100.00%)