From 28f3f846448bedc21098df2faa54986f3f7c3179 Mon Sep 17 00:00:00 2001
From: Bert Blommers <bblommers@users.noreply.github.com>
Date: Thu, 20 Apr 2023 21:12:43 +0000
Subject: [PATCH] SSM: Allow filtering by existence of tag-name (#6238)

---
 moto/ssm/models.py               |  7 +++++--
 moto/ssm/responses.py            |  6 +++---
 tests/test_ssm/test_ssm_boto3.py | 15 +++++++++------
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/moto/ssm/models.py b/moto/ssm/models.py
index f6763bbf2..3ae5247b6 100644
--- a/moto/ssm/models.py
+++ b/moto/ssm/models.py
@@ -1434,7 +1434,7 @@ class SimpleSystemManagerBackend(BaseBackend):
                     f"The following filter key is not valid: {key}. Valid filter keys include: [Type, KeyId]."
                 )
 
-            if not values:
+            if key in ["Name", "Type", "Path", "Tier", "Keyid"] and not values:
                 raise InvalidFilterValue(
                     "The following filter values are missing : null for filter key Name."
                 )
@@ -1636,7 +1636,7 @@ class SimpleSystemManagerBackend(BaseBackend):
             elif key.startswith("tag:"):
                 what = [tag["Value"] for tag in parameter.tags if tag["Key"] == key[4:]]
 
-            if what is None:
+            if what is None or what == []:
                 return False
             # 'what' can be a list (of multiple tag-values, for instance)
             is_list = isinstance(what, list)
@@ -1650,6 +1650,9 @@ class SimpleSystemManagerBackend(BaseBackend):
             elif option == "Contains" and not any(value in what for value in values):
                 return False
             elif option == "Equals":
+                if is_list and len(values) == 0:
+                    # User hasn't provided possible tag-values - they just want to know whether the tag exists
+                    return True
                 if is_list and not any(val in what for val in values):
                     return False
                 elif not is_list and not any(what == val for val in values):
diff --git a/moto/ssm/responses.py b/moto/ssm/responses.py
index 7ef8c9906..1469c4a51 100644
--- a/moto/ssm/responses.py
+++ b/moto/ssm/responses.py
@@ -2,15 +2,15 @@ import json
 
 from moto.core.responses import BaseResponse
 from .exceptions import ValidationException
-from .models import ssm_backends
+from .models import ssm_backends, SimpleSystemManagerBackend
 
 
 class SimpleSystemManagerResponse(BaseResponse):
-    def __init__(self):
+    def __init__(self) -> None:
         super().__init__(service_name="ssm")
 
     @property
-    def ssm_backend(self):
+    def ssm_backend(self) -> SimpleSystemManagerBackend:
         return ssm_backends[self.current_account][self.region]
 
     @property
diff --git a/tests/test_ssm/test_ssm_boto3.py b/tests/test_ssm/test_ssm_boto3.py
index fda67a08a..ad2074440 100644
--- a/tests/test_ssm/test_ssm_boto3.py
+++ b/tests/test_ssm/test_ssm_boto3.py
@@ -1039,14 +1039,17 @@ def test_describe_parameters_tags():
         Tags=[{"Key": "spam", "Value": "eggs"}],
     )
 
-    response = client.describe_parameters(
+    parameters = client.describe_parameters(
         ParameterFilters=[{"Key": "tag:spam", "Values": ["eggs"]}]
-    )
+    )["Parameters"]
+    assert len(parameters) == 1
+    assert parameters[0]["Name"] == "/spam/eggs"
 
-    parameters = response["Parameters"]
-    parameters.should.have.length_of(1)
-
-    parameters[0]["Name"].should.equal("/spam/eggs")
+    # Verify we can filter by the existence of a tag
+    filters = [{"Key": "tag:spam"}]
+    response = client.describe_parameters(ParameterFilters=filters)
+    assert len(response["Parameters"]) == 1
+    assert {p["Name"] for p in response["Parameters"]} == set(["/spam/eggs"])
 
 
 @mock_ssm