Fix javadoc errors

Release failed because Javadocs in scalafix-interfaces reported
warnings.

build.sbt

@@ -9,14 +9,21 @@ inThisBuild(
 
 noPublish
 
+// force javac to fork by setting javaHome to get error messages during compilation,
+// see https://github.com/sbt/zinc/issues/520
+def inferJavaHome() =
+  Some(file(System.getProperty("java.home")).getParentFile)
+
 lazy val interfaces = project
   .in(file("scalafix-interfaces"))
   .settings(
-    javaHome.in(Compile) := {
-      // force javac to fork by setting javaHome to get error messages during compilation,
-      // see https://github.com/sbt/zinc/issues/520
-      Some(file(sys.props("java.home")).getParentFile)
-    },
+    javacOptions.in(Compile) ++= List(
+      "-Xlint:all",
+      "-Werror"
+    ),
+    javacOptions.in(Compile, doc) := List("-Xdoclint:none"),
+    javaHome.in(Compile) := inferJavaHome(),
+    javaHome.in(Compile, doc) := inferJavaHome(),
     moduleName := "scalafix-interfaces",
     crossVersion := CrossVersion.disabled,
     crossScalaVersions := List(scala212),

project/ScalafixBuild.scala

@@ -178,6 +178,7 @@ object ScalafixBuild extends AutoPlugin with GhpagesKeys {
     commands += Command.command("ci-212") { s =>
       "++2.12.6" ::
         "unit/test" ::
+        "interfaces/doc" ::
         s
     },
     commands += Command.command("ci-211") { s =>

scalafix-interfaces/src/main/java/scalafix/interfaces/Scalafix.java

@@ -36,27 +36,27 @@ public interface Scalafix {
     String mainHelp(int screenWidth);
 
     /**
-     * @return The release version of the current Scalafix API instance.
+     * The release version of the current Scalafix API instance.
      */
     String scalafixVersion();
 
     /**
-     * @return The recommended Scalameta version to match the current Scalafix API instance.
+     * The recommended Scalameta version to match the current Scalafix API instance.
      */
     String scalametaVersion();
 
     /**
-     * @return The exact Scala versions that are supported by the recommended {@link #scalametaVersion()}
+     * The exact Scala versions that are supported by the recommended {@link #scalametaVersion()}
      */
     String[] supportedScalaVersions();
 
     /**
-     * @return The most recent Scala 2.11 version in {@link #supportedScalaVersions()}
+     * The most recent Scala 2.11 version in {@link #supportedScalaVersions()}
      */
     String scala211();
 
     /**
-     * @return The most recent Scala 2.12 version in {@link #supportedScalaVersions()}
+     * The most recent Scala 2.12 version in {@link #supportedScalaVersions()}
      */
     String scala212();
 

scalafix-interfaces/src/main/java/scalafix/interfaces/ScalafixException.java

@@ -4,6 +4,7 @@
  * An error occurred while classloading an instance of {@link Scalafix}.
  */
 public class ScalafixException extends Exception {
+    static final long serialVersionUID = 118L;
     ScalafixException(String message, Exception cause) {
         super(message, cause);
     }

scalafix-interfaces/src/main/java/scalafix/interfaces/ScalafixSeverity.java

@@ -1,5 +1,8 @@
 package scalafix.interfaces;
 
+/**
+ * The logging level at which Scalafix diagnostics are reported.
+ */
 public enum ScalafixSeverity {
     INFO,
     WARNING,