fix(eslint-plugin): [prefer-string-starts-ends-with] Check negative indices in the second position for slice (typescript-eslint#2696)

ginger-kang · web-flow · commit 66e9c6e29f9f · 2020-10-25T14:57:35.000-07:00
diff --git a/packages/eslint-plugin/src/rules/prefer-string-starts-ends-with.ts b/packages/eslint-plugin/src/rules/prefer-string-starts-ends-with.ts
@@ -575,7 +575,8 @@ export default createRule({
         const isStartsWith =
           !isEndsWith &&
           callNode.arguments.length === 2 &&
-          isNumber(callNode.arguments[0], 0);
+          isNumber(callNode.arguments[0], 0) &&
+          !isNegativeIndexExpression(callNode.arguments[1], node.object);
         if (!isStartsWith && !isEndsWith) {
           return;
         }
diff --git a/packages/eslint-plugin/tests/rules/prefer-string-starts-ends-with.test.ts b/packages/eslint-plugin/tests/rules/prefer-string-starts-ends-with.test.ts
@@ -230,6 +230,16 @@ ruleTester.run('prefer-string-starts-ends-with', rule, {
         x.test(s)
       }
     `,
+    `
+      function f(s: string) {
+        s.slice(0, -4) === "car"
+      }
+    `,
+    `
+      function f(x: string, s: string) {
+        x.endsWith('foo') && x.slice(0, -4) === 'bar'
+      }
+    `,
   ]),
   invalid: addOptional([
     // String indexing.
