fix: Support for generating enums when enums definition has null value

Author: Daniel DeMicco

.changeset/real-penguins-fold.md

@@ -0,0 +1,5 @@
+---
+"openapi-typescript": minor
+---
+
+Support for generating enums when enums definition has null value

packages/openapi-typescript/src/transform/schema-object.ts

@@ -94,23 +94,38 @@ export function transformSchemaObjectWithComposition(
     !("additionalProperties" in schemaObject)
   ) {
     // hoist enum to top level if string/number enum and option is enabled
-    if (options.ctx.enum && schemaObject.enum.every((v) => typeof v === "string" || typeof v === "number")) {
+    if (
+      options.ctx.enum &&
+      schemaObject.enum.every((v) => typeof v === "string" || typeof v === "number" || v === null)
+    ) {
       let enumName = parseRef(options.path ?? "").pointer.join("/");
       // allow #/components/schemas to have simpler names
       enumName = enumName.replace("components/schemas", "");
       const metadata = schemaObject.enum.map((_, i) => ({
         name: schemaObject["x-enum-varnames"]?.[i] ?? schemaObject["x-enumNames"]?.[i],
         description: schemaObject["x-enum-descriptions"]?.[i] ?? schemaObject["x-enumDescriptions"]?.[i],
       }));
-      const enumType = tsEnum(enumName, schemaObject.enum as (string | number)[], metadata, {
+
+      // enums can contain null values, but dont want to output them
+      let hasNull = false;
+      const validSchemaEnums = schemaObject.enum.filter((enumValue) => {
+        if (enumValue === null) {
+          hasNull = true;
+          return false;
+        }
+
+        return true;
+      });
+      const enumType = tsEnum(enumName, validSchemaEnums as (string | number)[], metadata, {
         shouldCache: options.ctx.dedupeEnums,
         export: true,
         // readonly: TS enum do not support the readonly modifier
       });
       if (!options.ctx.injectFooter.includes(enumType)) {
         options.ctx.injectFooter.push(enumType);
       }
-      return ts.factory.createTypeReferenceNode(enumType.name);
+      const ref = ts.factory.createTypeReferenceNode(enumType.name);
+      return hasNull ? tsUnion([ref, NULL]) : ref;
     }
     const enumType = schemaObject.enum.map(tsLiteral);
     if (

packages/openapi-typescript/test/transform/schema-object/string.test.ts

@@ -84,6 +84,13 @@ describe("transformSchemaObject > string", () => {
         want: '"A" | "B" | "C" | null',
       },
     ],
+    [
+      "enum + nullable + null value",
+      {
+        given: { type: ["string", "null"], enum: ["A", "B", "C", null] },
+        want: '"A" | "B" | "C" | null',
+      },
+    ],
     [
       "enum + nullable (deprecated syntax)",
       {