Misalignment When Comparing Files with "File: Compare Active File With" Command

[thiagojramos]

Does this issue occur when all extensions are disabled?: Yes

VS Code Version/OS Version:

Version: 1.91.0-insider (system setup) Commit: aea213b7fcc7de5c24ad797ac1af209b159d451f Date: 2024-06-28T05:56:20.804Z Electron: 29.4.0 ElectronBuildId: 9728852 Chromium: 122.0.6261.156 Node.js: 20.9.0 V8: 12.2.281.27-electron.0 SO: Windows_NT x64 10.0.22631

Description:

When using the File: Compare Active File With command in Visual Studio Code to compare two open tabs, a rendering misalignment occurs between the tabs in the comparison view.

Steps to Reproduce:

1. Open two text files in separate tabs.
2. Ensure the first tab (in the tab order) is on the left and the second tab is on the right.
3. Use the File: Compare Active File With command to compare the two tabs.

Expected Behavior:

The lines in the two files should be aligned correctly, with corresponding lines appearing on the same level across both tabs.

Actual Behavior:

• The second line of the left tab aligns with the fourth line of the right tab, regardless of the tab resizing (the part that divides the tabs).
• However, when swapping the sides of the compared tabs, the alignment is correct, with the second line of both tabs aligned.

Additional Information:

• Both files are plain text, and the first six lines have the same indentation and line breaks (when one line is split into multiple lines).
• When the second line (empty) of the right tab is moved from left to right, it not only moves the line but also merges the content of the second line (which is empty in both) and the third line. It seems to consider the first, second, and third lines of the right tab as only the first line of the left tab, since the second line of the left tab is aligned with the fourth line of the right tab.

Notes:

• The issue occurs even with all extensions disabled.

Screenshots:

Issue


After using the side-switch button


Line 1 moved from left to right


Attachments

Files used in the issue comparison:

• left_tab.txt

• right_tab.txt

[hediet]

• First Diff
• Second Diff

This is a worst-case input to the current diff algorithm implementation, as there are many ways to align the "description" "anchors". It also took me a while to notice that the left side has one line that does not start with "description".

I think the misalignment of this one line could be improved: Bad vs good.

All in all, I wouldn't say this is a bug in the algorithm (as the diff is correct), but a feature request.