fix(cli): make vim cc clear non-last and astral-character lines

[Pluviobyte]

Summary

Vim cc (change-line) silently does nothing on any non-last line of a multi-line buffer, and on a single line containing an astral character (e.g. an emoji). It clears the line correctly only when the cursor is on the buffer's last line and the line is ASCII/BMP-only.

Details

vim_change_line derived the end of the range with two helpers (getLineRangeOffsets / getPositionFromOffsets) that:

1. counted a trailing newline after the last changed line (when it isn't the buffer's last line), and
2. measured columns in UTF-16 code units.

So the computed end column landed one position past the end of the line (e.g. endCol = 12 for "hello world"), or split a surrogate pair (endCol = 2 for "😀"). replaceRangeInternal rejects a range whose endCol > cpLen(line) and returns the state unchanged — a silent no-op, while the UI still switched to INSERT mode.

The fix computes the range directly in code points: from column 0 of the first line to cpLen(lastChangedLine). This clears single lines, non-last lines, multi-line counts (collapsing them into a single empty line, matching Vim), and astral characters. The two offset helpers were only used here, so they are removed.

Before / after on ['hello world', 'foo'] with the cursor on line 0:

• before: cc → ['hello world', 'foo'] (unchanged)
• after: cc → ['', 'foo']

Related Issues

None — found while reviewing the text-buffer vim handlers. Happy to file a tracking issue if preferred.

How to Validate

cd packages/cli
npm run typecheck
npx vitest run src/ui/components/shared/vim-buffer-actions.test.ts src/ui/components/shared/text-buffer.test.ts

New tests in vim-buffer-actions.test.ts cover cc on a non-last line, on a single-line emoji buffer, and with a count (2cc). They fail on the previous implementation (the buffer is unchanged) and pass with this fix. Existing single-line cc, dd, and all text-buffer tests continue to pass (427 tests).

Pre-Merge Checklist

• Updated relevant documentation and README (not needed — behavior fix)
• Added/updated tests (regression tests for non-last line, emoji, and multi-count cc)
• Noted breaking changes (none — only fixes the broken no-op cases)
• Validated on required platforms/methods:
  • Linux
    • npm run (vitest + tsc --noEmit)

Note: platform-independent editor-logic fix covered by automated unit tests, validated via the package test suite on Linux.

Made with Cursor

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a bug in the Vim emulation layer where the cc command failed to execute correctly in several edge cases. By replacing an overly complex, offset-based range calculation with a direct code-point approach, the fix ensures that lines are cleared reliably regardless of their position in the buffer or the presence of multi-byte characters. This change improves editor stability and aligns the behavior more closely with standard Vim expectations.

Highlights

• Vim cc Command Fix: Resolved an issue where the cc (change-line) command would silently fail on non-last lines or lines containing astral characters (e.g., emojis) due to incorrect range calculations.
• Code Cleanup: Removed redundant getLineRangeOffsets and getPositionFromOffsets helper functions, simplifying the logic by calculating ranges directly in code points.
• Regression Testing: Added comprehensive unit tests to vim-buffer-actions.test.ts covering non-last line clearing, emoji support, and multi-line count operations.

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[gemini-code-assist]

Code Review

This pull request refactors the vim_change_line action in the text buffer to correctly handle astral characters (such as emojis) and non-last lines of multi-line buffers. It removes the offset-based helper functions getPositionFromOffsets and getLineRangeOffsets from text-buffer.ts and instead computes the target range directly using code point lengths (cpLen). Additionally, comprehensive unit tests have been added to verify these scenarios. There are no review comments, and I have no additional feedback to provide.