[Fix] prop-types: handle anonymous functions

[odinho]

Fixes #2728.

[sluukkonen]

I'm no expert in eslint, but is the check actually correct? I think an anonymous function could also be considered to be a stateless component.

I was thinking of something like

      if (
        node.type === 'FunctionDeclaration'
        && (node.id == null || isFirstLetterCapitalized(node.id.name))
        && utils.isReturningJSXOrNull(node)
      ) {

[odinho]

I'm no expert in eslint, but is the check actually correct? I think an anonymous function could also be considered to be a stateless component.

I was thinking of something like

      if (
        node.type === 'FunctionDeclaration'
        && (node.id == null || isFirstLetterCapitalized(node.id.name))
        && utils.isReturningJSXOrNull(node)
      ) {

As I read it, the code underneath will handle that case. It checks the variable that the anonymous function is being stored into.

[ljharb]

Thanks! This does need a regression test first.

[ljharb]

@odinho Since you made this PR from a fork that you don't own (whereby instead of odinho) I can't merge this yet. Can you please add me to https://github.com/whereby/eslint-plugin-react so I can force push to the PR branch?

[odinho]

@odinho Since you made this PR from a fork that you don't own (whereby instead of odinho) I can't merge this yet. Can you please add me to https://github.com/whereby/eslint-plugin-react so I can force push to the PR branch?

Oup. Why do I keep forgetting that this restriction exists. I've added you now 🤦

[jzabala]

This indeed will solve #2728 but then components defined this way won't be recognized:

export default function () {
  return <h1>Hello World</div>
}

I think a better check would be:

if (
        node.type === 'FunctionDeclaration'
        && (!node.id || isFirstLetterCapitalized(node.id.name)) // skip first letter check if the node.id doesn't exists
        && utils.isReturningJSXOrNull(node)
) {

[ljharb]

@jzabala thanks, i've added a test case and your suggested fix.