ob-core: Resolve named list references to simple lists

* lisp/ob-core.el (org-babel-read-list): Return a simple list instead
of list of lists.  Document this in the docstring.
* testing/lisp/test-ob-java.el (ob-java/read-return-list):
(ob-java/read-list-return-array):
(ob-java/read-return-list-with-package): Fix tests assuming previous
behavior.
* testing/lisp/test-ob.el (test-ob/simple-variable-resolution): Add
new tests.
* etc/ORG-NEWS (List references in source block variable assignments
are now proper lists): Document the change.

This commit fixes the broken promise in the manual section 16.4
Environment of a Code Block where the named references to lists should
be converted to simple lists consisting of the top-level items.

The inconsistency existed for a while and possibly lurked into some
third-party packages.  So, announcement in NEWS is required.

Reported-by: Alain.Cochard@unistra.fr
Link: https://orgmode.org/list/87pmdqfao4.fsf@localhost

etc/ORG-NEWS

@@ -778,6 +778,40 @@ If you prefer to keep the keybinding, you can add it back to
 (define-key org-mode-map (kbd "C-c SPC") #'org-table-blank-field)
 #+end_src
 
+*** List references in source block variable assignments are now proper lists
+
+List representation of named lists is now converted to a simple list
+as promised by the manual section [[info:org#Environment of a Code Block][org#Environment of a Code Block]].
+Previously, it was converted to a list of lists.
+
+Before:
+
+#+begin_src org
+,#+NAME: example-list
+- simple
+  - not
+  - nested
+- list
+
+,#+BEGIN_SRC emacs-lisp :var x=example-list :results value
+(format "%S" x)
+,#+END_SRC
+
+,#+RESULTS:
+: (("simple" (unordered ("not") ("nested"))) ("list"))
+#+end_src
+
+After:
+
+#+begin_src org
+,#+BEGIN_SRC emacs-lisp :var x=example-list :results value
+(format "%S" x)
+,#+END_SRC
+
+,#+RESULTS:
+: ("simple" "list")
+#+end_src
+
 ** New features
 
 *** New citation engine

lisp/ob-core.el

@@ -2239,8 +2239,15 @@ Return nil if ELEMENT cannot be read."
           (org-table-to-lisp)))
 
 (defun org-babel-read-list ()
-  "Read the list at point into emacs-lisp."
-  (mapcar (lambda (el) (org-babel-read el 'inhibit-lisp-eval))
+  "Read the list at point into emacs-lisp.
+
+Return the list of strings representing top level items:
+
+   (item1 item2 ...)
+
+Only consider top level items.  See Info node `(org)Environment of \
+a Code Block'."
+  (mapcar (lambda (el) (org-babel-read (car el) 'inhibit-lisp-eval))
 	  (cdr (org-list-to-lisp))))
 
 (defvar org-link-types-re)

testing/lisp/test-ob-java.el

@@ -379,8 +379,8 @@ return a;
       "#+begin_src java :dir 'nil :var a=java_list :results value silent
 import java.util.List;
 import java.util.Arrays;
-List<String> b = Arrays.asList(a.get(0).get(0),
-                               a.get(1).get(0));
+List<String> b = Arrays.asList(a.get(0),
+                               a.get(1));
 return b;
 #+end_src
 
@@ -394,7 +394,7 @@ return b;
   "Read a list and return an array."
   (org-test-with-temp-text
       "#+begin_src java :dir 'nil :var a=java_list :results value silent
-String[] b = {a.get(0).get(0), a.get(1).get(0)};
+String[] b = {a.get(0), a.get(1)};
 return b;
 #+end_src
 
@@ -411,8 +411,8 @@ return b;
 package pkg;
 import java.util.List;
 import java.util.Arrays;
-List<String> b = Arrays.asList(a.get(0).get(0),
-                               a.get(1).get(0));
+List<String> b = Arrays.asList(a.get(0),
+                               a.get(1));
 return b;
 #+end_src
 

testing/lisp/test-ob.el

@@ -204,7 +204,27 @@ list, then it should be treated as such; not as the symbol nil."
     (forward-line 5)
     (should (string= ": 4" (buffer-substring
 			    (point-at-bol)
-			    (point-at-eol))))))
+			    (point-at-eol)))))
+  ;; Test reading lists.
+  (org-test-with-temp-text-in-file "
+
+#+NAME: example-list
+- simple
+  - not
+  - nested
+- list
+
+<point>#+BEGIN_SRC emacs-lisp :var x=example-list
+(print x)
+#+END_SRC"
+
+    (should (equal '("simple" "list") (org-babel-execute-src-block)))
+    (forward-line 5)
+    (should (string=
+             "| simple | list |"
+             (buffer-substring
+	      (point-at-bol)
+	      (point-at-eol))))))
 
 (ert-deftest test-ob/block-content-resolution ()
   "Test block content resolution."
@@ -218,8 +238,8 @@ list, then it should be treated as such; not as the symbol nil."
 #+begin_src emacs-lisp :var four=four[]
   (length (eval (car (read-from-string four))))
 #+end_src"
-                                   (org-babel-next-src-block 2)
-                                   (should (= 4 (org-babel-execute-src-block)))))
+    (org-babel-next-src-block 2)
+    (should (= 4 (org-babel-execute-src-block)))))
 
 (ert-deftest test-ob/cons-cell-as-variable ()
   "Test that cons cell can be assigned as variable."