Implement shared response type classes in GraphQL client generator

[devin-ai-integration]

📝 Description

This PR implements shared response type classes in the GraphQL Kotlin client generator to eliminate duplicate type generation across operations. Previously, when multiple queries used the same GraphQL types, the generator would create separate classes in operation-specific packages (e.g., com.example.generated.firstquery.User and com.example.generated.secondquery.User). This PR changes the generator to create shared type classes in a common .types package when operations select identical fields.

Key Changes:

1. Generator-level type caching: Moved classNameCache, typeToSelectionSetMap, and enumClassToTypeSpecs from context-level to generator-level so they can be shared across all operations during generation.

2. Package structure change: Response types now use ${packageName}.types instead of ${packageName}.${operationName.lowercase()}, following the same pattern as existing shared types (.inputs, .enums).

3. Enhanced type collection:

   • Polymorphic types (interfaces/unions) are collected differently based on serialization strategy:
     • Kotlinx: Sealed class with all implementations in a single file (required by kotlinx.serialization)
     • Jackson: Interface and implementations in separate files
   • Non-polymorphic response types in the .types package are collected into shared types
   • Query processing is now sorted by filename for deterministic type numbering

4. Preserved functionality:

   • Type numbering logic (User, User2, User3) still works when different operations select different fields from the same GraphQL type
   • Enum default values (__UNKNOWN_VALUE) are preserved across operations
   • Fallback implementation classes for interfaces/unions use the shared package

Impact:

• Breaking change: Fully qualified type names have changed from operation-specific to shared packages
• Benefit: Reduces code duplication and allows operations to share type instances directly
• Test coverage: Updated 157 test expectation files to reflect new package structure

Example:

Before:

// FirstQuery.kt
import com.expediagroup.graphql.generated.firstquery.ComplexObject

// SecondQuery.kt  
import com.expediagroup.graphql.generated.secondquery.ComplexObject

After:

// Both queries import from shared package
import com.expediagroup.graphql.generated.types.ComplexObject
import com.expediagroup.graphql.generated.types.ComplexObject2  // Different field selection

🔗 Related Issues

Requested by: @arthurkkp-cog (Arthur Poon)
Link to Devin run: https://app.devin.ai/sessions/46723e01f5414e538819c44c6ee54652

🔍 Review Checklist

Critical areas to review:

1. Package structure change: This is a breaking change. Verify the new .types package naming is acceptable and aligns with project conventions.

2. Polymorphic type handling: Check the different logic paths for Kotlinx (sealed classes) vs Jackson (separate files). Pay special attention to:

   • GraphQLClientGenerator.kt lines 203-234
   • Verify sealed class implementations are all collected in the same file for Kotlinx

3. Type deduplication correctness: Verify that:

   • Types with identical field selections are actually shared (e.g., multiple_queries test case)
   • Types with different field selections get numbered variants (User2, User3)
   • The selection set comparison logic correctly identifies duplicates

4. Enum default values: Check that __UNKNOWN_VALUE enum defaults are preserved across all operations (see SecondQuery.kt test data).

5. Test expectations: With 157 test files updated, spot-check a few test cases to ensure expectations match actual generated output:

   • kotlinx/multiple_queries/* - shared types across queries
   • generator/interface_* - polymorphic types
   • generator/union_* - union type handling

6. Edge cases:

   • Nested object types with different selection sets
   • Named fragments
   • Interface/union fallback implementations
   • Custom scalars in shared types

[devin-ai-integration]

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