add syntactic extractor for assignment-like trees

There are three kinds of assign-like trees:

1. Assign(lhs, rhs)                          // $lhs = $rhs
3. AssignOrNamedArg(lhs, rhs)                // $lhs = $rhs
2. Apply(Select(f, nme.update), args :+ rhs) // $f(..$args) = $rhs

New syntactic combinator unifies all of them and lets users not to think
about these implementations details.

4 files changed, 27 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/api/BuildUtils.scala b/src/reflect/scala/reflect/api/BuildUtils.scala
index 60c2a81947..551c27bf9c 100644
--- a/src/reflect/scala/reflect/api/BuildUtils.scala
+++ b/src/reflect/scala/reflect/api/BuildUtils.scala
@@ -193,5 +193,12 @@ private[reflect] trait BuildUtils { self: Universe =>
       def apply(mods: Modifiers, name: TermName, tpt: Tree, rhs: Tree): ValDef
       def unapply(tree: Tree): Option[(Modifiers, TermName, Tree, Tree)]
     }
+
+    val SyntacticAssign: SyntacticAssignExtractor
+
+    trait SyntacticAssignExtractor {
+      def apply(lhs: Tree, rhs: Tree): Tree
+      def unapply(tree: Tree): Option[(Tree, Tree)]
+    }
   }
 }
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index 2584dcb117..1049f83d46 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -139,7 +139,7 @@ trait BuildUtils { self: SymbolTable =>
 
     object SyntacticApplied extends SyntacticAppliedExtractor {
       def apply(tree: Tree, argss: List[List[Tree]]): Tree =
-        argss.foldLeft(tree) { Apply(_, _) }
+        argss.foldLeft(tree) { (f, args) => Apply(f, args.map(treeInfo.assignmentToMaybeNamedArg)) }
 
       def unapply(tree: Tree): Some[(Tree, List[List[Tree]])] = {
         val treeInfo.Applied(fun, targs, argss) = tree
@@ -400,6 +400,16 @@ trait BuildUtils { self: SymbolTable =>
 
     object SyntacticValDef extends SyntacticValDefBase { val isMutable = false }
     object SyntacticVarDef extends SyntacticValDefBase { val isMutable = true }
+
+    object SyntacticAssign extends SyntacticAssignExtractor {
+      def apply(lhs: Tree, rhs: Tree): Tree = gen.mkAssign(lhs, rhs)
+      def unapply(tree: Tree): Option[(Tree, Tree)] = tree match {
+        case Assign(lhs, rhs) => Some((lhs, rhs))
+        case AssignOrNamedArg(lhs, rhs) => Some((lhs, rhs))
+        case Apply(Select(fn, nme.update), args :+ rhs) => Some((atPos(fn.pos)(Apply(fn, args)), rhs))
+        case _ => None
+      }
+    }
   }
 
   val build: BuildApi = new BuildImpl
diff --git a/src/reflect/scala/reflect/internal/StdNames.scala b/src/reflect/scala/reflect/internal/StdNames.scala
index 6407a3979c..f4eae5590a 100644
--- a/src/reflect/scala/reflect/internal/StdNames.scala
+++ b/src/reflect/scala/reflect/internal/StdNames.scala
@@ -602,6 +602,7 @@ trait StdNames {
     val SelectFromTypeTree: NameType   = "SelectFromTypeTree"
     val StringContext: NameType        = "StringContext"
     val SyntacticApplied: NameType     = "SyntacticApplied"
+    val SyntacticAssign: NameType      = "SyntacticAssign"
     val SyntacticBlock: NameType       = "SyntacticBlock"
     val SyntacticClassDef: NameType    = "SyntacticClassDef"
     val SyntacticDefDef: NameType      = "SyntacticDefDef"
diff --git a/src/reflect/scala/reflect/internal/TreeGen.scala b/src/reflect/scala/reflect/internal/TreeGen.scala
index 26adf20c52..0050df67d8 100644
--- a/src/reflect/scala/reflect/internal/TreeGen.scala
+++ b/src/reflect/scala/reflect/internal/TreeGen.scala
@@ -443,4 +443,12 @@ abstract class TreeGen extends macros.TreeBuilder {
     case head :: Nil => head
     case _ => gen.mkBlock(stats)
   }
+
+  /** Create a tree representing an assignment <lhs = rhs> */
+  def mkAssign(lhs: Tree, rhs: Tree): Tree = lhs match {
+    case Apply(fn, args) =>
+      Apply(atPos(fn.pos)(Select(fn, nme.update)), args :+ rhs)
+    case _ =>
+      Assign(lhs, rhs)
+  }
 }