date: -u flag ignored in some cases

[yachi]

Description

The -u flag doesn't work correctly for:

1. Pure digit strings (e.g., date -u -d "12")
2. --reference option
3. --resolution option

Output shows local timezone instead of UTC.

Reproduction

Run in non-UTC timezone:

# Bug #1: Pure digits
$ date -u -d "12" "+%Z"
BST  # Expected: UTC

# Bug #2: --reference
$ touch /tmp/testfile
$ date -u --reference /tmp/testfile "+%Z"
BST  # Expected: UTC

# Bug #3: --resolution
$ date -u --resolution "+%Z"
BST  # Expected: UTC

Cause

src/uu/date/src/date.rs:

• Line 279: --reference always uses TimeZone::try_system()
• Line 285: --resolution always uses TimeZone::system()
• Line 461: parse_date() ignores timezone offset in parsed string

None check the settings.utc flag.

[Agent-Hellboy]

Hi @cakebaker , I will take a look at it.