Add warning for non-positive max-items value (#8931)

Emit a warning when a non-positive integer is entered for the max-items pagination parameter.

.changes/next-release/enhancement-paginator-44130.json

@@ -0,0 +1,5 @@
+{
+  "type": "enhancement",
+  "category": "paginator",
+  "description": "Add warning when a non-positive value is provided for the max-items pagination parameter."
+}

awscli/customizations/paginate.py

@@ -24,8 +24,10 @@
 
 """
 import logging
+import sys
 from functools import partial
 
+from awscli.customizations.utils import uni_print
 from botocore import xform_name
 from botocore.exceptions import DataNotFoundError, PaginationError
 from botocore import model
@@ -266,6 +268,11 @@ def __init__(self, name, documentation, parse_type, serialized_name):
         self._parse_type = parse_type
         self._required = False
 
+    def _emit_non_positive_max_items_warning(self):
+        uni_print(
+            "warning: Non-positive values for --max-items may result in undefined behavior.\n",
+            sys.stderr)
+
     @property
     def cli_name(self):
         return '--' + self._name
@@ -292,6 +299,8 @@ def add_to_parser(self, parser):
 
     def add_to_params(self, parameters, value):
         if value is not None:
+            if self._serialized_name == 'MaxItems' and int(value) <= 0:
+                self._emit_non_positive_max_items_warning()
             pagination_config = parameters.get('PaginationConfig', {})
             pagination_config[self._serialized_name] = value
             parameters['PaginationConfig'] = pagination_config

tests/unit/customizations/test_paginate.py

@@ -10,6 +10,9 @@
 # distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
+import pytest
+
+from awscli.customizations.paginate import PageArgument
 from awscli.testutils import mock, unittest
 
 from botocore.exceptions import DataNotFoundError, PaginationError
@@ -18,6 +21,9 @@
 
 from awscli.customizations import paginate
 
+@pytest.fixture
+def max_items_page_arg():
+    return PageArgument('max-items', 'documentation', int, 'MaxItems')
 
 class TestPaginateBase(unittest.TestCase):
 
@@ -321,3 +327,20 @@ def test_can_handle_missing_page_size(self):
         del self.parsed_args.page_size
         self.assertIsNone(paginate.ensure_paging_params_not_set(
             self.parsed_args, {}))
+
+
+class TestNonPositiveMaxItems:
+    def test_positive_integer_does_not_raise_warning(self, max_items_page_arg, capsys):
+        max_items_page_arg.add_to_params({}, 1)
+        captured = capsys.readouterr()
+        assert captured.err == ""
+
+    def test_zero_raises_warning(self, max_items_page_arg, capsys):
+        max_items_page_arg.add_to_params({}, 0)
+        captured = capsys.readouterr()
+        assert "Non-positive values for --max-items" in captured.err
+
+    def test_negative_integer_raises_warning(self, max_items_page_arg, capsys):
+        max_items_page_arg.add_to_params({}, -1)
+        captured = capsys.readouterr()
+        assert "Non-positive values for --max-items" in captured.err