JS-1121 Fix FP on S2310: Allow intentional loop counter skip-ahead patterns

its/ruling/src/test/expected/jsts/TypeScript/javascript-S2310.json

@@ -1,7 +1,5 @@
 {
 "TypeScript:lib/tsc.js": [
-18167,
-22894,
 55986
 ]
 }

its/ruling/src/test/expected/jsts/TypeScript/typescript-S2310.json

@@ -1,14 +1,5 @@
 {
-"TypeScript:src/compiler/binder.ts": [
-1145
-],
-"TypeScript:src/compiler/checker.ts": [
-2890
-],
 "TypeScript:src/compiler/program.ts": [
 292
-],
-"TypeScript:src/services/documentHighlights.ts": [
-583
 ]
 }

its/ruling/src/test/expected/jsts/ace/javascript-S2310.json

@@ -1,60 +1,29 @@
 {
-"ace:lib/ace/mode/html/saxparser.js": [
-820
-],
 "ace:lib/ace/mode/javascript/jshint.js": [
 3345
 ],
-"ace:lib/ace/mode/yaml/yaml-lint.js": [
-623
-],
 "ace:src/edit_session.js": [
 1018
 ],
 "ace:src/edit_session/folding.js": [
 651
 ],
-"ace:src/editor.js": [
-1880,
-1889
-],
-"ace:src/ext/whitespace.js": [
-34
-],
-"ace:src/keyboard/vim.js": [
-5346
-],
 "ace:src/layer/text.js": [
 178
 ],
-"ace:src/lib/bidiutil.js": [
-330
-],
 "ace:src/mode/folding/xml.js": [
-67,
-72,
 72
 ],
-"ace:src/mode/text_highlight_rules.js": [
-165
-],
-"ace:src/range_list.js": [
-90
-],
 "ace:src/search.js": [
 138
 ],
 "ace:src/snippets.js": [
 320
 ],
 "ace:src/undomanager.js": [
-428,
-431,
-547,
-550
+431
 ],
 "ace:tool/tmlanguage.js": [
-50,
 127
 ]
 }

its/ruling/src/test/expected/jsts/desktop/typescript-S2310.json

@@ -3,15 +3,6 @@
 449
 ],
 "desktop:app/src/lib/git/diff.ts": [
-302,
-306,
 324
-],
-"desktop:app/src/lib/git/log.ts": [
-258,
-263
-],
-"desktop:app/src/lib/status-parser.ts": [
-80
 ]
 }

its/ruling/src/test/expected/jsts/jquery/javascript-S2310.json

@@ -1,12 +1,5 @@
 {
 "jquery:src/callbacks.js": [
-76,
 83
-],
-"jquery:src/effects.js": [
-651
-],
-"jquery:src/selector.js": [
-1367
 ]
 }

its/ruling/src/test/expected/jsts/knockout/javascript-S2310.json

@@ -4,11 +4,5 @@
 ],
 "knockout:src/binding/expressionRewriting.js": [
 88
-],
-"knockout:src/subscribables/observableArray.js": [
-28
-],
-"knockout:src/utils.domNodeDisposal.js": [
-47
 ]
 }

its/ruling/src/test/expected/jsts/p5.js/javascript-S2310.json

@@ -1,15 +1,6 @@
 {
-"p5.js:docs/yuidoc-p5-theme/assets/js/reference.js": [
-1346,
-2781
-],
 "p5.js:lib/addons/p5.sound.js": [
 1381,
-1381,
-2826,
-2828
-],
-"p5.js:src/typography/p5.Font.js": [
-757
+1381
 ]
 }

packages/jsts/src/rules/S2310/rule.ts

@@ -20,6 +20,7 @@ import type { Rule } from 'eslint';
 import type estree from 'estree';
 import {
   generateMeta,
+  getNodeParent,
   getParent,
   getVariableFromName,
   report,
@@ -50,6 +51,9 @@ export const rule: Rule.RuleModule = {
       }
       for (const ref of variable.references) {
         if (ref.isWrite() && isUsedInsideBody(ref.identifier, block)) {
+          if (isIntentionalSkipAhead(ref.identifier, block)) {
+            continue;
+          }
           report(
             context,
             {
@@ -95,7 +99,52 @@ function collectCountersFor(updateExpression: estree.Expression, counters: estre
   }
 }
 
+/**
+ * Checks if a loop counter modification is an intentional skip-ahead pattern
+ * (UpdateExpression or compound assignment) rather than a simple assignment.
+ * Modifications in nested for-loop update clauses are not considered skip-ahead.
+ */
+function isIntentionalSkipAhead(id: estree.Identifier, outerLoopBody: estree.Node): boolean {
+  if (isInNestedForLoopUpdate(id, outerLoopBody)) {
+    return false;
+  }
+  const parent = getNodeParent(id);
+  if (parent?.type === 'UpdateExpression') {
+    return true;
+  }
+  if (parent?.type === 'AssignmentExpression' && parent.operator !== '=') {
+    return true;
+  }
+  return false;
+}
+
 function isUsedInsideBody(id: estree.Identifier, loopBody: estree.Node) {
   const bodyRange = loopBody.range;
   return id.range && bodyRange && id.range[0] > bodyRange[0] && id.range[1] < bodyRange[1];
 }
+
+function isInNestedForLoopUpdate(id: estree.Identifier, outerLoopBody: estree.Node): boolean {
+  let node: estree.Node | undefined = id;
+  let parent = getNodeParent(node);
+  while (parent) {
+    // Stop if we've reached the outer loop body
+    if (parent === outerLoopBody) {
+      return false;
+    }
+    // Check if we're in a nested for-loop's update clause
+    if (parent.type === 'ForStatement' && parent.update) {
+      const updateRange = parent.update.range;
+      if (
+        updateRange &&
+        id.range &&
+        id.range[0] >= updateRange[0] &&
+        id.range[1] <= updateRange[1]
+      ) {
+        return true;
+      }
+    }
+    node = parent;
+    parent = getNodeParent(node);
+  }
+  return false;
+}