Add @AckType discriminated union extension generation

docs/api-reference/index.mdx

@@ -248,8 +248,12 @@ Annotate an existing schema variable or getter to generate an extension type wra
 - Primitives: `Ack.string()`, `Ack.integer()`, `Ack.double()`, `Ack.boolean()`
 - Collections: `Ack.list(...)`
 - Enums: `Ack.literal()`, `Ack.enumString()`, `Ack.enumValues()`
+- Discriminated unions: `Ack.discriminated(...)`
 
-**Unsupported:** `Ack.any()`, `Ack.anyOf()`, `Ack.discriminated()` (use `@AckModel` for discriminated unions)
+**Unsupported:** `Ack.any()`, `Ack.anyOf()`
+
+For `Ack.discriminated(...)` constraints with `@AckType`, see
+[Type-safe Schemas](../core-concepts/typesafe-schemas.mdx#ackdiscriminated-with-acktype-current-constraints).
 
 **Example:**
 ```dart

docs/core-concepts/json-serialization.mdx

@@ -181,7 +181,7 @@ if (result.isOk) {
 }
 ```
 
-**Note**: Nested schemas annotated with `@AckType()` generate their own extension types. When referenced in object fields or list elements, getters return the typed extension type (e.g., `AddressType`) when the reference can be resolved in the same library; unresolved references fall back to `Map<String, Object?>`.
+**Note**: Nested schemas annotated with `@AckType()` generate their own extension types. Object/list references must be statically resolvable for typed generation; unsupported or unresolved references fail generation instead of falling back to `Map<String, Object?>`. For current `Ack.discriminated(...)` limits, see [Type-safe Schemas](./typesafe-schemas.mdx#ackdiscriminated-with-acktype-current-constraints).
 
 `@AckType()` is only supported on top-level schema variables/getters, not classes.
 

docs/core-concepts/typesafe-schemas.mdx

@@ -113,9 +113,18 @@ After running `dart run build_runner build`, the part file contains:
 - Primitive schemas (`Ack.string`, `Ack.integer`, `Ack.double`, `Ack.boolean`)
 - Lists of supported schemas (`Ack.list(...)`)
 - Literal/enum helpers (`Ack.literal`, `Ack.enumValues`, `Ack.enumString`)
+- `Ack.discriminated(...)` (with constraints below)
 
-Unsupported helpers include `Ack.any`, `Ack.anyOf`, and `Ack.discriminated`.
-Use `@AckModel` for discriminated unions instead.
+Unsupported helpers include `Ack.any` and `Ack.anyOf`.
+
+### `Ack.discriminated(...)` with `@AckType` (Current constraints)
+
+- `schemas` must be a non-empty map literal.
+- Base schema cannot be nullable.
+- Each branch must be a top-level schema variable/getter reference.
+- Each branch must be `@AckType`, object-shaped, non-nullable, and declared in the same library.
+- Branch discriminator literal (`Ack.literal(...)`) must match the branch key in `schemas`.
+- A branch schema can belong to only one discriminated base.
 
 ## `@AckType` Resolution Requirements and Limitations
 

example/lib/schema_types_discriminated.dart

@@ -0,0 +1,23 @@
+import 'package:ack/ack.dart';
+import 'package:ack_annotations/ack_annotations.dart';
+
+part 'schema_types_discriminated.g.dart';
+
+/// Discriminated schema example for @AckType extension generation.
+@AckType()
+final catSchema = Ack.object({
+  'kind': Ack.literal('cat'),
+  'lives': Ack.integer(),
+});
+
+@AckType()
+ObjectSchema get dogSchema => Ack.object({
+  'kind': Ack.literal('dog'),
+  'bark': Ack.boolean(),
+}).passthrough();
+
+@AckType()
+final petSchema = Ack.discriminated(
+  discriminatorKey: 'kind',
+  schemas: {'cat': catSchema, 'dog': dogSchema},
+);

packages/ack_generator/CHANGELOG.md

@@ -1,3 +1,13 @@
+## Unreleased
+
+### Features
+
+* **`@AckType` discriminated unions**: Documented current `Ack.discriminated(...)` support and current constraints.
+
+### Bug Fixes
+
+* **Discriminated validation**: `@AckType` now fails generation when `Ack.discriminated(..., schemas: {})` is empty.
+
 ## 1.0.0-beta.7
 
 * See [release notes](https://github.com/btwld/ack/releases/tag/v1.0.0-beta.7) for details.
@@ -56,4 +66,4 @@
 
 ## 1.0.0-beta.1 (2025-10-06)
 
-* See [release notes](https://github.com/btwld/ack/releases/tag/v1.0.0-beta.1) for details.
+* See [release notes](https://github.com/btwld/ack/releases/tag/v1.0.0-beta.1) for details.

packages/ack_generator/lib/src/analyzer/model_analyzer.dart

@@ -86,11 +86,10 @@ class ModelAnalyzer {
       fields: fields,
       additionalProperties: additionalProperties,
       additionalPropertiesField: additionalPropertiesField,
-      // New discriminated properties
       discriminatorKey: discriminatedKey,
       discriminatorValue: discriminatedValue,
       // subtypes will be populated later in a second pass
-      subtypes: null,
+      subtypeNames: null,
     );
   }
 
@@ -237,6 +236,12 @@ class ModelAnalyzer {
     final subtypes = <ModelInfo>[];
 
     for (final modelInfo in modelInfos) {
+      if (modelInfo.isFromSchemaVariable) {
+        // Schema-variable models are linked in a separate pass.
+        updatedModelInfos.add(modelInfo);
+        continue;
+      }
+
       if (modelInfo.isDiscriminatedBase) {
         baseClasses.add(modelInfo);
       } else if (modelInfo.isDiscriminatedSubtype) {
@@ -250,7 +255,7 @@ class ModelAnalyzer {
     // For each base class, find and validate its subtypes
     for (final baseClass in baseClasses) {
       final discriminatorKey = baseClass.discriminatorKey!;
-      final matchingSubtypes = <String, ClassElement2>{};
+      final matchingSubtypeNames = <String, String>{};
 
       // Find subtypes that belong to this base class
       for (final subtype in subtypes) {
@@ -266,15 +271,15 @@ class ModelAnalyzer {
           final discriminatorValue = subtype.discriminatorValue!;
 
           // Validate no duplicate discriminator values
-          if (matchingSubtypes.containsKey(discriminatorValue)) {
+          if (matchingSubtypeNames.containsKey(discriminatorValue)) {
             throw ArgumentError(
               'Duplicate discriminator value "$discriminatorValue" found in '
-              '${subtype.className} and ${matchingSubtypes[discriminatorValue]!.name3}. '
+              '${subtype.className} and ${matchingSubtypeNames[discriminatorValue]}. '
               'Each discriminator value must be unique within the hierarchy.',
             );
           }
 
-          matchingSubtypes[discriminatorValue] = subtypeElement;
+          matchingSubtypeNames[discriminatorValue] = subtype.className;
 
           // Validate the discriminator field override
           _validateDiscriminatorOverride(
@@ -295,7 +300,7 @@ class ModelAnalyzer {
         additionalPropertiesField: baseClass.additionalPropertiesField,
         discriminatorKey: discriminatorKey,
         discriminatorValue: null,
-        subtypes: matchingSubtypes,
+        subtypeNames: matchingSubtypeNames,
       );
 
       updatedModelInfos.add(updatedBaseClass);
@@ -305,6 +310,7 @@ class ModelAnalyzer {
     for (final subtype in subtypes) {
       // Find the parent discriminator key for this subtype
       String? parentDiscriminatorKey;
+      String? parentBaseClassName;
       for (final baseClass in baseClasses) {
         final subtypeElement = elementsByName[subtype.className];
         if (subtypeElement == null) {
@@ -314,6 +320,7 @@ class ModelAnalyzer {
         }
         if (_isSubtypeOf(subtypeElement, baseClass.className)) {
           parentDiscriminatorKey = baseClass.discriminatorKey;
+          parentBaseClassName = baseClass.className;
           break;
         }
       }
@@ -329,7 +336,8 @@ class ModelAnalyzer {
         discriminatorKey:
             parentDiscriminatorKey, // Add parent's discriminator key
         discriminatorValue: subtype.discriminatorValue,
-        subtypes: null,
+        subtypeNames: null,
+        discriminatedBaseClassName: parentBaseClassName,
       );
 
       updatedModelInfos.add(updatedSubtype);
@@ -340,20 +348,9 @@ class ModelAnalyzer {
 
   /// Checks if a class extends another class (direct or indirect inheritance)
   bool _isSubtypeOf(ClassElement2 element, String baseClassName) {
-    // Check direct superclass
-    final supertype = element.supertype;
-    if (supertype?.element3.name3 == baseClassName) {
-      return true;
-    }
-
-    // Check indirect inheritance through supertypes
-    for (final supertype in element.allSupertypes) {
-      if (supertype.element3.name3 == baseClassName) {
-        return true;
-      }
-    }
-
-    return false;
+    return element.allSupertypes.any(
+      (supertype) => supertype.element3.name3 == baseClassName,
+    );
   }
 
   /// Validates that the discriminator field or getter is properly overridden in subtype
@@ -363,10 +360,12 @@ class ModelAnalyzer {
     String expectedValue,
   ) {
     // First check for field override
-    final discriminatorField = element.fields2.cast<FieldElement2?>().firstWhere(
-      (field) => field?.name3 == discriminatorKey,
-      orElse: () => null,
-    );
+    final discriminatorField = element.fields2
+        .cast<FieldElement2?>()
+        .firstWhere(
+          (field) => field?.name3 == discriminatorKey,
+          orElse: () => null,
+        );
 
     if (discriminatorField != null) {
       // For fields, we can't easily validate the returned value at compile time
@@ -383,10 +382,12 @@ class ModelAnalyzer {
     }
 
     // Check for getter override
-    final discriminatorGetter = element.getters2.cast<GetterElement?>().firstWhere(
-      (getter) => getter?.name3 == discriminatorKey,
-      orElse: () => null,
-    );
+    final discriminatorGetter = element.getters2
+        .cast<GetterElement?>()
+        .firstWhere(
+          (getter) => getter?.name3 == discriminatorKey,
+          orElse: () => null,
+        );
 
     if (discriminatorGetter != null) {
       // For getters, validate return type