[#11170][fix] Fix for mm placeholder counts

[2ez4bz]

Summary by CodeRabbit

• Bug Fixes

  • Improved multimodal content placeholder tracking in conversations—now handles per-message placeholder counts instead of global tracking, ensuring accurate insertion of multimodal placeholders across multiple messages.

• Tests

  • Added regression tests for per-message multimodal placeholder counting across various message scenarios.

Description

• Why?

As reported by #11170, when a single request contains multiple messages, and only a subset of those messages include multimodal data, the previous logic incorrectly adds placeholder tokens to subsequent messages that do not contain such data.

• What?

This commit fixes this issue, and adds unit tests that would have caught this.

Test Coverage

• Added unit test cases that would have caught this issue.

PR Checklist

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• PR description clearly explains what and why. If using CodeRabbit's summary, please make sure it makes sense.

• PR Follows TRT-LLM CODING GUIDELINES to the best of your knowledge.

• Test cases are provided for new code paths (see test instructions)

• Any new dependencies have been scanned for license and vulnerabilities

• CODEOWNERS updated if ownership changes

• Documentation updated as needed

• Update tava architecture diagram if there is a significant design change in PR.

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• Please check this after reviewing the above items as appropriate for this PR.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The changes modify multimodal placeholder tracking in the chat message processing pipeline. The add_data method now returns an optional placeholder string instead of implicitly returning None. Placeholder counting shifts from cumulative global tracking to per-message accumulation, with corresponding test coverage added.

Changes

Cohort / File(s)	Summary
Multimodal Data Tracker tensorrt_llm/inputs/utils.py	Updated add_data method signature to return Optional[str], propagating generated placeholder identifiers to callers instead of returning None.
Chat Message Processing tensorrt_llm/serve/chat_utils.py	Refactored parse_chat_messages_coroutines to track multimodal placeholders per-message using msg_placeholder_counts dictionary instead of cumulative global counts. Captures returned placeholders from add_data calls and applies per-message counts when updating message content.
Per-Message Placeholder Tests tests/unittest/llmapi/apps/test_chat_utils.py	Added TestMultimodalPlaceholderCounts class with parameterized test_per_message_counts method. Introduced module-level constants for model type (_MM_MODEL_TYPE), image placeholder, and video placeholder retrieved from MULTIMODAL_PLACEHOLDER_REGISTRY.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title '[#11170][fix] Fix for mm placeholder counts' clearly summarizes the main change: fixing a bug in multimodal placeholder counting logic, with specific reference to the issue number.
Description check	✅ Passed	The description includes the required sections (Why, What, Test Coverage) and explains the issue, solution, and test additions. It follows the repository template structure appropriately.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

No actionable comments were generated in the recent review. 🎉

🧹 Recent nitpick comments

tests/unittest/llmapi/apps/test_chat_utils.py (1)

233-239: Module-level registry lookups are fragile if import order changes.

_IMG_PLACEHOLDER and _VIDEO_PLACEHOLDER are resolved at module import time. If the registry isn't fully populated when this test module is imported (e.g., due to lazy registration or import reordering), these will raise at collection time with a confusing error. Consider moving these into a fixture or a helper method.

That said, this is a minor robustness concern for a test file — fine to keep as-is if the registry is always populated at import.

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[venkywonka]

lgtm!

[2ez4bz]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35752 [ run ] triggered by Bot. Commit: fff703b

[tensorrt-cicd]

PR_Github #35752 [ run ] completed with state SUCCESS. Commit: fff703b
/LLM/main/L0_MergeRequest_PR pipeline #27613 completed with status: 'FAILURE'

⚠️ Action Required:

• Please check the failed tests and fix your PR
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[2ez4bz]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35801 [ run ] triggered by Bot. Commit: e657e4b

[tensorrt-cicd]

PR_Github #35801 [ run ] completed with state SUCCESS. Commit: e657e4b
/LLM/main/L0_MergeRequest_PR pipeline #27653 completed with status: 'FAILURE'

⚠️ Action Required:

• Please check the failed tests and fix your PR
• If you cannot view the failures, ask the CI triggerer to share details
• Once fixed, request an NVIDIA team member to trigger CI again

[2ez4bz]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35839 [ run ] triggered by Bot. Commit: e657e4b

[tensorrt-cicd]

PR_Github #35839 [ run ] completed with state SUCCESS. Commit: e657e4b
/LLM/main/L0_MergeRequest_PR pipeline #27680 completed with status: 'FAILURE'

⚠️ Action Required:

• Please check the failed tests and fix your PR
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[2ez4bz]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35880 [ run ] triggered by Bot. Commit: e657e4b

[yechank-nvidia]

LGTM. Thanks for the work!

[tensorrt-cicd]

PR_Github #35880 [ run ] completed with state ABORTED. Commit: e657e4b
LLM/main/L0_MergeRequest_PR #27710 (Blue Ocean) completed with status: ABORTED

[2ez4bz]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35927 [ run ] triggered by Bot. Commit: e657e4b

[tensorrt-cicd]

PR_Github #35927 [ run ] completed with state SUCCESS. Commit: e657e4b
/LLM/main/L0_MergeRequest_PR pipeline #27745 completed with status: 'FAILURE'

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[2ez4bz]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #35944 [ run ] triggered by Bot. Commit: e657e4b

[tensorrt-cicd]

PR_Github #35944 [ run ] completed with state SUCCESS. Commit: e657e4b
/LLM/main/L0_MergeRequest_PR pipeline #27759 completed with status: 'SUCCESS'