Implement $0 as a snippet exit point (à la TextMate or Sublime Text)

[valkalon]

Prerequisites

• [x ] Put an X between the brackets on this line if you have done all of the following

Description

Hi! Since this is my first contribution here, I'm happy to receive feedback on how to improve.

Take the following snippet:

'.source.ts':
  'console log':
    'prefix': 'cl'
    'body': 'console.log($0)'

Current behavior
If you ype "cl" then "Tab" your snippet expands.

If you push "tab" again, nothing happens.

If you push "tab" again, a tab character is added

Expected behavior
If you type "cl" then "Tab" your snippet expands.

If you push "tab" again, a tab character is added (no "useless" tab)

Versions

Atom : 1.31.1
Electron: 2.0.7
Chrome : 61.0.3163.100
Node : 8.9.3
apm 2.1.1
npm 6.2.0
node 8.9.3 x64
atom 1.31.1
python 2.7.12
git 2.7.4
Ubuntu 16.04.4, 4.4.0-137-generic, Unity, 64bits

Why this enhancement would be useful
The current behavior feels strange when you push tab and nothing
happens.

The expected behavior saves a keystroke. It gives a meaning to $0
which becomes the "snippet exit point" variable.

It becomes more consistent with other text editor.

This enhancement is also related to the following issue:

Should snippets use $0?
atom/language-c#262

Other text editors or applications where this enhancement exists
Expected behavior is the behavior as described in TextMate documentation,
https://macromates.com/manual/en/snippets#tab_stops

it's also Sublime Text behavior.
http://sublimetext.info/docs/en/extensibility/snippets.html#fields

Additional Information

Would you like to help implementing this feature?
Yes, I've actually already implemented it locally.

To try it:
in file "lib/snippet-expansion.coffee"

replace your existing "goToNextTabStop" function by

goToNextTabStop: ->
  nextIndex = @tabStopIndex + 1
  if nextIndex < @tabStopMarkers.length
    if @setTabStopIndex(nextIndex)
      true
    else
      @goToNextTabStop()
  else
    if @snippet.tabStopList.list.Infinity? # If snippet uses $0 value, exit snippet
      succeeded = false
      @destroy()
    else
      succeeded = @goToEndOfLastTabStop()
      @destroy()
      succeeded

Does your modification break an existing feature?
Yes for those who use placeholders with $0

Ex. ${0:myplaceholder}

The placeholder won't work since $0 is the point where
the snippet exists.

[savetheclocktower]

Thanks so much for doing this research.

This behavior was introduced as part of #262, ostensibly by design. I think that the purpose of that PR seems to have been to introduce an implied $0 at the end of any snippet. But snippets with an explicit $0 get some of the same behavior applied, and whether this was intentional or not, I’d argue that they should be treated differently than #262 treats them.

I think if you’ve got this snippet…

foo.bar(${1:'baz'}, $2, $3);

…that it’s sensible, once you reach tab stop 3, for the next Tab to take you to the end of the snippet.

But if you’ve got…

foo.bar(${1:'baz'}, $2, $0);

…then you’re using $0 to explicitly indicate where the cursor should go at the end of the snippet. Once you hit tab stop 0, I don’t think that Tab should bring you to the end of the snippet, and I definitely don’t think that it should do nothing at all, as is the current behavior.

I think your fix brings us back to an intuitive behavior, @valkalon, but it breaks the unit test that got touched in #262, so I just want to get clarity on how this should behave before I proceed. @nathansobo, want to weigh in?

[savetheclocktower]

If another maintainer doesn’t weigh in, BTW, I’m inclined to move forward despite the behavior change, since you’re right about how Sublime Text behaves. A stated goal of #262 was to make Atom behave more like Sublime Text, which I’d take as further evidence that the current behavior is unintentional. I’ll just give it a few days to make sure.

[valkalon]

Your description is exactly what I have in mind as a natural snippet behavior. Thanks a lot for the feedback @savetheclocktower. I'm happy to provide further help if needed

[lee-dohm]

This sounds fine 👍