JS-1114 Fix S3504 FP: skip TypeScript ambient 'declare var' declarations (#6224)

Co-authored-by: Vibe Bot <vibe-bot@sonarsource.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: 3 people

its/ruling/src/test/expected/jsts/TypeScript/typescript-S3504.json

@@ -13,7 +13,6 @@
 20
 ],
 "TypeScript:scripts/createBenchmark.ts": [
-7,
 9,
 10,
 11,
@@ -29,12 +28,8 @@
 115
 ],
 "TypeScript:scripts/errorCheck.ts": [
-1,
 31
 ],
-"TypeScript:scripts/importDefinitelyTypedTests/importDefinitelyTypedTests.ts": [
-10
-],
 "TypeScript:scripts/ior.ts": [
 24,
 25,
@@ -127,9 +122,6 @@
 "TypeScript:src/harness/harness.ts": [
 33,
 34,
-35,
-36,
-38,
-39
+36
 ]
 }

its/ruling/src/test/expected/jsts/eigen/typescript-S3504.json

@@ -2,8 +2,5 @@
 "rxjs:src/testing/HotObservable.ts": [
 40,
 42
-],
-"rxjs:src/util/root.ts": [
-11
 ]
 }

its/ruling/src/test/expected/jsts/fireface/typescript-S3504.json

@@ -0,0 +1,43 @@
+// False positive scenario: TypeScript ambient declaration with 'declare var'
+// 'declare var' is a compile-time type annotation that describes an existing
+// external variable (like jQuery's $). It doesn't create a runtime variable
+// and cannot be changed to let/const.
+
+// Example 1: External library type declaration (e.g., jQuery)
+declare var $: any;
+
+// Example 2: Module globals from server-side rendering or global configuration
+declare var initConfig: { apiUrl: string; debug: boolean };
+declare var initPresets: string[];
+
+// Example 3: Build-time injected variables (webpack/Vite)
+declare var __CORE_VERSION__: string;
+declare var __VERSION__: string;
+
+// Example 4: React Refresh runtime globals
+declare var $RefreshHelpers$: any;
+declare var $RefreshReg$: any;
+declare var $RefreshSig$: any;
+
+// Example 5: Complex object type with methods (Node.js process)
+declare var process: {
+  argv: string[];
+  env: Record<string, string>;
+  exit(code?: number): void;
+};
+
+// Example 6: Interface-like type declaration (browser XMLHttpRequest)
+declare var XMLHttpRequest: {
+  new(): XMLHttpRequest;
+};
+
+// Regular var declarations should still be flagged
+function bar() {
+  var foo = 42; // Noncompliant [[qf1!]] {{Unexpected var, use let or const instead.}}
+//^^^^^^^
+// edit@qf1 {{  let foo = 42;}}
+
+  var x, y = 1; // Noncompliant [[qf2!]] {{Unexpected var, use let or const instead.}}
+//^^^^^
+// edit@qf2 {{  let x, y = 1;}}
+}

its/ruling/src/test/expected/jsts/rxjs/typescript-S3504.json

@@ -28,9 +28,16 @@ export function decorate(rule: Rule.RuleModule): Rule.RuleModule {
     (context, reportDescriptor) => {
       if ('node' in reportDescriptor) {
         const { node, ...rest } = reportDescriptor;
+        const varDecl = node as estree.VariableDeclaration & { declare?: boolean };
+
+        // Skip TypeScript ambient declarations (declare var)
+        if (varDecl.declare) {
+          return;
+        }
+
         const {
           declarations: [firstDecl, ..._],
-        } = node as estree.VariableDeclaration;
+        } = varDecl;
 
         const varToken = context.sourceCode.getTokenBefore(firstDecl.id);
         const identifierEnd = firstDecl.id.loc!.end;