improvement: the template resolver now resolves unions (#1221)

fern/apis/fdr/definition/templates.yml

@@ -1,4 +1,5 @@
 imports:
+  type: ./api/v1/read/type.yml
   commons: commons.yml
   snippets: snippets.yml
 
@@ -78,6 +79,24 @@ types:
   # Internal Snippet structure
   TemplateSentinel: literal<"$FERN_INPUT">
 
+  UnionTemplateMember:
+    properties:
+      type: type.TypeReference
+      template: Template
+
+  UnionTemplateV2:
+    properties:
+      imports: optional<list<string>>
+      isOptional:
+        type: boolean
+        docs: |
+          We might not need this, but the idea here is to be able to omit if it's optional and undefined,
+          or default if omitted and required.
+
+      templateString: string
+      members: list<UnionTemplateMember>
+      templateInput: optional<PayloadInput>
+
   UnionTemplate:
     properties:
       imports: optional<list<string>>
@@ -92,6 +111,7 @@ types:
         type: map<string, Template>
         docs: A map of the union member's typeID to the template.
       templateInput: optional<PayloadInput>
+
   DiscriminatedUnionTemplate:
     properties:
       imports: optional<list<string>>
@@ -175,6 +195,7 @@ types:
       enum: EnumTemplate
       discriminatedUnion: DiscriminatedUnionTemplate
       union: UnionTemplate
+      union_v2: UnionTemplateV2
       dict: DictTemplate
       iterable: IterableTemplate
 
@@ -206,12 +227,12 @@ types:
       clientInstantiation: ClientInstantiation
       functionInvocation: Template
 
-  ClientInstantiation: 
+  ClientInstantiation:
     discriminated: false
-    union: 
+    union:
       - string
-      - Template 
-  
+      - Template
+
   VersionedSnippetTemplate:
     audiences:
       - templateResolver
@@ -237,6 +258,7 @@ types:
     properties:
       sdk: snippets.SDK
       endpointId: commons.EndpointIdentifier
+      apiDefinitionId: optional<commons.ApiDefinitionId>
       snippetTemplate:
         type: VersionedSnippetTemplate
         docs: The default snippet template to use

packages/template-resolver/package.json

@@ -27,7 +27,8 @@
     "test": "vitest --run --passWithNoTests"
   },
   "dependencies": {
-    "prettier": "^3.3.2"
+    "prettier": "^3.3.2",
+    "@fern-api/fdr-sdk": "workspace:*"
   },
   "devDependencies": {
     "@fern-platform/configs": "workspace:*",

packages/template-resolver/src/ResolutionUtilities.ts

@@ -0,0 +1,48 @@
+import { APIV1Read } from "@fern-api/fdr-sdk";
+
+export class ObjectFlattener {
+    private flattenedObjects: Map<APIV1Read.TypeId, APIV1Read.ObjectProperty[]> = new Map<
+        APIV1Read.TypeId,
+        APIV1Read.ObjectProperty[]
+    >();
+
+    constructor(private readonly apiDefinition: APIV1Read.ApiDefinition) {}
+
+    public getFlattenedObjectPropertiesFromObjectType(objectType: APIV1Read.ObjectType): APIV1Read.ObjectProperty[] {
+        const flattenedProperties: APIV1Read.ObjectProperty[] = [];
+        flattenedProperties.push(...objectType.properties);
+        objectType.extends.forEach((ext) => {
+            flattenedProperties.push(...this.getFlattenedObjectProperties(ext));
+        });
+
+        return flattenedProperties;
+    }
+
+    public getFlattenedObjectProperties(typeId: APIV1Read.TypeId): APIV1Read.ObjectProperty[] {
+        if (this.flattenedObjects.has(typeId)) {
+            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+            return this.flattenedObjects.get(typeId)!;
+        }
+
+        const maybeType = this.apiDefinition.types[typeId];
+        if (maybeType == null) {
+            return [];
+        }
+
+        const flattenedProperties: APIV1Read.ObjectProperty[] = [];
+        switch (maybeType.shape.type) {
+            case "object":
+                flattenedProperties.push(...maybeType.shape.properties);
+                maybeType.shape.extends.forEach((ext) => {
+                    flattenedProperties.push(...this.getFlattenedObjectProperties(ext));
+                });
+                break;
+            default:
+                // This mirrors how we expand the properties in Python, we assume the extended type is an object
+                return [];
+        }
+
+        this.flattenedObjects.set(typeId, flattenedProperties);
+        return flattenedProperties;
+    }
+}