If the `source` files include any *type declaration* files, like `src/@types/my-modules/index.d.ts`, the result is: ``` [15:08:25] Starting scripts [15:08:25] scripts failed because Debug Failure. False expression: Output generation failed [15:08:25] Task chain was aborted! ``` It took a while to figure this out. If I change the code to: ```javascript yield fly.source(['src/**/*.ts', '!src/@types/**/*']).typescript().target('dist'); ``` then it will work.