Add advice to org-tangle to several files

Amazing advice from Tobias (emacs.stackexchange)

init/init-org.el

@@ -65,3 +65,66 @@
 (setq calendar-latitude 43.7)
 (setq calendar-longitude -79.4)
 (setq calendar-location-name "Toronto, ON Canada")
+
+;; some super-clever stuff
+;; [https://emacs.stackexchange.com/questions/39032/tangle-the-same-src-block-to-different-files]
+(defun org-babel-tangle-collect-blocks-handle-tangle-list (&optional language tangle-file)
+  "Can be used as :override advice for `org-babel-tangle-collect-blocks'.
+Handles lists of :tangle files."
+  (let ((counter 0) last-heading-pos blocks)
+    (org-babel-map-src-blocks (buffer-file-name)
+      (let ((current-heading-pos
+         (org-with-wide-buffer
+          (org-with-limited-levels (outline-previous-heading)))))
+    (if (eq last-heading-pos current-heading-pos) (cl-incf counter)
+      (setq counter 1)
+      (setq last-heading-pos current-heading-pos)))
+      (unless (org-in-commented-heading-p)
+    (let* ((info (org-babel-get-src-block-info 'light))
+           (src-lang (nth 0 info))
+           (src-tfiles (cdr (assq :tangle (nth 2 info))))) ; Tobias: accept list for :tangle
+      (unless (consp src-tfiles) ; Tobias: unify handling of strings and lists for :tangle
+        (setq src-tfiles (list src-tfiles))) ; Tobias: unify handling
+      (dolist (src-tfile src-tfiles) ; Tobias: iterate over list
+        (unless (or (string= src-tfile "no")
+            (and tangle-file (not (equal tangle-file src-tfile)))
+            (and language (not (string= language src-lang))))
+          ;; Add the spec for this block to blocks under its
+          ;; language.
+          (let ((by-lang (assoc src-lang blocks))
+            (block (org-babel-tangle-single-block counter)))
+        (setcdr (assoc :tangle (nth 4 block)) src-tfile) ; Tobias:
+        (if by-lang (setcdr by-lang (cons block (cdr by-lang)))
+          (push (cons src-lang (list block)) blocks)))))))) ; Tobias: just ()
+    ;; Ensure blocks are in the correct order.
+    (mapcar (lambda (b) (cons (car b) (nreverse (cdr b)))) blocks)))
+
+(defun org-babel-tangle-single-block-handle-tangle-list (oldfun block-counter &optional only-this-block)
+  "Can be used as :around advice for `org-babel-tangle-single-block'.
+If the :tangle header arg is a list of files. Handle all files"
+  (let* ((info (org-babel-get-src-block-info))
+     (params (nth 2 info))
+     (tfiles (cdr (assoc :tangle params))))
+    (if (null (and only-this-block (consp tfiles)))
+    (funcall oldfun block-counter only-this-block)
+      (cl-assert (listp tfiles) nil
+         ":tangle only allows a tangle file name or a list of tangle file names")
+      (let ((ret (mapcar
+          (lambda (tfile)
+            (let (old-get-info)
+              (cl-letf* (((symbol-function 'old-get-info) (symbol-function 'org-babel-get-src-block-info))
+                 ((symbol-function 'org-babel-get-src-block-info)
+                  `(lambda (&rest get-info-args)
+                     (let* ((info (apply 'old-get-info get-info-args))
+                        (params (nth 2 info))
+                        (tfile-cons (assoc :tangle params)))
+                       (setcdr tfile-cons ,tfile)
+                       info))))
+            (funcall oldfun block-counter only-this-block))))
+          tfiles)))
+    (if only-this-block
+        (list (cons (cl-caaar ret) (mapcar #'cadar ret)))
+      ret)))))
+
+(advice-add 'org-babel-tangle-collect-blocks :override #'org-babel-tangle-collect-blocks-handle-tangle-list)
+(advice-add 'org-babel-tangle-single-block :around #'org-babel-tangle-single-block-handle-tangle-list)