Feature Request: get new cursor position after formatting

[verhovsky]

Describe the Feature
We're using sql-formatter in a text box but after formatting the cursor is moved to the beginning. I would like to be able to pass the cursor's current position (as either an integer index or a line, column pair) before formatting and get the formatted query along with the cursor's new position after formatting so that the cursor stays in the logical place in the formatted code.

Supporting multiple cursors would be a bonus.

Why do you want this feature?
It's annoying when you have to move your cursor back after formatting, especially when your SQL query is very long. This would be useful for the VS Code extension.

[nene]

This is definitely a pretty large feature request. It would mean providing a separate API just for this specific purpose. Currently the formatter doesn't track any line number/position information internally, so it would be quite a substantial change internally as well.

What about trying a simpler approach first: just keeping the old position of the cursor instead of moving it to the very beginning.

[verhovsky]

a separate API just for this specific purpose

Yea. I came across prettier.formatWithCursor, which does what I want, except format SQL. You could implement this API and have the old API call it and throw out the cursor result. I don't know how they do it, but I don't think keeping track of line numbers is necessary, you just need to keep track of the cursor in the AST and when you're generating the result, change this code

sql-formatter/src/core/WhitespaceBuilder.ts

Line 82 in 2e47295

return this.query.map(item => this.itemToString(item)).join('');

to check each node for the cursor and if you ever see it you count the number of newlines you have so far in the result and the number of characters in the current line and add it to the cursor's position in the node you're about to add.

If the cursor is inside some AST node (e.g. its inside a string), I think those shouldn't change size so you store the position of the cursor in the node. It's harder when the cursor is between AST nodes because it's important that if the code left of the cursor on the same line as the cursor doesn't change, the cursor shouldn't move, because it would be surprising to users if they formatted some code, the formatting didn't change but their cursor moved because the formatter removed one space and replaced it with another space or something. I think you would need to add the cursor as its own AST node to handle some of those cases.

[nene]

Thanks for pointers. Much appreciated.

I'd label this feature as a nice-to-have, but at the moment not a priority. We have a bit larger reorganization of the parser going on at the moment.

If you are willing to implement this though, a PR would be welcome. I can also provide help if you get stuck with it. The implementation would indeed be something quite similar to what you outlined. Though the item in the code above is actually a string, not an AST node, so that part would need to be reorganized. In that regard, better to build it on top of #253, otherwise too much conflicts will ensue.