Plugin likely needs `filename` when used with babel's `transform`

Hi, I’ve been working to upgrade Thumbtack’s design system to Babel 7. Got stuck at babel-plugin-inline-react-svg with the error “Path must be a string. Received undefined.” It failed because iconPath was undefined:

https://github.com/airbnb/babel-plugin-inline-react-svg/blob/7ba334c641d252e7d478ae941fe689946e18bbe9/src/index.js#L47-L48

This happened because I use babel.transform(code, opts). Previously, Babel would set filename: "unknown" in opts. This seems to have changed in Babel 7.

Here’s a commit with a failing test case: https://github.com/danoc/babel-plugin-inline-react-svg/commit/82d475926fc6d5866f255e0b306295a84ab5c2e9. Adding filename: test/fixtures/test-import-read-file.jsx to opts (the second argument) fixes the test case.

I don’t think this is a bug in babel-plugin-inline-react-svg, but these changes may be helpful:

• Throw an error if iconPath is undefined (before dirname(iconPath)).
• Update README example to include filename.

[ljharb]

It seems like, altho you can use the API programmatically, the svgPath code kind of expects you’ll only use it on a file (ie, applyPlugin only takes a path).

I think the test case is great, but i think handling this properly might need a bit of refactoring. I’ll open a PR with your test case once I’ve got a solution.

[ljharb]

Fixed in #53.