Removed eslint rule that checks modules

[bestander]

Removed eslint rule that checks modules

After we updated to ESLint 2.x, ESLint started complaining 'use strict' is unnecessary inside of modules strict.
This is correct behaviour because according to spec modules are strict.
The problem is that our transforms don't transpile strict mode so we still need to have this pragma in all our code.

I did not find a way to make eslint require "use strict" for ES6 modules: eslint/eslint#2785
So I am removing this.

What stops us from automatically adding strict mode with babel?

Need your feedback, @frantic @martinbigio
David said that you Martin looked into this.

[facebook-github-bot]

By analyzing the blame information on this pull request, we identified @frantic, @spicyj and @ericvicenti to be potential reviewers.

[facebook-github-bot]

@bestander updated the pull request.

[corbt]

Related: #5796

[janicduplessis]

The babel transform is not currently adding strict mode but it should work since #5422 so we'd need to enable the strict mode transform as per #5796.
The best would be to keep the eslint rule and codemod out all the 'use strict'.

[frantic]

I agree with @janicduplessis, as long as we keep the code consistent it should be easy to write a codemod. cc @vjeux, do you remember why we opted into using 'use strict' manually?

[vjeux]

I do not know why we don't automatically insert use strict in es6 modules.

[ide]

When providesModule was introduced, there was some code that relied on CommonJS semantics which led to two things: 'use strict' was not enforced and people could write code that was valid inside of a function but not a module's top-level scope.

That said to my knowledge FB is still on require and doesn't use language-level ES6 modules (export default) so maybe we could do something where CommonJS modules need "use strict" but ES6 ones are always strict.

[martinbigio]

@facebook-github-bot shipit

[facebook-github-bot]

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[martinbigio]

As it has been mentioned on #5796, internally at FB we have a few modules which are not strict mode compliant. We can land #5796 as indicated on that issue