SI-8064 Automatic position repair for macro expansion

  - Replace NoPosition with the focus of the macro application
  - Focus all range positions, for example, those of spliced arguments

Author: retronym

src/compiler/scala/tools/nsc/typechecker/Macros.scala

@@ -761,7 +761,22 @@ trait Macros extends FastTrack with MacroRuntimes with Traces with Helpers {
             macroLogLite("" + expanded + "\n" + showRaw(expanded))
             val freeSyms = expanded.freeTerms ++ expanded.freeTypes
             freeSyms foreach (sym => MacroFreeSymbolError(expandee, sym))
-            Success(atPos(enclosingMacroPosition.focus)(expanded))
+            // Macros might have spliced arguments with range positions into non-compliant
+            // locations, notably, under a tree without a range position. Or, they might
+            // spice a tree that `resetAttrs` has assigned NoPosition.
+            //
+            // Here, we just convert all positions in the tree to offset positions, and
+            // convert NoPositions to something sensible.
+            //
+            // Given that the IDE now sees the expandee (by using -Ymacro-expand:discard),
+            // this loss of position fidelity shouldn't cause any real problems.
+            val expandedPos = enclosingMacroPosition.focus
+            def fixPosition(pos: Position) =
+              if (pos == NoPosition) expandedPos else pos.focus
+            expanded.foreach(t => t.pos = fixPosition(t.pos))
+
+            val result = atPos(enclosingMacroPosition.focus)(expanded)
+            Success(result)
           }
           expanded match {
             case expanded: Expr[_] if expandee.symbol.isTermMacro => validateResultingTree(expanded.tree)

test/files/pos/t8064.flags

@@ -0,0 +1 @@
+-Yrangepos

test/files/pos/t8064/Client_2.scala

@@ -0,0 +1,8 @@
+object Test {
+  Macro {
+    def s = ""
+    Macro(s): @unchecked
+    ???
+  }
+}
+// Was: a range position validation error (unpositioned tree)

test/files/pos/t8064/Macro_1.scala

@@ -0,0 +1,10 @@
+import language.experimental.macros
+import scala.reflect.macros.Context
+
+object Macro {
+  def apply(a: Any): Any = macro impl
+
+  def impl(c: Context)(a: c.Tree): c.Tree = {
+    c.resetLocalAttrs(a)
+  }
+}

test/files/pos/t8064b.flags

@@ -0,0 +1 @@
+-Yrangepos

test/files/pos/t8064b/Client_2.scala

@@ -0,0 +1,6 @@
+object Test {
+  Macro {
+    "".reverse
+  }
+}
+// Was: a range position validation error (tree with offset position enclosing tree with range position)

test/files/pos/t8064b/Macro_1.scala

@@ -0,0 +1,11 @@
+import language.experimental.macros
+import scala.reflect.macros.Context
+
+object Macro {
+  def apply(a: Any): Any = macro impl
+  def impl(c: Context)(a: c.Tree): c.Tree = {
+    import c.universe._
+
+    q"{$a; true}"
+  }
+}