feat(ffi)!: centralize object creation with CreateEmptyObject/HasCreator

[junrushao]

Summary

• Add CreateEmptyObject() and HasCreator() inline helpers in function.h that unify the two-step "check creator, call creator" pattern. These try the native metadata->creator fast path first, then fall back to the __ffi_new__ type attribute for Python-defined types.
• Deduplicate four call sites in creator.h, init.h, reflection_extra.cc, and serialization.cc to use the new centralized helpers.
• Qualify bare details:: references to ::tvm::ffi::details:: in reflection headers (overload.h, registry.h, init.h) to prevent ADL/lookup ambiguity when included from other namespaces.

Test plan

• Existing C++ tests pass (object creation via reflection, serialization roundtrip)
• Existing Python tests pass (c_class / py_class decorator, reflection-based construction)
• CI lint (clang-format, clang-tidy) passes on changed headers

[gemini-code-assist]

Summary of Changes

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This pull request significantly refactors the Foreign Function Interface (FFI) object creation mechanism by centralizing the logic into new helper functions. This change streamlines the codebase, reduces redundant code, and ensures a consistent approach to instantiating objects, whether they originate from C++ or Python. Additionally, it improves code robustness by explicitly qualifying namespace references in reflection-related headers, mitigating potential naming conflicts.

Highlights

• Centralized Object Creation: Introduced CreateEmptyObject() and HasCreator() inline helper functions in function.h to unify the process of creating objects, supporting both native C++ creators and Python-defined types with __ffi_new__ attributes.
• Code Deduplication: Deduplicated object creation logic across four key call sites in creator.h, init.h, reflection_extra.cc, and serialization.cc by adopting the new centralized helper functions.
• Namespace Qualification: Qualified bare details:: references to ::tvm::ffi::details:: in reflection headers (overload.h, registry.h, init.h) to prevent potential ambiguity issues with Argument-Dependent Lookup (ADL) when included from other namespaces.

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Changelog

• include/tvm/ffi/function.h
  • Added CreateEmptyObject function to handle object instantiation via native creators or __ffi_new__ attributes.
  • Added HasCreator function to check if a type supports reflection-based creation.
• include/tvm/ffi/reflection/creator.h
  • Updated ObjectCreator constructor to utilize the new HasCreator function for validation.
  • Modified ObjectCreator::operator() to use CreateEmptyObject for object instantiation.
• include/tvm/ffi/reflection/init.h
  • Replaced direct metadata and creator checks with the HasCreator helper in MakeInit.
  • Updated the MakeInit lambda to use CreateEmptyObject for object creation.
  • Fully qualified details::TypeSchemaImpl with ::tvm::ffi::details:: to prevent ADL issues.
• include/tvm/ffi/reflection/overload.h
  • Fully qualified details::OverloadedFunction, details::CreateNewOverload, details::TypeSchema, details::FunctionInfo, and details::OverloadBase with ::tvm::ffi::details::.
• include/tvm/ffi/reflection/registry.h
  • Fully qualified details::ObjectUnsafe, details::AnyUnsafe, details::FunctionInfo, and details::TypeSchemaImpl with ::tvm::ffi::details::.
• src/ffi/extra/reflection_extra.cc
  • Replaced the explicit check for metadata->creator and direct creator call with the CreateEmptyObject helper.
• src/ffi/extra/serialization.cc
  • Replaced the explicit check for metadata->creator and direct creator call with the CreateEmptyObject helper.

Activity

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[gemini-code-assist]

Code Review

This pull request is a great refactoring that centralizes object creation logic into CreateEmptyObject and HasCreator helpers. This significantly reduces code duplication across several files. The changes to qualify details:: namespaces are also a good improvement for code robustness.

I have a couple of suggestions for the new helper functions in include/tvm/ffi/function.h to improve correctness and maintainability. Please see the detailed comments.