Summary

Detects and errors on dependency cycles that would generate uncompilable Swift code, fixing a latent bug in both production and mock code generation. Also creates a dedicated mock error test file and adds comprehensive mock error test coverage.

Partially-lazy cycle detection

A partially-lazy cycle (mix of constant and Instantiator hops, e.g. A → B → Instantiator<C> → C → A) generates code with forward variable references that Swift rejects: closure captures 'X' before it is declared. This was a latent production bug — the existing test only did string comparison and never compiled the output.

New error case partiallyLazyDependencyCycleDetected with guidance to make all hops lazy:

Dependency cycle detected. Cycles with a mix of constant and lazy (Instantiator)
dependencies cannot be resolved. Make all dependencies in the cycle lazy by using Instantiator:
    A -> B -> Instantiator<C> -> A

Two-phase mock cycle validation

Mock-only types (generateMock: true without isRoot) need their own cycle validation because:

1. Pre-promotion validation (cyclesOnly: true on shared validatePropertiesAreFulfillable): Catches cycles visible in the pre-promotion scope map. Uses cyclesOnly flag to skip unfulfillable property checks (mock-only types have unfulfillable received properties by design — they become mock parameters). Non-root mock types are added as entry points alongside root types.

2. Post-promotion validation (validateMockRootScopeForCycles): Runs on each mock root scope AFTER createMockRootScopeGenerator promotes @Received dependencies. Catches cycles that only become visible after promotion (e.g., B @Receives Instantiator<A> where A instantiates B — promotion creates a cycle in the mock root scope that isn't visible pre-promotion).

No code duplication

The pre-promotion cycle check reuses the shared validatePropertiesAreFulfillable with a cyclesOnly: Bool parameter (no default — callers must be explicit). The post-promotion check is a separate validateMockRootScopeForCycles that walks the promoted scope tree checking both propertiesToGenerate and dependencies.

New SafeDIToolMockGenerationErrorTests.swift

Dedicated file for mock generation error tests (the mock test file was 12,725 lines). Contains 9 tests:

Production test changes

• Moved run_writesConvenienceExtensionOnRootOfTree_whenPartiallyLazyInstantiationCycleExists to error test file
• Removed corresponding DOT generation test (cycle now errors before DOT generation)

Test plan

• 768 tests pass across 20 suites
• Lint clean
• 100% coverage on modified source
• Fully-lazy and self-forwarding cycle tests unaffected

🤖 Generated with Claude Code