improve(environment): share common environment for specific commands

If the environment was configured using an alist. The default
environment is always merged into the specific command environment.
This makes sure that these don't need to repeat entries.

The values in the specific environment will override those of the
common one for shared keys.

ship-mate.el

@@ -619,9 +619,12 @@ ARG is passed to `ship-mate-command--buffers'."
   "Get the last environment for CMD or default.
 
 This is the currently set `compilation-environment' if it's
-non-nil. Otherwise it is either the local value of
-`ship-mate-environment' of the current CMD or the global
-value (corresponding to nil)."
+non-nil.
+
+Otherwise the result is based on the local value of
+`ship-mate-environment'. If it was defined per-command, the common
+environment (denoted by nil) and the command's environment are merged.
+If it's a plain list, it is used for all commands."
   (if-let* ((buffer-name (funcall compilation-buffer-name-function nil))
             (buffer (get-buffer buffer-name))
             (local (buffer-local-value 'compilation-environment buffer)))
@@ -630,9 +633,26 @@ value (corresponding to nil)."
 
     (when-let ((env (ship-mate--local-value 'ship-mate-environment)))
 
-      (or (alist-get cmd env)
-          (alist-get nil env)
-          env))))
+      (if (and (alist-get nil env)
+               (alist-get cmd env))
+
+          (let ((keys)
+                (combined (append (alist-get cmd env) (alist-get nil env)))
+                (merged))
+
+            (dolist (item combined)
+
+              (let ((key (car-safe (string-split item "="))))
+
+                (unless (member key keys)
+                  (push item merged)
+                  (push key keys))))
+
+            (reverse merged))
+
+        (or (alist-get cmd env)
+            (alist-get nil env)
+            env)))))
 
 ;;;; History
 

test/ship-mate-test.el

@@ -242,12 +242,15 @@
 
     (setq-local compilation-environment nil)
 
-    (bydi ((:mock ship-mate--local-value :return '((test . ("TES=TING")) (nil . ("MOC=KING")))))
+    (bydi ((:mock ship-mate--local-value :return '((test . ("TES=TING" "MOC=CA"))
+                                                   (nil . ("MOC=KING" "RE=SEARCH"))
+                                                   (research . ("LAB=BING")))))
 
       (let ((compilation-buffer-name-function (lambda (_) (buffer-name))))
 
-        (should (equal '("MOC=KING") (ship-mate-environment--current-environment 'mock)))
-        (should (equal '("TES=TING") (ship-mate-environment--current-environment 'test)))))))
+        (should (equal '("MOC=KING" "RE=SEARCH") (ship-mate-environment--current-environment 'mock)))
+        (should (equal '("TES=TING" "MOC=CA" "RE=SEARCH") (ship-mate-environment--current-environment 'test)))
+        (should (equal '("LAB=BING" "MOC=KING" "RE=SEARCH") (ship-mate-environment--current-environment 'research)))))))
 
 (ert-deftest ship-mate-command--has-run-p ()
   :tags '(meta)