[core] Fix SLF4J log levels (#1046)

I noticed that only `error` was enabled for my Kyo app, when I had it
set to info. Info logs should have shown up, but they didn't.

### Solution
Check the level of log level enabled in reverse order. In the previous
case, `error` was always enabled (unless `off`).

### Notes
- I changed `Level` to a `sealed abstract class`, enabling exhaustive
pattern matching. Avoiding `AnyVal` is generally better if we know we
will only have static instances.
- I also added a `CanEqual` for users.


### Checklist

- [X] Unit test all changes
- [X] Update scaladocs if needed
- [X] Update the README if needed

Co-authored-by: Flavio Brasil <[email protected]>

kyo-core/jvm/src/main/scala/kyo/internal/LogPlatformSpecific.scala

@@ -16,13 +16,14 @@ object LogPlatformSpecific:
         object SLF4J:
             def apply(name: String) = new SLF4J(org.slf4j.LoggerFactory.getLogger(name))
 
-        class SLF4J(logger: org.slf4j.Logger) extends Log.Unsafe:
+        final class SLF4J(logger: org.slf4j.Logger) extends Log.Unsafe:
             val level =
-                if logger.isErrorEnabled() then Level.error
-                else if logger.isWarnEnabled() then Level.warn
-                else if logger.isInfoEnabled() then Level.info
+                if logger.isTraceEnabled() then Level.trace
                 else if logger.isDebugEnabled() then Level.debug
-                else Level.trace
+                else if logger.isInfoEnabled() then Level.info
+                else if logger.isWarnEnabled() then Level.warn
+                else if logger.isErrorEnabled() then Level.error
+                else Level.silent
 
             inline def trace(msg: => String)(using frame: Frame, allow: AllowUnsafe): Unit =
                 if Level.trace.enabled(level) then logger.trace(s"[${frame.position.show}] $msg")

kyo-core/jvm/src/test/scala/kyo/internal/LogPlatformSpecificTest.scala

@@ -0,0 +1,39 @@
+package kyo.internal
+
+import kyo.Log.Level
+import kyo.Test
+import org.slf4j.LoggerFactory
+
+class LogPlatformSpecificTest extends Test:
+    private def loggerWithLevel(level: ch.qos.logback.classic.Level) =
+        val logger = LoggerFactory.getLogger("test")
+        logger.asInstanceOf[ch.qos.logback.classic.Logger].setLevel(level)
+        new LogPlatformSpecific.Unsafe.SLF4J(logger)
+    end loggerWithLevel
+
+    "SLF4J logger" - {
+        "trace" in {
+            assert(loggerWithLevel(ch.qos.logback.classic.Level.TRACE).level == Level.trace)
+        }
+
+        "debug" in {
+            assert(loggerWithLevel(ch.qos.logback.classic.Level.DEBUG).level == Level.debug)
+        }
+
+        "info" in {
+            assert(loggerWithLevel(ch.qos.logback.classic.Level.INFO).level == Level.info)
+        }
+
+        "warn" in {
+            assert(loggerWithLevel(ch.qos.logback.classic.Level.WARN).level == Level.warn)
+        }
+
+        "error" in {
+            assert(loggerWithLevel(ch.qos.logback.classic.Level.ERROR).level == Level.error)
+        }
+
+        "silent" in {
+            assert(loggerWithLevel(ch.qos.logback.classic.Level.OFF).level == Level.silent)
+        }
+    }
+end LogPlatformSpecificTest

kyo-core/shared/src/main/scala/kyo/Log.scala

@@ -21,15 +21,15 @@ end Log
 /** Logging utility object for Kyo applications. */
 object Log extends LogPlatformSpecific:
 
-    final case class Level private (private val priority: Int) extends AnyVal:
-        def enabled(maxLevel: Level) = maxLevel.priority <= priority
-
+    sealed abstract class Level(private val priority: Int) derives CanEqual:
+        def enabled(other: Level): Boolean = other.priority <= priority
     object Level:
-        val trace: Level = Level(10)
-        val debug: Level = Level(20)
-        val info: Level  = Level(30)
-        val warn: Level  = Level(40)
-        val error: Level = Level(50)
+        case object trace  extends Level(10)
+        case object debug  extends Level(20)
+        case object info   extends Level(30)
+        case object warn   extends Level(40)
+        case object error  extends Level(50)
+        case object silent extends Level(60)
     end Level
 
     private val local = Local.init(live)