Update Scala to 2.12.18 (#277)

Due to some security vulnerabilities in Scala 2.11 compiler, I switched `polyglot-scala` to Scala 2.12, which is the last version, for which there is a release of `com.twitter:util-eval`, which we use to compile and evaluate the `pom.scala` files.

Unfortunately, `util-eval` throws runtime exceptions when used as-is, which is mostly due to internal changes in the Scala compiler. Since `util-eval` doesn't work with Scala 2.12 and was even removed upstream for quite some time, I vendored the single file `Eval.scala` and applied some small refactorings to make it work. The imported file was licensed under the Apache Licence, version 2, which is identical to this project license.

Due to the version bump from Scala 2.11 to 2.12, I'd consider this pull request a breaking change. The next release number for polyglot(-scala) should be therefore `0.6.0` (if we apply early semantic versioning).

* Fix #276

I think it's worth investigating, whether we can follow up with a bump to Scala 2.13. I haven't tested it yet, due to some dependencies not available. But it looks like `com.googlecode.kiama` has moved to https://github.com/inkytonik/kiama, so there should be no blockers. But the `Eval` might break again due to expected compiler changes.

polyglot-scala/pom.xml

@@ -20,9 +20,8 @@
   <name>Polyglot :: Scala</name>
 
   <properties>
-    <!-- We cannot use 2.12+, as Maven 3.x requires us to run on Java7 -->
-    <scala.version>2.11.12</scala.version>
-    <scala.bin.version>2.11</scala.bin.version>
+    <scala.version>2.12.18</scala.version>
+    <scala.bin.version>2.12</scala.bin.version>
   </properties>
 
   <contributors>
@@ -45,10 +44,16 @@
 
     <dependency>
       <groupId>com.twitter</groupId>
-      <artifactId>util-eval_${scala.bin.version}</artifactId>
+      <artifactId>util-core_${scala.bin.version}</artifactId>
       <version>6.43.0</version>
     </dependency>
 
+    <dependency>
+      <groupId>org.scala-lang.modules</groupId>
+      <artifactId>scala-xml_${scala.bin.version}</artifactId>
+      <version>1.0.6</version>
+    </dependency>
+
     <dependency>
       <groupId>com.googlecode.kiama</groupId>
       <artifactId>kiama_${scala.bin.version}</artifactId>
@@ -98,7 +103,7 @@
       <plugin>
         <groupId>net.alchim31.maven</groupId>
         <artifactId>scala-maven-plugin</artifactId>
-        <version>4.8.0</version>
+        <version>4.8.1</version>
         <executions>
           <execution>
             <goals>

polyglot-scala/src/it/java-and-scala-project-MavenModel/pom.scala

@@ -6,22 +6,22 @@ Model(
   name = "Test for Java + Scala compilation",
   description = "Test for Java + Scala compilation",
   dependencies = Seq(
-    "org.scala-lang" % "scala-library" % "2.12.15"
+    "org.scala-lang" % "scala-library" % "2.12.18"
   ),
   build = Build(
     pluginManagement = PluginManagement(
       plugins = Seq(
         Plugin(
-          "net.alchim31.maven" % "scala-maven-plugin" % "4.3.1"
+          "net.alchim31.maven" % "scala-maven-plugin" % "4.8.1"
         ),
         Plugin(
-          "org.apache.maven.plugins" % "maven-compiler-plugin" % "2.0.2"
+          "org.apache.maven.plugins" % "maven-compiler-plugin" % "3.11.0"
         )
       )
     ),
     plugins = Seq(
       Plugin(
-        "net.alchim31.maven" % "scala-maven-plugin" % "4.3.1",
+        "net.alchim31.maven" % "scala-maven-plugin" % "4.8.1",
         executions = Seq(
           Execution(
             id = "scala-compile-first",

polyglot-scala/src/main/scala/org/sonatype/maven/polyglot/scala/ScalaModelReader.scala

@@ -11,7 +11,7 @@ import scala.collection.immutable
 import scala.language.implicitConversions
 
 import com.twitter.io.StreamIO
-import com.twitter.util.Eval
+import org.sonatype.maven.polyglot.scala.eval.Eval
 
 import java.io._
 import java.util
@@ -260,7 +260,7 @@ class ScalaModelReader @Inject() (executeManager: ExecuteManager) extends ModelR
     try {
       eval.apply[ScalaModel](sourcePomFile)
     } catch {
-      case e: eval.CompilerException =>
+      case e: Eval.CompilerException =>
         // ModuleParseException is able to provide exact position (line nr., column nr.), so if later
         // versions of CompilerException make those information available, we should map them here (instead of zeros).
         // Currently, the information is only available as text in the exeception message.