ox: Add `org-export-global-macros'

* lisp/ox.el (org-export-global-macros): New variable.
(org-export-as): Use new variable.
* doc/org.texi (Macro replacement): Document new variable.
* testing/lisp/test-ox.el (test-org-export/expand-macro): Add tests.

doc/org.texi

@@ -10790,13 +10790,15 @@ Visit the include file at point.
 @cindex macro replacement, during export
 @cindex #+MACRO
 
-You can define text snippets with
+@vindex org-export-global-macros
+Macros replace text snippets during export.  Macros are defined globally in
+@code{org-export-global-macros}, or document-wise with the following syntax:
 
 @example
 #+MACRO: name   replacement text $1, $2 are arguments
 @end example
 
-@noindent which can be referenced
+@noindent which can be referenced using
 @code{@{@{@{name(arg1, arg2)@}@}@}}@footnote{Since commas separate arguments,
 commas within arguments have to be escaped with a backslash character.
 Conversely, backslash characters before a comma, and only them, need to be

etc/ORG-NEWS

@@ -126,6 +126,8 @@ Where clue > 0
 This new function is meant to be used in back-ends supporting images
 as descriptions of links, a.k.a. image links.  See its docstring for
 details.
+**** Add global macros through ~org-export-global-macros~ 
+With this variable, one can define macros available for all documents.
 **** Horizontal rules are no longer ignored in LaTeX table math mode
 
 *** ~org-list-to-generic~ includes a new property: ~:ifmt~
@@ -149,8 +151,6 @@ For an equivalent to a ~nil~ value, set
 ~org-agenda-show-future-repeats~ to nil and
 ~org-agenda-prefer-last-repeat~ to ~t~.
 
-** Removed options
-
 *** ~org-publish-sitemap-file-entry-format~ is deprecated
 
 One can provide new ~:sitemap-format-entry~ property for a function

lisp/ox.el

@@ -883,6 +883,29 @@ HTML code while every other back-end will ignore it."
 	       (cl-every #'stringp (mapcar #'car x))
 	       (cl-every #'stringp (mapcar #'cdr x)))))
 
+(defcustom org-export-global-macros nil
+  "Alist between macro names and expansion templates.
+
+This variable defines macro expansion templates available
+globally.  Associations follow the pattern
+
+  (NAME . TEMPLATE)
+
+where NAME is a string beginning with a letter and consisting of
+alphanumeric characters only.
+
+TEMPLATE is the string to which the macro is going to be
+expanded.  Inside, \"$1\", \"$2\"... are place-holders for
+macro's arguments.  Moreover, if the template starts with
+\"(eval\", it will be parsed as an Elisp expression and evaluated
+accordingly."
+  :group 'org-export-general
+  :version "25.2"
+  :package-version '(Org . "9.1")
+  :type '(repeat
+	  (cons (string :tag "Name")
+		(string :tag "Template"))))
+
 (defcustom org-export-coding-system nil
   "Coding system for the exported file."
   :group 'org-export-general
@@ -3046,7 +3069,9 @@ Return code as a string."
 	 (org-export-expand-include-keyword)
 	 (org-export--delete-comments)
 	 (org-macro-initialize-templates)
-	 (org-macro-replace-all org-macro-templates nil parsed-keywords)
+	 (org-macro-replace-all
+	  (append org-macro-templates org-export-global-macros)
+	  nil parsed-keywords)
 	 ;; Refresh buffer properties and radio targets after
 	 ;; potentially invasive previous changes.  Likewise, do it
 	 ;; again after executing Babel code.

testing/lisp/test-ox.el

@@ -1255,6 +1255,27 @@ Footnotes[fn:2], foot[fn:test] and [fn:inline:inline footnote]
    (equal "#+MACRO: macro1 value\nvalue\n"
 	  (org-test-with-temp-text "#+MACRO: macro1 value\n{{{macro1}}}"
 	    (org-export-as (org-test-default-backend)))))
+  ;; Include global macros.  However, local macros override them.
+  (should
+   (equal "global\n"
+	  (org-test-with-temp-text "{{{M}}}"
+	    (let ((org-export-global-macros '(("M" . "global"))))
+	      (org-export-as (org-test-default-backend))))))
+  (should
+   (equal "global arg\n"
+	  (org-test-with-temp-text "{{{M(arg)}}}"
+	    (let ((org-export-global-macros '(("M" . "global $1"))))
+	      (org-export-as (org-test-default-backend))))))
+  (should
+   (equal "2\n"
+	  (org-test-with-temp-text "{{{M}}}"
+	    (let ((org-export-global-macros '(("M" . "(eval (+ 1 1))"))))
+	      (org-export-as (org-test-default-backend))))))
+  (should
+   (equal "#+MACRO: M local\nlocal\n"
+	  (org-test-with-temp-text "#+macro: M local\n{{{M}}}"
+	    (let ((org-export-global-macros '(("M" . "global"))))
+	      (org-export-as (org-test-default-backend))))))
   ;; Allow macro in parsed keywords and associated properties.
   ;; Standard macro expansion.
   (should