perf(linter): id-length: reduce allocations and add more ASCII checks (#14821)

Previous PR (#14767) implemented an initial ASCII check, but I forgot to add it to the other identifier checks as well. This now adds the fast path ASCII check to all of the branches for this rule.

In addition, we no longer need to call `.to_string()` to allocate for each identifier, we can simply do the exceptions check with `&str`.

This should greatly benefit large files which have lots of identifiers, but this will pretty much universally improve perf on every file since this rule runs on every identifier and almost every JS file has identifiers.

<img width="714" height="535" alt="image" src="https://github.com/user-attachments/assets/f67a43e8-0e91-4f6d-805b-a031f9881c74" />

Author: camchenry

crates/oxc_linter/src/rules/eslint/id_length.rs

@@ -210,7 +210,7 @@ impl IdLength {
         node: &AstNode,
         ctx: &LintContext,
     ) {
-        let ident_name = ident.name.to_string();
+        let ident_name = ident.name;
 
         if self.is_exception(&ident_name) {
             return;
@@ -269,17 +269,20 @@ impl IdLength {
     }
 
     fn handle_identifier_name(&self, ident: &IdentifierName, node: &AstNode, ctx: &LintContext) {
-        let ident_name = ident.name.to_string();
+        let ident_name = ident.name;
 
         if self.is_exception(&ident_name) {
             return;
         }
 
-        let segmenter = GraphemeClusterSegmenter::new();
-        let graphemes_length = segmenter.segment_str(&ident_name).count() - 1;
-
-        let is_too_long = self.is_too_long(graphemes_length);
-        let is_too_short = self.is_too_short(graphemes_length);
+        let (is_too_long, is_too_short) = if ident_name.is_ascii() {
+            let ident_length = ident_name.len();
+            (self.is_too_long(ident_length), self.is_too_short(ident_length))
+        } else {
+            let segmenter = GraphemeClusterSegmenter::new();
+            let graphemes_length = segmenter.segment_str(&ident_name).count() - 1;
+            (self.is_too_long(graphemes_length), self.is_too_short(graphemes_length))
+        };
 
         if !is_too_long && !is_too_short {
             return;
@@ -376,16 +379,20 @@ impl IdLength {
         node: &AstNode,
         ctx: &LintContext,
     ) {
-        let ident_name = ident.name.to_string();
+        let ident_name = ident.name;
 
         if self.is_exception(&ident_name) {
             return;
         }
 
-        let segmenter = GraphemeClusterSegmenter::new();
-        let graphemes_length = segmenter.segment_str(&ident_name).count() - 1;
-        let is_too_long = self.is_too_long(graphemes_length);
-        let is_too_short = self.is_too_short(graphemes_length);
+        let (is_too_long, is_too_short) = if ident_name.is_ascii() {
+            let ident_length = ident_name.len();
+            (self.is_too_long(ident_length), self.is_too_short(ident_length))
+        } else {
+            let segmenter = GraphemeClusterSegmenter::new();
+            let graphemes_length = segmenter.segment_str(&ident_name).count() - 1;
+            (self.is_too_long(graphemes_length), self.is_too_short(graphemes_length))
+        };
 
         if is_too_long {
             ctx.diagnostic(id_length_is_too_long_diagnostic(node.span(), self.max));
@@ -408,8 +415,8 @@ impl IdLength {
         )
     }
 
-    fn is_exception(&self, identifier: &String) -> bool {
-        if self.exceptions.contains(identifier) {
+    fn is_exception(&self, identifier: &str) -> bool {
+        if self.exceptions.iter().any(|exc| exc == identifier) {
             return true;
         }
         if self.exception_patterns.iter().any(|regex| regex.is_match(identifier)) {