[PATCH] org-capture: Update plist before finalizing

[Leo Vivier <leo.vivier+dev@gmail.com>]

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Hi there,

I’m working on the parallelisation of `org-capture' for Org-roam, and
I’ve run into a problem with the updating of `org-capture-plist'.

;;---------------------------------------------------------------------
;; DESCRIPTION
;;---------------------------------------------------------------------
We use the global-variable `org-capture-plist' to populate the
local-variable `org-capture-current-plist' on the init of the
`org-capture' buffer.  However, we do not do the opposite (i.e. update
the global-variable with the local-variable) on `org-capture-finalize'.

This is fine for the majority of `org-capture-finalize', since we’re
using the LOCAL arg of `org-capture-get' to read
`org-capture-current-plist' instead of `org-capture-list', but this
trick does not work for `org-capture-after-finalize', since the hook is
run after the `org-capture-buffer' has been closed.

This causes problem with `:kill-buffer t', and it limits what can be
done with cleanup functions in `org-capture-after-finalize'.

;;---------------------------------------------------------------------
;; DEMONSTRATION
;;---------------------------------------------------------------------
Tested in emacs -Q.

Summary:
- Start a capture process (A)
- Start another capture process (B)
- Cancel B
- Cancel A

Form:
--------------------------------[START]--------------------------------
;; Eval the following form:
(progn
  (setq org-capture-templates
        '(("a" "foo" plain (file "/tmp/foo.org") "* %?"
           :kill-buffer t)
          ("b" "bar" plain (file "/tmp/bar.org") "* %?"
           :kill-buffer t)))
  (let* ((a (save-window-excursion
              (org-capture nil "a")
              (current-buffer)))
         (b (save-window-excursion
              (org-capture nil "b")
              (current-buffer))))
    (with-current-buffer b
      (org-capture-kill))
    (with-current-buffer a
      (org-capture-kill))))

;; Result: (error "Selecting deleted buffer")
;; `foo.org' is still alive
---------------------------------[END]---------------------------------

;;---------------------------------------------------------------------
;; ANALYSIS
;;---------------------------------------------------------------------
The problem happens during `org-capture-after-finalize'. A’s
`org-capture-finalize' does not update `org-capture-plist' with the value
of `org-current-capture-plist' during its execution, which means that
`org-capture-plist' still holds B’s value, including :buffer.  Since B’s
base-buffer was killed, :buffer points to a killed buffer, which is what
is raising the error.

;;---------------------------------------------------------------------
;; PATCH
;;---------------------------------------------------------------------
I propose to update `org-capture-plist' early in `org-capture-finalize'.
I don’t think this would have unforeseen effects, since
`org-capture-list' is already meant to be transient, and we’d only be
expanding its use from init-only to init-and-exit.

HTH,

-- 
Leo Vivier

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From d14f15ab76d60c3f65837a6d14712dadabf324bf Mon Sep 17 00:00:00 2001
From: Leo Vivier <leo.vivier+dev@gmail.com>
Date: Sat, 25 Jul 2020 21:53:07 +0200
Subject: [PATCH] org-capture: Update plist before finalizing

* lisp/org-capture.el (org-capture-finalize): Update
`org-capture-plist' with local-value before finalizing.
---
 lisp/org-capture.el | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lisp/org-capture.el b/lisp/org-capture.el
index 2cc1ce394..223ed4124 100644
--- a/lisp/org-capture.el
+++ b/lisp/org-capture.el
@@ -728,6 +728,9 @@ captured item after finalizing."
 
   (run-hooks 'org-capture-prepare-finalize-hook)
 
+  ;; Update `org-capture-plist' with the local-value
+  (setq org-capture-plist org-capture-current-plist)
+
   ;; Did we start the clock in this capture buffer?
   (when (and org-capture-clock-was-started
 	     org-clock-marker
-- 
2.27.0