Setting 'allowJs' and 'declaration' options causes 'emit failed' error

[LPGhatguy]

This is very close to a continuation of #259.

I have a template project with typings output that has the option to source JS, but doesn't ship with any JS source. As such, declaration and allowJs are both set to true. This causes an emit failed error.

There are some closed issues that talk about this combination, but I'm not expecting typings to output from the JS portion of the code -- I just want everything to process successfully, or at least output with a useful error message!

Here's a repository that reproduces the error with just gulp, gulp-typescript, and merge-stream:

https://github.com/LPGhatguy/gulp-typescript-allowjs-bug

[ivogabe]

Looks like a duplicate of #317 and microsoft/TypeScript#7546

[LPGhatguy]

The behavior described by #317 implies that compilation succeeds, and JS is ignored, which would be okay, but the reply on the TypeScript error talks about there being an error.

[ivogabe]

Closing this in favour of microsoft/TypeScript#7546.