refactor: Remove picojson dependency, replace with tvm::ffi::json API

[MasterJH5574]

Migrate all picojson usages to the new tvm::ffi::json API built on the FFI type system.

[gemini-code-assist]

Summary of Changes

Hello @MasterJH5574, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request executes a substantial refactoring to unify JSON operations across the project. It replaces the picojson library with the tvm::ffi::json API, which is integrated with the FFI type system. This change affects build configurations, core data structures, and utility functions responsible for JSON parsing and serialization, leading to a more cohesive and robust JSON handling infrastructure.

Highlights

• Dependency Removal: The external picojson library has been completely removed from the codebase, streamlining dependencies.
• API Migration: All instances of picojson usage have been migrated to the new tvm::ffi::json API, which is built on the FFI type system for consistent JSON handling.
• Build System Updates: CMake configuration files were updated to remove picojson includes and compile definitions, while also ensuring xgrammar's bundled picojson dependency is correctly managed.
• JSON Handling Refactor: Core JSON parsing, lookup, and serialization logic across various C++ files have been updated to utilize tvm::ffi::json::Object, tvm::ffi::json::Array, and tvm::ffi::json::Value types, enhancing type safety and consistency.

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Changelog

• CMakeLists.txt
  • Removed picojson include and compile definitions
  • Added xgrammar's bundled picojson include for its dependency
• android/mlc4j/CMakeLists.txt
  • Removed picojson include from Android build configuration
• cpp/json_ffi/conv_template.cc
  • Updated FromJSON methods for ModelVisionConfig and Conversation to use tvm::ffi::json::Object and Array
  • Adjusted type casting for JSON values
• cpp/json_ffi/conv_template.h
  • Updated FromJSON method signatures to use tvm::ffi::json::Object
• cpp/json_ffi/json_ffi_engine.cc
  • Replaced picojson includes with tvm/ffi/extra/json.h
  • Updated JSON array/object creation and serialization for stream responses and model config loading
• cpp/json_ffi/openai_api_protocol.cc
  • Updated FromJSON and AsJSON methods for various OpenAI API protocol structs to use tvm::ffi::json types and methods
• cpp/json_ffi/openai_api_protocol.h
  • Updated method signatures for JSON parsing and serialization to use tvm::ffi::json types
• cpp/metadata/model.cc
  • Updated FromJSON methods for model metadata structures to use tvm::ffi::json::Object and Array
  • Adjusted type casting for JSON values
• cpp/metadata/model.h
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated method signatures for model metadata JSON handling
• cpp/multi_gpu/multi_gpu_loader.cc
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated JSON parsing for model configuration during multi-GPU loading
• cpp/serve/config.cc
  • Removed picojson.h include
  • Updated FromJSON and AsJSON methods for configuration structures (ResponseFormat, DisaggConfig, DebugConfig, GenerationConfig) to use tvm::ffi::json types
  • Updated EngineConfig JSON parsing and serialization logic
• cpp/serve/config.h
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated method signatures for configuration JSON handling
• cpp/serve/engine.cc
  • Updated GetTokenizerInfo and Create methods to use tvm::ffi::json::Object for model configurations
  • Updated JSON metrics serialization
• cpp/serve/engine_actions/action.h
  • Updated function signatures to use std::vector<tvm::ffi::json::Object> for model configurations
• cpp/serve/engine_actions/action_commons.cc
  • Updated function signature to use std::vector<tvm::ffi::json::Object> for model configurations
• cpp/serve/engine_actions/action_commons.h
  • Updated function signature to use std::vector<tvm::ffi::json::Object> for model configurations
• cpp/serve/engine_actions/batch_prefill_base.cc
  • Updated constructor to use std::vector<tvm::ffi::json::Object> for model configurations
• cpp/serve/engine_actions/batch_prefill_base.h
  • Updated constructor signature to use std::vector<tvm::ffi::json::Object>
• cpp/serve/engine_actions/disagg_prepare_recv.cc
  • Updated constructor to use tvm::ffi::json::Object for model configurations
  • Updated JSON serialization for response body and usage
• cpp/serve/engine_actions/disagg_remote_send.cc
  • Updated constructor signature to use tvm::ffi::json::Object for model configurations
• cpp/serve/engine_actions/eagle_new_request_prefill.cc
  • Updated constructor signature to use tvm::ffi::json::Object for model configurations
• cpp/serve/engine_actions/new_request_prefill.cc
  • Updated constructor signature to use tvm::ffi::json::Object for model configurations
• cpp/serve/engine_state.h
  • Removed picojson.h include
• cpp/serve/event_trace_recorder.cc
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated JSON serialization for event tracing
• cpp/serve/function_table.cc
  • Updated Init method and LoadParams to use tvm::ffi::json::Object and tvm::ffi::json::Stringify
• cpp/serve/function_table.h
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated Init method signature and model_config member type to tvm::ffi::json::Object
• cpp/serve/logit_processor.cc
  • Removed picojson.h include
• cpp/serve/metrics.cc
  • Updated AsJSON methods for TimeCost, SpecDecodeMetrics, RequestMetrics, and EngineMetrics to use tvm::ffi::json types and methods
• cpp/serve/metrics.h
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated method signatures for metrics JSON handling
• cpp/serve/model.cc
  • Updated Create and LoadModelConfig methods to use tvm::ffi::json::Object and tvm::ffi::json::Parse
• cpp/serve/model.h
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated method signatures for model JSON handling
• cpp/serve/request.cc
  • Updated RequestGetGenerationConfigJSON to use tvm::ffi::json::Stringify
• cpp/serve/threaded_engine.cc
  • Updated CreateRequest to use json::Object for parsing generation configuration
• cpp/serve/threaded_engine.h
  • Removed picojson.h include
• cpp/support/json_parser.h
  • Replaced picojson types with tvm::ffi::json types (Object, Array, Value) in all JSON utility functions
  • Updated ParseToJSONObject, Lookup, LookupOrDefault, LookupOptional, LookupWithResultReturn, LookupOrDefaultWithResultReturn, LookupOptionalWithResultReturn, and SymShapeTuple conversion logic
• cpp/tokenizers/tokenizers.cc
  • Replaced picojson.h include with tvm/ffi/extra/json.h
  • Updated AsJSONString and FromJSONString methods for TokenizerInfoNode to use tvm::ffi::json types and methods
  • Updated DetectTokenizerInfo to use tvm::ffi::json for parsing tokenizer configuration

Activity

• The author, MasterJH5574, initiated a comprehensive refactoring to replace the picojson dependency.
• Numerous code changes were implemented across various C++ files to adapt to the new tvm::ffi::json API.
• Build system files were modified to reflect the updated JSON library usage.

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[MasterJH5574]

Mark as draft since it still depends on a tvm-ffi fix apache/tvm-ffi#442. We won't be able to get this PR in before a new version of tvm-ffi is released.

[gemini-code-assist]

Code Review

This pull request is a large-scale refactoring to replace the picojson dependency with the tvm::ffi::json API. The changes are extensive and appear to be correctly implemented across the codebase, consistently applying the new API for JSON manipulation. The migration is well-executed, improving dependency management. I've found a minor inconsistency in how JSON arrays are iterated in one file and have provided suggestions to align it with the rest of the codebase for better maintainability.