Options `allowJs` and `declaration` don't play nice together

[siggiorn]

Expected behavior:
When using options.allowJs = true both .js and .ts sources get transpiled. When you add the option options.declaration = true, both .js and .ts sources should still get transpiled but now you should just also output definitions.

Actual behavior:
When you add the options.declaration = true option, only .ts sources get transpiled and .js is ignored.

Your gulpfile:

var gulp = require('gulp');
var ts = require('gulp-typescript');
var merge = require('merge2');  // Require separate installation

function doGulp(declaration) {
    var options = {
        declaration: declaration,
        allowJs: true,
        noExternalResolve: true,
    };

    var tsResult = gulp.src('src/**/*.{ts,js}')
        .pipe(ts(options));

    return merge([
        tsResult.dts.pipe(gulp.dest('release/definitions')),
        tsResult.js.pipe(gulp.dest('release/js'))
    ]);
}

gulp.task('with-declarations', function() {
    return doGulp(true);
});

gulp.task('without-declarations', function() {
    return doGulp(false);
});

Reproducing the issue
I have created a small project that reproduces the issue very clearly:
https://github.com/siggiorn/typescript-gulp-definitions-issue

The readme explains how to reproduce

[ivogabe]

Looks like a duplicate of microsoft/TypeScript#7546

[siggiorn]

I think you're right, I hope they add support for that soon