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Adds a StructuredLogger based on cats.mtl.Ask #900

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a5916fb
Add flake
rossabaker Mar 14, 2025
587267c
Rough draft of an MTL-based logger
rossabaker Mar 14, 2025
6fe9255
Plumb defaultContext effect into Slf4jLogger
rossabaker Mar 18, 2025
9b6fb27
Back out AskStructuredLogger
rossabaker Mar 18, 2025
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4 changes: 3 additions & 1 deletion build.sbt
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ ThisBuild / tlVersionIntroduced := Map("3" -> "2.1.1")

val catsV = "2.11.0"
val catsEffectV = "3.5.7"
val catsMtlV = "1.4.0"
val slf4jV = "1.7.36"
val munitCatsEffectV = "2.0.0"
val logbackClassicV = "1.2.13"
Expand All @@ -47,7 +48,8 @@ lazy val core = crossProject(JSPlatform, JVMPlatform, NativePlatform)
name := "log4cats-core",
libraryDependencies ++= Seq(
"org.typelevel" %%% "cats-core" % catsV,
"org.typelevel" %%% "cats-effect-std" % catsEffectV
"org.typelevel" %%% "cats-effect-std" % catsEffectV,
"org.typelevel" %%% "cats-mtl" % catsMtlV
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This dependency will be part of cats-effect-3.6, so I'm not feeling guilty for introducing it to core. Otherwise, this could be a log4cats-mtl module.

),
libraryDependencies ++= {
if (tlIsScala3.value) Seq.empty
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109 changes: 109 additions & 0 deletions flake.lock
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26 changes: 26 additions & 0 deletions flake.nix
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
{
inputs = {
typelevel-nix.url = "github:typelevel/typelevel-nix";
nixpkgs.follows = "typelevel-nix/nixpkgs";
flake-utils.follows = "typelevel-nix/flake-utils";
};

outputs = { self, nixpkgs, flake-utils, typelevel-nix }:
flake-utils.lib.eachDefaultSystem (system:
let
pkgs = import nixpkgs {
inherit system;
overlays = [ typelevel-nix.overlays.default ];
};
in {
devShell = pkgs.devshell.mkShell {
imports = [ typelevel-nix.typelevelShell ];
name = "log4cats";
typelevelShell = {
jdk.package = pkgs.jdk8;
native.enable = true;
nodejs.enable = true;
};
};
});
}
5 changes: 3 additions & 2 deletions slf4j/src/main/scala/org/typelevel/log4cats/slf4j/Slf4jLogger.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
package org.typelevel.log4cats
package slf4j

import cats.Applicative
import cats.effect.Sync
import org.typelevel.log4cats.slf4j.internal.Slf4jLoggerInternal
import org.slf4j.Logger as JLogger
Expand All @@ -33,10 +34,10 @@ object Slf4jLogger extends Slf4jLoggerCompat {
getLoggerFromSlf4j[F](org.slf4j.LoggerFactory.getLogger(clazz))

def getLoggerFromSlf4j[F[_]: Sync](logger: JLogger): SelfAwareStructuredLogger[F] =
new Slf4jLoggerInternal.Slf4jLogger(logger, Sync.Type.Delay)
new Slf4jLoggerInternal.Slf4jLogger(logger, Sync.Type.Delay, Applicative[F].pure(Map.empty))
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This (and line 40) wire nothing in yet. We'd need a parallel set of Ask or Local based constructors here.


def getLoggerFromBlockingSlf4j[F[_]: Sync](logger: JLogger): SelfAwareStructuredLogger[F] =
new Slf4jLoggerInternal.Slf4jLogger(logger, Sync.Type.Blocking)
new Slf4jLoggerInternal.Slf4jLogger(logger, Sync.Type.Blocking, Applicative[F].pure(Map.empty))

def create[F[_]: Sync](implicit name: LoggerName): F[SelfAwareStructuredLogger[F]] =
Sync[F].delay(getLoggerFromName(name.value))
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109 changes: 55 additions & 54 deletions slf4j/src/main/scala/org/typelevel/log4cats/slf4j/internal/Slf4jLoggerInternal.scala
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Expand Up @@ -36,39 +36,35 @@ private[slf4j] object Slf4jLoggerInternal {
def apply(t: Throwable)(msg: => String): F[Unit]
}

// Need this to make sure MDC is correctly cleared before logging
private[this] def noContextLog[F[_]](isEnabled: F[Boolean], logging: () => Unit)(implicit
F: Sync[F]
): F[Unit] =
contextLog[F](isEnabled, Map.empty, logging)

private[this] def contextLog[F[_]](
isEnabled: F[Boolean],
ctx: Map[String, String],
ctxF: F[Map[String, String]],
logging: () => Unit
)(implicit F: Sync[F]): F[Unit] = {

val ifEnabled = F.delay {
val backup =
try MDC.getCopyOfContextMap()
catch {
case e: IllegalStateException =>
// MDCAdapter is missing, no point in doing anything with
// the MDC, so just hope the logging backend can salvage
// something.
logging()
throw e
}

try {
// Once 2.12 is no longer supported, change this to MDC.setContextMap(ctx.asJava)
MDC.clear()
ctx.foreach { case (k, v) => MDC.put(k, v) }
logging()
} finally
if (backup eq null) MDC.clear()
else MDC.setContextMap(backup)
}
val ifEnabled = ctxF.flatMap(ctx =>
F.delay {
val backup =
try MDC.getCopyOfContextMap()
catch {
case e: IllegalStateException =>
// MDCAdapter is missing, no point in doing anything with
// the MDC, so just hope the logging backend can salvage
// something.
logging()
throw e
}

try {
// Once 2.12 is no longer supported, change this to MDC.setContextMap(ctx.asJava)
MDC.clear()
ctx.foreach { case (k, v) => MDC.put(k, v) }
logging()
} finally
if (backup eq null) MDC.clear()
else MDC.setContextMap(backup)
}
)

isEnabled.ifM(
ifEnabled,
Expand All @@ -77,14 +73,19 @@ private[slf4j] object Slf4jLoggerInternal {
}

@nowarn("msg=used")
final class Slf4jLogger[F[_]](val logger: JLogger, sync: Sync.Type = Sync.Type.Delay)(implicit
F: Sync[F]
) extends SelfAwareStructuredLogger[F] {
final class Slf4jLogger[F[_]](
val logger: JLogger,
sync: Sync.Type = Sync.Type.Delay,
defaultCtx: F[Map[String, String]]
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By getting the default context into the logger, as an effect, we are now able to avoid the asking and concatenation of the context map when the log is disabled. But this is a bit less conducive to the middleware approach: we don't want addContext to return a ModifiedContextStructuredLogger anymore.

)(implicit F: Sync[F])
extends SelfAwareStructuredLogger[F] {

@deprecated("Use constructor with sync", "2.6.0")
def this(logger: JLogger, sync: Sync.Type)(F: Sync[F]) =
this(logger, Sync.Type.Delay, F.pure(Map.empty))(F)

@deprecated("Use constructor with sync", "2.6.0")
def this(logger: JLogger)(
F: Sync[F]
) =
def this(logger: JLogger)(F: Sync[F]) =
this(logger, Sync.Type.Delay)(F)

override def isTraceEnabled: F[Boolean] = F.delay(logger.isTraceEnabled)
Expand All @@ -94,48 +95,48 @@ private[slf4j] object Slf4jLoggerInternal {
override def isErrorEnabled: F[Boolean] = F.delay(logger.isErrorEnabled)

override def trace(t: Throwable)(msg: => String): F[Unit] =
noContextLog(isTraceEnabled, () => logger.trace(msg, t))
contextLog(isTraceEnabled, defaultCtx, () => logger.trace(msg, t))
override def trace(msg: => String): F[Unit] =
noContextLog(isTraceEnabled, () => logger.trace(msg))
contextLog(isTraceEnabled, defaultCtx, () => logger.trace(msg))
override def trace(ctx: Map[String, String])(msg: => String): F[Unit] =
contextLog(isTraceEnabled, ctx, () => logger.trace(msg))
contextLog(isTraceEnabled, defaultCtx.map(_ ++ ctx), () => logger.trace(msg))
override def trace(ctx: Map[String, String], t: Throwable)(msg: => String): F[Unit] =
contextLog(isTraceEnabled, ctx, () => logger.trace(msg, t))
contextLog(isTraceEnabled, defaultCtx.map(_ ++ ctx), () => logger.trace(msg, t))

override def debug(t: Throwable)(msg: => String): F[Unit] =
noContextLog(isDebugEnabled, () => logger.debug(msg, t))
contextLog(isDebugEnabled, defaultCtx, () => logger.debug(msg, t))
override def debug(msg: => String): F[Unit] =
noContextLog(isDebugEnabled, () => logger.debug(msg))
contextLog(isDebugEnabled, defaultCtx, () => logger.debug(msg))
override def debug(ctx: Map[String, String])(msg: => String): F[Unit] =
contextLog(isDebugEnabled, ctx, () => logger.debug(msg))
contextLog(isDebugEnabled, defaultCtx.map(_ ++ ctx), () => logger.debug(msg))
override def debug(ctx: Map[String, String], t: Throwable)(msg: => String): F[Unit] =
contextLog(isDebugEnabled, ctx, () => logger.debug(msg, t))
contextLog(isDebugEnabled, defaultCtx.map(_ ++ ctx), () => logger.debug(msg, t))

override def info(t: Throwable)(msg: => String): F[Unit] =
noContextLog(isInfoEnabled, () => logger.info(msg, t))
contextLog(isInfoEnabled, defaultCtx, () => logger.info(msg, t))
override def info(msg: => String): F[Unit] =
noContextLog(isInfoEnabled, () => logger.info(msg))
contextLog(isInfoEnabled, defaultCtx, () => logger.info(msg))
override def info(ctx: Map[String, String])(msg: => String): F[Unit] =
contextLog(isInfoEnabled, ctx, () => logger.info(msg))
contextLog(isInfoEnabled, defaultCtx.map(_ ++ ctx), () => logger.info(msg))
override def info(ctx: Map[String, String], t: Throwable)(msg: => String): F[Unit] =
contextLog(isInfoEnabled, ctx, () => logger.info(msg, t))
contextLog(isInfoEnabled, defaultCtx.map(_ ++ ctx), () => logger.info(msg, t))

override def warn(t: Throwable)(msg: => String): F[Unit] =
noContextLog(isWarnEnabled, () => logger.warn(msg, t))
contextLog(isWarnEnabled, defaultCtx, () => logger.warn(msg, t))
override def warn(msg: => String): F[Unit] =
noContextLog(isWarnEnabled, () => logger.warn(msg))
contextLog(isWarnEnabled, defaultCtx, () => logger.warn(msg))
override def warn(ctx: Map[String, String])(msg: => String): F[Unit] =
contextLog(isWarnEnabled, ctx, () => logger.warn(msg))
contextLog(isWarnEnabled, defaultCtx.map(_ ++ ctx), () => logger.warn(msg))
override def warn(ctx: Map[String, String], t: Throwable)(msg: => String): F[Unit] =
contextLog(isWarnEnabled, ctx, () => logger.warn(msg, t))
contextLog(isWarnEnabled, defaultCtx.map(_ ++ ctx), () => logger.warn(msg, t))

override def error(t: Throwable)(msg: => String): F[Unit] =
noContextLog(isErrorEnabled, () => logger.error(msg, t))
contextLog(isErrorEnabled, defaultCtx, () => logger.error(msg, t))
override def error(msg: => String): F[Unit] =
noContextLog(isErrorEnabled, () => logger.error(msg))
contextLog(isErrorEnabled, defaultCtx, () => logger.error(msg))
override def error(ctx: Map[String, String])(msg: => String): F[Unit] =
contextLog(isErrorEnabled, ctx, () => logger.error(msg))
contextLog(isErrorEnabled, defaultCtx.map(_ ++ ctx), () => logger.error(msg))
override def error(ctx: Map[String, String], t: Throwable)(msg: => String): F[Unit] =
contextLog(isErrorEnabled, ctx, () => logger.error(msg, t))
contextLog(isErrorEnabled, defaultCtx.map(_ ++ ctx), () => logger.error(msg, t))
}
}