Better [un]used dependency checking

src/main/scala/higherkindness/rules_scala/used_deps/BUILD

@@ -0,0 +1,43 @@
+load("//rules:scalafmt.bzl", "scala_format_test")
+load("//rules:scala.bzl", "scala_library")
+
+scala_library(
+    name = "used_deps",
+    srcs = glob(["**/*.scala"]),
+    scala = "//external:scala_annex_scala",
+    visibility = ["//visibility:public"],
+    deps = [        
+        "@scala_annex_scala_2_12_scala_compiler//jar",
+        "@scala_annex_scala_2_12_scala_reflect//jar",
+    ],
+    resource_jars = [
+        ":resources",
+    ],
+)
+
+_gen_plugin_xml_cmd = """
+cat > $@ << EOF
+<plugin>
+  <name>name</name>
+  <classname>higherkindness.rules_scala.used_deps.UsedDepsPlugin</classname>
+</plugin>
+"""
+
+genrule(
+    name = "gen-scalac-plugin.xml",
+    outs = ["scalac-plugin.xml"],
+    cmd = _gen_plugin_xml_cmd,
+)
+
+java_binary(
+    name = "resources",
+    classpath_resources = [
+        ":gen-scalac-plugin.xml",
+    ],
+    create_executable = False,
+)
+
+scala_format_test(
+    name = "format",
+    srcs = glob(["**/*.scala"]),
+)

src/main/scala/higherkindness/rules_scala/used_deps/plugin.scala

@@ -0,0 +1,94 @@
+package higherkindness.rules_scala
+package used_deps
+
+import scala.reflect.io.AbstractFile
+import scala.reflect.io.NoAbstractFile
+import scala.reflect.internal.SymbolTable
+import scala.tools.nsc.Global
+import scala.tools.nsc.Phase
+import scala.tools.nsc.plugins.Plugin
+import scala.tools.nsc.plugins.PluginComponent
+import scala.util.matching.Regex
+
+import java.io.File
+
+final class UsedDepsPlugin(override val global: Global) extends Plugin {
+
+  override val name: String = "used-deps"
+  override val description: String = "tracks used dependencies"
+  override val components: List[PluginComponent] = usedDeps :: Nil
+
+  private object usedDeps extends PluginComponent {
+    override val global: Global = UsedDepsPlugin.this.global
+    override val phaseName: String = "unused-deps"
+    override val runsAfter: List[String] = global.refChecks.phaseName :: Nil
+
+    private[used_deps] var outputFile: Option[File] = None
+
+    override def newPhase(prev: Phase): Phase =
+      new StdPhase(prev) with UsedDepsPhase[global.type] {
+        val global = usedDeps.this.global
+      }
+  }
+
+  override val optionsHelp: Option[String] = Some(
+    "  -P:unused-deps:out=<path> Path to write output file (default: stdout)"
+  )
+
+  private implicit final class RegexInterpolator(sc: StringContext) {
+    def r = new Regex(sc.parts.mkString, sc.parts.tail.map(_ => "x"): _*)
+  }
+
+  override def init(options: List[String], error: String => Unit): Boolean = {
+    options.foreach {
+      case r"out=(.*)$out" =>
+        usedDeps.outputFile = Some(new File(out))
+      case arg =>
+        error(s"Unexpected argument: $arg")
+    }
+    true
+  }
+
+  {
+    hijackField(classOf[SymbolTable], "traceSymbolActivity", true)
+  }
+
+  if (global.traceSymbolActivity != true)
+    sys.error("unable to force tracing of symbol activity")
+
+  private[this] def hijackField[T](clazz: Class[_], name: String, newValue: T): T = {
+    val field = clazz.getDeclaredField(name)
+    field.setAccessible(true)
+    val oldValue = field.get(global).asInstanceOf[T]
+    field.set(global, newValue)
+    oldValue
+  }
+
+}
+
+
+trait UsedDepsPhase[G <: Global] {
+  val global: G
+  import global._
+
+  def apply(unit: CompilationUnit): Unit = {
+    val map = traceSymbols.allSymbols.values
+      .filter(_.associatedFile != NoAbstractFile)
+      .filter(_.associatedFile.file != null)
+      .foldLeft(Map.empty[File, List[Symbol]]) { (acc, sym) =>
+        val k = sym.associatedFile.file
+        acc.get(k) match {
+          case Some(vv) => acc + ((k, sym :: vv))
+          case None => acc + ((k, sym :: Nil))
+        }
+      }
+
+    map.foreach { case (k, v) =>
+      println(k)
+      v.foreach(sym => println(" " + sym))
+    }
+
+    ()
+  }
+
+}

src/test/scala/higherkindness/rules_scala/used_deps/BUILD

@@ -0,0 +1,47 @@
+load("//rules:scalafmt.bzl", "scala_format_test")
+load("//rules:scala.bzl", "scala_library")
+
+scala_library(
+    name = "LibA1",
+    srcs = [
+         "LibA1.scala",
+    ],
+    scala = "//external:scala_annex_scala",
+    plugins = [
+        "//src/main/scala/higherkindness/rules_scala/used_deps",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+scala_library(
+    name = "LibA2",
+    srcs = [
+         "LibA2.scala",
+    ],
+    scala = "//external:scala_annex_scala",
+    plugins = [
+        "//src/main/scala/higherkindness/rules_scala/used_deps",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+scala_library(
+    name = "LibB",
+    srcs = [
+         "LibB.scala",
+    ],
+    deps = [
+         ":LibA1",
+         ":LibA2",
+    ],
+    scala = "//external:scala_annex_scala",
+    plugins = [
+        "//src/main/scala/higherkindness/rules_scala/used_deps",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+scala_format_test(
+    name = "format",
+    srcs = glob(["**/*.scala"]),
+)

src/test/scala/higherkindness/rules_scala/used_deps/LibA1.scala

@@ -0,0 +1,4 @@
+package higherkindness.rules_scala
+package used_deps
+
+trait LibA1

src/test/scala/higherkindness/rules_scala/used_deps/LibA2.scala

@@ -0,0 +1,4 @@
+package higherkindness.rules_scala
+package used_deps
+
+trait LibA2

src/test/scala/higherkindness/rules_scala/used_deps/LibB.scala

@@ -0,0 +1,4 @@
+package higherkindness.rules_scala
+package used_deps
+
+trait LibB extends LibA1 with LibA2

src/test/scala/higherkindness/rules_scala/used_deps/test1.scala

@@ -0,0 +1,6 @@
+package higherkindness.rules_scala
+package test1
+
+class Test1 {
+
+}