fix: invalid data resolution for null parent types

[Noroth]

When resolving scalar value data from non list types in the context we can run into a panic. This PR adds additional checks to ensure we don't resolve data from an invalid context.

Summary by CodeRabbit

• New Features

  • Added a top-level category query and featuredCategory resolution for subcategories to fetch single categories and featured relations.

• Bug Fixes

  • Improved robustness by short-circuiting on invalid/null messages and adding explicit error for missing object fields.

• Tests

  • Added tests and tracing to verify category query behavior and that field resolvers are not invoked for null category results.

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between f8eb4d3 and 87268e1.

📒 Files selected for processing (1)

• v2/pkg/engine/datasource/grpc_datasource/mapping_test_helper.go

🚧 Files skipped from review as they are similar to previous changes (1)

• v2/pkg/engine/datasource/grpc_datasource/mapping_test_helper.go

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📝 Walkthrough

Walkthrough

Adds category support to the gRPC datasource: new QueryCategory and ResolveSubcategoryFeaturedCategory RPCs and proto messages, GraphQL schema entry, mapping and mock service updates, RPC-call tracing in tests, and defensive checks to avoid nil dereferences during path resolution and JSON flattening.

Changes

Cohort / File(s)	Summary
Proto & GraphQL schema v2/pkg/grpctest/product.proto, v2/pkg/grpctest/testdata/products.graphqls	Added QueryCategory and ResolveSubcategoryFeaturedCategory RPCs and supporting request/response/context/args/result messages; added category(id: ID!): Category to GraphQL Query.
GRPC mapping & test helper v2/pkg/engine/datasource/grpc_datasource/mapping_test_helper.go, v2/pkg/grpctest/mapping/mapping.go	Wired new category QueryRPC and featuredCategory resolve mapping for Subcategory, including argument name mappings (id → id, includeChildren → include_children).
Mock service v2/pkg/grpctest/mockservice_enums.go	Added QueryCategory implementation returning a Category with requested id, derived name, and kind.
Datasource spy tests v2/pkg/engine/datasource/grpc_datasource/grpc_datasource_spy_test.go	Added RPC-tracing counters and hook, new QueryCategory spy method and field-resolver spy methods, and test asserting field resolvers are not invoked when Category is null.
Path resolution & JSON builder v2/pkg/engine/datasource/grpc_datasource/compiler.go, v2/pkg/engine/datasource/grpc_datasource/json_builder.go	Added early validity checks in resolveDataForPath/resolveListDataForPath to short-circuit on invalid messages; flattenObject now errors if target field is missing to avoid nil dereference.
Module manifest go.mod	Indirect change listed in manifest (no public API changes).

Sequence Diagram(s)

mermaid
sequenceDiagram
participant Client
participant GraphQL_Server as GraphQL Server
participant GRPC_DS as gRPC Datasource
participant ProductSvc as ProductService
participant MockSvc as MockService (test)
Client->>GraphQL_Server: GraphQL query (category/id)
GraphQL_Server->>GRPC_DS: Resolve Query -> QueryCategory RPC
GRPC_DS->>ProductSvc: QueryCategory(Request{id})
ProductSvc->>MockSvc: (test) delegate to MockService.QueryCategory
MockSvc-->>ProductSvc: QueryCategoryResponse(Category or nil)
ProductSvc-->>GRPC_DS: Response with Category
GRPC_DS-->>GraphQL_Server: Mapped Category data
alt Category != null and has sub-resolvers
GraphQL_Server->>GRPC_DS: Resolve field (e.g., popularityScore)
GRPC_DS->>ProductSvc: ResolveCategoryPopularityScore RPC
ProductSvc-->>GRPC_DS: Field response
GRPC_DS-->>GraphQL_Server: Field value
else Category == null
Note over GraphQL_Server,GRPC_DS: Field resolvers not invoked
end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• fix: skip invocation for empty context in field resolvers #1413: Modifies the same path-resolution helpers (resolveDataForPath / resolveListDataForPath) to handle invalid/empty message contexts.
• fix: incorrect field resolver path #1363: Direct edits to resolveListDataForPath / resolveDataForPath functions; overlaps with defensive checks added here.
• feat: add composite type support for field resolvers #1341: Changes to grpc_datasource compiler and message/list path resolution logic that are related to the new mapping and resolver wiring.

🚥 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 summarizes the primary change: adding validity checks for null parent types in data resolution, which aligns with the core fixes in compiler.go, json_builder.go, and test coverage for null category handling.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch ludwig/eng-9091-check-invalid-data-for-message-types-in-proto-compiler

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[coderabbitai]

Actionable comments posted: 1

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

Inline comments:
In `@v2/pkg/engine/datasource/grpc_datasource/mapping_test_helper.go`:
- Around line 522-531: The gci formatting error is caused by the map literal
block containing entries like "categories", "category" and "categoriesByKind" in
mapping_test_helper.go; run the project's formatting tools (gci and
gofmt/goimports) on that file to reorder/imports and fix spacing so the
FieldArgumentMap and TargetName entries are properly formatted, then re-run CI
to ensure the gci lint passes.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 586c0d72-020b-4107-b6b0-a3f967f03c67

📥 Commits

Reviewing files that changed from the base of the PR and between 5940d31 and f8eb4d3.

⛔ Files ignored due to path filters (2)

• v2/pkg/grpctest/productv1/product.pb.go is excluded by !**/*.pb.go
• v2/pkg/grpctest/productv1/product_grpc.pb.go is excluded by !**/*.pb.go

📒 Files selected for processing (8)

• v2/pkg/engine/datasource/grpc_datasource/compiler.go
• v2/pkg/engine/datasource/grpc_datasource/grpc_datasource_spy_test.go
• v2/pkg/engine/datasource/grpc_datasource/json_builder.go
• v2/pkg/engine/datasource/grpc_datasource/mapping_test_helper.go
• v2/pkg/grpctest/mapping/mapping.go
• v2/pkg/grpctest/mockservice_enums.go
• v2/pkg/grpctest/product.proto
• v2/pkg/grpctest/testdata/products.graphqls