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/

[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

[bjornasm]

(I would suggest to teach user to navigate the history there rather than reimplementing the feature)

Regarding this, sadly - in scientific publishing some journals require tracking changes in the review process.

[rainer-rq-koelle]

Such a prose-based feature would be like crossing the rubicon for making qmd output fully workable in day-to-day business work.
For code chunks, I think we are speaking about another audience ... and this audience is able to handle diffs.

While I was able to pull over many people in my organisation to use (R/)quarto, the day-to-day test is still review of documents and being able to show changes, i.e., emulating the well-knows Word track change. I conquer with @lnnrtwttkhn that getting everyone into checking git diffs, it not sustainable/feasible.
While a generic feature, being able to show a track record of all changes would be fantastic, I understand the complexity.

From a day-to-day perspective, it would help already, if one could highlight (think the well-known track change side bar in Word) the paras that have changed. I see this more as a summary snapshot based on a "version" of the document, i.e., not necessarily every commit/push diff.
Being able to highlight/change the colour of the changed prose between the version would be the icing on the cake.

I am cognisant that I am using the term "version" here to describe the document after a certain commit (and less all diffs leading up to that point) and then the "delta" to a next "version" (that will typically comprise multiple of commits/diffs).

Obviously, purist will then ask for being able to "remove" such highlights for smaller changes (e.g., adding a comma, correcting a typo), but I can picture this to be a workflow / process step. Fix tiny things first - declare a "version" - include (major) changes to be highlighted. Alternatively, one can work out something like only change colour of version diff if not more than 1 or 2 characters are affected, if more than also highlight bar at para.

Thus, a +1 for such a feature.

[mcanouil]

Keep an eye on Quarto 2:

• Blog post: an early look at Quarto 2 #14323