Add CollectionIndexOnNonIndexedSeq rule to Scapegoat

src/main/scala/com/sksamuel/scapegoat/ScapegoatConfig.scala

@@ -39,6 +39,7 @@ object ScapegoatConfig extends App {
     new CatchFatal,
     new CatchThrowable,
     new ClassNames,
+    new CollectionIndexOnNonIndexedSeq,
     new CollectionNamingConfusion,
     new CollectionNegativeIndex,
     new CollectionPromotionToAny,

src/main/scala/com/sksamuel/scapegoat/inspections/collections/CollectionIndexOnNonIndexedSeq.scala

@@ -0,0 +1,29 @@
+package com.sksamuel.scapegoat.inspections.collections
+
+import com.sksamuel.scapegoat._
+
+/** @author Josh Rosen */
+class CollectionIndexOnNonIndexedSeq extends Inspection {
+
+  def inspector(context: InspectionContext): Inspector = new Inspector(context) {
+    override def postTyperTraverser = Some apply new context.Traverser {
+
+      import context.global._
+
+      private def isSeq(t: Tree) = t.tpe <:< typeOf[Seq[_]]
+      private def isIndexedSeq(t: Tree) = t.tpe <:< typeOf[IndexedSeq[_]]
+
+      override def inspect(tree: Tree): Unit = {
+        tree match {
+          case Apply(Select(lhs, TermName("apply")), List(_)) if isSeq(lhs) && !isIndexedSeq(lhs) =>
+            context.warn("Seq.apply() on a non-IndexedSeq may cause performance problems",
+              tree.pos,
+              Levels.Warning,
+              tree.toString().take(100),
+              CollectionIndexOnNonIndexedSeq.this)
+          case _ => continue(tree)
+        }
+      }
+    }
+  }
+}

src/test/scala/com/sksamuel/scapegoat/inspections/collections/CollectionIndexOnNonIndexedSeqTest.scala

@@ -0,0 +1,34 @@
+package com.sksamuel.scapegoat.inspections.collections
+
+import com.sksamuel.scapegoat.PluginRunner
+import org.scalatest.{ FreeSpec, Matchers, OneInstancePerTest }
+
+/** @author Josh Rosen */
+class CollectionIndexOnNonIndexedSeqTest extends FreeSpec with Matchers with PluginRunner with OneInstancePerTest {
+
+  override val inspections = Seq(new CollectionIndexOnNonIndexedSeq)
+
+  "collection index on non indexed Seq" - {
+    "should report warning" in {
+      val code = """object Test {
+                      List(1,2,3)(1)
+                      Seq(1,2,3)(2)
+                      val s: Seq[Int] = Array(1,2,3)
+                      s(2)
+                    } """.stripMargin
+
+      compileCodeSnippet(code)
+      compiler.scapegoat.feedback.warnings.size shouldBe 3
+    }
+    "should not report warning" in {
+      val code = """object Test {
+                      Array(1,2,3)(1)
+                      IndexedSeq(1,2,3)(2)
+                      Vector(1,2,3)(2)
+                    } """.stripMargin
+
+      compileCodeSnippet(code)
+      compiler.scapegoat.feedback.warnings.size shouldBe 0
+    }
+  }
+}