In org-tags-completion-function, completion-ignore-case force nil,
what about set it to t?
tags are case-sensitive, wile this function is used to search tag.
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(defun org-tags-completion-function (string _predicate &optional flag)
"Complete tag STRING.
FLAG specifies the type of completion operation to perform. This
function is passed as a collection function to `completing-read',
which see."
(let ((completion-ignore-case nil) ;tags are case-sensitive
(confirm (lambda (x) (stringp (car x))))
(prefix ""))
(when (string-match "^\\(.*[-+:&,|]\\)\\([^-+:&,|]*\\)$" string)
(setq prefix (match-string 1 string))
(setq string (match-string 2 string)))
(pcase flag
(`t (all-completions string org-last-tags-completion-table confirm))
(`lambda (assoc string org-last-tags-completion-table)) ;exact match?
(`nil
(pcase (try-completion string org-last-tags-completion-table confirm)
((and completion (pred stringp))
(concat prefix
completion
(if (and org-add-colon-after-tag-completion
(assoc completion org-last-tags-completion-table))
":"
"")))
(completion completion)))
(_ nil))))
