[PATCH] ob-tangle: source blocks without language can be tangled

[Thibaut Meyer via "General discussions about Org-mode." <emacs-orgmode@gnu.org>]

* lisp/ob-tangle.el: (org-babel-tangle-collect-blocks): source blocks
without a language are not ignored anymore, if they inherit a
src-tfile other than "yes" or "no".
* lisp/ob-core.el: adapts the org-babel-src-block-regexp regular
expression to make the language part of a source block optional.
* testing/lisp/test-ob-tangle.el: (ob-tangle/collect-blocks): Augment
the test with source blocks without language specifiers.
* etc/ORG-NEWS: (=ob-tangle= now tangles source blocks that do not
specify a =language= if an inherited property sets a tangle filename):
Document the new behaviour.
* doc/org-manual.org: (Structure of Code Blocks) Clarify what happens
when the language identifier is omitted.

TINYCHANGE
---
Here the same patch with the TINYCHANGE cookie. I'll get the fsf papers
anyway as I intend to commit more.
Thanks Ihor.

 doc/org-manual.org             |  3 ++-
 etc/ORG-NEWS                   |  8 ++++++++
 lisp/ob-core.el                |  4 ++--
 lisp/ob-tangle.el              |  8 ++++++--
 testing/lisp/test-ob-tangle.el | 16 ++++++++++++----
 5 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/doc/org-manual.org b/doc/org-manual.org
index 2d5fd57b3..f0c53265a 100644
--- a/doc/org-manual.org
+++ b/doc/org-manual.org
@@ -18028,7 +18028,8 @@ or
   block.  See [[*Languages]], for identifiers of supported languages.
 
   When =<language>= identifier is omitted, the block also cannot
-  have =<switches>= and =<header arguments>=.
+  have =<switches>= and =<header arguments>=.  Otherwise, the first
+  switch/argument will be treated as =<language>=.
 
   Language identifier is also used to fontify code blocks in Org
   buffers, when ~org-src-fontify-natively~ is set to non-~nil~.  See
diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index 2d4616fab..4aa628c7e 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -437,6 +437,14 @@ For example, given =H:3= and =toc:2= in =#+OPTIONS:=, all headings at
 the 1st and 2nd level appear in the table of contents and those at the
 3rd level do not.
 
+*** =ob-tangle= now tangles source blocks that do not specify a =language= if an inherited property sets a tangle filename
+
+Previously, all source blocks that did not specify a =language= where
+ignored by ~org-babel-tangle-collect-blocks~. Now, if it inherits a
+:tangle header argument with a value other than =no= or =yes= (that is, a
+filename), a source block without =language= will get tangled to that
+file.
+
 * Version 9.7
 
 ** Important announcements and breaking changes
diff --git a/lisp/ob-core.el b/lisp/ob-core.el
index ff021cbd3..cf56367f8 100644
--- a/lisp/ob-core.el
+++ b/lisp/ob-core.el
@@ -216,8 +216,8 @@ When matching, reference is stored in match group 1."
 
 (defvar org-babel-src-block-regexp
   (concat
-   ;; (1) indentation                 (2) lang
-   "^\\([ \t]*\\)#\\+begin_src[ \t]+\\([^ \f\t\n\r\v]+\\)[ \t]*"
+   ;; (1) indentation                      (2) lang
+   "^\\([ \t]*\\)#\\+begin_src\\(?:[ \t]+\\([^ \f\t\n\r\v]*\\)\\)?[ \t]*"
    ;; (3) switches
    "\\([^\":\n]*\"[^\"\n*]*\"[^\":\n]*\\|[^\":\n]*\\)"
    ;; (4) header arguments
diff --git a/lisp/ob-tangle.el b/lisp/ob-tangle.el
index 044212da2..d37d3c67f 100644
--- a/lisp/ob-tangle.el
+++ b/lisp/ob-tangle.el
@@ -508,9 +508,13 @@ code blocks by target file."
 	       (src-lang (nth 0 info))
 	       (src-tfile (cdr (assq :tangle (nth 2 info)))))
 	  (unless (or (string= src-tfile "no")
-                      (not src-lang) ;; src block without lang
+                      ;; src block without lang
+                      (and (not src-lang) (string= src-tfile "yes"))
 		      (and tangle-file (not (equal tangle-file src-tfile)))
-		      (and lang-re (not (string-match-p lang-re src-lang))))
+                      ;; lang-re but either no lang or lang doesn't match
+		      (and lang-re
+                           (or (not src-lang)
+                               (not (string-match-p lang-re src-lang)))))
 	    ;; Add the spec for this block to blocks under its tangled
 	    ;; file name.
 	    (let* ((block (org-babel-tangle-single-block counter))
diff --git a/testing/lisp/test-ob-tangle.el b/testing/lisp/test-ob-tangle.el
index e13bca0cb..6e95c4c91 100644
--- a/testing/lisp/test-ob-tangle.el
+++ b/testing/lisp/test-ob-tangle.el
@@ -628,6 +628,10 @@ another block
 \"H1: :tangle ~/../../tmp/absolute.el\"
 #+end_src
 
+#+begin_src
+\"H1: no language and inherited :tangle relative.el in properties\"
+#+end_src
+
 * H2 without :tangle in properties
 
 #+begin_src emacs-lisp
@@ -660,6 +664,10 @@ another block
 
 #+begin_src emacs-lisp :tangle ~/../../tmp/absolute.el
 \"H2: :tangle ~/../../tmp/absolute.el\"
+#+end_src
+
+#+begin_src
+\"H2: without language and thus without :tangle\"
 #+end_src"
                     `((?a . ,el-file-abs)
                       (?r . ,el-file-rel))))
@@ -684,7 +692,7 @@ another block
                                               collected-blocks)))))
         (should (equal (funcall normalize-expected-targets-alist
                                 `(("/tmp/absolute.el" . 4)
-                                  ("relative.el" . 5)
+                                  ("relative.el" . 6)
                                   ;; file name differs between tests
                                   (,el-file-abs . 4)))
                        (funcall count-blocks-in-target-files
@@ -699,11 +707,11 @@ another block
           (should (equal
                    (funcall normalize-expected-targets-alist
                             `(("/tmp/absolute.el" . 4)
-                              ("relative.el" . 5)
+                              ("relative.el" . 6)
                               ;; Default :tangle header now also
                               ;; points to the file name derived from the name of
-                              ;; the Org file, so 5 blocks should go there.
-                              (,el-file-abs . 5)))
+                              ;; the Org file, so 6 blocks should go there.
+                              (,el-file-abs . 6)))
                    (funcall count-blocks-in-target-files
                             (org-babel-tangle-collect-blocks)))))))))
 
-- 
2.47.1