no-constant-condition doesn't respect generator function expressions

[helixbass]

Tell us about your environment
Came across this while working on eslint-plugin-coffee custom parser

• ESLint Version:
  5.4.0
• Node Version:
  8.11.4
• npm Version:
  6.2.0

What parser (default, Babel-ESLint, etc.) are you using?
Coffeescript, but the issue seems to apply regardless of parser

Please show your full configuration:
The relevant config would be no-constant-condition: 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.
I was attempting to run equivalent Coffeescript versions of the tests in tests/lib/rules/no-constant-condition.js against the no-constant-condition rule. I saw tests fail eg this was expected to throw an error but didn't:

while true
  foo = -> yield

Which would be basically equivalent in JS to:

while (true) {
  const foo = function*() { yield }
}

What did you expect to happen?
For the test to pass (the nested yield shouldn't suppress the warning for the constant while condition)

What actually happened? Please include the actual, raw output from ESLint.
The test failed (no warning was reported by no-constant-condition)

Looking at the source code for lib/rules/no-constant-condition.js, I saw that it only "resets the yield checker" when entering a FunctionDeclaration (but not a FunctionExpression). Coffeescript doesn't generate FunctionDeclarations so that's why I ran into this

It seems to me that generator FunctionExpressions should behave the same way as generator FunctionDeclarations

Will submit a fixing PR momentarily

[not-an-aardvark]

Closing because this was fixed by #10827.