Fix compiled inline JSON rendering for primitive collections

[dchuk]

Inline render json: with a primitive Hash or Array currently emits ActionController::JsonRender.encode, which is absent from the compiled Spinel tree. A generic controller rendering { message: "hello", count: 2 } therefore compiles but raises NameError at runtime.

Use the existing target JSON encoder when inferred types or literal structure prove the payload contains only JSON primitives. Recursive checks cover nested and empty collections, plus conditional unions whose alternatives are all primitive collections; unknown/custom values and nested Time values retain the existing Rails serializer path. This is limited to direct inline payloads.

Closes #371.

Validation (Ruby 4.0.4, Rust 1.98.1, Spinel based on 1d26ef67c):

• The generic native reproduction fails before the change with uninitialized constant ActionController::JsonRender.
• cargo test --test render_json_primitives -- --include-ignored --nocapture --test-threads=1: 3 passed, including CRuby and native Spinel execution, nested/empty collections, both branches of a conditional Hash/Array union, escaping, response status/content type, and the nested-Time serialization control.
• bin/rh verify --test render_json_declared_as_json --json: passed (923 library tests, 1 ignored; 4 serializer integration tests).
• roundhouse-ast --round-trip on an inline JSON render expression: passed.
• git diff --check: passed.

Examples and tests are standalone generic Rails code.

Please apply ci:full for the complete PR matrix, as recommended by the contribution guidelines for changes to shared or whole-app lowering. The validation above describes the checks executed locally.

Summary by CodeRabbit

• Performance
  • Inline JSON rendering of values with primitive contents—including nested arrays and objects—now uses the target’s JSON encoder.
• Compatibility
  • Values requiring Rails-specific serialization, such as nested timestamps, continue to use Rails’ runtime encoder.
• Tests
  • Added coverage for nested primitive payloads and conditional array or hash responses across CRuby and Spinel, along with a check that nested timestamps retain Rails serialization behavior.

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📥 Commits

Reviewing files that changed from the base of the PR and between e8c3e5e and 9e8208c.

📒 Files selected for processing (2)

• src/lower/controller_to_library/rewrites.rs
• tests/render_json_primitives.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• tests/render_json_primitives.rs
• src/lower/controller_to_library/rewrites.rs

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📝 Walkthrough

Walkthrough

Inline JSON rendering now uses JSON.generate for collections inferred to contain JSON primitives. Other values retain the Rails encoder path. Regression tests cover nested primitive collections and nested Time serialization.

Changes

Primitive JSON Rendering

Layer / File(s)	Summary
Primitive collection encoder selection src/lower/controller_to_library/rewrites.rs, src/lower/as_json_poro.rs, docs/pipeline/runtime.md	Encoder selection checks collection types and literal contents recursively. Primitive collections use JSON.generate; other values retain ActionController::JsonRender.encode. The documentation and comments describe the runtime encoder cases.
Encoder regression coverage tests/render_json_primitives.rs	Integration tests check response status, content type, and exact JSON output, including nested collections and Rails-formatted nested Time serialization. The primitive assertions also have an ignored Spinel test.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant Controller
  participant EncoderSelection
  participant JSON_generate as JSON.generate
  participant JsonRender as ActionController::JsonRender.encode
  Controller->>EncoderSelection: pass inline JSON value
  alt inferred primitive collection
    EncoderSelection->>JSON_generate: encode value
    JSON_generate-->>Controller: serialized JSON
  else other value
    EncoderSelection->>JsonRender: encode value
    JsonRender-->>Controller: serialized JSON
  end

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Merge Risk: ⚪ Minimal · up to 9e820

The inline JSON change appears ready to merge after normal checks. No actionable rendering regression remains identified.

Security Architecture Review

Security architecture risk: 🔵 Low · up to e8c3e

The encoder change is narrowly gated, and values requiring custom serialization retain their existing path. No newly exposed endpoint or weakened authorization is established. Native-runtime encoding behavior remains only partially verified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The potential exposure is response serialization at inline render sites that reach this shared helper and satisfy its primitive-collection gate. It is not confined to the example fixture, but the reviewed evidence does not enumerate deployed applications, tenants, or production endpoints using those sites.

Trust Boundaries and Controls

• observed — The flagged routes are constructed inside a test application. Assertions instantiate controllers and call process_action directly; the supplied parameter only chooses between fixed primitive payload shapes. These sources do not establish a newly exposed production entrypoint or an authentication bypass.
• observed — Values outside the primitive proof retain the as_json-aware fallback, including explicit Time normalization. This limits the intended serializer bypass to values that do not require those hooks; it is not an identity or authorization decision.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the fix and its scope: compiled inline JSON rendering for primitive collections.
Linked Issues check	✅ Passed	Issue #371 requires direct inline primitive Hash and Array payloads to render without ActionController::JsonRender. The lowering now selects JSON.generate for collections proven primitive by infer…
Out of Scope Changes check	✅ Passed	The lowering change, regression tests, and runtime documentation support issue #371. The changes remain limited to direct inline JSON payload encoding and do not introduce unrelated behavior.
Docstring Coverage	✅ Passed	Docstring coverage is 90.91% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 3 files.

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Inline comments:
Review comments at @src/lower/controller_to_library/rewrites.rs:
- Around line 900-902: Update the collection-type gate in json_render_encode to
accept a nonempty Ty::Union only when every variant is a Hash, Array, Record, or
Tuple. Keep json_primitive_value as the primitive-content check and preserve the
existing handling of individual collection types.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 88426cdb-066d-467e-9fef-f757aa70a523

📥 Commits

Reviewing files that changed from the base of the PR and between e87957f and cae39eb.

📒 Files selected for processing (4)

• docs/pipeline/runtime.md
• src/lower/as_json_poro.rs
• src/lower/controller_to_library/rewrites.rs
• tests/render_json_primitives.rs

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