prefer-object-spread: add parens in shorthand arrow function

src/rules/preferObjectSpreadRule.ts

@@ -64,9 +64,10 @@ function walk(ctx: Lint.WalkContext<void>) {
 
 function createFix(node: ts.CallExpression, sourceFile: ts.SourceFile): Lint.Fix {
     const args = node.arguments;
+    const objectNeedsParens = node.parent!.kind === ts.SyntaxKind.ArrowFunction;
     const fix = [
-        Lint.Replacement.replaceFromTo(node.getStart(sourceFile), args[0].getStart(sourceFile), "{"),
-        new Lint.Replacement(node.end - 1, 1, "}"),
+        Lint.Replacement.replaceFromTo(node.getStart(sourceFile), args[0].getStart(sourceFile), `${objectNeedsParens ? "(" : ""}{`),
+        new Lint.Replacement(node.end - 1, 1, `}${objectNeedsParens ? ")" : ""}`),
     ];
     for (let i = 0; i < args.length; ++i) {
         const arg = args[i];

test/rules/prefer-object-spread/test.ts.fix

@@ -21,3 +21,6 @@ foo({...original, c: 3});
 // allowed
 result = Object.assign(new Foo(), {});
 result = Object.assign(createFoo(), {});
+
+let fn = () => ({...original});
+

test/rules/prefer-object-spread/test.ts.lint

@@ -35,5 +35,8 @@ Object.assign({}, {},);
 result = Object.assign(new Foo(), {});
 result = Object.assign(createFoo(), {});
 
+let fn = () => Object.assign({}, original);
+               ~~~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+
 [0]: Use the object spread operator instead.
-[1]: 'Object.assign' returns the first argument. Prefer object spread if you want a new object.
+[1]: 'Object.assign' returns the first argument. Prefer object spread if you want a new object.