fix(zod): generate z.discriminatedUnion for multi-value discriminator mappings

When an OpenAPI discriminator maps multiple values to the same schema
(e.g. mapping: { one: Bar, two: Bar }), the zod plugin previously fell
back to z.union(), losing discriminator-aware narrowing.

- Extend tryBuildDiscriminatedUnion to recognise the IR's
  logicalOperator:'or' of const-items shape for multi-value mappings
- Add buildDiscriminatorExpression helper: z.literal for scalars,
  z.enum for all-string arrays, z.union of literals for non-string arrays
- v3 dialect expands non-string multi-value members to one branch per
  literal (ZodUnion is not a valid v3 discriminator node)
- v4 and mini emit z.union of literals directly (valid via _zod.values
  flattening in $ZodDiscriminatedUnion)
- Add discriminator-mapped-many and discriminator-mapped-many-number
  scenarios to all four test cells (zod v3/v4 x OpenAPI 3.0.x/3.1.x)

Author: CallumJHays

.changeset/fix-zod-discriminated-union-multi-value.md

@@ -0,0 +1,5 @@
+---
+'@hey-api/openapi-ts': patch
+---
+
+fix(zod): generate z.discriminatedUnion when discriminator maps multiple values to the same schema

packages/openapi-ts-tests/zod/v3/__snapshots__/3.0.x/mini/discriminator-mapped-many-number/zod.gen.ts

@@ -0,0 +1,16 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod/v4-mini';
+
+export const zBar = z.object({
+    code: z.optional(z.union([z.literal(1), z.literal(2)]))
+});
+
+export const zBaz = z.object({
+    code: z.optional(z.literal(3))
+});
+
+export const zFoo = z.discriminatedUnion('code', [
+    z.extend(zBar, { code: z.union([z.literal(1), z.literal(2)]) }),
+    z.extend(zBaz, { code: z.literal(3) })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.0.x/mini/discriminator-mapped-many/zod.gen.ts

@@ -0,0 +1,21 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod/v4-mini';
+
+export const zBar = z.object({
+    foo: z.optional(z.enum(['one', 'two']))
+});
+
+export const zBaz = z.object({
+    foo: z.optional(z.enum(['three']))
+});
+
+export const zSpæcial = z.object({
+    foo: z.optional(z.enum(['four']))
+});
+
+export const zFoo = z.discriminatedUnion('foo', [
+    z.extend(zBar, { foo: z.enum(['one', 'two']) }),
+    z.extend(zBaz, { foo: z.literal('three') }),
+    z.extend(zSpæcial, { foo: z.literal('four') })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.0.x/v3/discriminator-mapped-many-number/zod.gen.ts

@@ -0,0 +1,17 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { z } from 'zod';
+
+export const zBar = z.object({
+    code: z.union([z.literal(1), z.literal(2)]).optional()
+});
+
+export const zBaz = z.object({
+    code: z.literal(3).optional()
+});
+
+export const zFoo = z.discriminatedUnion('code', [
+    zBar.extend({ code: z.literal(1) }),
+    zBar.extend({ code: z.literal(2) }),
+    zBaz.extend({ code: z.literal(3) })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.0.x/v3/discriminator-mapped-many/zod.gen.ts

@@ -0,0 +1,21 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { z } from 'zod';
+
+export const zBar = z.object({
+    foo: z.enum(['one', 'two']).optional()
+});
+
+export const zBaz = z.object({
+    foo: z.enum(['three']).optional()
+});
+
+export const zSpæcial = z.object({
+    foo: z.enum(['four']).optional()
+});
+
+export const zFoo = z.discriminatedUnion('foo', [
+    zBar.extend({ foo: z.enum(['one', 'two']) }),
+    zBaz.extend({ foo: z.literal('three') }),
+    zSpæcial.extend({ foo: z.literal('four') })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.0.x/v4/discriminator-mapped-many-number/zod.gen.ts

@@ -0,0 +1,16 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod/v4';
+
+export const zBar = z.object({
+    code: z.union([z.literal(1), z.literal(2)]).optional()
+});
+
+export const zBaz = z.object({
+    code: z.literal(3).optional()
+});
+
+export const zFoo = z.discriminatedUnion('code', [
+    zBar.extend({ code: z.union([z.literal(1), z.literal(2)]) }),
+    zBaz.extend({ code: z.literal(3) })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.0.x/v4/discriminator-mapped-many/zod.gen.ts

@@ -0,0 +1,21 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod/v4';
+
+export const zBar = z.object({
+    foo: z.enum(['one', 'two']).optional()
+});
+
+export const zBaz = z.object({
+    foo: z.enum(['three']).optional()
+});
+
+export const zSpæcial = z.object({
+    foo: z.enum(['four']).optional()
+});
+
+export const zFoo = z.discriminatedUnion('foo', [
+    zBar.extend({ foo: z.enum(['one', 'two']) }),
+    zBaz.extend({ foo: z.literal('three') }),
+    zSpæcial.extend({ foo: z.literal('four') })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/mini/discriminator-mapped-many-number/zod.gen.ts

@@ -0,0 +1,16 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod/v4-mini';
+
+export const zBar = z.object({
+    code: z.optional(z.union([z.literal(1), z.literal(2)]))
+});
+
+export const zBaz = z.object({
+    code: z.optional(z.literal(3))
+});
+
+export const zFoo = z.discriminatedUnion('code', [
+    z.extend(zBar, { code: z.union([z.literal(1), z.literal(2)]) }),
+    z.extend(zBaz, { code: z.literal(3) })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/mini/discriminator-mapped-many/zod.gen.ts

@@ -0,0 +1,21 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import * as z from 'zod/v4-mini';
+
+export const zBar = z.object({
+    foo: z.optional(z.enum(['one', 'two']))
+});
+
+export const zBaz = z.object({
+    foo: z.optional(z.enum(['three']))
+});
+
+export const zSpæcial = z.object({
+    foo: z.optional(z.enum(['four']))
+});
+
+export const zFoo = z.discriminatedUnion('foo', [
+    z.extend(zBar, { foo: z.enum(['one', 'two']) }),
+    z.extend(zBaz, { foo: z.literal('three') }),
+    z.extend(zSpæcial, { foo: z.literal('four') })
+]);

packages/openapi-ts-tests/zod/v3/__snapshots__/3.1.x/v3/discriminator-mapped-many-number/zod.gen.ts

@@ -0,0 +1,17 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { z } from 'zod';
+
+export const zBar = z.object({
+    code: z.union([z.literal(1), z.literal(2)]).optional()
+});
+
+export const zBaz = z.object({
+    code: z.literal(3).optional()
+});
+
+export const zFoo = z.discriminatedUnion('code', [
+    zBar.extend({ code: z.literal(1) }),
+    zBar.extend({ code: z.literal(2) }),
+    zBaz.extend({ code: z.literal(3) })
+]);