Change log timestamps from the custom format to ISO 8601 with UTC
indicator:
Before: 2026-05-14 (10:31:47) | DEBUG: ...
After: 2026-05-14T10:31:47Z | DEBUG: ...
The previous format used parentheses around the time and omitted any
timezone indicator, making timestamps ambiguous. The logger uses
std::chrono::system_clock which measures time since Unix epoch (UTC
on all platforms), but the old format did not communicate this.
ISO 8601 with the Z suffix is an unambiguous, universally-recognized
format parseable by standard functions across languages:
- C++ (C++20): std::chrono::from_stream(ss, "%FT%TZ", tp)
- C: strptime(s, "%Y-%m-%dT%H:%M:%SZ", &tm)
- Python: datetime.fromisoformat("2026-05-14T10:31:47Z")
This matters for correlating btop log events with system logs (e.g.,
macOS pmset power events) that use local time with explicit timezone
offsets.
This will only allocate the log message if a log file exists and the log
level is enabled. The interface forwards it's arguments to fmt::format.
This gets also rid of some global state and hides it in the btop_log.cpp
translation unit.
Closes: https://github.com/aristocratos/btop/issues/1347
