[Fix] Move SamplingParams.adjust after set prompt

[yeahdongcn]

Motivation

While following the Readme to use diffusion, I found an error:

Traceback (most recent call last):
  File "/ws/gen.py", line 23, in <module>
    main()
  File "/ws/gen.py", line 15, in main
    video = generator.generate(
  File "/ws/python/sglang/multimodal_gen/runtime/entrypoints/diffusion_generator.py", line 272, in generate
    current_sampling_params.adjust(self.server_args)
  File "/ws/python/sglang/multimodal_gen/configs/sample/base.py", line 207, in adjust
    raise TypeError(f"`prompt` must be a string, but got {type(self.prompt)}")
TypeError: `prompt` must be a string, but got <class 'NoneType'>

Modifications

Move SamplingParams.adjust after set prompt

Accuracy Tests

N/A

Benchmarking and Profiling

N/A

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.
• Follow the SGLang code style guidance.
• Work with maintainers to merge your PR. See the PR Merge Process

[gemini-code-assist]

Summary of Changes

Hello @yeahdongcn, 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 addresses a critical runtime error encountered during multimodal content generation, specifically a TypeError arising from SamplingParams.adjust being invoked prematurely. The fix involves a precise reordering of operations within the diffusion_generator.py file, ensuring that the prompt is assigned to the current_sampling_params object before its adjust method is called. This change resolves the traceback and allows the diffusion generation process to execute as intended, improving the stability and reliability of the generation pipeline.

Highlights

• Bug Fix: Resolved a TypeError that occurred when SamplingParams.adjust was called with a NoneType prompt, preventing multimodal generation.
• Code Reordering: The call to SamplingParams.adjust has been moved to ensure it is executed after the prompt attribute is properly set on the current_sampling_params object.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a TypeError by moving the SamplingParams.adjust call to a point after the prompt has been set. While this resolves the crash, it introduces a subtle bug where output filenames are not generated based on the prompt. I've added a review comment with a code suggestion to fix this filename issue. I also noted a minor performance consideration for future improvement.