Re: [PATCH v2] org-attach.el: ID to path functions may return nil

[Max Nikulin <manikulin@gmail.com>]

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On 08/11/2022 12:08, Ihor Radchenko wrote:
> 
> I feel like this makes the docstring confusing.
> 
> Note that `org-attach-id-to-path-function-list':

I have tried to update the docstrings.

>> if: No attachment directory is associated with the current node, adjust
>> ‘org-attach-id-to-path-function-list’
>>
>> I do not think this message is unhelpful.
> 
> With your patch, such message will be displayed even when
> `org-attach-preferred-new-method' is set to something other than 'id.
> And the message will be wrong then.

I have moved `error' call despite I have not figured out how to trigger 
the error for other options.

>> +(defun org-attach-id-fallback-folder-format (id)
>> +  "May be added last to `org-attach-id-path-function-list'.
> 
> This is not a proper first line in a function docstring. First line must
> describe what the function does.

I am still unsure that in this case effect is more important than 
purpose. The function is too specific.

P.S. At first I believed that you have some objections concerning 
changed role of the first function in the list, not just how it is 
documented.

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From dfc35f46f59d5938f1a520b860c3eda36f49a9d5 Mon Sep 17 00:00:00 2001
From: Max Nikulin <manikulin@gmail.com>
Date: Mon, 7 Nov 2022 23:48:02 +0700
Subject: [PATCH v2] org-attach.el: ID to path functions may return nil

* lisp/org-attach.el (org-attach-dir-from-id): Ignore nil values
returned by entries from `org-attach-id-to-path-function-list'.
(org-attach-dir-get-create): Update error message to suggest
customization of `org-attach-id-to-path-function-list'.
(org-attach-id-to-path-function-list): Add to the docstring examples
how to handle unusual IDs.
(org-attach-id-uuid-folder-format, org-attach-id-ts-folder-format):
Return nil if ID is too short.
(org-attach-id-fallback-folder-format): New function that may be added
as the last element of `org-attach-id-path-function-list' to handle
unexpectedly short IDs.

Earlier an obscure error like 'org-attach-id-ts-folder-format: Args out
of range: "ftt", 0, 6' was signalled in the case of unexpectedly short
ID.

Reported by Janek F <xerusx@pm.me>
https://list.orgmode.org/KC8PcypJapBpJQtJxM0kX5N7Z0THL2Lq6EQjBMzpw1-vgQf72egZ2JOIlTbPYiqAVD4MdSBhrhBZr2Ykf5DN1mocm1ANvvuKKZShlkgzKYM=@pm.me
---
 lisp/org-attach.el | 98 ++++++++++++++++++++++++++++++----------------
 1 file changed, 65 insertions(+), 33 deletions(-)

diff --git a/lisp/org-attach.el b/lisp/org-attach.el
index ef183474e..bd3034992 100644
--- a/lisp/org-attach.el
+++ b/lisp/org-attach.el
@@ -166,26 +166,56 @@ When set to `query', ask the user instead."
   "Translate an UUID ID into a folder-path.
 Default format for how Org translates ID properties to a path for
 attachments.  Useful if ID is generated with UUID."
-  (format "%s/%s"
-	  (substring id 0 2)
-	  (substring id 2)))
+  (and (< 2 (length id))
+       (format "%s/%s"
+               (substring id 0 2)
+               (substring id 2))))
 
 (defun org-attach-id-ts-folder-format (id)
   "Translate an ID based on a timestamp to a folder-path.
 Useful way of translation if ID is generated based on ISO8601
 timestamp.  Splits the attachment folder hierarchy into
 year-month, the rest."
-  (format "%s/%s"
-	  (substring id 0 6)
-	  (substring id 6)))
+  (and (< 6 (length id))
+       (format "%s/%s"
+               (substring id 0 6)
+               (substring id 6))))
+
+(defun org-attach-id-fallback-folder-format (id)
+  "Use \"__/ID\" folder path as a dumb fallback.
+May be added as the last element of `org-attach-id-path-function-list'
+to avoid errors for customized ID values that other functions
+are unable to handle. An example is too short ID for
+`org-attach-id-ts-folder-format'.  However it is better to define
+a more specific function spreading entries over subfolders."
+  (format "__/%s" id))
 
 (defcustom org-attach-id-to-path-function-list '(org-attach-id-uuid-folder-format
 						 org-attach-id-ts-folder-format)
-  "List of functions parsing an ID string into a folder-path.
-The first function in this list defines the preferred function
-which will be used when creating new attachment folders.  All
-functions of this list will be tried when looking for existing
-attachment folders based on ID."
+  "List of functions tried to get a folder path for an ID string.
+Functions are called in order till some of them returns an existing
+folder.  If no folder has been created yet for the given ID
+then first value defines folder name that will be created
+to store an attachment.  Nil values are skipped.
+
+Preferred storage policy depends on `org-id-method' and should be chosen
+to avoid excessive number of entries in a single directory.  List
+of functions allows to handle the case of mixed ID styles after
+change of ID generator.
+
+If format of some ID strings differs from `org-id-method' you may
+add `org-attach-id-fallback-folder-format' to the end of the list.
+A better option is to keep attachments inside a dedicated folder.
+A function like the following one may be added as first element
+of the list.
+
+    (defun my/attach-id-custom-folder-format (id)
+      (let ((case-fold-search t))
+	(unless
+	    (or (org-uuidgen-p id)
+		(string-match-p \"[0-9a-z]\\\\=\\{12\\\\}\" id)
+                (string-match-p \"[0-9]\\\\=\\{8\\\\}T[0-9]\\\\=\\{6\\\\}\\.[0-9]\\\\=\\{6\\\\}\" id))
+          (format \"important/%s/%s\" (substring id 0 1) id))))"
   :group 'org-attach
   :package-version '(Org . "9.3")
   :type '(repeat (function :tag "Function with ID as input")))
@@ -360,7 +390,7 @@ If no attachment directory can be derived, return nil."
       (org-attach-check-absolute-path attach-dir))
      ((setq id (org-entry-get nil "ID" org-attach-use-inheritance))
       (org-attach-check-absolute-path nil)
-      (setq attach-dir (org-attach-dir-from-id id 'try-all))))
+      (setq attach-dir (org-attach-dir-from-id id 'existing))))
     (if no-fs-check
 	attach-dir
       (when (and attach-dir (file-directory-p attach-dir))
@@ -381,7 +411,11 @@ If the attachment by some reason cannot be created an error will be raised."
 	  (setq answer (read-char-exclusive)))
 	(cond
 	 ((or (eq org-attach-preferred-new-method 'id) (eq answer ?1))
-	  (setq attach-dir (org-attach-dir-from-id (org-id-get nil t))))
+	  (let ((id (org-id-get nil t)))
+	    (or (setq attach-dir (org-attach-dir-from-id id))
+		(error "Failed to get folder for id %s, \
+adjust `org-attach-id-to-path-function-list'"
+		        id))))
 	 ((or (eq org-attach-preferred-new-method 'dir) (eq answer ?2))
 	  (setq attach-dir (org-attach-set-directory)))
 	 ((eq org-attach-preferred-new-method 'nil)
@@ -392,27 +426,25 @@ If the attachment by some reason cannot be created an error will be raised."
       (make-directory attach-dir t))
     attach-dir))
 
-(defun org-attach-dir-from-id (id  &optional try-all)
+(defun org-attach-dir-from-id (id  &optional existing)
   "Return a folder path based on `org-attach-id-dir' and ID.
-If TRY-ALL is non-nil, try all id-to-path functions in
-`org-attach-id-to-path-function-list' and return the first path
-that exist in the filesystem, or the first one if none exist.
-Otherwise only use the first function in that list."
-  (let ((attach-dir-preferred (expand-file-name
-			       (funcall (car org-attach-id-to-path-function-list) id)
-			       (expand-file-name org-attach-id-dir))))
-    (if try-all
-	(let ((attach-dir attach-dir-preferred)
-	      (fun-list (cdr org-attach-id-to-path-function-list)))
-	  (while (and fun-list (not (file-directory-p attach-dir)))
-	    (setq attach-dir (expand-file-name
-			      (funcall (car fun-list) id)
-			      (expand-file-name org-attach-id-dir)))
-	    (setq fun-list (cdr fun-list)))
-	  (if (file-directory-p attach-dir)
-	      attach-dir
-	    attach-dir-preferred))
-      attach-dir-preferred)))
+Try id-to-path functions in `org-attach-id-to-path-function-list'
+ignoring nils. If EXISTING is non-nill then return the first path
+found in the filesystem. Otherwise return the first non nil value."
+  (let ((fun-list org-attach-id-to-path-function-list)
+        (base-dir (expand-file-name org-attach-id-dir))
+        preferred first)
+    (while (and fun-list
+                (not preferred))
+      (let* ((name (funcall (car fun-list) id))
+             (candidate (and name (expand-file-name name base-dir))))
+        (setq fun-list (cdr fun-list))
+        (when candidate
+          (if (or (not existing) (file-directory-p candidate))
+              (setq preferred candidate)
+            (unless first
+              (setq first candidate))))))
+    (or preferred first)))
 
 (defun org-attach-check-absolute-path (dir)
   "Check if we have enough information to root the attachment directory.
-- 
2.25.1