From ada2a8aafaad65ca78d1141ae8be86003c26ab6f Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Mon, 29 Jan 2018 11:07:13 +0000
Subject: [PATCH] Give SourcePosition a macro instance creator

---
 build.sbt                                     | 14 ++++--
 .../scala/sbt/internal/util/Positions.scala   | 46 +++++++++++++++++++
 .../internal/util/SourcePositionSpec.scala    | 18 ++++++++
 3 files changed, 73 insertions(+), 5 deletions(-)
 create mode 100644 internal/util-position/src/test/scala/sbt/internal/util/SourcePositionSpec.scala

diff --git a/build.sbt b/build.sbt
index 5945c0429..cc43f2c35 100644
--- a/build.sbt
+++ b/build.sbt
@@ -94,11 +94,15 @@ lazy val utilControl = (project in internalPath / "util-control").settings(
   mimaSettings,
 )
 
-val utilPosition = (project in file("internal") / "util-position").settings(
-  commonSettings,
-  name := "Util Position",
-  mimaSettings,
-)
+val utilPosition = (project in file("internal") / "util-position")
+  .dependsOn(utilTesting % Test)
+  .settings(
+    commonSettings,
+    name := "Util Position",
+    scalacOptions += "-language:experimental.macros",
+    libraryDependencies += scalaReflect.value,
+    mimaSettings,
+  )
 
 // logging
 lazy val utilLogging = (project in internalPath / "util-logging")
diff --git a/internal/util-position/src/main/scala/sbt/internal/util/Positions.scala b/internal/util-position/src/main/scala/sbt/internal/util/Positions.scala
index a11ae9c24..ca3626db1 100644
--- a/internal/util-position/src/main/scala/sbt/internal/util/Positions.scala
+++ b/internal/util-position/src/main/scala/sbt/internal/util/Positions.scala
@@ -18,3 +18,49 @@ final case class LineRange(start: Int, end: Int) {
 final case class RangePosition(path: String, range: LineRange) extends FilePosition {
   def startLine = range.start
 }
+
+object SourcePosition {
+
+  /** Creates a SourcePosition by using the enclosing position of the invocation of this method.
+   * @see [[scala.reflect.macros.Enclosures#enclosingPosition]]
+   * @return SourcePosition
+   */
+  def fromEnclosing(): SourcePosition = macro SourcePositionMacro.fromEnclosingImpl
+
+}
+
+import scala.annotation.tailrec
+import scala.reflect.macros.blackbox
+import scala.reflect.internal.util.UndefinedPosition
+
+final class SourcePositionMacro(val c: blackbox.Context) {
+  import c.universe.{ NoPosition => _, _ }
+
+  def fromEnclosingImpl(): Expr[SourcePosition] = {
+    val pos = c.enclosingPosition
+    if (!pos.isInstanceOf[UndefinedPosition] && pos.line >= 0 && pos.source != null) {
+      val f = pos.source.file
+      val name = constant[String](ownerSource(f.path, f.name))
+      val line = constant[Int](pos.line)
+      reify { LinePosition(name.splice, line.splice) }
+    } else
+      reify { NoPosition }
+  }
+
+  private[this] def ownerSource(path: String, name: String): String = {
+    @tailrec def inEmptyPackage(s: Symbol): Boolean =
+      s != NoSymbol && (
+        s.owner == c.mirror.EmptyPackage
+          || s.owner == c.mirror.EmptyPackageClass
+          || inEmptyPackage(s.owner)
+      )
+
+    c.internal.enclosingOwner match {
+      case ec if !ec.isStatic       => name
+      case ec if inEmptyPackage(ec) => path
+      case ec                       => s"(${ec.fullName}) $name"
+    }
+  }
+
+  private[this] def constant[T: WeakTypeTag](t: T): Expr[T] = c.Expr[T](Literal(Constant(t)))
+}
diff --git a/internal/util-position/src/test/scala/sbt/internal/util/SourcePositionSpec.scala b/internal/util-position/src/test/scala/sbt/internal/util/SourcePositionSpec.scala
new file mode 100644
index 000000000..6fa955171
--- /dev/null
+++ b/internal/util-position/src/test/scala/sbt/internal/util/SourcePositionSpec.scala
@@ -0,0 +1,18 @@
+package sbt.internal.util
+
+import org.scalatest._
+
+class SourcePositionSpec extends FlatSpec {
+  "SourcePosition()" should "return a sane SourcePosition" in {
+    val filename = "SourcePositionSpec.scala"
+    val lineNumber = 9
+    SourcePosition.fromEnclosing() match {
+      case LinePosition(path, startLine) => assert(path === filename && startLine === lineNumber)
+      case RangePosition(path, range)    => assert(path === filename && inRange(range, lineNumber))
+      case NoPosition                    => fail("No source position found")
+    }
+  }
+
+  private def inRange(range: LineRange, lineNo: Int) =
+    range.start until range.end contains lineNo
+}