Commits on Aug 28, 2024

1. feat: new promslog and promslog/flag packages to wrap log/slog …

   Prereq for prometheus/prometheus#14355
   
   This adds a new `promslog` package to create an opinionated slog logger
   for use within the prometheus ecosystem. By default, logs are written at
   `info` level and formatted to add a kv pair for the source caller. If
   backwards compatibility for the literal output format of the logging is
   required, logs can be styled in a format that is similar to how the
   `promlog` package formatted it's go-kit/log output [1].  The `promslog`
   package also makes use of an `slog.LevelVar` to dynamically adjust the
   level of an existing logger. Similar to the old `promlog` package, we
   provide means to log in `logfmt` and `json` output formats.
   
   Creating a logger is similar to the old promlog package -- optionally
   populate a `Config` struct, and then call `New()` with the config.
   
   In order to dynamically adjust the logger's level, retain the `Config`
   struct as it's own variable to access the `AllowedLevel.Set()` method,
   which internally updates the `AllowedLevel`'s slog.LevelVar to the
   desired log level. Ex:
   
   ```go
   config := &promslog.Config{} // Retain as variable if you need to dynamically adjust log level
   logger := promslog.New(config)
   config.Level.Set("debug")
   logger.Debug("your message here", "hello", "world")
   ```
   
   To use go-kit style log output:
   ```go
   config := &promslog.Config{Style: promslog.GoKitStyle} // Retain as variable if you need to dynamically adjust log level
   logger := promslog.New(config)
   config.Level.Set("debug")
   logger.Debug("your message here", "hello", "world")
   ```
   
   1. When using the `go-kit` log style, the following changes are made to the
   default slog output:
   - adjusts slog default timestamp key from `timestamp` -> `ts`
   - adjusts the timestamp value to use the same time format string
     ("2006-01-02T15:04:05.000Z07:00")
   - adjusts slog default sourcecode key from `source` -> `caller`
   - adjusts the formatting of the sourcecode values to trim paths with
     `filepath.Base()`. The formatting of the sourcecode value is similar
   to the go-kit/log usage, with the addition of the source function in
   parenthesis when debug logging is enabled.
   
   Signed-off-by: TJ Hoplock <t.hoplock@gmail.com>

   

   tjhop committed Aug 28, 2024
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