Fix FP S6594 (sonar-prefer-regexp-exec): Ignore match count use case

its/ruling/src/test/expected/jsts/desktop/typescript-S6594.json

@@ -1,7 +1,4 @@
 {
-"desktop:app/src/crash/crash-app.tsx": [
-65
-],
 "desktop:app/src/lib/actions-log-parser/action-log-parser.ts": [
 140,
 219,
@@ -30,35 +27,19 @@
 200,
 226
 ],
-"desktop:app/src/lib/markdown-filters/emoji-filter.ts": [
-64
-],
 "desktop:app/src/lib/markdown-filters/issue-link-filter.ts": [
 112
 ],
 "desktop:app/src/lib/parse-pac-string.ts": [
 72
 ],
-"desktop:app/src/lib/progress/lfs.ts": [
-54
-],
-"desktop:app/src/lib/remove-remote-prefix.ts": [
-10
-],
 "desktop:app/src/models/app-menu.ts": [
 161
 ],
-"desktop:app/src/models/branch.ts": [
-73,
-87
-],
 "desktop:app/src/models/commit-identity.ts": [
 23
 ],
 "desktop:app/src/models/git-author.ts": [
 3
-],
-"desktop:script/changelog/parser.ts": [
-20
 ]
 }

its/ruling/src/test/expected/jsts/reddit-mobile/javascript-S6594.json

@@ -1,6 +1,5 @@
 {
 "reddit-mobile:assets/js/trackingEvents.es6.js": [
-62,
 67
 ]
 }

packages/jsts/src/rules/S6594/cb.fixture.js

@@ -6,3 +6,14 @@ foo.match(/foo/);
 //    ^^^^^
 // fix@qf1 {{Replace with "RegExp.exec()"}}
 // edit@qf1 [[ec=19]] {{RegExp(/bar/).exec('foo');}}
+
+const m1 = 'foo'.match(/bar/); // Compliant: we're checking `m1.length` below
+if (m1.length > 0) {
+  console.log(m1[0]);
+}
+
+let m2;
+m2 = 'foo'.match(/bar/); // Compliant: we're checking `m2?.length` below
+if (m2?.length > 0) {
+  console.log(m2[0]);
+}

packages/jsts/src/rules/S6594/rule.ts

@@ -21,7 +21,13 @@
 
 import { Rule } from 'eslint';
 import * as estree from 'estree';
-import { isRequiredParserServices, isString } from '../helpers';
+import {
+  getNodeParent,
+  getVariableFromName,
+  isMemberWithProperty,
+  isRequiredParserServices,
+  isString,
+} from '../helpers';
 import { getParsedRegex } from '../helpers/regex';
 
 export const rule: Rule.RuleModule = {
@@ -44,11 +50,22 @@ export const rule: Rule.RuleModule = {
           if (!isString(object, services)) {
             return;
           }
+
           const callExpr = (memberExpr as any).parent as estree.CallExpression;
           const regex = getParsedRegex(callExpr.arguments[0], context);
           if (regex?.flags.global) {
             return;
           }
+
+          const variable = getLhsVariable(callExpr);
+          for (const ref of variable?.references ?? []) {
+            const id = ref.identifier;
+            const parent = getNodeParent(id);
+            if (isMemberWithProperty(parent, 'length')) {
+              return;
+            }
+          }
+
           context.report({
             node: property,
             messageId: 'useExec',
@@ -66,5 +83,23 @@ export const rule: Rule.RuleModule = {
           });
         },
     };
+
+    /**
+     * Extracts the left-hand side variable of expressions
+     * like `x` in `const x = <node>` or `x` in `x = <node>`.
+     */
+    function getLhsVariable(node: estree.Node) {
+      const parent = getNodeParent(node);
+      let ident: estree.Identifier | undefined;
+      if (parent.type === 'VariableDeclarator' && parent.id.type === 'Identifier') {
+        ident = parent.id;
+      } else if (parent.type === 'AssignmentExpression' && parent.left.type === 'Identifier') {
+        ident = parent.left;
+      }
+      if (ident) {
+        return getVariableFromName(context, ident.name);
+      }
+      return null;
+    }
   },
 };