Visualize changes in documents, i.e., git diff

[lnnrtwttkhn]

Description

Thanks for all your work on Quarto, I really love it.

A feature that would be very cool would be way to visualize changes in documents, e.g., leveraging the output of git diff.
The main use-case that I regularly have is that I want to be able to show what recently has changed in a document and provide a way to show the revision history to users without them having to know Git or visit the remote repository.
Specifically, some feature that I have in mind:

• Visualize changes in the same (current) Quarto document
• Select which change(s) to show: Full history, only latest change, or specific change (i.e., change between two arbitrary commits)
• Visualize changes in other Quarto documents (i.e., in index.qmd I can visualize the changes in functions.R.

Please let me know if I should provide more details. Curious to hear what others think about this or if something along those lines has already been implemented somewhere. Thanks!

[mcanouil]

I'm not sure Quarto will do something on that in the future or at least in a near future.

I would suggest you get acquainted with the extension mechanism which is there precisely for you to extend and add such features, see https://quarto.org/docs/extensions/.

if something along those lines has already been implemented somewhere

I am not aware of something like that but you can take a look at all the extensions listed on https://m.canouil.dev/quarto-extensions/

[mcanouil]

Thanks for sharing the idea! That's how extensions get created ;)

[gordonwoodhull]

It would be easy enough to do a text diff on the qmd and other source files. It's the diff on anything structural or stylistic that would be really difficult.

I'd suggest starting with plain text diff, then add formatting the lines based on whether they start with + or -.

I've done this in the past (in straight HTML) and it wasn't hard to get decent formatting. Since Quarto is multi-format you'd want to depend on something like https://m.canouil.dev/quarto-highlight-text/ to format the lines, and then use a monospace font. (It's not possible to format code directly right now.)

[mcanouil]

You could also leverage the ```diff code block where lines with - are red and with + are green.

And beyond the highlight part, a diff needs a reference. How do you define it? The last commit (head)? Then, it means you need to do massive commits if you still want the diff?

Making all this a general framework/workflow is really not trivial and has a lot of design choices.

[gordonwoodhull]

Much easier! Here is a trivial Python example, works across formats.

```{python}
import subprocess
from IPython.core.display import display, Markdown

diff = subprocess.Popen(['diff', 'a.txt', 'b.txt'], stdout= subprocess.PIPE)
display(Markdown(
  '```diff\n' +
  diff.stdout.read().decode('utf-8') +
  '\n```\n'))
```

I agree making a general extension might be complex, seems like the display part is already there!

[mcanouil]

I mean displaying the diff of the plain text input inside the document is "easy" but having the corresponding diff such as having the new sentence from the markdown diff be in green in the HTML/Typst/Docx/etc. is way harder and I believe that's the target.
Something close to the track change feature of Microsoft word.

The diff could be added as something close to the "code-tools".

But having the "whole history" means to store the whole git history of a file.
It's really like reimplementing GitHub/GitLab inside Quarto at some level.😅 (I would suggest to teach user to navigate the history there rather than reimplementing the feature)

Edit: adding a link to file history might even be the easiest and most effective way to achieve the desired goal: https://github.com/<user>/<repo>/commits/main/path/to/file.qmd