feat: add g_ motion (move to last non-blank character)

[legalcodes]

Manual Review

I tested using this motion in the replit link -- it worked.

Adds the g_ motion, which moves the cursor to the last non-whitespace character on the line.

Behavior

• g_ moves to the last non-blank character of the current line
• 2g_ moves to the last non-blank of the next line (count - 1 lines down)
• Works with operators: dg_ deletes to the last non-blank, preserving trailing whitespace
• Inclusive motion, matching vim's native behavior

This is the counterpart to ^ (first non-blank), which is already implemented. Currently g_ is unmapped and does nothing.

Implementation

• New helper findLastNonWhiteSpaceCharacter() mirrors the existing findFirstNonWhiteSpaceCharacter()
• New motion moveToLastNonWhiteSpaceCharacter registered with inclusive: true
• Tests cover basic movement, no-trailing-whitespace lines, count support, and operator interaction

Test plan

• Added automated tests in vim_test.js
• Manual verification via web demo

Open web-demo @ d6eeff49181ef1b2a41ff8f40aba9e6ee427cc96

[Copilot]

Pull request overview

Adds Vim’s g_ motion to move the cursor to the last non-blank character on a line (inclusive), including count support and operator compatibility, aligning behavior with existing whitespace-aware motions.

Changes:

• Register g_ as an inclusive motion mapped to moveToLastNonWhiteSpaceCharacter.
• Implement moveToLastNonWhiteSpaceCharacter and findLastNonWhiteSpaceCharacter() helper.
• Add automated tests covering basic movement, count usage, and dg_ behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/vim.js	Adds the g_ keybinding, implements the motion, and introduces a helper to find the last non-whitespace character.
test/vim_test.js	Adds a new test case for g_ movement, count behavior, and delete-operator interaction.

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[Copilot]

moveToLastNonWhiteSpaceCharacter computes line = head.line + motionArgs.repeat - 1 and immediately calls cm.getLine(line) without clipping the line number to the document bounds. With a large count (e.g. 100g_ near EOF) this can produce an out-of-range line and return a Pos with an invalid line, which then flows into operator selections (dg_, etc.) without being clipped and can break selection logic. Clamp the target line to [cm.firstLine(), cm.lastLine()] (or use cm.clipPos(new Pos(line, 0)).line) before calling getLine and before returning the Pos.

Suggested change

	var lineText = cm.getLine(line);
	var lastNonWS = findLastNonWhiteSpaceCharacter(lineText);
	return new Pos(line, Math.max(0, lastNonWS));
	var clippedLine = cm.clipPos(new Pos(line, 0)).line;
	var lineText = cm.getLine(clippedLine);
	var lastNonWS = findLastNonWhiteSpaceCharacter(lineText);
	return new Pos(clippedLine, Math.max(0, lastNonWS));

[Copilot]

The new g_ tests cover a small count (2g_) but don’t cover boundary behavior when the count would move past the end of the document. Since g_ is countable, adding a test like 100g_ on a short buffer (and asserting it lands on the last line’s last non-blank without throwing) would help lock in correct clipping behavior.