Proposal: change no-redeclare default behavior

[mysticatea]

What rule do you want to change?

• no-redeclare

Does this change cause the rule to produce more or fewer warnings?

• More Warnings.

How will the change be implemented? (New option, new default behavior, etc.)?

• It changes the default value of builtinGlobals option to true.

Please provide some example code that this change will affect:

/*eslint-env browser */
/*eslint no-redeclare: error */

var top = 100

What does the rule currently do for this code?

• No errors.

What will the rule do after it's changed?

• Warn the top variable as a redeclaration because browser environment has it.

Are you willing to submit a pull request to implement this change?

Yes.

Context:

• We cannot redeclare the top variable, browsers ignore the var top declaration silently. This can cause confusion and I believe that it's worth to warn by default.
• Originate no-undef rule had warned redeclarations of globals by default, but it was removed in Redeclaring global variables should trigger "no-redeclare", not "no-undef". #4504. I think that we can re-enable it on no-redeclare rule.

[platinumazure]

👍 Yes! This is a sensible default. My guess is we had to implement the option with a default disabled state so it wasn't a breaking change, but we should absolutely change this in the next major release.

[not-an-aardvark]

This issue was accepted in today's TSC meeting.