[Misc] improve error msg

[reidliu41]

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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Purpose

improves the user experience for data parallel configuration by enhancing help text
and error messages. Users will now understand parameter requirements before encountering
errors, reducing configuration mistakes and debugging time.

Test Plan

Test Result

(Optional) Documentation Update

[gemini-code-assist]

Summary of Changes

Hello @reidliu41, 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 focuses on improving the user experience for data parallel configuration within the CLI. My aim is to make the system more intuitive by providing clearer guidance through enhanced error messages and more informative help text, thereby reducing common configuration mistakes and debugging time for users.

Highlights

• Improved Error Message: I've enhanced the ValueError message for data_parallel_start_rank when used without --headless. The new message now explicitly advises users to 'Add --headless flag to enable headless mode.', making it more actionable and user-friendly.
• Enhanced Help Text: I've updated the help text for the --data-parallel-start-rank (-dpr) command-line argument. It now clearly states that this parameter 'Requires --headless', providing crucial information upfront to prevent configuration errors.

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[gemini-code-assist]

Code Review

This pull request improves the user experience for data parallel configuration by enhancing a help text and an error message. The changes are clear and achieve the stated goal. I've identified a minor formatting issue in the new error message that results in a double space and have suggested a fix to improve the code's correctness and maintainability.

[gemini-code-assist]

The implicit string concatenation here introduces an extra space in the error message before 'in headless mode.'. This can be fixed by removing the leading space in the second part of the string. This improves the correctness of the user-facing message and the maintainability of the code.

Suggested change

	"data_parallel_start_rank is only applicable "
	" in headless mode. "
	"Add --headless flag to enable headless mode.")
	"data_parallel_start_rank is only applicable "
	"in headless mode. "
	"Add --headless flag to enable headless mode.")

[github-actions]

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