curly 'multi' autofix produces syntax errors with lexical declarations

Tell us about your environment

• ESLint Version: 6.0.1 (same with 5.16.0)
• Node Version: 10.16.0
• npm Version: 6.9.0

What parser (default, Babel-ESLint, etc.) are you using?

default

Please show your full configuration:

Configuration

module.exports = {
  parserOptions: {
    ecmaVersion: 6,
  },
  rules: {
    "curly": ["error", "multi"]
  }
};

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

if (foo) {
  let bar;
}

eslint index.js --fix

What did you expect to happen?

No errors, similar to how multi-or-nest works.

What actually happened? Please include the actual, raw output from ESLint.

if (foo) 
  let bar; // SyntaxError: Lexical declaration cannot appear in a single-statement context

Are you willing to submit a pull request to fix this bug?

Yes.

[mdjermanovic]

It’s most likely a bad practice to have a function declaration anywhere other than directly in the body.

Perhaps ESLint should never modify such code, i.e. never move function declarations to {} or out from its existing {}, because it can produce some unpredictable differences even if it isn’t a syntax error.

[mdjermanovic]

Ok, I’m working on this.

It might take some time, all options have to be checked and the consistent modifier adds some complexity.