fix(immutable-data): handle immediate mutation of arrays generated from strings

fix #759

Author: RebeccaStevens

src/rules/immutable-data.ts

@@ -165,7 +165,7 @@ const objectConstructorMutatorFunctions = new Set([
 ]);
 
 /**
- * Object constructor functions that return a new array.
+ * Object constructor functions that return new objects.
  */
 const objectConstructorNewObjectReturningMethods = [
   "create",
@@ -180,6 +180,13 @@ const objectConstructorNewObjectReturningMethods = [
   "values",
 ];
 
+/**
+ * String constructor functions that return new objects.
+ *
+ * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#Methods
+ */
+const stringConstructorNewObjectReturningMethods = ["split"];
+
 /**
  * Check if the given assignment expression violates this rule.
  */
@@ -393,6 +400,16 @@ function isInChainCallAndFollowsNew(
     ) {
       return true;
     }
+
+    // Check for: "".split("")
+    if (
+      stringConstructorNewObjectReturningMethods.some(
+        isExpected(node.object.callee.property.name),
+      ) &&
+      getTypeOfNode(node.object.callee.object, context).isStringLiteral()
+    ) {
+      return true;
+    }
   }
 
   return false;

tests/rules/immutable-data/ts/array/valid.ts

@@ -330,6 +330,14 @@ const tests: Array<ValidTestCaseSet<OptionsOf<typeof rule>>> = [
     `,
     optionsSet: [[{ ignoreImmediateMutation: true }]],
   },
+  {
+    code: dedent`
+      "foo".split("").sort();
+      const bar = "bar";
+      bar.split("").sort();
+    `,
+    optionsSet: [[{ ignoreImmediateMutation: true }]],
+  },
 ];
 
 export default tests;