Tell us about your environment

• ESLint Version: master
• Node Version: 12.1.0
• npm Version: 6.9.0

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

default

Please show your full configuration:

rules:
  no-extra-parens: error

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

for (let a = (b in c); ;);

eslint --fix

What did you expect to happen?

I expected ESLint to not produce an error because removing the parentheses would cause a syntax error.

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

ESLint produced the following invalid autofix:

for (let a = b in c; ;);

This is interpreted as an initializer in a for-in loop, which is a syntax error in most cases (and is not the intended semantics of the code).

Demo

This issue was detected by running the fuzzer locally.

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

Yes, but not sure when I'll have time.