Check that lmcoursier is the only ns in lm-coursier-shaded JAR

build.sbt

@@ -58,7 +58,13 @@ lazy val `lm-coursier-shaded` = project
       "org.scala-lang.modules" %% "scala-xml" % "1.2.0", // depending on that one so that it doesn't get shaded
       "org.scala-sbt" %% "librarymanagement-ivy" % "1.2.4",
       "org.scalatest" %% "scalatest" % "3.0.8" % Test
-    )
+    ),
+    packageBin.in(Shading) := {
+      val jar = packageBin.in(Shading).value
+      // ignoreFiles is there temporarily, until https://github.com/coursier/coursier/pull/1317 is merged
+      Check.onlyNamespace("lmcoursier", jar, ignoreFiles = Set("coursier.properties"))
+      jar
+    }
   )
 
 lazy val `sbt-coursier-shared` = project

project/Check.scala

@@ -0,0 +1,25 @@
+import java.io.File
+import java.util.zip.ZipFile
+
+import scala.collection.JavaConverters._
+
+object Check {
+
+  def onlyNamespace(ns: String, jar: File, ignoreFiles: Set[String] = Set.empty): Unit = {
+    val zf = new ZipFile(jar)
+    val unrecognized = zf.entries()
+      .asScala
+      .map(_.getName)
+      .filter { n =>
+        !n.startsWith("META-INF/") && !n.startsWith(ns + "/") &&
+          n != "reflect.properties" && // scala-reflect adds that
+          !ignoreFiles(n)
+      }
+      .toVector
+      .sorted
+    for (u <- unrecognized)
+      System.err.println(s"Unrecognized: $u")
+    assert(unrecognized.isEmpty)
+  }
+
+}