Implementing the v:register variable

[jphalip]

In Vim (and IdeaVim), if you select some text then yank it, your cursor moves to the start of the selection after yanking. To change this behavior and keep the cursor in the original position, I've got this key map, which works in Vim:

vnoremap <expr> y 'm`"' . v:register . 'y``'

For example in Vim, if you do V2j"ay, then it stores the selected text in the a register and keeps your cursor in the original position.

This doesn't work in IdeaVim because the v:register variable isn't implemented yet.

So I tried to implement it in VimVariableServiceBase.getVimVariable():

"register" -> {
    val registerChar = if (editor.carets().size == 1) injector.registerGroup.currentRegister else injector.registerGroup.getCurrentRegisterForMulticaret()
    VimString(registerChar.toString())
}

However, here registerChar doesn't contain the register set by the command. I also tried with injector.registerGroup.lastRegisterChar.

Can you tell what I might be missing?

[citizenmatt]

The problem is that you're looking at the register used for the currently executing command, rather than the register that should be used once the command has been completed.

When we type "adw, the a register is selected before invoking DeleteMotionAction. When deleting text, injector.registerGroup.lastRegisterChar or .currentRegister will return this selected register and use it to store the deleted text. I think we then reset this stored register once the command has finished (I'd need to confirm that).

But the mapping you provided is evaluated while the command is being built and before it's executed, so the register hasn't been set yet. You'll need to look at CommandBuilder.register to see what's currently been entered, if anything. If it's null, you should be able to fall back to injector.registerGroup.defaultRegister to get the required behaviour of v:register based on the 'clipboard' option (again, would need testing).

You'll notice a TODO comment that wants to remove CommandBuilder.register. This is because there are very few reasons to be looking at the in-progress state of a command. Most of the time, callers don't want the in-progress state and should wait for the complete command. This is a legitimate reason for accessing in-progress state, so don't worry about the comment. Maybe we'll rename the accessor at some point, so it's more obvious that it's probably not what most people are looking for, and could still change depending on the rest of the entered command (like we did with calculateCount0Snapshot).

[jphalip]

Thanks again for the detailed explanation. I propose renaming the attribute registerInEffect and then here's an implementation:

"register" -> {
        // The name of the register in effect for the current normal mode
        // command (regardless of whether that command actually used a
        // register). Or for the currently executing normal mode mapping
        // (use this in custom commands that take a register).
        // If none is supplied it is the default register '"', unless
        // 'clipboard' contains "unnamed" or "unnamedplus", then it is
        // "*" or '+' ("unnamedplus" prevails).
        val register = KeyHandler.getInstance().keyHandlerState.commandBuilder.registerInEffect
          ?: when {
            injector.globalOptions().clipboard.contains("unnamedplus") -> '+'
            injector.globalOptions().clipboard.contains("unnamed") -> '*'
            else -> injector.registerGroup.defaultRegister
          }
        VimString(register.toString())
      }

I've based this on the documentation (https://neovim.io/doc/user/vvars.html#v%3Aregister) and Vim source code (https://github.com/vim/vim/blob/45e0704d9670c10bfaf2bb408d6a5cd639d23835/src/clipboard.c#L2210).

I'm going to look at adding some tests for it and then submit a PR. Let me know if you have any tips about the tests.

[citizenmatt]

Cool. Let's go with registerSnapshot or even a function getSelectedRegisterSnapshot to be consistent with calculateCount0Snapshot. The key thing is that it is a snapshot of the value, because further typing could change the register before the command is built - e.g. something like "ad"bw would return the a register if the d operator was mapped, and then b if the w motion was mapped (and the command will run with the b register selected).

Also, have you checked if defaultRegister already does the 'clipboard' logic for you? I think we update the value when the option changes, so I think you might just be able to use defaultRegister.

[jphalip]

Oh right, yes the 'clipboard' logic seems to be handled here:

ideavim/vim-engine/src/main/kotlin/com/maddyhome/idea/vim/register/VimRegisterGroupBase.kt

Lines 84 to 98 in 365b58e

	private val onClipboardChanged: () -> Unit = {
	val clipboardOptionValue = injector.globalOptions().clipboard
	defaultRegisterChar = when {
	"unnamedplus" in clipboardOptionValue -> {
	if (isPrimaryRegisterSupported()) {
	CLIPBOARD_REGISTER
	} else {
	PRIMARY_REGISTER // for some reason non-X systems use PRIMARY_REGISTER as a clipboard storage
	}
	}
	"unnamed" in clipboardOptionValue -> PRIMARY_REGISTER
	else -> UNNAMED_REGISTER
	}
	lastRegisterChar = defaultRegisterChar
	}

[jphalip]

@citizenmatt So I've had to default to currentRegister instead of defaultRegister to handle a sequence like this: "a:echo v:register, which should return a because the register has already been recorded by the time you run the echo command.

Here's the PR: #1046

I also have a few other open PRs if you have a chance to review them. Thanks again for your help!

[citizenmatt]

Nice catch! I didn't realise that "a:echo v:register would work in Vim 😁

I'm only a contributor, so I can't really review your PRs, that's for @AlexPl292. I can take a look and leave a comment though.