add capture_args macro for type-safe embedding of stringly typed apis

2 files changed, 61 insertions, 0 deletions

diff --git a/libraries/capture_args/build/build.scala b/libraries/capture_args/build/build.scala
new file mode 100644
index 0000000..24c1faa
--- /dev/null
+++ b/libraries/capture_args/build/build.scala
@@ -0,0 +1,11 @@
+package cbt_build.cbt.capture_args
+import cbt._
+class Build(val context: Context) extends BaseBuild{
+  override def dependencies = (
+    super.dependencies ++ // don't forget super.dependencies here for scala-library, etc.
+    Resolver( mavenCentral ).bind(
+      MavenDependency( "org.scala-lang", "scala-reflect", scalaVersion )
+    )
+  )
+  override def scalacOptions = super.scalacOptions :+ "-language:experimental.macros"
+}
diff --git a/libraries/capture_args/macros.scala b/libraries/capture_args/macros.scala
new file mode 100644
index 0000000..8f2d747
--- /dev/null
+++ b/libraries/capture_args/macros.scala
@@ -0,0 +1,50 @@
+package cbt.capture_args
+import scala.reflect._
+import scala.reflect.macros.blackbox.Context
+
+case class Argument( annotations: Seq[annotation.Annotation], name: String, values: Option[Seq[String]] ){
+  def toSeqOption = values.map( name +: _ )
+}
+case class Signature( name: String, args: Seq[Argument] )
+object `package`{
+  def captureArgsImplementation(c: Context): c.Tree = {
+    import c.universe._
+
+    def literal( a: Any ) = Literal(Constant(a))
+    def ident( name: String ) = Ident(TermName(name))
+
+    def findOwnerRecursive(symbol: Symbol, predicate: Symbol => Boolean): Option[Symbol] = {
+      Option(symbol).flatMap{
+        s =>
+        if(s == NoSymbol) None else if(predicate(s)) Some(s) else findOwnerRecursive(s.owner, predicate)
+      }
+    }
+
+    val method: MethodSymbol = (
+      findOwnerRecursive(c.internal.enclosingOwner, _.isMethod).map(_.asMethod)
+      orElse
+      findOwnerRecursive(c.internal.enclosingOwner, _.isClass).map(_.asClass.primaryConstructor.asMethod)
+      getOrElse {
+        c.error(
+          c.enclosingPosition,
+          "embed needs to be called in the body of a qualified method"
+        )
+        ???
+      }
+    )
+    val name = literal(method.name.decodedName.toString)
+    // Note: method.paramLists requires explicitly annotated result type
+    val params = method.paramLists.flatten.map(_.asTerm)
+
+    val args = params.map{ s =>
+      val name = literal( s.name.decodedName.toString )
+      val i = ident( s.name.toString )
+      q"_root_.cbt.capture_args.Argument( _root_.scala.Seq( ..${s.annotations.map(_.tree)} ), $name, valueToStrings($i) )"
+    }
+    val tree = q"""
+    _root_.cbt.capture_args.Signature( name = $name, args = Seq( ..$args ) )
+    """
+    tree
+  }
+  def captureArgs: Signature = macro captureArgsImplementation
+}