2732 slurp barf multicursor

[pbwolf]

What has changed?

• Slurp and barf support multi-cursor editing (backward and forward: four commands in all).
• Internally (paredit.ts), multi-cursor concerns are factored out and separated from per-command strategy:
  • The core algorithm of each command - the calculation of ModelEdits for a single cursor - is extracted to a new function.
    • Following the example of rewrapSexpr, the new functions produce an array of changeRange edits. Previous use of deleteRange or insertString by slurp and barf is changed to changeRange.
      • The 100% changeRange technique worked OK in VS Code but flunked the unit tests, exposing a bug and requiring a correction in the model's emulation of how VS Code moves cursors after edits.
  • A single new shared multi-cursor-collation function to deduplicate and sort all cursors' ModelEdits is extracted from rewrapSexpr.
  • In sum: rewrap, slurp, and barf all use the same multi-cursor coordination heuristics, which may be general enough to help extend further editing commands for multiple cursors.
• Barf no longer requires an async touch-up of the selection positions: reducing likelihood of a race condition between two barf commands issued in rapid succession. (Slurp already did not require it.)
• New multi-cursor tests of slurp and barf, forward and backward, are based on the first and simplest single-cursor test of the four respective functions.
• Single-cursor tests of slurp and barf are not modified.
• Reformat-as-you-type reformats all edited points, and preserves all cursors so you can proceed to issue further multi-cursor editing commands.
  • It no longer relies on editing commands to provide a formatDepth. Instead, the ranges to reformat are computed from the list of edits.
  • It preserves multiple cursors by translating the reformatted text blob into little changeRange edits that only adjust the whitespace.

Loose ends:

• Slurp, barf, and rewrap do not check whether the user enabled multi-cursor features (nor is a {multicursor:false} option heeded), because the single-cursor case is not a distinct procedure. This deviation from documentation could be remedied in the documentation... but on the other hand, paredit's other multi-cursor support has been established for two or three years and the burden of supporting a feature flag might no longer be required?

Wobbly parts:

• The multicursor-capable reformat-as-you-type is rather ambitious, and it affects all commands that edit via the MirrorDocument, even if there is just 1 cursor.

Addresses #2732

My Calva PR Checklist

I have:

• [x] Read How to Contribute.
• [x] Directed this pull request at the dev branch. (Or have specific reasons to target some other branch.)
• [x] Made sure I have changed the PR base branch, so that it is not published. (Sorry for the nagging.)
• [x] Made sure there is an issue registered with a clear problem statement that this PR addresses, (created the issue if it was not present).
  • [x] Updated the [Unreleased] entry in CHANGELOG.md, linking the issue(s) that the PR is addressing.
• [x] Figured if anything about the fix warrants tests on Mac/Linux/Windows/Remote/Whatever, and either tested it there if so, or mentioned it in the PR.
• [x] Added to or updated docs in this branch, if appropriate
• [x] Tests
  • [x] Tested the particular change
  • [x] Figured if the change might have some side effects and tested those as well.
• [x] Formatted all JavaScript and TypeScript code that was changed. (use the prettier extension or run npm run prettier-format)
• [x] Confirmed that there are no linter warnings or errors (use the eslint extension, run npm run eslint before creating your PR, or run npm run eslint-watch to eslint as you go).

Ping @pez, @bpringe, @corasaurus-hex, @Cyrik

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[PEZ]

You are awesome, @pbwolf! ❤️

I will have a closer look tomorrow. Must 💤 now.

[PEZ]

I found this issue, don't know if you are aware:

[:a |:b]

barf forward

Expected:

[:a|] :b

Actual:

[:a] |:b

It's as if it attaches the cursor position to the closest form. Barfing forward from here works as expected:

[:a| :b]

[pbwolf]

@pez I added 2 unit tests to check that barf forward keeps the cursor within the shortened list, and made it do so.

[pbwolf]

Hmm. Barf backward, also, can leave the cursor outside the narrowed form, unlike in version 486.

[pbwolf]

Added a unit test that barf backward keeps the cursor within the shortened list, and made it do so.

[PEZ]

I forgot to report back that I tested the barf forward after your fix and that it worked great. Now have also tested barf backward and it behaves beautifully. And I am getting addicted to multi cursor slurp and barf!

[pbwolf]

"Undo" treats the formatting and the slurp/barf as two distinct events. Is that tolerable? (It has the benefit, that if something surprises you, you can distinguish a-surprise-during-formatting from a-surprise-during-structural-editing.)

[PEZ]

Undo is a bit strange also in current Calva. Now tried with this branch, since you mentioned it. I think it is acceptable, as in I rather have multi cursor slurp and barf with these extra undo's than staying on single cursor. But it is a bit confusing. Especially when the formatting didn't do anything. We could release as is and try make it better later?

[pbwolf]

Undo is a bit strange also in current Calva. Now tried with this branch, since you mentioned it. I think it is acceptable, as in I rather have multi cursor slurp and barf with these extra undo's than staying on single cursor. But it is a bit confusing. Especially when the formatting didn't do anything. We could release as is and try make it better later?

I agree

[PEZ]

What's your plan for this, @pbwolf? Asking for a friend who longs for it. 😀

[pbwolf]

Since multi-cursor formatting (a simple matter) has been resolved separately, I made a new, greatly-simplified PR #2816 for Slurp and Barf. I will try pressing the Close button on this PR that had combined the two enhancements.