Be more consistent about treating tags as case-sensitive

* lisp/org-agenda.el (org-agenda-finalize):
(org-agenda-format-item): Do not downcase tags.
(org-downcase-keep-props): Remove unused function.
(org-agenda-filter-expand-tags): Do not case-fold search.

* lisp/org.el (org-tags-expand): Document `downcased' argument as
obsolete and do not allow to expand downcased tags.

* testing/lisp/test-org.el (test-org/tags-expand): Remove test for
downcased tags expansion.

* doc/org-manual.org (TODO keywords, tags, properties, etc.):
Suggest that user-defined are usually lowercase, but don't make it
a requirement.

Reported-by: David Masterson <dsmasterson92630@outlook.com>
Link: https://orgmode.org/list/SJ0PR03MB5455D8D0C4F71AA495A9ABF79B709@SJ0PR03MB5455.namprd03.prod.outlook.com/

doc/org-manual.org

@@ -344,7 +344,7 @@ conventions:
 
 - =boss=, =ARCHIVE= ::
 
-  Tags are case-sensitive.  User-defined tags are written in
+  Tags are case-sensitive.  User-defined tags are usually written in
   lowercase; built-in tags with special meaning are written as they
   should appear in the document, usually with all capitals.
 

lisp/org-agenda.el

@@ -3919,7 +3919,7 @@ agenda display, configure `org-agenda-finalize-hook'."
 		  (put-text-property (point-at-bol) (point-at-eol)
 				     'tags
 				     (org-with-point-at mrk
-				       (mapcar #'downcase (org-get-tags)))))))))
+				       (org-get-tags))))))))
 	(setq org-agenda-represented-tags nil
 	      org-agenda-represented-categories nil)
 	(when org-agenda-top-headline-filter
@@ -6731,7 +6731,7 @@ Any match of REMOVE-RE will be removed from TXT."
 	(remove-text-properties 0 (length rtn) '(line-prefix t wrap-prefix t) rtn)
 	(org-add-props rtn nil
 	  'org-category category
-	  'tags (mapcar 'org-downcase-keep-props tags)
+	  'tags tags
 	  'org-priority-highest org-priority-highest
 	  'org-priority-lowest org-priority-lowest
 	  'time-of-day time-of-day
@@ -6776,12 +6776,6 @@ The modified list may contain inherited tags, and tags matched by
 			  (if have-i "::" ":"))))))
   txt)
 
-(defun org-downcase-keep-props (s)
-  (let ((props (text-properties-at 0 s)))
-    (setq s (downcase s))
-    (add-text-properties 0 (length s) props s)
-    s))
-
 (defvar org-agenda-sorting-strategy) ;; because the def is in a let form
 
 (defun org-agenda-add-time-grid-maybe (list ndays todayp)
@@ -8074,7 +8068,7 @@ If the line does not have an effort defined, return nil."
 When NO-OPERATOR is non-nil, do not add the + operator to
 returned tags."
   (if org-group-tags
-      (let ((case-fold-search t) rtn)
+      (let (case-fold-search rtn)
 	(mapc
 	 (lambda (f)
 	   (let (f0 dir)
@@ -8082,7 +8076,7 @@ returned tags."
 		 (setq dir (match-string 1 f) f0 (match-string 2 f))
 	       (setq dir (if no-operator "" "+") f0 f))
 	     (setq rtn (append (mapcar (lambda(f1) (concat dir f1))
-				       (org-tags-expand f0 t t))
+				       (org-tags-expand f0 t))
 			       rtn))))
 	 filter)
 	(reverse rtn))

lisp/org.el

@@ -11760,22 +11760,18 @@ When the optional argument SINGLE-AS-LIST is non-nil, MATCH is
 assumed to be a single group tag, and the function will return
 the list of tags in this group.
 
-When DOWNCASED is non-nil, expand downcased TAGS."
+The DOWNCASED argument is obsolete and has no effect."
   (unless (org-string-nw-p match) (error "Invalid match tag: %S" match))
   (let ((tag-groups
-	 (let ((g (or org-tag-groups-alist-for-agenda org-tag-groups-alist)))
-	   (if (not downcased) g
-	     (mapcar (lambda (s) (mapcar #'downcase s)) g)))))
+         (or org-tag-groups-alist-for-agenda org-tag-groups-alist)))
     (cond
-     (single-as-list (org--tags-expand-group
-		      (list (if downcased (downcase match) match))
-		      tag-groups nil))
+     (single-as-list (org--tags-expand-group (list match) tag-groups nil))
      (org-group-tags
       (let* ((case-fold-search t)
 	     (tag-syntax org-mode-syntax-table)
 	     (group-keys (mapcar #'car tag-groups))
 	     (key-regexp (concat "\\([+-]?\\)" (regexp-opt group-keys 'words)))
-	     (return-match (if downcased (downcase match) match)))
+	     (return-match match))
 	;; Mark regexp-expressions in the match-expression so that we
 	;; do not replace them later on.
 	(let ((s 0))
@@ -11795,7 +11791,7 @@ When DOWNCASED is non-nil, expand downcased TAGS."
 		 m			;regexp tag: ignore
 	       (let* ((operator (match-string 1 m))
 		      (tag-token (let ((tag (match-string 2 m)))
-				   (list (if downcased (downcase tag) tag))))
+				   (list tag)))
 		      regexp-tags regular-tags)
 		 ;; Partition tags between regexp and regular tags.
 		 ;; Remove curly bracket syntax from regexp tags.

testing/lisp/test-org.el

@@ -7172,14 +7172,7 @@ Paragraph<point>"
    (equal "{A+}"
 	  (org-test-with-temp-text "#+TAGS: [ A : B C ]"
 	    (org-mode-restart)
-	    (let ((org-tag-alist-for-agenda nil)) (org-tags-expand "{A+}")))))
-  ;; Uppercase MATCH works with a non-nil DOWNCASED and SINGLE-AS-LIST.
-  (should
-   (equal (list "a" "b" "c")
-	  (org-test-with-temp-text "#+TAGS: [ A : B C ]"
-	    (org-mode-restart)
-	    (let ((org-tag-alist-for-agenda nil))
-	      (sort (org-tags-expand "A" t t) #'string-lessp))))))
+	    (let ((org-tag-alist-for-agenda nil)) (org-tags-expand "{A+}"))))))
 
 
 ;;; TODO keywords