Eval bug: `params_schema.type` can be JSON array, but autoparser assumes it as string

[cr0sh]

Name and Version

version: 7990 (5abd9666d)
built with AppleClang 17.0.0.17000404 for Darwin arm64

Operating systems

Mac

GGML backends

Metal

Hardware

Apple M4 Max, 40 GPU cores, 64G Unified Memory

Models

Huggingface unsloth/Qwen3-Coder-Next:MXFP4_MOE

Problem description & steps to reproduce

With some MCP tools enabled (namely Chrome Devtools MCP) and using Opencode, llama-server instantly crashes with initial prompt.

Automatic parser generation failed: [json.exception.type_error.302] type must be string, but is array
llama.cpp/common/chat.cpp:1260: Unable to generate parser for this template.

I dug into LLDB backtraces and found out that the crashing point is

llama.cpp/common/chat-auto-parser-generator.cpp

Line 293 in 5abd966

auto type = param_schema.value("type", "object");

. Looking at the inspected value, Chrome Devtools MCP allows the fieldtype be "nullable" and expresses it as ["<type>", null] where the autoparser expects to be string. Unhandled type error occurs.

I didn't followed up how the autoparser's strategy will be when nullability is allowed, so I didn't try to implement a fix on my own. Maybe just recognize if it's nullable then silently ignore it?

First Bad Commit

No response

Relevant log output

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