Block scope transform not included when targeting Safari 10

[babel-bot]

Issue originally reported by @ssilve1989 in babel/babel-preset-env#411

Specifying a target of "safari >= 10" doesn't use the transform-es2015-block-scoping plugin. Yet Safari 10 does need this because of this bug.

Ex:

{
  let a = 3
}

let a = 3

is an error in Safari 10.1.2 resulting in SyntaxError: Can't create duplicate variable that shadows a global property: 'a'.

I've had to manually include this plugin in the include option to get Safari working.

[babel-bot]

Comment originally made by @existentialism

@ssilve1989 thanks for the report! since we source our mappings via compat-table, mind reporting this over there?

[babel-bot]

Comment originally made by @ssilve1989

@existentialism done

[wessberg]

This was resolved and merged in compat-table/compat-table#1183.

I just ran into this issue when using @babel/preset-env when testing on Safari 10.1.
Which surprises me given that @babel/preset-env is depending on a version of compat-data based on the following PR: compat-table/compat-table#1458.

[existentialism]

@wessberg the compat table mapping shows:

https://github.com/kangax/compat-table/blob/gh-pages/data-es6.js#L561

safari10: null,
safari10_1: true,

So preset-env treats safari >= 10.1 as passing that test. I haven't tested (and it doesn't look like the author of PR tested it either), but if 10.1 doesn't pass, then we should update compat-table!

[wessberg]

I’ve made a simple repro: http://safari_10_1_repro.surge.sh/ with the following code:

function func(a = 1) {
    for (let a = 2; ;) {
        break;
    }
}
func();

I’ve tested it in Safari 10.1 and can confirm that it doesn’t work. We get SyntaxError: Cannot declare a let variable twice ‘a’.

I have updated the old issue on the compat-table repository with this information. I hope we’ll get it resolved.

[existentialism]

@wessberg thanks!

[wessberg]

It has been fixed and merged into compat-table!

[existentialism]

@wessberg awesome, thank so much for getting that taken care of!

Just pushed: #10127