Fix bug when indexing Scala package repo

Previously, we tried to infer the Scala version from the name of the jar
of the dependency that we were indexing. Now, we infer from the first
jar on the classpath that matches the `2_VERSION` pattern. The old logic
didn't work for the sbt package repo, which doesn't include the `_2.12`
suffix.

Author: olafurpg

lsif-java/src/main/scala/com/sourcegraph/lsif_java/buildtools/LsifBuildTool.scala

@@ -165,11 +165,11 @@ class LsifBuildTool(index: IndexCommand) extends BuildTool("LSIF", index) {
       return CommandResult(0, Nil)
     }
 
-    val compileAttemtps = ListBuffer.empty[Try[Unit]]
-    compileAttemtps += compileJavaFiles(tmp, deps, config, javaFiles)
-    compileAttemtps += compileScalaFiles(deps, scalaFiles)
-    compileAttemtps += compileKotlinFiles(deps, config, kotlinFiles)
-    val errors = compileAttemtps.collect { case Failure(exception) =>
+    val compileAttempts = ListBuffer.empty[Try[Unit]]
+    compileAttempts += compileJavaFiles(tmp, deps, config, javaFiles)
+    compileAttempts += compileScalaFiles(deps, scalaFiles)
+    compileAttempts += compileKotlinFiles(deps, config, kotlinFiles)
+    val errors = compileAttempts.collect { case Failure(exception) =>
       exception
     }
 
@@ -179,6 +179,9 @@ class LsifBuildTool(index: IndexCommand) extends BuildTool("LSIF", index) {
     val isSemanticdbGenerated = Files
       .isDirectory(targetroot.resolve("META-INF"))
     if (errors.nonEmpty && !isSemanticdbGenerated) {
+      errors.foreach { error =>
+        index.app.reporter.log(Diagnostic.exception(error))
+      }
       CommandResult(1, Nil)
     } else {
       if (errors.nonEmpty && isSemanticdbGenerated) {
@@ -376,8 +379,9 @@ class LsifBuildTool(index: IndexCommand) extends BuildTool("LSIF", index) {
   )(fn: PresentationCompiler => T): T = {
     val scalaVersion = deps
       .classpath
-      .headOption
+      .iterator
       .flatMap(jar => ScalaVersion.inferFromJar(jar))
+      .nextOption()
       .getOrElse {
         throw new IllegalArgumentException(
           s"failed to infer the Scala version from the dependencies: " +