Typescript 2.6 errors on export default

[sandersn]

Version

3.0.0

Reproduction link

microsoft/TypeScript#18444

Steps to reproduce

• git clone https://github.com/vuejs/vuex.git
• cd vuex
• npm install
• npm install typescript@next
• cd types
• tsc -p test/tsconfig.json

What is expected?

No error.

What is actually happening?

Error: The expression of an export assignment must be an identifier or qualified name in an ambient context.

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This error is new in Typescript 2.6. It disallows the export of expressions, including object literals like { Store, install }. We found this error when testing popular packages with Typescript 2.6 RC.