Improve problem reporting

Report the summary (previously "found $count potential binary...") at
error or warn level, like the problem details themselves.

Note that `log`, here, is MiMa's Logging interface, which wires its info
level to sbt's _debug_ level.  So logging to "info" will mostly never be
seen.

Therefore, this, in particular, brings to the foreground:

* the module version (".. check against org.scala-sbt:main_2.12:1.1.2!")
* the number of filtered problems (".. (filtered 111)")

Also, don't log the project name with sys.error: sbt's task error
reporting prints the message with the project-specific task name, e.g.:

    [error] (mainProj / mimaReportBinaryIssues) Main: Binary compatibility check failed!

Author: dwijnand

sbtplugin/src/main/scala/com/typesafe/tools/mima/plugin/MimaPlugin.scala

@@ -68,22 +68,17 @@ object MimaPlugin extends AutoPlugin {
   private def binaryIssuesIterator = Def.task {
     val s = streams.value
     val previousClassfiles = mimaPreviousClassfiles.value
-
-    if (previousClassfiles.isEmpty) {
-      val projectName = name.value
-      var msg = s"$projectName: mimaPreviousArtifacts is empty, not analyzing binary compatibility."
-      if (previousClassfiles eq NoPreviousClassfiles) {
-        msg = s"$projectName: mimaPreviousArtifacts not set, not analyzing binary compatibility."
-        if (mimaFailOnNoPrevious.value)
-          sys.error(msg)
-      }
-      s.log.info(msg)
-    }
-
     val currentClassfiles = mimaCurrentClassfiles.value
     val cp = (fullClasspath in mimaFindBinaryIssues).value
     val log = new SbtLogger(s)
 
+    if (previousClassfiles eq NoPreviousClassfiles) {
+      val msg = "mimaPreviousArtifacts not set, not analyzing binary compatibility"
+      if (mimaFailOnNoPrevious.value) sys.error(msg) else s.log.info(s"${name.value}: $msg")
+    } else if (previousClassfiles.isEmpty) {
+      s.log.info(s"${name.value}: mimaPreviousArtifacts is empty, not analyzing binary compatibility.")
+    }
+
     previousClassfiles.iterator.map { case (moduleId, prevClassfiles) =>
       moduleId -> SbtMima.runMima(prevClassfiles, currentClassfiles, cp, mimaCheckDirection.value, log)
     }

sbtplugin/src/main/scala/com/typesafe/tools/mima/plugin/SbtMima.scala

@@ -64,15 +64,15 @@ object SbtMima {
     val count = backErrors.size + forwErrors.size
     val filteredCount = backward.size + forward.size - count
     val filteredNote = if (filteredCount > 0) s" (filtered $filteredCount)" else ""
-    log.info(s"$projectName: found $count potential binary incompatibilities while checking against $module$filteredNote")
+    val msg = s"Failed binary compatibility check against $module! Found $count potential problems$filteredNote"
+    val doLog = if (count == 0) log.info(_) else if (failOnProblem) log.error(_) else log.warn(_)
 
-    (backErrors.iterator.map(pretty("current")) ++ forwErrors.iterator.map(pretty("other"))).foreach { msg =>
-      if (failOnProblem) log.error(msg)
-      else log.warn(msg)
-    }
+    doLog(s"$projectName: $msg")
+    for (p <- backErrors) doLog(pretty("current")(p))
+    for (p <- forwErrors) doLog(pretty("other")(p))
 
     if (failOnProblem && count > 0) {
-      sys.error(s"$projectName: Binary compatibility check failed!")
+      sys.error(msg)
     }
   }