core: add completion "eval_variables", used in completion of /eval

ChangeLog.adoc

@@ -15,6 +15,7 @@ For a list of important changes that require manual actions, please look at rele
 
 New features::
 
+  * core: add completion "eval_variables", used in completion of `/eval`
   * core: add command `/sys` to show resource limits/usage and suspend WeeChat process, add key kbd:[Ctrl+z] to suspend WeeChat (issue #985)
   * core: ignore key bindings with empty command
   * core: add support of quotes in commands `/key bind` and `/key bindctxt`

src/core/wee-command.c

@@ -8414,7 +8414,7 @@ command_init ()
            "  /eval -n -c abcd !~ abc                 ==> 0\n"
            "  /eval -n -c abcd =* a*d                 ==> 1\n"
            "  /eval -n -c abcd =- bc                  ==> 1"),
-        "-n|-s|-c -n|-s|-c",
+        "-n|-s|-c|%(eval_variables)|%*",
         &command_eval, NULL, NULL);
     hook_command (
         NULL, "filter",