Support Truecolor in prompt_toolkit sessions

[rolandwalker]

Description

Support Truecolor in prompt_toolkit sessions if the environment variable $COLORTERM contains "truecolor"; otherwise fall back to 8-bit color depth, the prompt_tookit default.

I must admit that between this and dbcli/cli_helpers#102 I cannot yet see a difference. But there was a request for it, which is reasonable.

It would be great if someone attached some screenshots showing the difference.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[scottnemes]

Think you'd have to being using gradients or similar to be able to notice this, so it's a pretty niche use case from what I can gather anyway.

[github-actions]

Findings

1. Potential regression: forcing 8‑bit color when COLORTERM isn’t set
   PromptSession will now always get ColorDepth.DEPTH_8_BIT unless COLORTERM contains truecolor. That can downgrade users whose terminals support truecolor but don’t export COLORTERM, and it also bypasses prompt_toolkit’s own autodetection if it improves in newer versions.
   File: mycli/main.py:1172
   Suggestion: fall back to ColorDepth.DEPTH_DEFAULT (or omit color_depth) when COLORTERM doesn’t indicate truecolor. Example:

   • color_depth = ColorDepth.DEPTH_24_BIT if is_truecolor else ColorDepth.DEPTH_DEFAULT

2. Case‑sensitivity and variant strings
   The check is case‑sensitive and only matches truecolor. Common variants include TrueColor, TRUECOLOR, and 24bit.
   File: mycli/main.py:1172
   Suggestion: normalize and handle 24bit, e.g. val = os.getenv("COLORTERM","").lower() and check for "truecolor" or "24bit".

Missing tests / edge cases

• No tests cover the COLORTERM logic. Add a small unit test around the session creation logic (or a helper) to confirm:
  • COLORTERM=truecolor → 24‑bit
  • COLORTERM=24bit → 24‑bit
  • COLORTERM unset / empty / mixed‑case → default behavior (not forced to 8‑bit)

If you want, I can propose a minimal refactor to make this testable without integration testing.

[github-actions]

Findings (ordered by severity)

1. Potential compatibility edge case: PromptSession(..., color_depth=...) is passed None when COLORTERM doesn’t include truecolor. If the installed prompt_toolkit version doesn’t accept None for color_depth, this will raise at runtime. Consider omitting the parameter entirely in that case, or passing the explicit default enum. File: mycli/main.py:1169.

2. Edge case: Some terminals advertise truecolor via COLORTERM=24bit (or truecolour). Current check only looks for truecolor, so those users won’t get 24‑bit even if supported. Consider matching both truecolor and 24bit (and maybe truecolour). File: mycli/main.py:1169.

Missing tests / coverage

1. There are no tests covering the COLORTERM detection logic. A small unit test that patches os.environ to verify color_depth selection would guard against regressions. File: mycli/main.py:1169.

I didn’t run tests.

If you want, I can draft a minimal test and adjust the detection logic.