Merge pull request #3120 from hey-api/copilot/fix-wrong-discriminator-issue

.changeset/happy-points-run.md

···
+---
+"@hey-api/openapi-ts": patch
+---
+
+**plugin(@hey-api/typescript)**: improve type narrowing in discriminated types

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/discriminator-all-of/types.gen.ts

···
     id: string;
 };
 
-export type Bar = Foo & {
+export type Bar = Omit<Foo, 'id'> & {
     bar?: string;
     id: 'Bar';
 };
 
-export type Baz = Foo & {
+export type Baz = Omit<Foo, 'id'> & {
     baz?: string;
     id: 'Baz';
 };
 
-export type Qux = Foo & {
+export type Qux = Omit<Foo, 'id'> & {
     qux?: boolean;
     id: 'Qux';
 };
···
     id: string;
 };
 
-export type BarMapped = FooMapped & {
+export type BarMapped = Omit<FooMapped, 'id'> & {
     bar?: string;
     id: 'bar';
 };
 
-export type BazMapped = FooMapped & {
+export type BazMapped = Omit<FooMapped, 'id'> & {
     baz?: string;
     id: 'baz';
 };
 
-export type QuxMapped = FooMapped & {
+export type QuxMapped = Omit<FooMapped, 'id'> & {
     qux?: boolean;
     id: 'QuxMapped';
 };

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/discriminator-allof-nested/types.gen.ts

···
     id: number;
 };
 
-export type CarDto = VehicleDto & {
+export type CarDto = Omit<VehicleDto, '$type'> & {
     modelName: string;
-    $type: 'Car' | 'Volvo';
+    $type: 'Car';
 };
 
-export type VolvoDto = CarDto & {
+export type VolvoDto = Omit<CarDto, '$type'> & {
     seatbeltCount: number;
     $type: 'Volvo';
 };

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/types.gen.ts

···
     bar: 'foo' | 'bar' | 'baz';
 };
 
-export type Baz = Qux & {
+export type Baz = Omit<Qux, 'id'> & {
     foo: number;
     bar: Date;
     baz: 'foo' | 'bar' | 'baz';

packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/discriminator-all-of/types.gen.ts

···
     id: string;
 };
 
-export type Bar = Foo & {
+export type Bar = Omit<Foo, 'id'> & {
     bar?: string;
     id: 'Bar';
 };
 
-export type Baz = Foo & {
+export type Baz = Omit<Foo, 'id'> & {
     baz?: string;
     id: 'Baz';
 };
 
-export type Qux = Foo & {
+export type Qux = Omit<Foo, 'id'> & {
     qux?: boolean;
     id: 'Qux';
 };
···
     id: string;
 };
 
-export type BarMapped = FooMapped & {
+export type BarMapped = Omit<FooMapped, 'id'> & {
     bar?: string;
     id: 'bar';
 };
 
-export type BazMapped = FooMapped & {
+export type BazMapped = Omit<FooMapped, 'id'> & {
     baz?: string;
     id: 'baz';
 };
 
-export type QuxMapped = FooMapped & {
+export type QuxMapped = Omit<FooMapped, 'id'> & {
     qux?: boolean;
     id: 'QuxMapped';
 };

packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/discriminator-allof-nested/types.gen.ts

···
     id: number;
 };
 
-export type CarDto = VehicleDto & {
+export type CarDto = Omit<VehicleDto, '$type'> & {
     modelName: string;
-    $type: 'Car' | 'Volvo';
+    $type: 'Car';
 };
 
-export type VolvoDto = CarDto & {
+export type VolvoDto = Omit<CarDto, '$type'> & {
     seatbeltCount: number;
     $type: 'Volvo';
 };

packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/types.gen.ts

···
     bar: 'foo' | 'bar' | 'baz';
 };
 
-export type Baz = Qux & {
+export type Baz = Omit<Qux, 'id'> & {
     foo: number;
     bar: Date;
     baz: 'foo' | 'bar' | 'baz';

packages/openapi-ts/src/ir/types.d.ts

···
    */
   logicalOperator?: 'and' | 'or';
   /**
+   * When used with `$ref` or `symbolRef`, specifies properties to omit from the referenced schema.
+   * Useful for handling discriminator property conflicts in allOf compositions.
+   */
+  omit?: ReadonlyArray<string>;
+  /**
    * When type is `object`, `patternProperties` can be used to define a schema
    * for properties that match a specific regex pattern.
    */

packages/openapi-ts/src/openApi/3.0.x/parser/schema.ts

···
 };
 
 /**
- * Gets all discriminator values for a schema and its children in the inheritance hierarchy.
- * For intermediate schemas (those that are extended by others), returns a union of all values.
+ * Gets the discriminator value for a schema.
+ * Returns only the schema's own discriminator value, not child values.
  */
 const getAllDiscriminatorValues = ({
-  context,
   discriminator,
   schemaRef,
 }: {
-  context: Context;
   discriminator: NonNullable<SchemaObject['discriminator']>;
   schemaRef: string;
 }): Array<string> => {
···
     if (mappedSchemaRef === schemaRef) {
       // This is the current schema's own value
       values.push(value);
-      continue;
-    }
-
-    // Check if the mapped schema extends the current schema
-    const mappedSchema = context.resolveRef<SchemaObject>(mappedSchemaRef);
-    if (mappedSchema.allOf) {
-      for (const item of mappedSchema.allOf) {
-        if ('$ref' in item && item.$ref === schemaRef) {
-          // This schema extends the current schema, add its value
-          values.push(value);
-          break;
-        }
-      }
     }
   }
 
···
   for (const { discriminator, isRequired, values } of discriminatorsToAdd) {
     // Get all discriminator values including children for union types
     const allValues = getAllDiscriminatorValues({
-      context,
       discriminator,
       schemaRef: state.$ref!,
     });
···
             logicalOperator: 'or',
           }
         : valueSchemas[0]!;
+
+    // Check if any $ref schemas in schemaItems have this discriminator property
+    // If yes, mark them to omit it to avoid conflicts
+    for (const item of schemaItems) {
+      if (item.$ref || item.symbolRef) {
+        // Check if the referenced schema has this property
+        const hasProperty = (() => {
+          if (!item.$ref) return false;
+          try {
+            const refSchema = context.resolveRef<SchemaObject>(item.$ref);
+            // Check if the discriminator property exists in the ref schema
+            return (
+              refSchema.properties?.[discriminator.propertyName] !==
+                undefined ||
+              (refSchema.allOf &&
+                refSchema.allOf.some((allOfItem) => {
+                  const resolved =
+                    '$ref' in allOfItem
+                      ? context.resolveRef<SchemaObject>(allOfItem.$ref)
+                      : allOfItem;
+                  return (
+                    resolved.properties?.[discriminator.propertyName] !==
+                    undefined
+                  );
+                }))
+            );
+          } catch {
+            return false;
+          }
+        })();
+
+        if (hasProperty) {
+          // Mark this ref to omit the discriminator property
+          if (!item.omit) {
+            item.omit = [discriminator.propertyName];
+          } else if (!item.omit.includes(discriminator.propertyName)) {
+            item.omit = [...item.omit, discriminator.propertyName];
+          }
+        }
+      }
+    }
 
     // Find the inline schema (non-$ref) to merge the discriminator property into
     // The inline schema should be the last non-$ref item in schemaItems

packages/openapi-ts/src/openApi/3.1.x/parser/schema.ts

···
 };
 
 /**
- * Gets all discriminator values for a schema and its children in the inheritance hierarchy.
- * For intermediate schemas (those that are extended by others), returns a union of all values.
+ * Gets the discriminator value for a schema.
+ * Returns only the schema's own discriminator value, not child values.
  */
 const getAllDiscriminatorValues = ({
-  context,
   discriminator,
   schemaRef,
 }: {
-  context: Context;
   discriminator: NonNullable<SchemaObject['discriminator']>;
   schemaRef: string;
 }): Array<string> => {
···
     if (mappedSchemaRef === schemaRef) {
       // This is the current schema's own value
       values.push(value);
-      continue;
-    }
-
-    // Check if the mapped schema extends the current schema
-    const mappedSchema = context.resolveRef<SchemaObject>(mappedSchemaRef);
-    if (mappedSchema.allOf) {
-      for (const item of mappedSchema.allOf) {
-        if (item.$ref && item.$ref === schemaRef) {
-          // This schema extends the current schema, add its value
-          values.push(value);
-          break;
-        }
-      }
     }
   }
 
···
   for (const { discriminator, isRequired, values } of discriminatorsToAdd) {
     // Get all discriminator values including children for union types
     const allValues = getAllDiscriminatorValues({
-      context,
       discriminator,
       schemaRef: state.$ref!,
     });
···
             logicalOperator: 'or',
           }
         : valueSchemas[0]!;
+
+    // Check if any $ref schemas in schemaItems have this discriminator property
+    // If yes, mark them to omit it to avoid conflicts
+    for (const item of schemaItems) {
+      if (item.$ref || item.symbolRef) {
+        // Check if the referenced schema has this property
+        const hasProperty = (() => {
+          if (!item.$ref) return false;
+          try {
+            const refSchema = context.resolveRef<SchemaObject>(item.$ref);
+            // Check if the discriminator property exists in the ref schema
+            return (
+              refSchema.properties?.[discriminator.propertyName] !==
+                undefined ||
+              (refSchema.allOf &&
+                refSchema.allOf.some((allOfItem) => {
+                  const resolved = allOfItem.$ref
+                    ? context.resolveRef<SchemaObject>(allOfItem.$ref)
+                    : allOfItem;
+                  return (
+                    resolved.properties?.[discriminator.propertyName] !==
+                    undefined
+                  );
+                }))
+            );
+          } catch {
+            return false;
+          }
+        })();
+
+        if (hasProperty) {
+          // Mark this ref to omit the discriminator property
+          if (!item.omit) {
+            item.omit = [discriminator.propertyName];
+          } else if (!item.omit.includes(discriminator.propertyName)) {
+            item.omit = [...item.omit, discriminator.propertyName];
+          }
+        }
+      }
+    }
 
     // Find the inline schema (non-$ref) to merge the discriminator property into
     // The inline schema should be the last non-$ref item in schemaItems

packages/openapi-ts/src/plugins/@hey-api/typescript/v1/plugin.ts

···
   schema: IR.SchemaObject;
 }): MaybeTsDsl<TypeTsDsl> => {
   if (schema.symbolRef) {
-    return $.type(schema.symbolRef);
+    const baseType = $.type(schema.symbolRef);
+    if (schema.omit && schema.omit.length > 0) {
+      // Render as Omit<Type, 'prop1' | 'prop2'>
+      const omittedKeys =
+        schema.omit.length === 1
+          ? $.type.literal(schema.omit[0]!)
+          : $.type.or(...schema.omit.map((key) => $.type.literal(key)));
+      return $.type('Omit').generics(baseType, omittedKeys);
+    }
+    return baseType;
   }
 
   if (schema.$ref) {
···
       resource: 'definition',
       resourceId: schema.$ref,
     });
-    return $.type(symbol);
+    const baseType = $.type(symbol);
+    if (schema.omit && schema.omit.length > 0) {
+      // Render as Omit<Type, 'prop1' | 'prop2'>
+      const omittedKeys =
+        schema.omit.length === 1
+          ? $.type.literal(schema.omit[0]!)
+          : $.type.or(...schema.omit.map((key) => $.type.literal(key)));
+      return $.type('Omit').generics(baseType, omittedKeys);
+    }
+    return baseType;
   }
 
   if (schema.type) {