Adding logic to handle "oneOf" for Zod

src/zod/index.ts

@@ -50,7 +50,7 @@ export class ZodSchemaVisitor extends BaseSchemaVisitor {
             .withName('Properties<T>')
             .withContent(['Required<{', '  [K in keyof T]: z.ZodType<T[K], any, T[K]>;', '}>'].join('\n'))
             .string,
-          // Unfortunately, zod doesn’t provide non-null defined any schema.
+          // Unfortunately, zod doesn't provide non-null defined any schema.
           // This is a temporary hack until it is fixed.
           // see: https://github.com/colinhacks/zod/issues/884
           new DeclarationBlock({}).asKind('type').withName('definedNonNullAny').withContent('{}').string,
@@ -77,6 +77,12 @@ export class ZodSchemaVisitor extends BaseSchemaVisitor {
         const visitor = this.createVisitor('input');
         const name = visitor.convertName(node.name.value);
         this.importTypes.push(name);
+        // Check for @oneOf directive
+        const hasOneOf = node.directives?.some(d => d.name.value === 'oneOf');
+        if (hasOneOf) {
+          return this.buildOneOfInputFields(node.fields ?? [], visitor, name);
+        }
+
         return this.buildInputFields(node.fields ?? [], visitor, name);
       },
     };
@@ -274,6 +280,52 @@ export class ZodSchemaVisitor extends BaseSchemaVisitor {
           .string;
     }
   }
+
+  protected buildOneOfInputFields(
+    fields: readonly InputValueDefinitionNode[],
+    visitor: Visitor,
+    name: string,
+  ): string {
+    // Generate discriminated union variants
+    const variants = fields.map((selectedField) => {
+      const fieldName = selectedField.name.value;
+      // Get the raw schema without nullish wrapper for discriminated union
+      const fieldSchema = generateFieldTypeZodSchema(this.config, visitor, selectedField, selectedField.type, {
+        kind: Kind.NON_NULL_TYPE,
+        type: {
+          kind: Kind.NAMED_TYPE,
+          name: selectedField.name,
+        }
+      });
+      return indent(`z.object({\n`, 2) +
+        indent(`  __type: z.literal("${fieldName}"),\n`, 2) +
+        indent(`  ${fieldName}: ${fieldSchema}\n`, 2) +
+        indent(`})`, 2);
+    }).join(',\n');
+
+    switch (this.config.validationSchemaExportType) {
+      case 'const':
+        return new DeclarationBlock({})
+          .export()
+          .asKind('const')
+          .withName(`${name}Schema`)
+          .withContent(`z.discriminatedUnion("__type", [\n  ${variants}\n])`)
+          .string;
+
+      case 'function':
+      default:
+        return new DeclarationBlock({})
+          .export()
+          .asKind('function')
+          .withName(`${name}Schema(): z.ZodSchema<${name}>`)
+          .withBlock([
+            indent(`return z.discriminatedUnion("__type", [`),
+            variants,
+            indent(`]);`),
+          ].join('\n'))
+          .string;
+    }
+  }
 }
 
 function generateFieldZodSchema(config: ValidationSchemaPluginConfig, visitor: Visitor, field: InputValueDefinitionNode | FieldDefinitionNode, indentCount: number): string {

tests/zod.spec.ts

@@ -1797,4 +1797,54 @@ describe('zod', () => {
       "
     `)
   });
+
+  it('with @oneOf directive', async () => {
+    const schema = buildSchema(/* GraphQL */ `
+      input UpdateUserInput @oneOf {
+        email: String
+        phoneNumber: String
+        profile: UpdateUserProfileInput
+      }
+
+      input UpdateUserProfileInput {
+        name: String
+        age: Int
+      }
+    `);
+    const result = await plugin(
+      schema,
+      [],
+      {
+        schema: 'zod',
+      },
+      {},
+    );
+    expect(removedInitialEmitValue(result.content)).toMatchInlineSnapshot(`
+      "
+      export function UpdateUserInputSchema(): z.ZodSchema<UpdateUserInput> {
+        return z.discriminatedUnion("__type", [
+          z.object({
+            __type: z.literal("email"),
+            email: z.string()
+          }),
+          z.object({
+            __type: z.literal("phoneNumber"),
+            phoneNumber: z.string()
+          }),
+          z.object({
+            __type: z.literal("profile"),
+            profile: UpdateUserProfileInputSchema()
+          })
+        ]);
+      }
+
+      export function UpdateUserProfileInputSchema(): z.ZodObject<Properties<UpdateUserProfileInput>> {
+        return z.object({
+          name: z.string().nullish(),
+          age: z.number().nullish()
+        })
+      }
+      "
+    `)
+  });
 });