| Q | A <!--(Can use an emoji 👍) -->
| ------------------------ | ---
| Fixed Issues? |
| Patch: Bug Fix? | Y
| Major: Breaking Change? | N
| Minor: New Feature? |
| Tests Added + Pass? | Yes
| Documentation PR | <!-- If so, add `[skip ci]` to your commit message to skip CI -->
| Any Dependency Changes? |
| License | MIT
Currently the `opts.filename` value exposed to plugins is just whatever the user passed. While it _could_ be relative to the working directory, if Babel was passed an absolute URL, it'll be absolute.
This PR explicitly ensures the filename is a relative path based on the working directory. This also exposes an officially endorsed API for reading the working directory path.
For better tooling support it's important to include absolute file name for JSX
elements. However, having them inline will inflate resulting file size, so we
move the file name to a constant declared at the beginning of the file and
reference it from `__source` attribute.
