esnext features not transpiled within method declarations in object literals with spread elements

[Yogu]

TypeScript Version: 2.4.0

compilerOptions.target = ES5

Code

const obj = {};
const a = {
    ...obj,
    prop() {
        return {
            ...obj,
            metadata: 213
        }
    }
};

Expected behavior:

It compiles and transpiles the object spread operator to a call to Object.assign.

Actual behavior:

The object spread operator is not transpiled but simply kept. This can lead to the following error:

 TypeError: Cannot read property 'kind' of undefined
    at visitObjectLiteralExpression (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:56775:34)
    at visitJavaScript (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:55245:28)
    at visitor (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:55182:24)
    at visitNode (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:49197:23)
    at Object.visitEachChild (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:49479:46)
    at visitReturnStatement (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:55345:23)
    at visitJavaScript (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:55293:28)
    at visitor (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:55182:24)
    at Object.visitNodes (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:49248:48)
    at transformFunctionBody (C:\_myplace\next\graphql-proxy\node_modules\typescript\lib\typescript.js:56282:44)

Problem source:

The esnext transformer cuts off at method declarations within object literals that have an spread element, thus it never sees the inner object literal node.

[DanielRosenwasser]

I currently can't repro this in master, but the PR should still be taken for the regression test.