When the babel-compiler package is processing files, it will now read
their package.json files looking for a "babel" section with "presets" or
"plugins" fields. If found, these presets or plugins will be appended to
the existing babelOptions.presets or babelOptions.plugins arrays.
Note that no other Babel options are currently supported, and the
"babel-preset-meteor" preset cannot be removed, though additional presets
and/or plugins can be added to it. This is by design: Meteor cannot
support your configuration it uses babel-preset-meteor, at least.
The preset and/or plugin modules listed in package.json must be installed
locally somewhere such that the given file can import them. If they are
top-level identifiers, they will be prefixed with "babel-plugin-" or
"babel-preset-", the same as Babel does it. Otherwise they will be
required as-is, so that you can implement your own Babel plugins locally,
rather than always using plugins installed from npm.
See the included tests for a concrete example.
Fixes#6351.
7c63a8e704