child_process #2824

I think I discovered some missing type definitions for stdio options to child_process calls to execFileSync, execSync and spawnSync.

Actually this is also seems to be missing in node.js documentation (see nodejs/node#9636).

The options.stdio argument to execFileSync, execSync and spawnSync can actually be a string and an array.

In lib/node.js it also seems that execFileSync is using the incorrect options type... It should use child_process$execSyncOpts not child_process$execFileOpts. https://github.com/facebook/flow/blob/c6c6b3cdc9ae804f5f72a2672e66e9f1a594cc5e/lib/node.js#L241