SI-6931 cleans up the position API

I have finally overcome my fear of positions and got to cleaning up its
public interface.

Apparently it isn’t so bad, since there’s a sane core of methods (thanks
to whoever wrote the comments to internal#Position):
  1) Checks to distinguish offsets, opaque ranges and transparent ranges
  2) Essentials that inclide start, point, end and source
  3) Factories that create new positions based on existing ones

It looks like methods from the 3rd group are exactly what we’ve been looking
for in SI-6931, so we have nothing to add in this commit.

4 files changed, 30 insertions, 1 deletions

diff --git a/test/files/neg/t6931.check b/test/files/neg/t6931.check
new file mode 100644
index 0000000000..7cf804a936
--- /dev/null
+++ b/test/files/neg/t6931.check
@@ -0,0 +1,10 @@
+Test_2.scala:3: error: 1
+  err"123"
+      ^
+Test_2.scala:3: error: 2
+  err"123"
+       ^
+Test_2.scala:3: error: 3
+  err"123"
+        ^
+three errors found
diff --git a/test/files/neg/t6931/Macros_1.scala b/test/files/neg/t6931/Macros_1.scala
new file mode 100644
index 0000000000..56da075d1f
--- /dev/null
+++ b/test/files/neg/t6931/Macros_1.scala
@@ -0,0 +1,15 @@
+import scala.language.experimental.macros
+import scala.reflect.macros.blackbox.Context
+
+object Macros {
+  implicit class Error(ctx: StringContext) {
+    def err(args: Any*): Unit = macro impl
+  }
+
+  def impl(c: Context)(args: c.Tree*): c.Tree = {
+    import c.universe._
+    val q"Macros.Error(scala.StringContext.apply($arg)).err()" = c.macroApplication
+    for (i <- 1 to 3) c.error(arg.pos.withPoint(arg.pos.point + i - 1), i.toString)
+    q"()"
+  }
+}
\ No newline at end of file
diff --git a/test/files/neg/t6931/Test_2.scala b/test/files/neg/t6931/Test_2.scala
new file mode 100644
index 0000000000..6a6f645904
--- /dev/null
+++ b/test/files/neg/t6931/Test_2.scala
@@ -0,0 +1,4 @@
+object Test extends App {
+  import Macros._
+  err"123"
+}
\ No newline at end of file
diff --git a/test/files/pos/t8013/inpervolator_1.scala b/test/files/pos/t8013/inpervolator_1.scala
index 89b7c22709..612e1d727d 100644
--- a/test/files/pos/t8013/inpervolator_1.scala
+++ b/test/files/pos/t8013/inpervolator_1.scala
@@ -18,7 +18,7 @@ object Perverse {
   def pImpl(c: Context)(args: c.Expr[Any]*): c.Expr[String] = {
     import c.universe._
     val macroPos = c.macroApplication.pos
-    val text = macroPos.lineContent substring macroPos.column
+    val text = macroPos.source.lineToString(macroPos.line - 1) substring macroPos.column
     val tt = Literal(Constant(text))
     val tree = q"t8013.Perverse.pervert($tt)"
     c.Expr[String](tree)