bugfix: Make absolute path from relative plugin paths

Otherwise this doesn't work, looks like Bloop and sbt's working dir have a mismatch?

Fixes #1421 finally

integrations/sbt-bloop/src/main/scala/bloop/integrations/sbt/SbtBloop.scala

@@ -1,8 +1,10 @@
 package bloop.integrations.sbt
 
+import java.io.File
 import java.nio.charset.StandardCharsets
 import java.nio.file.Files
 import java.nio.file.Path
+import java.nio.file.Paths
 import java.nio.file.StandardCopyOption
 import java.util.concurrent.ConcurrentHashMap
 
@@ -990,9 +992,31 @@ object BloopDefaults {
               Config.Test(frameworks, options)
             }
 
+            val pluginOpt = "-Xplugin:"
+
+            def makePluginPathAbsolute(opt: String) = {
+              if (opt.startsWith(pluginOpt)) {
+                val pluginPath = opt.stripPrefix(pluginOpt)
+                if (Paths.get(pluginPath).isAbsolute()) opt
+                else {
+                  val absolutePluginPath = cwd + File.separator + pluginPath
+                  if (Paths.get(absolutePluginPath).toFile().exists())
+                    pluginOpt + absolutePluginPath
+                  else opt
+                }
+              } else {
+                opt
+              }
+            }
             val javacOptions = Keys.javacOptions.in(Keys.compile).in(configuration).value.toList
             val scalacOptions = {
-              val options = Keys.scalacOptions.in(Keys.compile).in(configuration).value.toList
+              val options = Keys.scalacOptions
+                .in(Keys.compile)
+                .in(configuration)
+                .value
+                .toList
+                .map(makePluginPathAbsolute)
+
               val internalClasspath = BloopKeys.bloopInternalClasspath.value
               replaceScalacOptionsPaths(options, internalClasspath, logger)
             }

integrations/sbt-bloop/src/sbt-test/sbt-bloop/wartremover/bar/src/test/scala/Bar.scala

@@ -0,0 +1 @@
+trait BarTest

integrations/sbt-bloop/src/sbt-test/sbt-bloop/wartremover/build.sbt

@@ -0,0 +1,21 @@
+import java.nio.file.Paths
+import bloop.integrations.sbt.BloopDefaults
+
+val foo = project
+  .in(file(".") / "foo")
+  .settings(
+    wartremoverWarnings := Warts.all
+  )
+
+val checkBloopFiles = taskKey[Unit]("Check bloop file contents")
+checkBloopFiles in ThisBuild := {
+  import java.nio.file.Files
+  val bloopDir = Keys.baseDirectory.value./(".bloop")
+  val fooConfigFile = bloopDir./("foo.json")
+
+  val fooConfig = BloopDefaults.unsafeParseConfig(fooConfigFile.toPath)
+
+  val pluginPath =
+    fooConfig.project.scala.get.options.find(_.startsWith("-Xplugin")).get.stripPrefix("-Xplugin:")
+  assert(Paths.get(pluginPath).toFile.exists())
+}

integrations/sbt-bloop/src/sbt-test/sbt-bloop/wartremover/foo/src/main/scala/Foo.scala

@@ -0,0 +1 @@
+class Foo

integrations/sbt-bloop/src/sbt-test/sbt-bloop/wartremover/project/plugins.sbt

@@ -0,0 +1,3 @@
+addSbtPlugin("ch.epfl.scala" % "sbt-bloop" % sys.props.apply("plugin.version"))
+
+addSbtPlugin("org.wartremover" % "sbt-wartremover" % "3.1.8")

integrations/sbt-bloop/src/sbt-test/sbt-bloop/wartremover/test

@@ -0,0 +1,2 @@
+> bloopInstall
+> checkBloopFiles