JS arrow functions are difficult to type in strict mode

[nickserv]

Expected behavior

I can type () => {} or any other valid JS ES6 arrow function and strict mode will allow me to type the > without matching it with a <.

Actual behavior

I'm prevented from typing > on its own so I have to type C-u > every time. Basically, smartparents doesn't know this is valid syntax so it assumes it's an unmatched angle bracket.

Steps to reproduce the problem

1. Open any supported JS mode
2. Enable smartparens-strict-mode
3. Type () => {} or any other valid JS ES6 arrow function

Environment & version information

• smartparens version: 20171201.242
• Active major-mode: web-mode
• Emacs version (M-x emacs-version): GNU Emacs 25.3.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version 10.9.5 (Build 13F1911)) of 2017-09-12
• Emacs config: https://github.com/nickmccurdy/dotfiles/blob/master/home/.emacs
• OS: darwin

[Fuco1]

Is > a standard pair in javascript? If so we could configure it out of the box.

I can see how this could be handled with js2-mode where we could access the AST. I don't think we can do much better than some sort of regex hack for js-mode.

[nickserv]

I'm not sure exactly what you mean by "standard pair". As far as I'm aware, the spec itself doesn't have any matching angle brackets, but JSX (which is a non-standard syntax frequently seen in the same file and supported by js2-mode and web-mode) does allow them to represent HTML tags. So it would depend on is smartparens has JSX represented as a separate syntax or a part of the JS syntax. Either way I doubt => would be valid for anything other than an arrow even in JSX, so a regex hack should hopefully be easy.

[LilyMGoh]

+1 I'm experiencing the same problem and would love to see this fixed.

[Ionshard]

I have solved this problem by removing the < and > pairs from smartparens with the following line:

(sp-local-pair '(react-mode) "<" ">" :actions nil)

I am specifically doing this for react-mode because I am using spacemacs and that's the major mode that enables JSX handling. This completely removes the < and > handling, which I am mostly okay with because I just use emmet mode anyways.

I tried following some information from https://github.com/Fuco1/smartparens/wiki/Permissions#filters to try and allow > to be typed only after an = but could not figure it out. Any advice would be helpful!

[Fuco1]

There are two things that need to be done. First, you need to specify a predicate in :unless filter to only enable the insertion when there is no= in front.

Second is to set up :skip-match to ignore the > in case there is a = in front of it so as not to try to pair it with a (non-existing) opening <.

The logic is pretty much the same as in smartparens-text.el which adds support for emoticons, such that :-) the paren is not being matched to ( because there is none.

[Ionshard]

Thanks that was the push I needed. For others the following worked for me:

  ;;;; Allow ES6 arrow '=>' in react-mode
  (defun sp-after-equals-p (_id action _context)
    (when (memq action '(insert navigate))
      (sp--looking-back-p "=>" 2)))

  (defun sp-after-equals-skip (ms mb _me)
    (when (eq ms ">")
      (save-excursion
        (goto-char mb)
        (sp--looking-back-p "=" 1))))

  (sp-local-pair '(react-mode) "<" nil
                 :unless '(:add sp-after-equals-p)
                 :skip-match 'sp-after-equals-skip-p)

There's still a weird issue where if I try to put => in the JSX it will put = (e.g. replace the > with a space) but I shouldn't be doing that so I will ignore it. I am pretty sure that's something in web-mode

[Fuco1]

@Kasuko Sweet job! Would you be interested in making a pull request?

I don't understand your last comment about "trying to put => in JSX", can you show an example?

[Ionshard]

Sure, I could make a pull request, I just don't know where this would go. I actually use Spacemacs so this issue arose when installing the react layer, which adds a react major mode, but I don't know if that's accurate to the emacs situation as a whole. If I am just editing javascript then the < > pairs are not even present so adding a => works just fine. If you tell me where this should go, I'd be happy to put it there.

As for the strange => JSX thing I have captured a gif

So when I enter the > after an = inside of the JSX parts (e.g. after the <div> tag) it just doesn't show up and seems to be replaced with a space. I'm not sure what the sp--post-self-insert-hook-handler error indicates.

I am aware that placing the => in that location is invalid syntax, which is why I am not super worried about it.

If I attempt to place the => in a proper JS block in the JSX e.g.

<div>
  {() => (<span>"Something"</span>}
</div>

it works fine, which is what seems to me to indicate it's some kind of web-mode interaction that is causing the odd behaviour.

[Fuco1]

Thanks for the gif, that is superb! I think there is some issue in smartparens and the post insert handler. As you say it's probably not super high priority.

The code can go to smartparens-javascript.el. Am I right to assume react-mode is in fact this: https://github.com/felipeochoa/rjsx-mode ? In which case it will get autoloaded properly because that mode extends js2-mode.

You should then change the prefix of the methods to sp-react-- to avoid possible conflicts.

[Ionshard]

I don't think it's rjsx-mode this is defined here https://github.com/syl20bnr/spacemacs/blob/master/layers/%2Bframeworks/react/packages.el#L66

I am quite unfamiliar with emacs-lisp but I am learning. I think that react-mode is declared directly in that layer (which is a spacemacs only concept) and it is derived from the web-mode major mode.

Does this change where/if I would add that code?