feat(envparse): add merge mode for global+stack env layering

deploy/envparse.py

@@ -15,12 +15,26 @@ def parse_env(path):
             pairs.append((k, v))
     return pairs
 
+def merge_envs(base_path, override_path):
+    """Merge two env files. Keys in override_path win over base_path."""
+    base = dict(parse_env(base_path))
+    override = dict(parse_env(override_path))
+    merged = {**base, **override}
+    return list(merged.items())
+
 mode = sys.argv[1]
 if mode == 'export':
     for k, v in parse_env(sys.argv[2]):
         print('export {}={}'.format(k, repr(v)))
+elif mode == 'export_merged':
+    # export_merged <global.env> <stack.env>
+    for k, v in merge_envs(sys.argv[2], sys.argv[3]):
+        print('export {}={}'.format(k, repr(v)))
 elif mode == 'vars':
     print(' '.join('$' + k for k, v in parse_env(sys.argv[2])))
+elif mode == 'vars_merged':
+    # vars_merged <global.env> <stack.env>
+    print(' '.join('$' + k for k, v in merge_envs(sys.argv[2], sys.argv[3])))
 elif mode == 'strip':
     t = sys.stdin.read()
     t = re.sub(r'[ \t]*env_file:[ \t]*\n([ \t]+-[^\n]*\n)+', '', t)