ob-core: Add "link" results format

* lisp/ob-core.el (org-babel-execute-src-block): Handle "link" :results
  format.

* doc/org-manual.org: Add document for new result format "link".

* testing/lisp/test-ob.el (test-ob/result-file-link-type-header-argument):
  New test.

doc/org-manual.org

@@ -17224,6 +17224,19 @@ follows from the type specified above.
      =raw= or =org= results for later scripting and automated
      processing.  Usage example: =:results value drawer=.
 
+- =link= ::
+
+     Result is a link to the file specified in =:file= header
+     argument.  However, unlike plain =:file=, nothing is written to
+     the disk.  The block is used for its side-effects only, as in the
+     following example:
+
+     #+begin_example
+     ,#+begin_src shell :results link :file "download.tar.gz"
+     wget -c "http://example.com/download.tar.gz"
+     ,#+end_src
+     #+end_example
+
 *** Handling
 :PROPERTIES:
 :UNNUMBERED: notoc

etc/ORG-NEWS

@@ -113,6 +113,20 @@ now sort according to the locale’s collation rules instead of by
 code-point.
 
 ** New features
+*** Add ~:results link~ support for Babel
+
+With this output format, create a link to the file specified in
+~:file~ header argument, without actually writing any result to it:
+
+#+begin_example
+,#+begin_src shell :dir "data/tmp" :results link :file "crackzor_1.0.c.gz"
+wget -c "http://ben.akrin.com/crackzor/crackzor_1.0.c.gz"
+,#+end_src
+
+,#+results:
+[[file:data/tmp/crackzor_1.0.c.gz]]
+#+end_example
+
 *** Add ~:session~ support of ob-js for js-comint
 #+begin_src js :session "*Javascript REPL*"
 console.log("stardiviner")
@@ -202,11 +216,11 @@ You can have a file =bananas.org= containing:
 ... and when going to the top of that file and entering column view
 you should expect to see something like:
 
-| ITEM            | CONFIRMED | Bananas | Confirmed Bananas |
-|-----------------+-----------+---------+-------------------|
-| All shipments   |           |      11 |                 4 |
-| Shipment 1      | [X]       |       4 |                 4 |
-| Shipment 2      | [ ]       |       7 |                 7 |
+| ITEM          | CONFIRMED | Bananas | Confirmed Bananas |
+|---------------+-----------+---------+-------------------|
+| All shipments |           |      11 |                 4 |
+| Shipment 1    | [X]       |       4 |                 4 |
+| Shipment 2    | [ ]       |       7 |                 7 |
 
 #+BEGIN_EXAMPLE
   ,#+STARTUP: shrink
@@ -3219,7 +3233,7 @@ See https://orgmode.org/elpa/
    | =C-c C-x E=     | =E=    | [[doc::org-inc-effort][org-inc-effort]]              |
    |                 | =#=    | [[doc::org-toggle-comment][org-toggle-comment]]          |
    |                 | =:=    | [[doc::org-columns][org-columns]]                 |
-   |                 | =W=    | Set =APPT_WARNTIME=          |
+   |                 | =W=    | Set =APPT_WARNTIME=         |
    | =k=             |        | [[doc::org-agenda-capture][org-agenda-capture]]          |
    | C-c ,           | ,      | [[doc::org-priority][org-priority]]                |
 

lisp/ob-core.el

@@ -414,7 +414,7 @@ then run `org-babel-switch-to-session'."
     (post       . :any)
     (prologue   . :any)
     (results	. ((file list vector table scalar verbatim)
-		   (raw html latex org code pp drawer)
+		   (raw html latex org code pp drawer link)
 		   (replace silent none append prepend)
 		   (output value)))
     (rownames	. ((no yes)))
@@ -706,14 +706,16 @@ block."
 	      (let ((file (cdr (assq :file params))))
 		;; If non-empty result and :file then write to :file.
 		(when file
-		  (let ((graphics?
-			 (member "graphics" (cdr (assq :result-params params)))))
-		    ;; Handle :results graphics :file case.  Don't
-		    ;; write result to file if result is graphics.
-		    (when (and result (not graphics?))
-		      (with-temp-file file
-			(insert (org-babel-format-result
-				 result (cdr (assq :sep params)))))))
+		  ;; If `:results' are special types like `link' or
+		  ;; `graphics', don't write result to `:file'.  Only
+		  ;; insert a link to `:file'.
+		  (when (and result
+			     (not (or (member "link" result-params)
+				      (member "graphics" result-params))))
+		    (with-temp-file file
+		      (insert (org-babel-format-result
+			       result
+			       (cdr (assq :sep params))))))
 		  (setq result file))
 		;; Possibly perform post process provided its
 		;; appropriate.  Dynamically bind "*this*" to the

testing/lisp/test-ob.el

@@ -996,6 +996,21 @@ trying to find the :END: marker."
     (should (search-forward "[[file:foo][bar]]" nil t))
     (should (search-forward "[[file:foo][foo]]" nil t))))
 
+(ert-deftest test-ob/result-file-link-type-header-argument ()
+  "Ensure that the result is a link to a file.
+The file is just a link to `:file' value.  Inhibit non-empty
+result write to `:file' value."
+  (org-test-with-temp-text "
+<point>#+begin_src shell :results value link :file \"/tmp/test.txt\"
+echo \"hello\" > /tmp/test.txt
+echo \"test\"
+#+end_src"
+   (org-babel-execute-src-block)
+   (should (search-forward "[[file:/tmp/test.txt]]" nil nil))
+   (should (with-temp-buffer
+	     (insert-file-contents "/tmp/test.txt")
+	     (string= "hello\n" (buffer-string))))))
+
 (ert-deftest test-ob/inline-src_blk-preceded-punct-preceded-by-point ()
   (let ((test-line ".src_emacs-lisp[ :results verbatim ]{ \"x\"  }")
 	(org-babel-inline-result-wrap "=%s="))