guided decoding parameters for tensorrt_llm backend must be present even if not needed

[InCogNiTo124]

System Info

Nvidia rtx 3090 ti
nvcr.io/nvidia/tritonserver:25.05-trtllm-python-py3

Who can help?

@ncomly-nvidia

Information

• The official example scripts
• My own modified scripts

Tasks

• An officially supported task in the examples folder (such as GLUE/SQuAD, ...)
• My own task or dataset (give details below)

Reproduction

Steps to reproduce the behaviour:

1. take any tensorrt_llm compiled plan
2. delete from config.pbtxt parameters tokenizer_dir, xgrammar_tokenizer_info_path or guided_decoding_backend

Expected behavior

tensorrtllm_backend should start normally

actual behavior

tensorrtllm_backend crashes with a message that a parameter is missing, although it's not used.

additional notes

TensorRT-LLM/triton_backend/inflight_batcher_llm/src/model_instance_state.cc

Lines 410 to 453 in 7b210ae

	std::optional<executor::GuidedDecodingConfig> ModelInstanceState::getGuidedDecodingConfigFromParams()
	{
	std::optional<executor::GuidedDecodingConfig> guidedDecodingConfig = std::nullopt;
	std::string tokenizerDir = model_state_->GetParameter<std::string>("tokenizer_dir");
	std::string tokenizerInfoPath = model_state_->GetParameter<std::string>("xgrammar_tokenizer_info_path");
	std::string guidedDecodingBackendStr = model_state_->GetParameter<std::string>("guided_decoding_backend");
	if (!tokenizerDir.empty() && tokenizerDir != "${tokenizer_dir}")
	{
	TLLM_LOG_INFO(
	"Guided decoding C++ workflow does not use tokenizer_dir, this parameter will "
	"be ignored.");
	}
	if (guidedDecodingBackendStr.empty() || guidedDecodingBackendStr == "${guided_decoding_backend}"
	|| tokenizerInfoPath.empty() || tokenizerInfoPath == "${xgrammar_tokenizer_info_path}")
	{
	return guidedDecodingConfig;
	}
	TLLM_CHECK_WITH_INFO(std::filesystem::exists(tokenizerInfoPath),
	"Xgrammar's tokenizer info path at %s does not exist.", tokenizerInfoPath.c_str());
	auto const tokenizerInfo = nlohmann::json::parse(std::ifstream{std::filesystem::path(tokenizerInfoPath)});
	auto const encodedVocab = tokenizerInfo["encoded_vocab"].template get<std::vector<std::string>>();
	auto const tokenizerStr = tokenizerInfo["tokenizer_str"].template get<std::string>();
	auto const stopTokenIds
	= tokenizerInfo["stop_token_ids"].template get<std::vector<tensorrt_llm::runtime::TokenIdType>>();
	executor::GuidedDecodingConfig::GuidedDecodingBackend guidedDecodingBackend;
	if (guidedDecodingBackendStr == "xgrammar")
	{
	guidedDecodingBackend = executor::GuidedDecodingConfig::GuidedDecodingBackend::kXGRAMMAR;
	}
	else
	{
	TLLM_THROW(
	"Guided decoding is currently supported with 'xgrammar' backend. Invalid guided_decoding_backend parameter "
	"provided.");
	}
	guidedDecodingConfig
	= executor::GuidedDecodingConfig(guidedDecodingBackend, encodedVocab, tokenizerStr, stopTokenIds);
	return guidedDecodingConfig;
	}

[VALLIS-NERIA]

@SimengLiu-nv @Tabrizian Can you please help to triage?