compose: fix environment interpolation from the client

For an environment variable defined in the yaml without value,
the value needs to be propagated from the client, as in Docker Compose.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

command/stack/deploy_composefile.go

@@ -115,6 +115,16 @@ func getConfigDetails(opts deployOptions) (composetypes.ConfigDetails, error) {
 	}
 	// TODO: support multiple files
 	details.ConfigFiles = []composetypes.ConfigFile{*configFile}
+	env := os.Environ()
+	details.Environment = make(map[string]string, len(env))
+	for _, s := range env {
+		// if value is empty, s is like "K=", not "K".
+		if !strings.Contains(s, "=") {
+			return details, fmt.Errorf("unexpected environment %q", s)
+		}
+		kv := strings.SplitN(s, "=", 2)
+		details.Environment[kv[0]] = kv[1]
+	}
 	return details, nil
 }