otellogrus: Fix logrus.Level conversion

[vkuptcov]

Logrus severity transformation is broken right now as all severity levels are counterintuitively transformed to various trace levels.
Logrus has the next levels from 0 (the highest) to 6 (lowest):

const (
	// PanicLevel level, highest level of severity. Logs and then calls panic with the
	// message passed to Debug, Info, ...
	PanicLevel Level = iota
	// FatalLevel level. Logs and then calls `logger.Exit(1)`. It will exit even if the
	// logging level is set to Panic.
	FatalLevel
	// ErrorLevel level. Logs. Used for errors that should definitely be noted.
	// Commonly used for hooks to send errors to an error tracking service.
	ErrorLevel
	// WarnLevel level. Non-critical entries that deserve eyes.
	WarnLevel
	// InfoLevel level. General operational entries about what's going on inside the
	// application.
	InfoLevel
	// DebugLevel level. Usually only enabled when debugging. Very verbose logging.
	DebugLevel
	// TraceLevel level. Designates finer-grained informational events than the Debug.
	TraceLevel
)

while otel has a huge number of levels from 0 (the lowest) to 24 (the highest):

const (
	// SeverityUndefined represents an unset Severity.
	SeverityUndefined Severity = 0 // UNDEFINED

	// A fine-grained debugging log record. Typically disabled in default
	// configurations.
	SeverityTrace1 Severity = 1 // TRACE
	SeverityTrace2 Severity = 2 // TRACE2
	SeverityTrace3 Severity = 3 // TRACE3
	SeverityTrace4 Severity = 4 // TRACE4

	// A debugging log record.
	SeverityDebug1 Severity = 5 // DEBUG
	SeverityDebug2 Severity = 6 // DEBUG2
	SeverityDebug3 Severity = 7 // DEBUG3
	SeverityDebug4 Severity = 8 // DEBUG4

	// An informational log record. Indicates that an event happened.
	SeverityInfo1 Severity = 9  // INFO
	SeverityInfo2 Severity = 10 // INFO2
	SeverityInfo3 Severity = 11 // INFO3
	SeverityInfo4 Severity = 12 // INFO4

	// A warning log record. Not an error but is likely more important than an
	// informational event.
	SeverityWarn1 Severity = 13 // WARN
	SeverityWarn2 Severity = 14 // WARN2
	SeverityWarn3 Severity = 15 // WARN3
	SeverityWarn4 Severity = 16 // WARN4

	// An error log record. Something went wrong.
	SeverityError1 Severity = 17 // ERROR
	SeverityError2 Severity = 18 // ERROR2
	SeverityError3 Severity = 19 // ERROR3
	SeverityError4 Severity = 20 // ERROR4

	// A fatal log record such as application or system crash.
	SeverityFatal1 Severity = 21 // FATAL
	SeverityFatal2 Severity = 22 // FATAL2
	SeverityFatal3 Severity = 23 // FATAL3
	SeverityFatal4 Severity = 24 // FATAL4

	// Convenience definitions for the base severity of each level.
	SeverityTrace = SeverityTrace1
	SeverityDebug = SeverityDebug1
	SeverityInfo  = SeverityInfo1
	SeverityWarn  = SeverityWarn1
	SeverityError = SeverityError1
	SeverityFatal = SeverityFatal1
)

Right now the conversion is done via offset

const sevOffset = logrus.Level(log.SeverityDebug) - logrus.DebugLevel
record.SetSeverity(log.Severity(e.Level + sevOffset))

and produces pretty strange and unexpected results, when all logrus levels become debug or trace

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: vkuptcov / name: Vladimir Kuptsov (aed69c8, 48c45ab, f84c1d1, 8f3ffe5, 043b7df, af1b522)
• ✅ login: pellared / name: Robert Pająk (1aaa293, 753e426, d85a3be)
• ✅ login: dmathieu / name: Damien Mathieu (259bd67)

[dmathieu]

Could you sign the CLA?

[vkuptcov]

Could you sign the CLA?

done

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.0%. Comparing base (fb4466f) to head (259bd67).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
bridges/otellogrus/hook.go	89.4%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6191   +/-   ##
=====================================
  Coverage   67.0%   67.0%           
=====================================
  Files        194     194           
  Lines      12692   12709   +17     
=====================================
+ Hits        8510    8525   +15     
- Misses      3903    3905    +2     
  Partials     279     279           

Files with missing lines	Coverage Δ
bridges/otellogrus/hook.go	97.5% <89.4%> (-1.5%)	⬇️

[pellared]

Can you add unit tests for severity level transformations and add a changelog entry?

[vkuptcov]

@pellared done. All stages are fine, except the check-links stage but fails also in the main branch.