[nomaster] typecheck(q"class C") no longer crashes

MemberDefs alone can't be typechecked as is, because namer only names
contents of PackageDefs, Templates and Blocks. And, if not named, a tree
can't be typed.

This commit solves this problem by wrapping typecheckees in a trivial block
and then unwrapping the result when it returns back from the typechecker.

(cherry picked from commit 609047ba372ceaf06916d3361954bc949a6906ee)

1 files changed, 15 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 53b9b1d88e..0e5985face 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -1538,6 +1538,21 @@ trait Trees extends api.Trees { self: SymbolTable =>
 
   def duplicateAndKeepPositions(tree: Tree) = new Duplicator(focusPositions = false) transform tree
 
+  def wrapIntoTerm(tree: Tree): Tree = {
+    if (!tree.isTerm) Block(List(tree), Literal(Constant(()))) else tree
+  }
+
+  // this is necessary to avoid crashes like https://github.com/scalamacros/paradise/issues/1
+  // when someone tries to c.typecheck a naked MemberDef
+  def wrappingIntoTerm(tree0: Tree)(op: Tree => Tree): Tree = {
+    val neededWrapping = !tree0.isTerm
+    val tree1 = wrapIntoTerm(tree0)
+    op(tree1) match {
+      case Block(tree2 :: Nil, Literal(Constant(()))) if neededWrapping => tree2
+      case tree2 => tree2
+    }
+  }
+
   // ------ copiers -------------------------------------------
 
   def copyDefDef(tree: Tree)(