fix: detect color support for xterm-* TERM values (xterm-color, xterm-kitty)

[Sanjays2402]

What

ColorSupport.from_env() only recognised the bare TERM=xterm value. Any decorated variant — xterm-color, xterm-16color, xterm-kitty, xterm-ghostty, … — fell through to ColorSupport.NONE and the progress bar rendered without any color at all.

Root cause

The xterm branch used an exact-equality check while its sibling 256 branch uses containment:

elif '256' in value:
    support = max(cls.XTERM_256, support)
elif value == 'xterm':          # <-- exact match, misses xterm-color, xterm-kitty, ...
    support = max(cls.XTERM, support)

This is inconsistent with three things in the same codebase:

1. The method's own docstring: "If they contain xterm, we will enable 16 color support." (containment, not equality)
2. The sibling branch one line up already uses '256' in value.
3. is_ansi_terminal(), whose ANSI_TERM_RE = ^([xe]|bv)term… matches xterm as a prefix. So the two public entry points disagreed:

TERM	is_ansi_terminal()	from_env() before	from_env() after
xterm	True	XTERM	XTERM
xterm-color	True	NONE	XTERM
xterm-16color	True	NONE	XTERM
xterm-kitty	True	NONE	XTERM
xterm-ghostty	True	NONE	XTERM
xterm-256color	True	XTERM_256	XTERM_256

from_env() gates all color output — Color.ansi (in terminal/base.py) returns None when COLOR_SUPPORT is NONE — so this silently disabled color for a large class of extremely common real-world terminals.

Fix

One-line change: value == 'xterm' → 'xterm' in value. The 256 branch is checked first, so xterm-256color still resolves to XTERM_256; only values that would otherwise have been NONE are promoted to XTERM (16-color), matching the documented contract.

Test

Added test_color_support_from_env_term, which asserts the resolved ColorSupport for bare xterm, the previously-broken xterm-* variants, and the 256 cases (so the ordering guarantee is locked in too).

Proof it guards the bug (stash the source fix, run the test):

# without the fix:
FAILED tests/test_color.py::test_color_support_from_env_term[xterm-color-16]
FAILED tests/test_color.py::test_color_support_from_env_term[xterm-16color-16]
FAILED tests/test_color.py::test_color_support_from_env_term[xterm-kitty-16]
FAILED tests/test_color.py::test_color_support_from_env_term[xterm-ghostty-16]
4 failed, 3 passed
AssertionError: assert <ColorSupport.NONE: 0> == <ColorSupport.XTERM: 16>

# with the fix:
7 passed

Full tests/test_color.py + tests/test_utils.py = 100 passed (both orders), broader suite 463 passed, 12 skipped — no regressions. ruff check and ruff format --check clean on both changed files. +27 / -1.

[gemini-code-assist]

Code Review

This pull request updates the color support detection in progressbar/env.py to check if 'xterm' is contained within the environment variable value instead of performing an exact match, and adds corresponding unit tests in tests/test_color.py. The review feedback suggests making the 'xterm' check case-insensitive by using value.lower() and adding an uppercase test case to verify this behavior.

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[gemini-code-assist]

The environment variable check for 'xterm' is case-sensitive. Since terminal environment variables (like TERM or COLORTERM) can sometimes be set in uppercase or mixed case (e.g., XTERM, Xterm), it is safer to perform a case-insensitive check by lowercasing the value before checking.

Suggested change

	elif 'xterm' in value:
	elif 'xterm' in value.lower():

[gemini-code-assist]

To ensure that case-insensitive terminal names (like XTERM) are correctly supported, we should add a test case with uppercase characters.

Suggested change

	('xterm', env.ColorSupport.XTERM),
	('xterm-color', env.ColorSupport.XTERM),
	('xterm-16color', env.ColorSupport.XTERM),
	('xterm-kitty', env.ColorSupport.XTERM),
	('xterm-ghostty', env.ColorSupport.XTERM),
	('xterm', env.ColorSupport.XTERM),
	('XTERM', env.ColorSupport.XTERM),
	('xterm-color', env.ColorSupport.XTERM),
	('xterm-16color', env.ColorSupport.XTERM),
	('xterm-kitty', env.ColorSupport.XTERM),
	('xterm-ghostty', env.ColorSupport.XTERM),