Handle function name inference

The best way to explain things is via a repo: https://github.com/kentcdodds/issue-babel-plugin-istanbul-fn-name

Here’s a copy/paste of the README:

issue-babel-plugin-istanbul-fn-name

This demonstrates that due to how babel-plugin-istanbul wraps functions, the name of the function is lost

This is a bug and should be fixed.

Why?

This is causing issues with Jest snapshot testing of React components

Reproduce:

See the npm scripts, or just run things manually:

node test.js

Everything passes fine

babel-node --plugins istanbul test.js

You get two failures. One for the Foobar function:

const Foobar = function() {}

And the other for the Bar function:

const Bar = () => {}

The istanbul-transformed (babel --plugins istanbul index.js) version of these functions looks like this:

const Bar = (++cov_1788vtfzzh.s[0], () => {
  ++cov_1788vtfzzh.f[1];
});

const Foobar = (++cov_1788vtfzzh.s[2], function () {
  ++cov_1788vtfzzh.f[3];
});

This makes it so the JS engine can’t do function name inference which causes the issue.

I’m not sure what the babel plugin can do about arrow functions… Can’t really give those a name. Definitely possible, but you’d have to do some fancy work to make things work.

But for the function expression that’s simple enough.

[kentcdodds]

Poof!

~/Desktop/issue-babel-plugin-istanbul-fn-name (master)
⛄  $ npm run test:babel-node

> issue-babel-plugin-istanbul-fn-name@1.0.0 test:babel-node /Users/kdodds/Desktop/issue-babel-plugin-istanbul-fn-name
> babel-node --plugins istanbul test.js

Passed! 💚

[bcoe]

@kentcdodds could I convince you to try out:

npm cache clear; npm i babel-plugin-istanbul@next? I believe it has some new logic for handling inferred function names which should solve this issue.