Handle non-zero exit status from psql more gracefully

* lisp/progmodes/sql.el (sql-postgres-list-databases): Handle non-zero
exit statuses from `psql -ltX' more gracefully by returning nil.

* test/lisp/progmodes/sql-tests.el
(sql-tests-postgres-list-databases-error): New test.

1 files changed, 10 insertions, 0 deletions

diff --git a/test/lisp/progmodes/sql-tests.el b/test/lisp/progmodes/sql-tests.el
index 27a72aa2c23..f75005f737f 100644
--- a/test/lisp/progmodes/sql-tests.el
+++ b/test/lisp/progmodes/sql-tests.el
@@ -43,5 +43,15 @@
     (should (equal (sql-postgres-list-databases)
                    '("db-name-1" "db_name_2")))))
 
+(ert-deftest sql-tests-postgres-list-databases-error ()
+  "Test that nil is returned when `psql -ltX' fails."
+  (cl-letf
+      (((symbol-function 'executable-find)
+        (lambda (_command) t))
+       ((symbol-function 'process-lines)
+        (lambda (_program &rest _args)
+          (error))))
+    (should-not (sql-postgres-list-databases))))
+
 (provide 'sql-tests)
 ;;; sql-tests.el ends here