N/A; icalendar export doesn't guarantee unique UIDs

[Tassilo Horn <thorn@fastmail.fm>]

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I use the icalendar export to feed my schedule into the google calendar
(only one-way: Org -> Google).  Basically that works fine (except for
google not understanding Umlauts...), but there's a big problem with
entries that contain more than one timestamp.

For example, I have entries like

*** Meeting with Max
    :PROPERTIES:
    :ID:       e1c32cb4-bd1f-4302-8067-1723d1958a88
    :END:
    <2012-03-13 Tue 12:00-13:00>
    <2012-03-21 Wed 15:00-16:00>
    <2012-03-29 Thu 10:00-11:00>
    <2012-04-10 Tue 12:00-13:00>
    <2012-04-18 Wed 11:00-11:30>
    <2012-04-25 Wed 10:00-11:00>
    <2012-05-10 Thu 12:00-13:00>

They should show up at any date/time listed there.  That's true for the
org agenda with `org-agenda-skip-additional-timestamps-same-entry' set
to nil.  The icalendar export also creates multiple VEVENTS for the
above org entry, *but they all have the same UID* (which is strictly
VERBOTEN by the icalendar spec).  The result is that the google calendar
only shows one appointment, and that seems to be arbitrary.  In the
example above, it shows the meeting on 2012-04-18.

Bye,
Tassilo

Emacs  : GNU Emacs 24.1.50.1 (x86_64-pc-linux-gnu)
 of 2012-05-07 on thinkpad
Package: N/A

current state:
==============
(setq
 org-export-preprocess-before-selecting-backend-code-hook '(org-beamer-select-beamer-code)
 org-tab-first-hook '(org-hide-block-toggle-maybe
		      org-src-native-tab-command-maybe
		      org-babel-hide-result-toggle-maybe
		      org-babel-header-arg-expand)
 outline-minor-mode-hook '(th-outline-minor-mode-init)
 org-speed-command-hook '(org-speed-command-default-hook
			  org-babel-speed-command-hook)
 org-gnus-prefer-web-links t
 org-special-ctrl-k t
 org-occur-hook '(org-first-headline-recenter)
 org-src-tab-acts-natively t
 org-metaup-hook '(org-babel-load-in-session-maybe)
 org-icalendar-include-todo t
 org-export-preprocess-before-normalizing-links-hook '(org-remove-file-link-modifiers)
 org-log-done 'time
 org-confirm-shell-link-function 'yes-or-no-p
 org-complete-tags-always-offer-all-agenda-tags t
 org-finalize-agenda-hook '(th-org-agenda-to-appt)
 org-columns-default-format "%50ITEM %TODO %ALLTAGS %SCHEDULED %DEADLINE"
 org-export-latex-final-hook '(org-beamer-amend-header org-beamer-fix-toc
			       org-beamer-auto-fragile-frames
			       org-beamer-place-default-actions-for-lists)
 org-agenda-restore-windows-after-quit t
 org-special-ctrl-a/e 'reversed
 org-export-latex-after-initial-vars-hook '(org-beamer-after-initial-vars)
 org-agenda-custom-commands '(("n" "Next 21 days" agenda ""
			       ((org-agenda-span 21)))
			      ("^" "Calfw Month Calendar"
			       th-calfw-open-calendar)
			      )
 org-return-follows-link t
 org-agenda-time-leading-zero t
 org-capture-templates '(("n" "NORMAL" entry
			  (file "/home/horn/Repos/org/remember.org")
			  "* %?\n  :PROPERTIES:\n  :created: %U\n  :link: %a\n  :END:\n	%i")
			 ("t" "TODO" entry
			  (file "/home/horn/Repos/org/remember.org")
			  "* TODO %?\n  :PROPERTIES:\n  :created: %U\n  :link: %a\n  :END:\n  %i")
			 ("i" "IDEA" entry
			  (file "/home/horn/Repos/org/remember.org")
			  "* IDEA %?\n  :PROPERTIES:\n  :created: %U\n  :link: %a\n  :END:\n  %i")
			 )
 org-after-todo-state-change-hook '(org-clock-out-if-current)
 org-icalendar-include-body t
 org-src-mode-hook '(org-src-babel-configure-edit-buffer
		     org-src-mode-configure-edit-buffer)
 org-agenda-before-write-hook '(org-agenda-add-entry-text)
 org-babel-pre-tangle-hook '(save-buffer)
 org-mode-hook '(th-org-mode-init
		 #[nil "\300\301\302\303\304$\207"
		   [org-add-hook change-major-mode-hook org-show-block-all
		    append local]
		   5]
		 #[nil "\300\301\302\303\304$\207"
		   [org-add-hook change-major-mode-hook
		    org-babel-show-result-all append local]
		   5]
		 org-babel-result-hide-spec org-babel-hide-all-hashes)
 org-refile-targets '((org-agenda-files :maxlevel . 5))
 org-attach-method 'mv
 org-ctrl-c-ctrl-c-hook '(org-babel-hash-at-point
			  org-babel-execute-safely-maybe)
 org-refile-use-outline-path 'file
 org-directory "/home/horn/Repos/org"
 org-enforce-todo-dependencies t
 org-cycle-hook '(org-cycle-hide-archived-subtrees org-cycle-hide-drawers
		  org-cycle-show-empty-lines
		  org-optimize-window-after-visibility-change)
 org-export-latex-format-toc-function 'org-export-latex-format-toc-default
 org-export-blocks '((src org-babel-exp-src-block nil)
		     (export-comment org-export-blocks-format-comment t)
		     (ditaa org-export-blocks-format-ditaa nil)
		     (dot org-export-blocks-format-dot nil))
 org-export-first-hook '(org-beamer-initialize-open-trackers)
 org-attach-directory "/home/horn/Repos/org/attachments"
 org-icalendar-date-time-format ":%Y%m%dT%H%M%SZ"
 org-archive-default-command 'org-archive-set-tag
 org-export-interblocks '((src org-babel-exp-non-block-elements))
 org-refile-allow-creating-parent-nodes 'confirm
 org-icalendar-categories '(all-tags category)
 org-todo-keywords '((sequence "TODO(t)" "STARTED(s)" "DELEGATED(g)"
		      "IDEA(i)" "|" "DONE(d)" "CANCELLED(c)")
		     )
 org-modules '(org-icalendar org-attach org-protocol org-id org-bibtex
	       org-docview org-gnus org-info org-irc org-capture
	       org-mobile)
 org-confirm-elisp-link-function 'yes-or-no-p
 org-metadown-hook '(org-babel-pop-to-session-maybe)
 org-log-into-drawer "LOGBOOK"
 org-blocker-hook '(org-block-todo-from-children-or-siblings-or-parent)
 org-mobile-directory "~/Dropbox/MobileOrg"
 org-agenda-mode-hook '(th-org-agenda-mode-init)
 org-agenda-files '("/home/horn/Repos/org")
 org-clock-out-hook '(org-clock-remove-empty-clock-drawer)
 org-link-frame-setup '((vm . vm-visit-folder)
			(gnus . org-gnus-no-new-news)
			(file . find-file-other-window))
 org-mobile-inbox-for-pull "~/Repos/org/from-org-mobile.org"
 org-src-fontify-natively t
 )