validation: make environment property mandatory in serial steps

Closes reanahub/reana-client#679.

CHANGES.rst

@@ -6,6 +6,7 @@ Version 0.9.4 (UNRELEASED)
 
 - Changes the REANA specification schema to use the ``draft 2020-12`` version of the JSON schema specification.
 - Changes validation of REANA specification to expose functions for loading workflow input parameters and workflow specifications.
+- Changes the validation schema of the REANA specification to make the ``environment`` property mandatory for the steps of serial workflows.
 - Fixes the mounting of CVMFS volumes for the REANA deployments that use non-default Kubernetes namespace.
 
 Version 0.9.3 (2023-09-26)

reana_commons/validation/schemas/reana_analysis_schema.json

@@ -68,7 +68,20 @@
         "specification": {
           "$id": "/properties/workflow/properties/specification",
           "type": "object",
-          "title": "Workflow specification in yaml format."
+          "title": "Workflow specification in yaml format.",
+          "properties": {
+            "steps": {
+              "id": "/properties/workflow/properties/specification/properties/steps",
+              "type": "array",
+              "title": "Serial workflow steps.",
+              "description": "List of steps which represent the workflow.",
+              "items": {
+              "required": [
+                  "environment"
+                ]
+              }
+            }
+          }
         },
         "file": {
           "$id": "/properties/workflow/properties/file",

reana_commons/validation/utils.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 #
 # This file is part of REANA.
-# Copyright (C) 2022 CERN.
+# Copyright (C) 2022, 2023 CERN.
 #
 # REANA is free software; you can redistribute it and/or modify it
 # under the terms of the MIT License; see LICENSE file for more details.
@@ -77,6 +77,8 @@ def validate_reana_yaml(reana_yaml: Dict) -> Dict:
     """Validate REANA specification file according to jsonschema.
 
     :param reana_yaml: Dictionary which represents REANA specification file.
+    :returns: Dictionary of non-critical warnings, in the form of
+    {warning_key: [warning_value1, warning_value2, ...]}.
     :raises ValidationError: Given REANA spec file does not validate against
         REANA specification schema.
     """