fix(protographic): enforce using __typename in composite types for requires

protographic/.gitignore

@@ -2,4 +2,5 @@ dist
 out
 node_modules
 .env
-.eslintcache
+.eslintcache
+coverage

protographic/SDL_PROTO_RULES.md

@@ -43,8 +43,6 @@ Rules should follow [Proto Best Practices](https://protobuf.dev/best-practices/d
 #### Federation Features
 
 - ✗ Federation entity lookups with nested keys
-- ✗ Abstract types (interfaces/unions) in @requires field selections
-- ✗ Inline fragments in @requires field selections
 
 #### GraphQL Features
 
@@ -289,6 +287,115 @@ message RequireProductNameByIdFields {
 - Only the selected fields from nested types are included (e.g., `description` and `reviewSummary` from `ProductDetails`, not `id` or `title`)
 - Field order in the proto matches the normalized selection order
 
+#### Composite Types in Required Fields (Interfaces & Unions)
+
+When `@requires` references a field whose type is an interface or union, the required field selection must include inline fragments to specify which fields to extract from each concrete type.
+
+##### The `__typename` Requirement
+
+When using inline fragments on an interface or union field in `@requires`, `__typename` must be present in the selection set. This is required for the engine to determine which concrete type to deserialize at runtime. Validation produces errors with field paths (e.g., `in "pet.friend"`) for nested selections missing `__typename`.
+
+Example:
+
+```graphql
+@requires(fields: "primaryItem { __typename ... on PalletItem { name } ... on ContainerItem { name } }")
+```
+
+##### Selection Normalization
+
+Before proto generation, selections are normalized by distributing parent-level fields into each inline fragment. For example:
+
+```graphql
+media { id ... on Book { author } ... on Movie { director } }
+```
+
+Normalizes to:
+
+```graphql
+media { ... on Book { id author } ... on Movie { id director } }
+```
+
+This ensures each fragment is self-contained. Nested inline fragments on sub-interfaces are also flattened to concrete types. For example, given `Employee` (interface) with implementors `Manager`, `Engineer`, `Contractor`, and `Intern` — where `Engineer` and `Contractor` also implement `Managed`:
+
+```graphql
+# Before normalization:
+members {
+  id
+  ... on Managed { supervisor }
+}
+
+# After normalization — expanded to all concrete types,
+# with `supervisor` only on types that implement Managed:
+members {
+  ... on Manager { id }
+  ... on Engineer { id supervisor }
+  ... on Contractor { id supervisor }
+  ... on Intern { id }
+}
+```
+
+##### Proto Mapping — Interface/Union Becomes `oneof`
+
+The interface or union type maps to a message with `oneof instance` containing each concrete type. `__typename` is consumed during validation only — it does **not** appear in the generated proto.
+
+```graphql
+type Storage @key(fields: "id") {
+  id: ID!
+  primaryItem: StorageItem! @external
+  itemInfo: String!
+    @requires(
+      fields: "primaryItem { __typename ... on PalletItem { name palletCount } ... on ContainerItem { name containerSize } }"
+    )
+}
+
+interface StorageItem {
+  name: String!
+}
+
+type PalletItem implements StorageItem {
+  name: String!
+  palletCount: Int!
+}
+
+type ContainerItem implements StorageItem {
+  name: String!
+  containerSize: String!
+}
+```
+
+Maps to (Fields message only):
+
+```protobuf
+message RequireStorageItemInfoByIdFields {
+  message PalletItem {
+    string name = 1;
+    int32 pallet_count = 2;
+  }
+
+  message ContainerItem {
+    string name = 1;
+    string container_size = 2;
+  }
+
+  message StorageItem {
+    oneof instance {
+      ContainerItem container_item = 1;
+      PalletItem pallet_item = 2;
+    }
+  }
+
+  StorageItem primary_item = 1;
+}
+```
+
+**Key Points**:
+
+- `__typename` is absent from the proto — it is consumed during validation only
+- The interface type becomes a message with `oneof instance`
+- Each implementing type gets its own message with only the fields selected in its fragment
+- All type messages (`StorageItem`, `PalletItem`, `ContainerItem`) are **nested inside** the `Fields` message. This scoping ensures they don't collide with the root-level messages of the same name, which contain all fields of the type — while the nested versions contain only the subset selected in `@requires`
+- The same pattern applies to union types (union member types instead of implementing types)
+
 ## Field Resolvers
 
 Field resolvers allow you to define custom resolution logic for specific fields within a GraphQL type. Using the `@connect__fieldResolver` directive, you can specify which fields should be resolved through dedicated RPC methods, enabling lazy loading, computed fields, or integration with external data sources.

protographic/src/abstract-selection-rewriter.ts

@@ -630,7 +630,7 @@ export class AbstractSelectionRewriter {
       // the wrong inline fragments.
       const fieldsToAdd = fields
         .filter((field) => !existingFields.has(field.name.value))
-        .filter((field) => inlineFragmentType.getFields()[field.name.value]);
+        .filter((field) => field.name.value === '__typename' || inlineFragmentType.getFields()[field.name.value]);
 
       // Add the interface fields to the fragment. We always prepend them for now.
       // TODO: Check if fields should be inserted in the order of appearance in the selection set.

protographic/src/required-fields-visitor.ts

@@ -365,7 +365,7 @@ export class RequiredFieldsVisitor {
    * @throws Error if the field definition is not found on the current type
    */
   private onEnterField(ctx: VisitContext<FieldNode>): void {
-    if (!this.current) {
+    if (!this.current || ctx.node.name.value === '__typename') {
       return;
     }
 

protographic/src/sdl-validation-visitor.ts

@@ -13,8 +13,13 @@ import {
   NamedTypeNode,
   GraphQLID,
   ConstArgumentNode,
+  GraphQLObjectType,
+  GraphQLSchema,
+  buildASTSchema,
 } from 'graphql';
-import { CONNECT_FIELD_RESOLVER, CONTEXT } from './string-constants.js';
+import { safeParse } from '@wundergraph/composition';
+import { CONNECT_FIELD_RESOLVER, CONTEXT, FIELDS, REQUIRES_DIRECTIVE_NAME } from './string-constants.js';
+import { SelectionSetValidationVisitor } from './selection-set-validation-visitor.js';
 
 /**
  * Type mapping from Kind enum values to their corresponding AST node types
@@ -48,8 +53,6 @@ interface LintingRule<K extends keyof KindToNodeTypeMap = keyof KindToNodeTypeMa
   name: string;
   /** Human-readable description of what this rule validates */
   description?: string;
-  /** Whether this validation rule is currently active */
-  enabled: boolean;
   /** The AST node kind this rule applies to */
   nodeKind: K;
   /** The validation function to execute for matching nodes */
@@ -89,6 +92,7 @@ export class SDLValidationVisitor {
   private readonly validationResult: ValidationResult;
   private lintingRules: LintingRule<any>[] = [];
   private visitor: ASTVisitor;
+  private parsedSchema: GraphQLSchema;
 
   /**
    * Creates a new SDL validation visitor for the given GraphQL schema
@@ -101,6 +105,8 @@ export class SDLValidationVisitor {
       warnings: [],
     };
 
+    this.parsedSchema = buildASTSchema(parse(schema), { assumeValid: true, assumeValidSDL: true });
+
     this.initializeLintingRules();
     this.visitor = this.createASTVisitor();
   }
@@ -114,36 +120,88 @@ export class SDLValidationVisitor {
     const objectTypeRule: LintingRule<Kind.OBJECT_TYPE_DEFINITION> = {
       name: 'nested-key-directives',
       description: 'Validates that @key directives do not contain nested field selections',
-      enabled: true,
       nodeKind: Kind.OBJECT_TYPE_DEFINITION,
       validationFunction: (ctx) => this.validateObjectTypeKeyDirectives(ctx),
     };
 
     const listTypeRule: LintingRule<Kind.LIST_TYPE> = {
       name: 'nullable-items-in-list-types',
       description: 'Validates that list types do not contain nullable items',
-      enabled: true,
       nodeKind: Kind.LIST_TYPE,
       validationFunction: (ctx) => this.validateListTypeNullability(ctx),
     };
 
     const providesRule: LintingRule<Kind.FIELD_DEFINITION> = {
       name: 'use-of-provides',
       description: 'Validates usage of @provides directive which is not yet supported',
-      enabled: true,
       nodeKind: Kind.FIELD_DEFINITION,
       validationFunction: (ctx) => this.validateProvidesDirective(ctx),
     };
 
     const resolverContextRule: LintingRule<Kind.FIELD_DEFINITION> = {
       name: 'use-of-invalid-resolver-context',
       description: 'Validates whether a resolver context can be extracted from a type',
-      enabled: true,
       nodeKind: Kind.FIELD_DEFINITION,
       validationFunction: (ctx) => this.validateInvalidResolverContext(ctx),
     };
 
-    this.lintingRules = [objectTypeRule, listTypeRule, providesRule, resolverContextRule];
+    const compositeTypeReflectionRule: LintingRule<Kind.FIELD_DEFINITION> = {
+      name: 'use-of-typename',
+      description: 'Validates that __typename is present for composite types in @requires selections',
+      nodeKind: Kind.FIELD_DEFINITION,
+      validationFunction: (ctx) => this.validateCompositeTypeReflection(ctx),
+    };
+
+    this.lintingRules = [objectTypeRule, listTypeRule, providesRule, resolverContextRule, compositeTypeReflectionRule];
+  }
+
+  private validateCompositeTypeReflection(ctx: VisitContext<FieldDefinitionNode>): void {
+    const directive = ctx.node.directives?.find((directive) => directive.name.value === REQUIRES_DIRECTIVE_NAME);
+    if (!directive) {
+      return;
+    }
+
+    const fieldSet = directive.arguments?.find((arg) => arg.name.value === FIELDS);
+    if (!fieldSet) {
+      return;
+    }
+
+    if (fieldSet.value.kind !== Kind.STRING) {
+      this.addError('Invalid @requires directive: fields argument must be a string', fieldSet.loc);
+      return;
+    }
+
+    const fieldSetValue = fieldSet.value.value;
+    const { error, documentNode } = safeParse('{' + fieldSetValue + '}');
+    if (error || !documentNode) {
+      this.addError('Invalid @requires directive: fields argument must be a valid GraphQL selection set', fieldSet.loc);
+      return;
+    }
+
+    const parentNode = ctx.ancestors.at(-1);
+    if (!parentNode || !this.isASTObjectTypeNode(parentNode)) {
+      this.addError('Invalid @requires directive: fields argument must be a valid GraphQL selection set', fieldSet.loc);
+      return;
+    }
+
+    const objectType = this.parsedSchema.getType(parentNode.name.value) as GraphQLObjectType;
+    if (!objectType) {
+      this.addError('Invalid @requires directive: parent type not found', fieldSet.loc);
+      return;
+    }
+
+    const visitor = new SelectionSetValidationVisitor(documentNode, objectType, this.parsedSchema);
+
+    visitor.visit();
+
+    const { errors, warnings } = visitor.getValidationResult();
+    for (const error of errors) {
+      this.addError(error, fieldSet.loc);
+    }
+
+    for (const warning of warnings) {
+      this.addWarning(warning, fieldSet.loc);
+    }
   }
 
   /**
@@ -213,7 +271,7 @@ export class SDLValidationVisitor {
    * @private
    */
   private executeValidationRules(ctx: VisitContext<ASTNode>): void {
-    const applicableRules = this.lintingRules.filter((rule) => rule.nodeKind === ctx.node.kind && rule.enabled);
+    const applicableRules = this.lintingRules.filter((rule) => rule.nodeKind === ctx.node.kind);
 
     for (const rule of applicableRules) {
       // Type assertion is safe here because we've filtered by nodeKind
@@ -572,45 +630,6 @@ export class SDLValidationVisitor {
     return !Array.isArray(node) && 'kind' in node && node.kind === Kind.OBJECT_TYPE_DEFINITION;
   }
 
-  /**
-   * Enable or disable a specific validation rule by name
-   * @param ruleName - The name of the rule to configure
-   * @param enabled - Whether the rule should be enabled
-   * @returns true if the rule was found and configured, false otherwise
-   */
-  public configureRule(ruleName: string, enabled: boolean): boolean {
-    const rule = this.lintingRules.find((gate) => gate.name === ruleName);
-    if (rule) {
-      rule.enabled = enabled;
-      return true;
-    }
-    return false;
-  }
-
-  /**
-   * Get information about all available validation rules
-   * @returns Array of rule configurations
-   */
-  public getAvailableRules(): Readonly<LintingRule<any>[]> {
-    return Object.freeze([...this.lintingRules]);
-  }
-
-  /**
-   * Check if the validation found any critical errors
-   * @returns true if errors were found, false otherwise
-   */
-  public hasErrors(): boolean {
-    return this.validationResult.errors.length > 0;
-  }
-
-  /**
-   * Check if the validation found any warnings
-   * @returns true if warnings were found, false otherwise
-   */
-  public hasWarnings(): boolean {
-    return this.validationResult.warnings.length > 0;
-  }
-
   /**
    * Add a warning to the validation results
    * @param message - The warning message