Repository: elastic/elasticsearch-py

Issue:
TasksClient.get() requiring an argument on v7.5.1
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<!-- Bug report -->

**Elasticsearch version** (`bin/elasticsearch --version`): 7.1.1, 7.5.1

**`elasticsearch-py` version (`elasticsearch.__versionstr__`)**: 7.5.1

Please make sure the major version matches the Elasticsearch server you are running.

**Description of the problem including expected versus actual behavior**:

Elasticsearch().tasks.get() fails using elasticsearch-py 7.5.1, whereas it succeeds using 7.1.1.

```
>>> import elasticsearch
>>> elasticsearch.__versionstr__
'7.5.1'
>>> elasticsearch.Elasticsearch().tasks.get()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/nfox/myenv-7.5.1/lib/python3.7/site-packages/elasticsearch/client/utils.py", line 84, in _wrapped
    return func(*args, params=params, **kwargs)
TypeError: get() missing 1 required positional argument: 'task_id'
```

```
>>> import elasticsearch
>>> elasticsearch.__versionstr__
'7.1.0'
>>> elasticsearch.Elasticsearch().tasks.get()
{'nodes': {'GkSSDiZPTBq4Tlv5xV9wtg': {'name': 'e6a01a4d549f', 'transport_address': '172.17.0.3:9300', 'host': '172.17.0.3', 'ip': '172.17.0.3:9300', 'roles': ['ingest', 'master', 'data', 'ml'], 'attributes': {'ml.machine_memory': '4129972224', 'xpack.installed': 'true', 'ml.max_open_jobs': '20'}, 'tasks': {'GkSSDiZPTBq4Tlv5xV9wtg:56': {'node': 'GkSSDiZPTBq4Tlv5xV9wtg', 'id': 56, 'type': 'direct', 'action': 'cluster:monitor/tasks/lists[n]', 'start_time_in_millis': 1582238526445, 'running_time_in_nanos': 8142200, 'cancellable': False, 'parent_task_id': 'GkSSDiZPTBq4Tlv5xV9wtg:55', 'headers': {}}, 'GkSSDiZPTBq4Tlv5xV9wtg:55': {'node': 'GkSSDiZPTBq4Tlv5xV9wtg', 'id': 55, 'type': 'transport', 'action': 'cluster:monitor/tasks/lists', 'start_time_in_millis': 1582238526442, 'running_time_in_nanos': 11192200, 'cancellable': False, 'headers': {}}}}}}
```

I've verified this against running both ES 7.5.1 and ES 7.1.1 (via docker on localhost)

**Steps to reproduce**:
run `elasticsearch.Elasticsearch().tasks.get()` while using elasticsearch-py 7.5.1

Ultimately, this is breaking curator's DeleteSnapshot as it checks for tasks.

Discussion:

Patch:
diff --git a/elasticsearch/client/tasks.py b/elasticsearch/client/tasks.py
index 0f253ca1..4c4f6d1f 100644
--- a/elasticsearch/client/tasks.py
+++ b/elasticsearch/client/tasks.py
@@ -1,3 +1,4 @@
+import warnings
 from .utils import NamespacedClient, query_params, _make_path, SKIP_IN_PATH
 
 
@@ -58,7 +59,7 @@ class TasksClient(NamespacedClient):
         )
 
     @query_params("timeout", "wait_for_completion")
-    def get(self, task_id, params=None, headers=None):
+    def get(self, task_id=None, params=None, headers=None):
         """
         Returns information about a task.
         `<https://www.elastic.co/guide/en/elasticsearch/reference/master/tasks.html>`_
@@ -70,7 +71,11 @@ class TasksClient(NamespacedClient):
             complete (default: false)
         """
         if task_id in SKIP_IN_PATH:
-            raise ValueError("Empty value passed for a required argument 'task_id'.")
+            warnings.warn(
+                "Calling client.tasks.get() without a task_id is deprecated "
+                "and will be removed in v8.0. Use client.tasks.list() instead.",
+                DeprecationWarning,
+            )
 
         return self.transport.perform_request(
             "GET", _make_path("_tasks", task_id), params=params, headers=headers
diff --git a/utils/generate_api.py b/utils/generate_api.py
index 0e76617d..183934e4 100644
--- a/utils/generate_api.py
+++ b/utils/generate_api.py
@@ -146,6 +146,13 @@ class API:
                 p in url.get("parts", {}) for url in self._def["url"]["paths"]
             )
 
+            # This piece of logic corresponds to calling
+            # client.tasks.get() w/o a task_id which was erroneously
+            # allowed in the 7.1 client library. This functionality
+            # is deprecated and will be removed in 8.x.
+            if self.namespace == "tasks" and self.name == "get":
+                parts["task_id"]["required"] = False
+
         for k, sub in SUBSTITUTIONS.items():
             if k in parts:
                 parts[sub] = parts.pop(k)
diff --git a/utils/templates/overrides/tasks/get b/utils/templates/overrides/tasks/get
new file mode 100644
index 00000000..ca855ab9
--- /dev/null
+++ b/utils/templates/overrides/tasks/get
@@ -0,0 +1,12 @@
+{% extends "base" %}
+{% block request %}
+        if task_id in SKIP_IN_PATH:
+            warnings.warn(
+                "Calling client.tasks.get() without a task_id is deprecated "
+                "and will be removed in v8.0. Use client.tasks.list() instead.",
+                DeprecationWarning,
+            )
+
+        {{ super()|trim }}
+{% endblock %}
+


Test patch:
diff --git a/test_elasticsearch/test_client/__init__.py b/test_elasticsearch/test_client/__init__.py
index b7fa18ad..5fa01f76 100644
--- a/test_elasticsearch/test_client/__init__.py
+++ b/test_elasticsearch/test_client/__init__.py
@@ -1,4 +1,5 @@
 from __future__ import unicode_literals
+import warnings
 
 from elasticsearch.client import _normalize_hosts, Elasticsearch
 
@@ -110,3 +111,27 @@ class TestClient(ElasticsearchTestCase):
         self.client.index(index="my-index", id=0, body={})
 
         self.assert_url_called("PUT", "/my-index/_doc/0")
+
+    def test_tasks_get_without_task_id_deprecated(self):
+        warnings.simplefilter("always", DeprecationWarning)
+        with warnings.catch_warnings(record=True) as w:
+            self.client.tasks.get()
+
+        self.assert_url_called("GET", "/_tasks")
+        self.assertEquals(len(w), 1)
+        self.assertIs(w[0].category, DeprecationWarning)
+        self.assertEquals(
+            str(w[0].message),
+            "Calling client.tasks.get() without a task_id is deprecated "
+            "and will be removed in v8.0. Use client.tasks.list() instead.",
+        )
+
+    def test_tasks_get_with_task_id_not_deprecated(self):
+        warnings.simplefilter("always", DeprecationWarning)
+        with warnings.catch_warnings(record=True) as w:
+            self.client.tasks.get("task-1")
+            self.client.tasks.get(task_id="task-2")
+
+        self.assert_url_called("GET", "/_tasks/task-1")
+        self.assert_url_called("GET", "/_tasks/task-2")
+        self.assertEquals(len(w), 0)