feat: format timestamp

[atusy]

This PR enables formatting timestamp of logs by specifying functions to the following options

• logger.format_time
• logger.format_time.{namespace} (has priority)

I actually wanted to achieve the feature without using options, but I find no suitable place to implement it...

Note that the behavior is not yet documented because I am not sure where to document it.
Do you have any ideas?

Some use cases are below

• modifying timezone
• get sub-second precision

withr::with_options(
  list(`logger.format_time` = function(x) format(x, "%Y-%m-%d %H:%M:%OS6 %Z", tz = "UTC")),
  {
    logger::log_formatter(logger::formatter_logging)
    logger::log_layout(logger::layout_logging)
    logger::log_info("foo")

    logger::log_formatter(logger::formatter_json)
    logger::log_layout(logger::layout_json_parser(fields = "time"))
    logger::log_warn(message = "foo")
  }
)
2025-01-25 14:45:39.519480 UTC INFO::foo
{"time":"2025-01-25 14:45:39.565330 UTC","message":"foo"}

[daroczig]

Hm, that's a good question 👍

But I before getting into the details, I might try to defend the original design and let the layout fn handle the time format: how the time is rendered seems to be part of the layout to me. In the layout fn, the time could be converted to M/D/Y or UNIX timestamp etc.

Please let me know what's the benefit of detaching the time formatter function from the layout.

[atusy]

@daroczig
Thanks. I agree with you. I first tried make changes on layout functions.
However, I realized this approach is applicable to layout_* functions that generates the layout functions (e.g., layout_json)

layout_json(fields = c("time"), format_time = function(x) format(x))

Other layout_* functions are not customizable (e.g., layout_logging).

The another choice is to add an argument to log_layout.
However, this looks ugly because format_time semantically part of the layout, but is apart from the layout argument...
Also, it requires internal setter/getter function that treats the format function.

log_layout(layout = layout_json(...), format_time = function(x) format(x))