Ignore custom resource Ref (#3965)

Author: kddejong

src/cfnlint/rules/functions/RefFormat.py

@@ -8,6 +8,7 @@
 from copy import deepcopy
 from typing import Any
 
+from cfnlint.helpers import is_custom_resource
 from cfnlint.jsonschema import ValidationResult, Validator
 from cfnlint.jsonschema._utils import Unset
 from cfnlint.rules.formats._schema_comparer import compare_schemas
@@ -62,16 +63,20 @@ def validate(
         if instance not in validator.context.resources:
             return
         t = validator.context.resources[instance].type
+
+        # When using a custom resource you can set the physical ID
+        # which results in a usable Ref
+        if is_custom_resource(t):
+            return
+
         for (
             regions,
             resource_schema,
         ) in PROVIDER_SCHEMA_MANAGER.get_resource_schemas_by_regions(
             t, validator.context.regions
         ):
             region = regions[0]
-
             ref_schema = validator.context.resources[instance].ref(region)
-
             ref_schema = self._filter_schema(validator, t, instance, ref_schema)
 
             err = compare_schemas(schema, ref_schema)

test/unit/rules/functions/test_ref_format.py

@@ -21,6 +21,7 @@ def template():
         "Resources": {
             "MyBucket": {"Type": "AWS::S3::Bucket"},
             "MyVpc": {"Type": "AWS::EC2::VPC"},
+            "MyCustomResource": {"Type": "Custom::MyResource"},
         },
     }
 
@@ -34,6 +35,12 @@ def template():
             {"format": "AWS::EC2::VPC.Id"},
             [],
         ),
+        (
+            "Valid Ref with a good format",
+            "MyCustomResource",
+            {"format": "AWS::EC2::VPC.Id"},
+            [],
+        ),
         (
             "Invalid Ref with a bad format",
             "MyVpc",