Programmatic front matter

[dominikh]

Would it be possible to have a hook or callback that let's us insert custom Hugo front matter at the time of export? Concretely, I want to set lastmod to the modification time of the Org file (using "one post per Org file") without having to materialize it in the Org file's front matter.

Such a hook could be used for other computable front matter, too. For example, one could set the section based on the file name.

One possible API would be a configurable callback, that takes the Org buffer as input and returns a list of key/value pairs of Hugo front matter to insert.

[kaushalmodi]

There's isn't a generic solution.

But specific to your usecase, there something already available: #+hugo_auto_set_lastmod: t.

Search for "auto_set" on https://ox-hugo.scripter.co/doc/dates/.

[dominikh]

#+hugo_auto_set_lastmod: t

Doesn't that set lastmod to the current time? I want to set it to the file's mtime. I export all my notes in batch, not only those that have changed. So with auto_set_lastmod, all posts have the current time as the lastmod time.

There's isn't a generic solution.

I know, I was wondering if one should be added.

[kaushalmodi]

I want to set it to the file's mtime.

That would work only for file based export flow.

I was wondering if one should be added.

I would accept a pull request if the feature is complete with documentation and tests.

[kaushalmodi]

This works.

Subtree based flow

#+hugo_base_dir: .

* Post
:PROPERTIES:
:EXPORT_FILE_NAME: foo
:EXPORT_HUGO_CUSTOM_FRONT_MATTER: :lastmod (format-time-string "%Y-%m-%dT%T%z" (nth 5 (file-attributes (buffer-file-name))))
:END:
Hello

File based flow

#+hugo_base_dir: .

#+title: Post
#+export_file_name: foo

#+hugo_custom_front_matter: :lastmod (format-time-string "%Y-%m-%dT%T%z" (nth 5 (file-attributes (buffer-file-name))))

Hello

[kaushalmodi]

@dominikh To make the above a bit succinct, you can choose to define your own defun called mtime that calls (format-time-string "%Y-%m-%dT%T%z" (nth 5 (file-attributes (buffer-file-name)))) and then do #+hugo_custom_front_matter: :lastmod (mtime).

[dominikh]

I wasn't aware hugo_custom_front_matter could contain lisp expressions, that's great.

Now, if one could set that as a variable (e.g. via let), then that'd be perfect; similar to how you can set org-hugo-auto-set-lastmod. That way, it could go in .dir-locals.el and work for all notes automatically.

[kaushalmodi]

This is also possible:

Org setup file mysetup.org

#+hugo_custom_front_matter: :lastmod (format-time-string "%Y-%m-%dT%T%z" (nth 5 (file-attributes (buffer-file-name))))

Post file mypost.org

#+hugo_base_dir: .
#+setupfile: mysetup.org

#+title: Post
#+export_file_name: foo

Hello

Then, you only need #+setupfile: mysetup.org in all your post files, and you can load up mysetup.org will all the elisp-based front-matter you need 😄 .

[dominikh]

Thank you, I'll play around with that.

[dominikh]

I've arrived at the following fully programatic way that doesn't require any changes to the Org files themselves:

(defun dh/org-export-before-parsing (backend)
  (when (string= backend "hugo")
	(org-roam-set-keyword
	 "hugo_lastmod"
	 (format-time-string "%Y-%m-%d" (file-attribute-modification-time (file-attributes (buffer-file-name)))))))

(add-to-list 'org-export-before-parsing-functions #'dh/org-export-before-parsing)