Rework empty abbrev table omitting

There were two problems with the original implementation:

1. It changed the behavior of insert-abbrev-table-description when
READABLE is nil to sometimes insert one Emacs Lisp expression and
sometimes insert nothing.
2. It broke the tests.

This commit reworks this so that insert-abbrev-table-description
always inserts an expressions even if no abbrevs need to be saved and
making only write-abbrev-file check that a table has any abbrevs to
save before calling insert-abbrev-table-description.  This duplicates
the work of filtering the table for savable abbrevs, but the benefit
of keeping the API is worth it.

* doc/lispref/abbrevs.texi (Abbrev Tables): Update documentation.
* lisp/abbrev.el (write-abbrev-file): Skip tables without user abbrevs
(insert-abbrev-table-description): Always insert the define
expression.
(abbrev--table-symbols): New function.
* test/lisp/abbrev-tests.el (abbrev--table-symbols-test):
Add test for abbrev--table-symbols.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/lisp/abbrev-tests.el b/test/lisp/abbrev-tests.el
index facf097815e..e50f931cef5 100644
--- a/test/lisp/abbrev-tests.el
+++ b/test/lisp/abbrev-tests.el
@@ -64,6 +64,14 @@
     (should (= (length table) obarray-default-size))
     (should (eq (abbrev-table-get table 'foo) 'bar))))
 
+(ert-deftest abbrev--table-symbols-test ()
+  (let ((ert-test-abbrevs (setup-test-abbrev-table)))
+    (define-abbrev ert-test-abbrevs "sys" "system abbrev" nil :system t)
+    (should (equal (mapcar #'symbol-name (abbrev--table-symbols 'ert-test-abbrevs))
+                   '("a-e-t")))
+    (should (equal (mapcar #'symbol-name (abbrev--table-symbols 'ert-test-abbrevs t))
+                   '("a-e-t" "sys")))))
+
 (ert-deftest abbrev-table-get-put-test ()
   (let ((table (make-abbrev-table)))
     (should-not (abbrev-table-get table 'foo))