refactor: consolidate fringe management functions

[gggion]

Fringe management functions consolidated into:

;;;;; Core Operations
(defun org-transclusion--make-fringe-string (face))
(defun org-transclusion--prefix-has-fringe-p (prefix))

;;;;; Region Operations
(defun org-transclusion-add-fringes (buffer beg end face))
(defun org-transclusion-remove-fringes (buffer beg end))

With this I’ve also adapted all places where the previous fringe placemente functions where being called in org-transclusion.el and org-transclusion-indent-mode.el

such as

org-transclusion-indent-mode.el

-(declare-function org-transclusion-prefix-has-fringe-p "org-transclusion" (prefix))
-(declare-function org-transclusion-add-fringe-to-region "org-transclusion" (buffer beg end face))
-(declare-function org-transclusion-remove-fringe-from-region "org-transclusion" (buffer beg end))
+(declare-function org-transclusion--prefix-has-fringe-p "org-transclusion" (prefix))
+(declare-function org-transclusion-add-fringes "org-transclusion" (buffer beg end face))
+(declare-function org-transclusion-remove-fringes "org-transclusion" (buffer beg end))

-                                 (not (org-transclusion-prefix-has-fringe-p line-prefix)))
-                        (org-transclusion-add-fringe-to-region
+                                 (not (org-transclusion--prefix-has-fringe-p line-prefix)))
+                        (org-transclusion-add-fringes

-                (org-transclusion-add-fringe-to-region
+                (org-transclusion-add-fringes

-      (org-transclusion-remove-fringe-from-region src-buf src-beg src-end))))
+      (org-transclusion-remove-fringes src-buf src-beg src-end))))

Same deal on org-transclusion.el

Besides refactoring the fringe functions, I’ve also added an hybrid approach that applies fringes through different mechanisms depending on org-indent-mode being enabled or not.

This was due to the following problem: If indent-mode and the transclusion-indent-mode extension are disabled, the per-line text property approach is unable to preserve fringes in the source when executing revert-buffer. The original implementation before the indent-mode additions did not have this issue because it placed the fringes as overlay properties, which survived buffer-revert and other changes to the buffer..

So, since fringe placement through overlays is only an issue if we want to preserve indentation, I’ve made it so fringes will be placed through overlays WHEN org-indent-mode is disabled. If not, then we’ll default to the per line text property approach.

[!NOTE] If the extension org-transclusion-indent-mode is not enabled but org-indent-mode is, indentation will be preserved, but fringes will still be lost to revert-buffer and other font locking operations on the transclusion source buffer, so the extension is still necessary if we want fringes to work properly with indent-mode.

Another detail is that when org-indent-mode is active without the transclusion-indent-mode extension loaded, fringes can still be reapplied during normal buffer modifications via the overlay modification hook, but NOT after revert-buffer (which doesn't trigger modification hooks when content is unchanged). Users who need full org-indent-mode support including buffer reverts should load the org-transclusion-indent-mode extension.

SUMMARY:

Retaining fringes - Scenarios	Normal Editing	revert-buffer, font-lock/etc	Description
indent-mode OFF	YES (overlay)	YES (overlay)	Works as intented, overlay ensures fringe is retained and adapts to changes in buffer
indent-mode ON, no extension	YES (hook)	NO	Fringe will survive manual buffer modification, but will be lost on font-lock and other buffer operations such as rever-buffer
indent-mode ON, with extension	YES (extension)	YES (extension)	Fringe will be reapplied in case of text-property erasure, works without issues.

[gggion]

STATUS: currently debugging graphical and terminal emacs instances:

• org-indent-mode: enabled/disabled

• org-transclusion-indent-mode enabled/disabled

• org-modern: this seems to be tricky, apparently there's a lot of font-locking business going on that make fringe and text properties behave differently when org-indent-mode is enabled or disabled, if there's no workaround it might require a new user option to set fringe placement mechanism (for example always use overlays regardless).

• org-modern-indent-mode enabled/disabled.

[gggion]

@nobiot one question: would it be better to make this PR directly to the feat/transient branch?
I've made it for main but since it'll be merged to feat/transient and have to undergo other changes for compatibility, I'm thinking of making this for feature/transient in the first place since that feature branch willl be merged with main eventually anyways.

[nobiot]

@gggion ,

one question: would it be better to make this PR directly to the feat/transient branch?

I have just merged the feat/transient branch with main branch. It is significantly diverged from the main branch before the merge. Could I ask you to look into rebasing before proceeding any further?