Merge pull request scala#5296 from retronym/ticket/SD-186

SD-186 Fix positions in trait method bytecode

Author: lrytz

src/compiler/scala/tools/nsc/ast/TreeGen.scala

@@ -350,7 +350,7 @@ abstract class TreeGen extends scala.reflect.internal.TreeGen with TreeDSL {
       case mt @ MethodType(params, res) => copyMethodType(mt, selfParamSym :: params, res)
     })
     val selfParam = ValDef(selfParamSym)
-    val rhs = orig.rhs.substituteThis(newSym.owner, atPos(newSym.pos)(gen.mkAttributedIdent(selfParamSym)))
+    val rhs = orig.rhs.substituteThis(newSym.owner, gen.mkAttributedIdent(selfParamSym)) // SD-186 intentionally leaving Ident($this) is unpositioned
       .substituteSymbols(origParams, newSym.info.params.drop(1)).changeOwner(origSym -> newSym)
     treeCopy.DefDef(orig, orig.mods, orig.name, orig.tparams, (selfParam :: orig.vparamss.head) :: Nil, orig.tpt, rhs).setSymbol(newSym)
   }

test/junit/scala/tools/nsc/backend/jvm/BytecodeTest.scala

@@ -168,4 +168,23 @@ class BytecodeTest extends BytecodeTesting {
     assertEquals(x.start, labels(1))
     assertEquals(x.end, labels(7))
   }
+
+  @Test // wrong line numbers for rewritten `this` references in trait static methods
+  def sd186_traitLineNumber(): Unit = {
+    val code =
+      """trait T {
+        |  def t(): Unit = {
+        |    toString
+        |    toString
+        |  }
+        |}
+      """.stripMargin
+    val t = compileClass(code)
+    val tMethod = getMethod(t, "t$")
+    val invoke = Invoke(INVOKEVIRTUAL, "java/lang/Object", "toString", "()Ljava/lang/String;", false)
+    assertSameCode(tMethod.instructions,
+      List(Label(0), LineNumber(3, Label(0)), VarOp(ALOAD, 0), invoke, Op(POP),
+        Label(5), LineNumber(4, Label(5)), VarOp(ALOAD, 0), invoke, Op(POP), Op(RETURN), Label(11))
+    )
+  }
 }