Rule Proposal: no-strict-with-complex-params

function foo(a = 1) {
    "use strict"
}

This is a valid code in ES2015, but this is an invalid code (syntax error) in ES2016.

It is a Syntax Error if ContainsUseStrict of FunctionBody is true and IsSimpleParameterList of FormalParameters is false. https://tc39.github.io/ecma262/2016/#sec-function-definitions-static-semantics-early-errors

So a combination of a non-simple parameter list and a "use strict" directive is going to break the software in future.

The purpose of this rule is that it protects software from the break.

/*eslint no-strict-with-complex-params: error*/

// ✘ BAD
function foo(a = 1) {
    "use strict"
}
function foo({a, b}) {
    "use strict"
}

// ✔ GOOD
function foo(a, b, c) {
    "use strict"
}
function foo(a = 1) {
}
function foo({a, b}) {
}

I think this is a good rule for eslint:recommended, so I separated this rule proposal from strict rule. I’m happy to work on this if accepted.

[platinumazure]

I’m not sure strict is stylistic anymore. Should we consider changing its category?

[mikesherov]

To me this absolutely must modify default behavior, but because it’s essentially a bug fix that might start failing builds, it’d need to go out in a minor release.