[Bugfix][Frontend] GLM-4.7: guided-decode forced tool calls when strict tool-calling is disabled

[ifaddict1]

Purpose

On GLM-4.7 / GLM-5.2, forced tool calls (tool_choice="required" or a named function) return unconstrained native tool syntax (or an empty tool_calls list) when VLLM_ENFORCE_STRICT_TOOL_CALLING=0, which then fails downstream argument-schema validation — most visibly for tool schemas that use nested $defs/$ref.

There are two halves to the bug, and fixing only one is not enough:

1. Parse side. Glm47MoeModelToolParser hardcodes supports_required_and_named = False, overriding ToolParser.__init_subclass__. So even at strict=0, GLM never takes the JSON-based parse path for forced calls (every other structural-tag parser flips this to True at strict=0). This is the change in Allow GLM-4.7 required tool parsing when strict mode is disabled #47146.
2. Encode side. At strict=0 the structural-tag path is skipped (get_structural_tag(...) is None) and nothing else installs a grammar for forced tool calls. The request therefore goes to the engine with no structured-outputs grammar, the model free-generates native tool syntax, and the now-JSON-based parse path cannot validate it. Flipping the flag alone (Allow GLM-4.7 required tool parsing when strict mode is disabled #47146 on its own) helps flat schemas but still leaves nested-schema forced calls unconstrained.

This PR fixes both:

• glm47_moe_tool_parser: drop the hardcoded flag and let __init_subclass__ govern it via VLLM_ENFORCE_STRICT_TOOL_CALLING, like every other structural-tag parser.
• DelegatingParser: when no structural tag applies (strict=0) but tool_choice is required/named, build StructuredOutputsParams(json=...) from the request's own tool schema (mirroring the response_format json path). For required, the parameters are nested under {name, parameters} to match the list[FunctionDefinition] shape the parse path validates, and any $defs are hoisted to the top level so #/$defs/... refs stay resolvable after nesting.

The grammar is built entirely from the caller's existing tool definitions (no transpilation/heuristics), so a forced call is constrained to exactly the schema the caller already declared. The change only takes effect when supports_required_and_named is True (i.e. strict=0) and structured_outputs is not already set, so the structural-tag (strict=1) and response_format paths are untouched.

Builds on #47146 (parse-side flag) by adding the missing encode-side grammar.

Test Plan

Unit tests (tests/tool_parsers/test_structural_tag_registry.py):

pytest tests/tool_parsers/test_structural_tag_registry.py -k "build_tool_choice or glm47_does_not_pin or honors_strict_env_toggle"

End-to-end on a GLM-4.7-family model served with --enable-auto-tool-choice --tool-call-parser glm47 and VLLM_ENFORCE_STRICT_TOOL_CALLING=0, sending a tool whose parameters contain a nested object referenced via $defs/$ref, with tool_choice="required", a named tool_choice, and a response_format json_schema control.

Test Result

Unit tests: 4 passed (flag toggle is honored; GLM-4.7 no longer pins the flag; _build_tool_choice_json_schema returns the function params for a named choice and an array-of-{name, parameters} with hoisted $defs for required).

E2E (GLM-5.2, strict=0):

• Before: tool_choice="required" → empty tool_calls; named tool_choice → arguments contained raw native tool syntax; both failed schema validation on nested fields.
• After: both required and named return schema-valid JSON with the nested object populated (e.g. {"location": {"file": "app.py", "line": 14}, ...}). response_format json output is unchanged.

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• The purpose of the PR.
• The test plan.
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• (Optional) Documentation update — n/a (behavior fix, no new surface).

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[bbartels]

We are running into this issue as well, thanks for raising!

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @ifaddict1.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[sfeng33]

Thanks for the work! Closing in favor of #47512. On current main, ToolParser.adjust_request already builds the JSON grammar for required/named calls, including moving $defs to the top level, so the encode-side change isn't needed. The actual bug was that grammar being applied to parsers that read their native format. We're fixing that by skipping the JSON constraint for those parsers rather than switching GLM-4.7 to JSON parsing. For enforced forced calls on GLM, keep VLLM_ENFORCE_STRICT_TOOL_CALLING=1 (the default), which uses the structural tag.