Special-case the error messages for min/maxItems' special values.

minItems 1 really means "non-empty", and maxItems 0 is a long way of
writing {"const": []} but means "empty".

Author: Julian

jsonschema/_keywords.py

@@ -192,12 +192,14 @@ def multipleOf(validator, dB, instance, schema):
 
 def minItems(validator, mI, instance, schema):
     if validator.is_type(instance, "array") and len(instance) < mI:
-        yield ValidationError(f"{instance!r} is too short")
+        message = "should be non-empty" if mI == 1 else "is too short"
+        yield ValidationError(f"{instance!r} {message}")
 
 
 def maxItems(validator, mI, instance, schema):
     if validator.is_type(instance, "array") and len(instance) > mI:
-        yield ValidationError(f"{instance!r} is too long")
+        message = "is expected to be empty" if mI == 0 else "is too long"
+        yield ValidationError(f"{instance!r} {message}")
 
 
 def uniqueItems(validator, uI, instance, schema):

jsonschema/tests/test_validators.py

@@ -509,6 +509,14 @@ def test_maxItems(self):
         message = self.message_for(instance=[1, 2, 3], schema={"maxItems": 2})
         self.assertEqual(message, "[1, 2, 3] is too long")
 
+    def test_minItems_1(self):
+        message = self.message_for(instance=[], schema={"minItems": 1})
+        self.assertEqual(message, "[] should be non-empty")
+
+    def test_maxItems_0(self):
+        message = self.message_for(instance=[1, 2, 3], schema={"maxItems": 0})
+        self.assertEqual(message, "[1, 2, 3] is expected to be empty")
+
     def test_prefixItems_with_items(self):
         message = self.message_for(
             instance=[1, 2, "foo"],