Spike - auto indentation

[luabud]

To understand where do we start

[karthiknadig]

Figure out what work needs to be done to use formatOnType, what limitations are there, and how we can get it to work appropriately. LS is not going to do format on type.

[kimadeline]

• look at the code we have that implements format on type
• see if it can be reworked to only do indentation, or will we have to drop it

[karrtikr]

There are three approaches to solve this:

1. VSCode Language Configuration

VSCode provides OnEnterRules and indentationRules which dedents/indents the block given the previous line matches the regex. But regexes can't be used to cover every case, and the current rules are not powerful enough. microsoft/vscode#66235
Also sometimes just knowledge of previous line is not sufficient to make a decision on the indent.

2. On-type indenting

When editor.formatOnType is set to true, one can intervene in between when a user types and indent accordingly. We currently use this in onEnterFormatter.ts and other places. We can use this to cover all the cases one by one. But on-type formatting is not enabled by default nor is very popular (and enables a slew of formatting rules other than cursor alignment), so forcing users to enable on-type formatting as a whole would be good to avoid.

3. Add a key binding for enter

We can add something like

"keybindings": [
    {
        "command": "<Command key>",
        "key": "enter",
        "when": "editorTextFocus && editorLangId == python"
    }
],

(may need more modifying)

and use that to intervene. This way we don't need to have editor.formatOnType enabled. However we need to keep in mind that in this case we're responsible for cursor alignment after the user presses enter, otherwise cursor would stay where it is.

As there is no progress on vscode upstream issues related to 1., going with 3. makes the most sense at this point.

https://github.com/kbrose/vsc-python-indent/blob/master/src/indent.ts seems like a wonderful place to take help from. It covers most cases (#481) we currently have open issues for and is well documented. We can use npm package python-indent-parser similarly to the way @kbrose does.

Also another thing to note here is that having both language configuration and key bindings can override each other sometimes. So we should be moving away from regexes when we solve work items for this.

EDIT: We've decided to go with 2.

Work items

• Modify onEnterFormatter.ts to support only indenting.
• Move languageConfiguration.ts to .json.
• Cut down regexes in language configuration so that it doesn't conflict with onTypeIndenting.
• Look into how https://github.com/kbrose/vsc-python-indent/blob/master/src/indent.ts solves each of these issues. I've verified it works fine for most of these.
  Improve auto-indentation behaviour #481 (function call)
  Meta issue for formatting #684 (meta issue)
  Create unit tests for auto indentation #1314 (tests)
  async for and async with are not automatically indenting #7344 (async for and async with)
  Unexpected indentation behavior after latest update #6886 (moving a line breaks things)
  Indent when doing line breaks #3284 (trailing slash)

[karrtikr]

Closed in favor of #8996 (comment)