1 files changed, 99 insertions, 0 deletions
diff --git a/src/main/scala/xyz.driver.sbt/LintPlugin.scala b/src/main/scala/xyz.driver.sbt/LintPlugin.scala
new file mode 100644
index 0000000..7d882cb
--- /dev/null
+++ b/src/main/scala/xyz.driver.sbt/LintPlugin.scala
@@ -0,0 +1,99 @@
+package xyz.driver.sbt
+
+import org.scalafmt.sbt.ScalafmtPlugin
+import org.scalafmt.sbt.ScalafmtPlugin.autoImport._
+import org.scalastyle.sbt.ScalastylePlugin
+import org.scalastyle.sbt.ScalastylePlugin.autoImport.{scalastyle, scalastyleConfig}
+import sbt.Keys._
+import sbt.{Def, _}
+
+import scala.collection.JavaConverters._
+
+/** Enforces common formatting and catches compiler warnings. */
+object LintPlugin extends AutoPlugin {
+
+  override def requires = ScalafmtPlugin && ScalastylePlugin
+  override def trigger  = allRequirements
+
+  lazy val formatSettings: Seq[Def.Setting[_]] = Seq(
+    scalafmtConfig := {
+      val packaged = getClass.getClassLoader.getResourceAsStream("scalafmt.conf")
+      val out      = file(".scalafmt.conf")
+      IO.write(out, IO.readBytes(packaged))
+      Some(out)
+    },
+    test in Test := {
+      (test in Test).value
+      scalafmtCheck.value
+    }
+  )
+
+  lazy val scalastyleSettings: Seq[Def.Setting[_]] = Seq(
+    scalastyleConfig := {
+      val stream = getClass.getClassLoader.getResourceAsStream("scalastyle-config.xml")
+      val out    = file("scalastyle-config.xml")
+      IO.write(out, IO.readBytes(stream))
+      out
+    },
+    test in Test := {
+      (test in Test).value
+      (scalastyle in Test).toTask("").value
+    }
+  )
+
+  lazy val scalacSettings: Seq[Def.Setting[_]] = Seq(
+    scalacOptions in Compile ++= Seq(
+      "-language:higherKinds",
+      "-language:implicitConversions",
+      "-language:postfixOps",
+      "-language:reflectiveCalls", // TODO this should be discouraged
+      "-unchecked",
+      "-deprecation",
+      "-feature",
+      "-encoding",
+      "utf8",
+      "-Xlint:_,-unused,-missing-interpolator",
+      "-Ywarn-numeric-widen",
+      "-Ywarn-dead-code",
+      "-Ywarn-unused:_,-explicits,-implicits"
+    ),
+    // Currently, scalac does not provide a way to fine-tune the treating of
+    // warnings as errors. Either all are considered errors
+    // (with -Xfatal-warnings), or none are. This hack analyzes the compiler's
+    // output and treats all warnings as errors, except for deprecations.
+    compile in Compile := {
+      val log      = streams.value.log
+      val compiled = (compile in Compile).value
+      val problems = compiled.readSourceInfos().getAllSourceInfos.asScala.flatMap {
+        case (_, info) => info.getReportedProblems
+      }
+      var deprecationsOnly = true
+      problems.foreach {
+        problem =>
+          if (!problem.message().contains("is deprecated")) {
+            deprecationsOnly = false
+            val pos  = problem.position
+            val file = pos.sourcePath.asScala.getOrElse("?")
+            val line = pos.line.asScala.map(_.toString).getOrElse("?")
+            val col  = pos.pointer.asScala.map(_.toString).getOrElse("?")
+            val msg  = problem.message
+            val desc = pos.lineContent() + "\n" + pos.pointerSpace.asScala
+              .getOrElse("") + "^"
+            log.error(s"[fatal warning] $file:$line:$col $msg\n$desc")
+          }
+      }
+      if (!deprecationsOnly) {
+        throw new MessageOnlyException(
+          "Fatal warnings: some warnings other than deprecations were found. " +
+            "This failure can be ignored by removing the lint plugin from the sbt project. " +
+            "(E.g. add `disablePlugins(LintPlugin)` to build.sbt).")
+      }
+      compiled
+    }
+  )
+
+  lazy val lintSettings: Seq[Def.Setting[_]] = formatSettings ++ scalastyleSettings ++ scalacSettings
+
+  override def projectSettings: Seq[Def.Setting[_]] = inConfig(Compile)(lintSettings) ++ inConfig(Test)(lintSettings)
+
+}