Org-roam: Allow providing a function for `org-roam-graph-viewer`

[grzm]

Brief Abstract

On macOS, the common way of opening a file in Safari from the command line is open -a Safari $file. Currently, org-roam-graph-viewer is expected to be the path to an executable. It would be convenient to be able to provide a function for org-roam-graph-viewer so that one can customize within Emacs how the file is opened.

Long Description

The current implementation of org-roam-graph--open assumes org-roam-graph-viewer is the path to an executable (checking using executable-find), and calls call-process to open the generated svg file.

https://github.com/jethrokuan/org-roam/blob/4af4d2e4d5f18422fe0f90d5d83fe4c10ef1a20f/org-roam-graph.el#L203-L208

This implementation does not permit passing any additional arguments to the executable. On macOS, the executable is open, and to specify the application (Safari), one passes -a Safari as an option. This can be worked around by creating a simple script that wraps open -a Safari $1, and provide the path to the script as org-roam-graph-viewer (which is what I've currently done). The downside of this approach is that it requires the creation of this additional script. While not unduly burdensome, it's less than ideal.

Another option as mentioned in https://github.com/jethrokuan/org-roam/issues/115#issuecomment-587248405 is to assign Safari as default application for svg files. This seems too be too big of a hammer, however. Choosing an svg viewer for org-roam specifically shouldn't require designating the default application for all svg files.

One could also override org-roam-graph--open entirely to provide the desired functionality, but the issue seems general enough that an in-the-box solution

Proposed Implementation (if any)

In org-roam-graph--open, check if org-roam-graph-viewer is a string or a function. If it's a function, call the function passing the file as an argument. If it's a string, assume its the path to an executable and use the current call-process path.

Please check the following:

• [X] No similar feature requests

The topic has been mentioned tangentially in https://github.com/jethrokuan/org-roam/issues/115#issuecomment-587248405 (elaborated on above).

[progfolio]

I implemented this a little bit ago, forgot to make a pull request for it:
https://github.com/progfolio/org-roam/commit/7a0191f761a7f0e2e267e4fd8341c0e34b3feaa6
I'll take a look at it later tonight and submit pull.

[progfolio]

@grzm: sorry for the delay. Didn't forget, just had to get some other work out of the way first.

[grzm]

No worries at all! This is an enhancement to eliminate the need for my current workaround. Thanks!

[jethrokuan]

This was closed by #488.