Reduce CLI startup latency by deferring eager startup paths

[wolph]

Fixes #10726

Summary

This change reduces startup latency by removing several eager startup paths that were being triggered even for lightweight or non-interactive invocations.

What changed

• Added a --version fast path in packages/cli/index.ts so version checks return before loading the full CLI runtime.
• Broke command parsing import cycles by moving initializeOutputListenersAndFlush into src/utils/outputListeners.ts and updating command modules to import from that utility.
• Deferred AppContainer loading to interactive startup (startInteractiveUI) instead of importing it at module load time.
• Avoided automatic child-process relaunch for non-interactive runs (kept for interactive mode).
• Avoided eager editor command probing at module import time by computing editor availability lazily in EditorSettingsManager.
• Added/updated tests for new startup behavior and lazy editor discovery.

Benchmarks

Measured on Windows (same machine), using local built CLI (
ode packages/cli/dist/index.js).

Before (clean checkout, pre-patch):

• --version: avg 10,393.4 ms
• --help: avg 9,562.7 ms
• -p /quit: avg 27,780.1 ms

After (this branch):

• --version: avg 85.4 ms
• --help: avg 7,223.8 ms
• -p /quit: avg 7,157.1 ms

Validation

• ✅
  pm run typecheck --workspace @google/gemini-cli
• ✅
  px eslint on all modified files
• ✅
  pm run test --workspace @google/gemini-cli -- src/gemini.test.tsx src/commands/extensions.test.tsx src/commands/skills.test.tsx src/commands/mcp.test.ts src/ui/editors/editorSettingsManager.test.ts
• ⚠️
  pm run test --workspace @google/gemini-cli (full suite) still has pre-existing environment-specific failures unrelated to touched files (policy-engine integration expectations, terminal notification assertions, and snapshot differences in stats/session summary components).

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[gemini-code-assist]

Summary of Changes

Hello, 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 significantly enhances the CLI's startup performance by strategically deferring several eager initialization paths. The changes ensure that heavyweight modules and UI components are only loaded when strictly necessary, such as for interactive sessions, while providing a rapid response for lightweight commands like --version. This optimization aims to provide a snappier user experience across various CLI invocations.

Highlights

• Version Fast Path: Implemented a --version fast path in packages/cli/index.ts to allow version checks to return quickly without loading the full CLI runtime, drastically reducing startup time for this specific command.
• Command Parsing Import Cycle Resolution: Resolved command parsing import cycles by moving the initializeOutputListenersAndFlush function into a new utility file (src/utils/outputListeners.ts) and updating all command modules to import it from the new location.
• Deferred UI Loading: Deferred the loading of AppContainer and related UI initialization to occur only during interactive startup (startInteractiveUI), preventing unnecessary UI component loading for non-interactive invocations.
• Conditional Child-Process Relaunch: Modified the CLI to avoid automatic child-process relaunch for non-interactive runs, retaining this behavior only for interactive mode to optimize non-interactive command execution.
• Lazy Editor Command Probing: Prevented eager editor command probing at module import time by implementing lazy computation of editor availability within EditorSettingsManager.
• Test Updates: Added and updated tests to cover the new startup behavior and the lazy editor discovery mechanism.

Changelog

• packages/cli/index.ts
  • Added a fast path for --version and -v arguments to immediately print the CLI version and exit.
  • Refactored the main execution logic into an asynchronous run function.
  • Dynamically imported core CLI modules (./src/gemini.js, @google/gemini-cli-core, ./src/utils/cleanup.js) using Promise.all to defer their loading.
• packages/cli/src/commands/extensions.test.tsx
  • Updated the mock path for initializeOutputListenersAndFlush to reflect its new location.
• packages/cli/src/commands/extensions.tsx
  • Updated the import path for initializeOutputListenersAndFlush from ../gemini.js to ../utils/outputListeners.js.
• packages/cli/src/commands/hooks.tsx
  • Updated the import path for initializeOutputListenersAndFlush from ../gemini.js to ../utils/outputListeners.js.
• packages/cli/src/commands/mcp.ts
  • Updated the import path for initializeOutputListenersAndFlush from ../gemini.js to ../utils/outputListeners.js.
• packages/cli/src/commands/skills.test.tsx
  • Updated the mock path for initializeOutputListenersAndFlush to reflect its new location.
• packages/cli/src/commands/skills.tsx
  • Updated the import path for initializeOutputListenersAndFlush from ../gemini.js to ../utils/outputListeners.js.
• packages/cli/src/gemini.tsx
  • Removed the eager import of AppContainer and deferred its loading until startInteractiveUI is called.
  • Removed OutputPayload, ConsoleLogPayload, UserFeedbackPayload, and CoreEvent type imports, as initializeOutputListenersAndFlush was moved.
  • Moved the initializeOutputListenersAndFlush function to a new dedicated utility file.
  • Introduced conditional UI initialization logic, ensuring initializeApp and related UI setup only run if interactive mode or Zed integration is required.
  • Adjusted the relaunchAppInChildProcess call to only occur if partialConfig.isInteractive() is true.
• packages/cli/src/ui/editors/editorSettingsManager.test.ts
  • Added a new test file to verify the lazy computation of editor availability in editorSettingsManager.
• packages/cli/src/ui/editors/editorSettingsManager.ts
  • Modified EditorSettingsManager to lazily compute availableEditors only when getAvailableEditorDisplays() is first called, rather than during construction.
• packages/cli/src/utils/outputListeners.ts
  • Added a new file containing the initializeOutputListenersAndFlush function, previously located in gemini.tsx.

Activity

• The pull request was created by wolph to address startup latency issues.

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[gemini-code-assist]

Code Review

This pull request introduces significant startup latency improvements by deferring expensive initialization paths. The strategies employed, such as adding a fast path for --version, lazy loading UI components and editor checks, and avoiding unnecessary process relaunches for non-interactive runs, are well-executed and the benchmark results are impressive. The refactoring to break an import cycle is also a good structural improvement. The feedback regarding outputListeners.ts has been retained as it does not contradict any existing rules.

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