CloudFormation: Implement Fn::Sub variable mapping (#6124)

moto/cloudformation/parsing.py

@@ -1,3 +1,4 @@
+import string
 import functools
 import json
 import logging
@@ -189,40 +190,41 @@ def clean_json(resource_json: Any, resources_map: "ResourceMap") -> Any:
             return select_list[select_index]
 
         if "Fn::Sub" in resource_json:
-            if isinstance(resource_json["Fn::Sub"], list):
+            template = resource_json["Fn::Sub"]
-                warnings.warn(
+
-                    "Tried to parse Fn::Sub with variable mapping but it's not supported by moto's CloudFormation implementation"
+            if isinstance(template, list):
-                )
+                template, mappings = resource_json["Fn::Sub"]
-            else:
+                for key, value in mappings.items():
-                fn_sub_value = clean_json(resource_json["Fn::Sub"], resources_map)
+                    template = string.Template(template).safe_substitute(
-                to_sub = re.findall(r'(?=\${)[^!^"]*?}', fn_sub_value)
+                        **{key: str(clean_json(value, resources_map))}
-                literals = re.findall(r'(?=\${!)[^"]*?}', fn_sub_value)
-                for sub in to_sub:
-                    if "." in sub:
-                        cleaned_ref = clean_json(
-                            {
-                                "Fn::GetAtt": re.findall(r'(?<=\${)[^"]*?(?=})', sub)[
-                                    0
-                                ].split(".")
-                            },
-                            resources_map,
-                        )
-                    else:
-                        cleaned_ref = clean_json(
-                            {"Ref": re.findall(r'(?<=\${)[^"]*?(?=})', sub)[0]},
-                            resources_map,
-                        )
-                    if cleaned_ref is not None:
-                        fn_sub_value = fn_sub_value.replace(sub, str(cleaned_ref))
-                    else:
-                        # The ref was not found in the template - either it didn't exist, or we couldn't parse it
-                        pass
-                for literal in literals:
-                    fn_sub_value = fn_sub_value.replace(
-                        literal, literal.replace("!", "")
                     )
-                return fn_sub_value
+
-            pass
+            fn_sub_value = clean_json(template, resources_map)
+            to_sub = re.findall(r'(?=\${)[^!^"]*?}', fn_sub_value)
+            literals = re.findall(r'(?=\${!)[^"]*?}', fn_sub_value)
+            for sub in to_sub:
+                if "." in sub:
+                    cleaned_ref = clean_json(
+                        {
+                            "Fn::GetAtt": re.findall(r'(?<=\${)[^"]*?(?=})', sub)[
+                                0
+                            ].split(".")
+                        },
+                        resources_map,
+                    )
+                else:
+                    cleaned_ref = clean_json(
+                        {"Ref": re.findall(r'(?<=\${)[^"]*?(?=})', sub)[0]},
+                        resources_map,
+                    )
+                if cleaned_ref is not None:
+                    fn_sub_value = fn_sub_value.replace(sub, str(cleaned_ref))
+                else:
+                    # The ref was not found in the template - either it didn't exist, or we couldn't parse it
+                    pass
+            for literal in literals:
+                fn_sub_value = fn_sub_value.replace(literal, literal.replace("!", ""))
+            return fn_sub_value
 
         if "Fn::ImportValue" in resource_json:
             cleaned_val = clean_json(resource_json["Fn::ImportValue"], resources_map)

tests/test_cloudformation/test_stack_parsing.py

@@ -137,6 +137,33 @@ sub_num_template = {
     },
 }
 
+sub_mapping_template = {
+    "AWSTemplateFormatVersion": "2010-09-09",
+    "Parameters": {
+        "TestRef": {"Type": "String"},
+    },
+    "Conditions": {
+        "IsApple": {"Fn::Equals": [{"Ref": "TestRef"}, "apple"]},
+    },
+    "Resources": {
+        "Queue": {
+            "Type": "AWS::SQS::Queue",
+            "Properties": {
+                "QueueName": {
+                    "Fn::Sub": [
+                        "${AWS::StackName}-queue-${TestRef}-${TestFn}",
+                        {
+                            "TestRef": {"Ref": "TestRef"},
+                            "TestFn": {"Fn::If": ["IsApple", "yes", "no"]},
+                        },
+                    ],
+                },
+                "VisibilityTimeout": 60,
+            },
+        },
+    },
+}
+
 export_value_template = {
     "AWSTemplateFormatVersion": "2010-09-09",
     "Resources": {
@@ -191,6 +218,7 @@ ssm_parameter_template_json = json.dumps(ssm_parameter_template)
 split_select_template_json = json.dumps(split_select_template)
 sub_template_json = json.dumps(sub_template)
 sub_num_template_json = json.dumps(sub_num_template)
+sub_mapping_json = json.dumps(sub_mapping_template)
 export_value_template_json = json.dumps(export_value_template)
 import_value_template_json = json.dumps(import_value_template)
 
@@ -521,6 +549,30 @@ def test_sub_num():
     queue.name.should.equal("test_stack-queue-42")
 
 
+def test_sub_mapping():
+    stack = FakeStack(
+        stack_id="test_id",
+        name="test_stack",
+        template=sub_mapping_json,
+        parameters={"TestRef": "apple"},
+        account_id=ACCOUNT_ID,
+        region_name="us-west-1",
+    )
+    queue = stack.resource_map["Queue"]
+    queue.name.should.equal("test_stack-queue-apple-yes")
+
+    stack = FakeStack(
+        stack_id="test_id",
+        name="test_stack",
+        template=sub_mapping_json,
+        parameters={"TestRef": "banana"},
+        account_id=ACCOUNT_ID,
+        region_name="us-west-1",
+    )
+    queue = stack.resource_map["Queue"]
+    queue.name.should.equal("test_stack-queue-banana-no")
+
+
 def test_import():
     export_stack = FakeStack(
         stack_id="test_id",