gemini-cli - 💡(How to fix) Fix UI Regression in v0.40.0+: Incorrect prompt background and height in WSL (TrueColor detection failure) [1 participants]

What happened?

Description:

After upgrading to Gemini CLI v0.40.0+, the prompt input field in WSL (Windows Subsystem for Linux) is rendered with an incorrect background color (light gray) and excessive height compared to the Windows/Native version.

Screenshots:

• Bug in WSL:

  <img width="1682" height="343" alt="Image" src="https://github.com/user-attachments/assets/63c3df30-7ad2-4393-9693-22cc596c194d" />

• Correct in Windows:

  <img width="1676" height="360" alt="Image" src="https://github.com/user-attachments/assets/d46b24fa-64d5-4ba0-8f10-c2d869d15b47" />

Environment:

• OS: Windows 11 / WSL 2
• Gemini CLI Version: v0.40.1
• Node.js Version: v20+
• Terminal: WSL (Ubuntu/bash) inside Windows Terminal

Diagnostics:

Running node -e "console.log('Depth:', process.stdout.getColorDepth(), 'ColorTerm:', process.env.COLORTERM)" in the affected WSL environment returns: Depth: 8 ColorTerm: undefined

Technical Analysis:

The issue stems from the HalfLinePaddedBox component. In v0.40.0+, the CLI relies on supportsTrueColor() to decide between a "thin" UI (using ▄ and ▀ characters) and a fallback UI. In WSL, supportsTrueColor() returns false because COLORTERM is not set and getColorDepth() returns 8.

This triggers the following fallback in interactiveCli-XXXX.js:

if (noTrueColor) {
  return (0, import_jsx_runtime.jsx)(Box_default, { 
    width: terminalWidth, 
    backgroundColor, 
    paddingY: 1, 
    children 
  });
}

The paddingY: 1 causes the field to be 3 lines tall, and the 8-bit color mapping for backgroundColor results in a light-gray color that clashes with the theme.

Temporary Workaround:

Manually setting export COLORTERM=truecolor in ~/.bashrc fixes the issue, but this should be handled automatically by the CLI for better out-of-the-box experience in WSL.

What did you expect to happen?

Expected behavior:

The prompt should detect TrueColor support in modern WSL environments (which usually support it) or provide a more compact fallback UI that matches the theme's aesthetics even in 8-bit mode.

Client information

About Gemini CLI                                                                                
                                                                                                
CLI Version                                 0.40.1                                              
Git Commit                                  7a382e066                                           
Model                                       Auto (Gemini 3)                                     
Sandbox                                     no sandbox                                          
OS                                          linux                                               
Auth Method                                 Signed in with Google (***)   
Tier                                        Gemini Code Assist in Google One AI Pro

Login information

No response

Anything else we need to know?

No response