feat: add progress bar to experiments

[colodenn]

Problem

When running experiments with many items, developers have no feedback on progress or estimated time. A progress bar has been requested in langfuse/langfuse#11718 so we can see:

• how many items have been processed
• percentage complete
• estimated time remaining

Changes

• Progress bar: TTY-style progress bar for experiment runs in Node.js when stderr is a TTY (e.g. Experiment [:bar] :current/:total :percent :eta)
• progress option: new experiment.run({ progress?: boolean }) to control behavior
• Optional dependency: progress is in optionalDependencies so it doesn’t block browser or edge usage. If the import fails, the experiment runs without the bar.
• Tests: E2E tests for progress: true and progress: false in tests/e2e/experiments.e2e.test.ts

Release info Sub-libraries affected

Bump level

• Major
• Minor
• Patch

Libraries affected

• All of them
• langfuse
• langfuse-node

Changelog notes

• experiment: Added optional progress bar for experiment runs in Node.js with a TTY. Use progress: true to show it even when not a TTY, or progress: false to disable it.

---

Important

Adds optional TTY-style progress bar for experiment runs in Node.js with a progress option in ExperimentParams and tests for its functionality.

• Behavior:
  • Adds a TTY-style progress bar for experiment runs in Node.js when stderr is a TTY, using progress package.
  • Introduces progress option in ExperimentParams to control progress bar visibility.
  • Progress bar updates after each item completes in ExperimentManager.run().
• Dependencies:
  • Adds progress as an optionalDependency in package.json.
  • Adds @types/progress as a devDependency.
• Error Handling:
  • Implements try-catch for dynamic import of progress in ExperimentManager.ts.
• Tests:
  • Adds E2E tests for progress bar enabled/disabled states in experiments.e2e.test.ts.

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---

Disclaimer: Experimental PR review

Greptile Overview

Greptile Summary

This PR adds an optional TTY-style progress bar for experiment runs in Node.js. The implementation uses the progress package as an optional dependency to avoid blocking browser or edge environments. The progress bar displays current/total items, percentage, and ETA during experiment execution.

Critical Issues:

• Duplicate if (canShowBar) statement on lines 213-214 creates a syntax error
• Extra closing brace on line 231 due to the duplicate if statement
• Dynamic import of progress module violates the project's style guideline requiring imports at module top

Approach:

• Progress bar defaults to showing when stderr is a TTY, can be controlled via progress option
• Optional dependency pattern ensures graceful degradation when module is unavailable
• Tests added for both enabled and disabled states

Confidence Score: 2/5

• This PR has critical syntax errors that will prevent it from compiling or running correctly
• The duplicate if statement and extra closing brace create syntax errors that must be fixed before merging. Additionally, the dynamic import pattern violates the project's style guidelines.
• Pay close attention to packages/client/src/experiment/ExperimentManager.ts - contains duplicate conditional and extra brace causing syntax errors

Important Files Changed

Filename	Overview
packages/client/src/experiment/ExperimentManager.ts	Added progress bar with duplicate if statement and extra closing brace causing syntax errors; dynamic import violates style guide
packages/client/src/experiment/types.ts	Added progress parameter with clear documentation
packages/client/package.json	Added progress as optional dependency and @types/progress as dev dependency

Sequence Diagram

sequenceDiagram
    participant User
    participant ExperimentManager
    participant ProgressBar
    participant Task

    User->>ExperimentManager: run(config with progress option)
    ExperimentManager->>ExperimentManager: Check progressOption & TTY
    alt canShowBar is true
        ExperimentManager->>ProgressBar: import("progress")
        ProgressBar-->>ExperimentManager: Progress constructor
        ExperimentManager->>ProgressBar: new Progress(format, options)
    end
    
    loop For each batch
        loop For each item in batch
            ExperimentManager->>Task: runItem(item)
            Task-->>ExperimentManager: result
            ExperimentManager->>ProgressBar: tick(1)
        end
    end
    
    ExperimentManager-->>User: ExperimentResult

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Context used:

• Rule from dashboard - Move imports to the top of the module instead of placing them within functions or methods. (source)

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