Merge pull request #191 from valydia/lazy-val

Evaluate lazy vals lazily (fixes #179)

mdoc/src/main/scala/mdoc/internal/markdown/Instrumenter.scala

@@ -6,6 +6,7 @@ import scala.meta._
 import scala.meta.inputs.Position
 import Instrumenter.position
 import mdoc.internal.markdown.Instrumenter.Binders
+import scala.meta.Mod.Lazy
 
 class Instrumenter(sections: List[SectionInput]) {
   def instrument(): String = {
@@ -122,6 +123,7 @@ object Instrumenter {
     def binders(pat: Pat): List[Name] =
       pat.collect { case m: Member => m.name }
     def unapply(tree: Tree): Option[List[Name]] = tree match {
+      case Defn.Val(mods, _, _, _) if mods.exists(_.isInstanceOf[Lazy]) => Some(Nil)
       case Defn.Val(_, pats, _, _) => Some(pats.flatMap(binders))
       case Defn.Var(_, pats, _, _) => Some(pats.flatMap(binders))
       case _: Defn => Some(Nil)

tests/unit/src/test/scala/tests/markdown/DefaultSuite.scala

@@ -69,6 +69,62 @@ class DefaultSuite extends BaseMarkdownSuite {
       """.stripMargin
   )
 
+  check(
+    "lazy-val",
+    """
+      |```scala mdoc
+      |lazy val x = ???
+      |List(1).map(_ + 1)
+      |res0.length
+      |```
+      |
+      |```scala mdoc
+      |println(1)
+      |```
+    """.stripMargin,
+    """|```scala
+       |lazy val x = ???
+       |List(1).map(_ + 1)
+       |// res0: List[Int] = List(2)
+       |res0.length
+       |// res1: Int = 1
+       |```
+       |
+       |```scala
+       |println(1)
+       |// 1
+       |```
+    """.stripMargin
+  )
+
+  check(
+    "lazy-val 2",
+    """
+      |```scala mdoc
+      |lazy val x = 3
+      |List(1).map(_ + x)
+      |res0.length
+      |```
+      |
+      |```scala mdoc
+      |println(1)
+      |```
+    """.stripMargin,
+    """|```scala
+       |lazy val x = 3
+       |List(1).map(_ + x)
+       |// res0: List[Int] = List(4)
+       |res0.length
+       |// res1: Int = 1
+       |```
+       |
+       |```scala
+       |println(1)
+       |// 1
+       |```
+    """.stripMargin
+  )
+
   check(
     "defn",
     """