feat: add discriminator to IRUnion

Author: mnahkies

packages/openapi-code-generator/src/core/normalization/schema-normalizer.spec.ts

@@ -512,6 +512,39 @@ describe("core/input - SchemaNormalizer", () => {
         }),
       )
     })
+
+    it("handles a discriminator", () => {
+      const actual = schemaNormalizer.normalize({
+        type: "object",
+        discriminator: {
+          propertyName: "type",
+          mapping: {
+            foo: "#/components/schemas/Foo",
+            bar: "#/components/schemas/Bar",
+          },
+        },
+        oneOf: [
+          {$ref: "#/components/schemas/Foo"},
+          {$ref: "#/components/schemas/Bar"},
+        ],
+      })
+
+      expect(actual).toStrictEqual(
+        ir.union({
+          discriminator: {
+            propertyName: "type",
+            mapping: {
+              foo: ir.ref("/components/schemas/Foo"),
+              bar: ir.ref("/components/schemas/Bar"),
+            },
+          },
+          schemas: [
+            ir.ref("/components/schemas/Foo"),
+            ir.ref("/components/schemas/Bar"),
+          ],
+        }),
+      )
+    })
   })
 
   describe("empty schemas / additionalProperties", () => {

packages/openapi-code-generator/src/core/normalization/schema-normalizer.ts

@@ -3,6 +3,7 @@ import {generationLib} from "../generation-lib"
 import type {InputConfig} from "../input"
 import {logger} from "../logger"
 import type {
+  Discriminator,
   Reference,
   Schema,
   SchemaNumber,
@@ -191,7 +192,11 @@ export class SchemaNormalizer {
           {...base, nullable},
           hasOwnProperties ? [...allOf, result] : allOf,
         )
-        const maybeUnion = this.union({...base, nullable}, [...oneOf, ...anyOf])
+        const maybeUnion = this.union(
+          {...base, nullable},
+          [...oneOf, ...anyOf],
+          schemaObject.discriminator,
+        )
 
         if (maybeIntersection && maybeUnion) {
           return this.intersection({...base, nullable}, [
@@ -375,6 +380,29 @@ export class SchemaNormalizer {
     }
   }
 
+  private normalizeDiscriminator(
+    discriminator: Discriminator | undefined,
+  ): IRModelUnion["discriminator"] | undefined {
+    if (!discriminator) {
+      return undefined
+    }
+
+    if (!discriminator.mapping) {
+      // todo: cna we support this if the discriminated property is an enum of one element?
+      logger.warn("discriminators without a mapping are ignored.")
+      return undefined
+    }
+
+    return {
+      propertyName: discriminator.propertyName,
+      mapping: Object.fromEntries(
+        Object.entries(discriminator.mapping).map(([key, value]) => {
+          return [key, {$ref: value}]
+        }),
+      ),
+    }
+  }
+
   private normalizeComposition(
     items: (Schema | Reference)[] = [],
     parent: SchemaObject,
@@ -511,6 +539,7 @@ export class SchemaNormalizer {
   private union(
     base: IRModelBase,
     schemas: MaybeIRModel[],
+    discriminator: Discriminator | undefined,
   ): MaybeIRModel | IRModelUnion | undefined {
     // (A|B)|(C|D) is the same as (A|B|C|D)
     // todo: merge repeated in-line schemas
@@ -530,6 +559,7 @@ export class SchemaNormalizer {
       return {
         ...base,
         type: "union",
+        discriminator: this.normalizeDiscriminator(discriminator),
         schemas,
       }
     }

packages/openapi-code-generator/src/core/openapi-types-normalized.ts

@@ -79,6 +79,16 @@ export interface IRModelUnion extends IRModelBase {
   //       of this.
   type: "union"
   schemas: NonEmptyArray<MaybeIRModel>
+
+  discriminator?:
+    | {
+        propertyName: string
+        mapping: {
+          [propertyValue: string]: IRRef
+        }
+        //todo: support defaultMapping
+      }
+    | undefined
 }
 
 export interface IRModelObject extends IRModelBase {

packages/openapi-code-generator/src/core/openapi-types.ts

@@ -359,8 +359,9 @@ export interface xInternalPreproccess {
 export interface Discriminator {
   propertyName: string
   mapping?: {
-    [k: string]: string
+    [propertyValue: string]: string
   }
+  defaultMapping?: string
 }
 
 export interface Example {

packages/openapi-code-generator/src/test/ir-model.fixtures.test-utils.ts

@@ -115,6 +115,7 @@ const extension = {
     schemas: [base.any],
     nullable: false,
     default: undefined,
+    discriminator: undefined,
     "x-internal-preprocess": undefined,
   } satisfies IRModelUnion,
   null: {
@@ -178,7 +179,6 @@ export const irFixture = {
   ref(path: string, file = ""): IRRef {
     return {
       $ref: `${file}#${path}`,
-      "x-internal-preprocess": undefined,
     }
   },
   any(partial: Partial<IRModelAny> = {}): IRModelAny {