Ensure scala-kernel-api doesn't bring slf4j-api

As no logger implem would exist alongside by default, slf4j would
fail to initialize, complain loudly to stderr, and default to
NOP logging

build.sc

@@ -144,10 +144,28 @@ class ScalaKernelApi(val crossScalaVersion: String) extends AlmondModule with De
         scala.`jupyter-api`()
       )
   def ivyDeps = Agg(
-    Deps.ammoniteCompiler(crossScalaVersion),
-    Deps.ammoniteReplApi(crossScalaVersion),
+    Deps.ammoniteCompiler(crossScalaVersion)
+      .exclude(("org.slf4j", "slf4j-api")),
+    Deps.ammoniteReplApi(crossScalaVersion)
+      .exclude(("org.slf4j", "slf4j-api")),
     Deps.jvmRepr
   )
+
+  def resolvedIvyDeps = T {
+    // Ensure we don't depend on slf4j-api
+    // As no logger implem would be loaded alongside it by default, slf4j would fail to initialize,
+    // complain in stderr, and default to NOP logging.
+    val value = super.resolvedIvyDeps()
+    val jarNames = value
+      .map(_.path.last)
+      .filter(_.endsWith(".jar"))
+      .map(_.stripSuffix(".jar"))
+    val slf4jJars = jarNames.filter(_.startsWith("slf4j-"))
+    if (slf4jJars.nonEmpty)
+      sys.error(s"Found slf4j JARs: ${slf4jJars.mkString(", ")}")
+    value
+  }
+
   def propertyFilePath = "almond/almond.properties"
   def propertyExtra = Seq(
     "default-scalafmt-version" -> Deps.scalafmtDynamic.dep.version,
@@ -253,6 +271,8 @@ class ScalaKernel(val crossScalaVersion: String) extends AlmondModule with Exter
 
   def resolvedIvyDeps = T {
     // Ensure we stay on slf4j 1.x
+    // Kind of unnecessary now that scala-kernel-api doesn't bring slf4j-api any more,
+    // but keeping that just in case…
     val value = super.resolvedIvyDeps()
     val jarNames = value
       .map(_.path.last)