feat: add type mismatch relaxation config for field selection merging

[jensneuse]

Summary

• Adds RelaxSubgraphOperationFieldSelectionMergingTypeMismatch config flag that allows completely different field types (e.g., Int vs String) on fields within non-overlapping concrete object types inside inline fragments
• This is a deliberate, safe relaxation of GraphQL spec section 5.3.2 (SameResponseShape) — when enclosing types are distinct concrete objects, only one branch contributes to the response at runtime
• The new flag is a superset of the existing RelaxSubgraphOperationFieldSelectionMergingNullability flag: when set, it allows any type difference (including nullability), not just nullability mismatches

Test plan

• 9 new validation rule test cases covering flag combinations, interface overlap rejection, and superset behavior
• 1 new planning test verifying discriminated resolve.Field entries with OnTypeNames
• 3 new end-to-end execution tests verifying rejection without flag, Int response, and String response
• All existing tests pass (go test ./v2/... and go test ./execution/...)

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• New Features

  • Added support for relaxing type mismatch validation during field selection merging in subgraph operations, providing more flexible handling of type incompatibilities in specific scenarios.
  • Introduced configurable validation options to enable type mismatch relaxation at the engine and planner levels.

• Tests

  • Added comprehensive test coverage for field merging with different types on union types, validating behavior with and without relaxation enabled.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR extends the field selection merging validation framework by introducing a type-mismatch relaxation option that parallels the existing nullability relaxation. The feature is integrated across validation rules, planner configuration, execution engine initialization, and data source factory configuration.

Changes

Cohort / File(s)	Summary
Validation Core v2/pkg/astvalidation/operation_rule_field_selection_merging.go, v2/pkg/astvalidation/operation_validation.go	Adds FieldSelectionMergingOptions struct with RelaxTypeMismatchCheck flag; updates FieldSelectionMerging API from variadic bool parameter to pointer-based options; implements canRelaxTypeMismatch method for centralized relaxation logic; extends DefaultOperationValidator to propagate both nullability and type-mismatch relaxation settings.
Configuration & Planner v2/pkg/engine/plan/configuration.go, v2/pkg/engine/plan/datasource_configuration.go	Adds RelaxSubgraphOperationFieldSelectionMergingTypeMismatch field to Configuration; introduces SubgraphFieldSelectionMergingTypeMismatchRelaxer interface; updates planner logic to delegate to type-mismatch relaxation when configured, with fallback to nullability relaxation.
Engine & Datasource execution/engine/execution_engine.go, v2/pkg/engine/datasource/graphql_datasource/graphql_datasource.go	Adds conditional validation option registration in ExecutionEngine constructor when type-mismatch relaxation is enabled; introduces typeMismatchRelaxedPrintKitPool and EnableSubgraphFieldSelectionMergingTypeMismatchRelaxation factory method for GraphQL data source.
Tests execution/engine/execution_engine_test.go, v2/pkg/astvalidation/operation_validation_test.go, v2/pkg/astvalidation/reference/testsgo/harness_test.go, v2/pkg/engine/datasource/graphql_datasource/graphql_datasource_test.go	Updates all FieldSelectionMerging invocations to use explicit options pointers; adds new test helper relaxFieldSelectionMergingTypeMismatch(); introduces test scenarios validating field merging behavior with type mismatches on non-overlapping union types, both with and without relaxation.

Sequence Diagram

sequenceDiagram
    participant Client
    participant Planner as Planner/Config
    participant DataSource as GraphQL DataSource
    participant Engine as Execution Engine
    participant Validator as AST Validator

    Client->>Planner: Create plan with config
    alt RelaxSubgraphOperationFieldSelectionMergingTypeMismatch enabled
        Planner->>DataSource: EnableSubgraphFieldSelectionMergingTypeMismatchRelaxation()
        DataSource->>DataSource: Use typeMismatchRelaxedPrintKitPool
        DataSource->>DataSource: Apply WithRelaxFieldSelectionMergingTypeMismatch()
    end
    
    Planner->>Engine: Initialize with relaxation flags
    Engine->>Validator: Append validation options
    
    alt Type mismatch in field selection
        Validator->>Validator: canRelaxTypeMismatch() check
        alt Relaxation enabled
            Validator->>Validator: Allow merge (type mismatch relaxed)
        else Relaxation disabled
            Validator->>Validator: Reject merge (type mismatch error)
        end
    end
    
    Validator-->>Engine: Validation result
    Engine-->>Client: Execution result

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• feat: add flag for relaxed nullability checks on same shape #1378: Extends the nullability relaxation infrastructure for field selection merging by introducing a parallel type-mismatch relaxation option and wiring it through the same astvalidation, planner, and execution paths.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and clearly describes the main feature being added: a new type mismatch relaxation configuration for field selection merging validation.

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✨ Finishing Touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch jensneuse/type-mismatch-config

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[coderabbitai]

🧹 Nitpick comments (2)

v2/pkg/astvalidation/operation_validation_test.go (2)

5802-5838: Unused BotKind enum can be removed or used.

BotKind isn’t referenced in entityDefinition; either wire it into Bot for test coverage or remove it to keep the schema focused.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@v2/pkg/astvalidation/operation_validation_test.go` around lines 5802 - 5838,
The BotKind enum is declared but unused in the test schema; either remove the
unused enum BotKind or add a field on the Bot type that references it (e.g., a
"kind: BotKind" field) so BotKind is exercised; update the union Entity/ Bot
type accordingly (look for symbols BotKind, type Bot, and union Entity) and
adjust any tests expecting the previous shape.

---

1118-1215: Add an overlap guard test for scalar type mismatches.

You already assert that RelaxTypeMismatchCheck doesn’t apply when an interface overlap is possible (nullability case). Consider adding a scalar-type mismatch case (e.g., Int vs String) on overlapping interface/union types to ensure the relaxation never leaks beyond non‑overlapping concrete objects.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@v2/pkg/astvalidation/operation_validation_test.go` around lines 1118 - 1215,
Add a new test that mirrors the nullability overlap guard but for scalar type
mismatches: call runWithDefinition with the overlapping interface/union
definition (e.g., use boxDefinition or another interface-based definition that
makes potentiallySameObject=true), a query that selects the same scalar field
(e.g., score) on two overlapping inline fragments returning different scalar
types (Int vs String), pass
FieldSelectionMerging(&FieldSelectionMergingOptions{RelaxTypeMismatchCheck:
true}) and assert Invalid with a validation error like "fields 'score' conflict
because they return conflicting types 'Int' and 'String'". Place this alongside
the existing tests and follow their pattern using runWithDefinition,
FieldSelectionMerging, FieldSelectionMergingOptions, and withValidationErrors.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@v2/pkg/astvalidation/operation_validation_test.go`:
- Around line 5802-5838: The BotKind enum is declared but unused in the test
schema; either remove the unused enum BotKind or add a field on the Bot type
that references it (e.g., a "kind: BotKind" field) so BotKind is exercised;
update the union Entity/ Bot type accordingly (look for symbols BotKind, type
Bot, and union Entity) and adjust any tests expecting the previous shape.
- Around line 1118-1215: Add a new test that mirrors the nullability overlap
guard but for scalar type mismatches: call runWithDefinition with the
overlapping interface/union definition (e.g., use boxDefinition or another
interface-based definition that makes potentiallySameObject=true), a query that
selects the same scalar field (e.g., score) on two overlapping inline fragments
returning different scalar types (Int vs String), pass
FieldSelectionMerging(&FieldSelectionMergingOptions{RelaxTypeMismatchCheck:
true}) and assert Invalid with a validation error like "fields 'score' conflict
because they return conflicting types 'Int' and 'String'". Place this alongside
the existing tests and follow their pattern using runWithDefinition,
FieldSelectionMerging, FieldSelectionMergingOptions, and withValidationErrors.