Complete the "env" directive in firejail-mode.el

elisp/firejail-mode.el

@@ -508,6 +508,21 @@ With NO-ABSOLUTE, don't complete absolute file names."
          (append (seq-take (nth ,index ,args) 2)
                  (list (seq-difference ,evaled-vals ,present)))))))
 
+(defun firejail--get-all-env-keys ()
+  "Return the name of every current environment variable."
+  (mapcar (lambda (elt)
+            (if-let ((sep (cl-position ?= elt)))
+                (substring elt 0 sep)
+              elt))
+          process-environment))
+
+(defun firejail--complete-env (index args _directive)
+  "Complete the arg numbered INDEX in ARGS for an \"env\" directive."
+  (cl-destructuring-bind (start _end text) (nth index args)
+    (let ((sep-pos (or (cl-position ?= text) (length text))))
+      (when (<= (point) (+ start sep-pos))
+        (list start (+ start sep-pos) (firejail--get-all-env-keys))))))
+
 (defconst firejail-profile--keyword-handlers
   (let ((ht (make-hash-table :test 'equal)))
     (cl-flet* ((complete (args fun dirs)
@@ -583,7 +598,8 @@ With NO-ABSOLUTE, don't complete absolute file names."
       (complete-all (firejail--complete-many-from-set
                      '(mapcar 'number-to-string
                               (number-sequence 0 (firejail--get-num-cpus))))
-                    "cpu"))
+                    "cpu")
+      (complete 1 #'firejail--complete-env "env"))
     ht)
   "Hash table mapping firejail profile directives to their handler.
 Each handler is a function of three arguments.  The first is the index of the