Add a way to construct custom position in TASTy Reflect

compiler/src/dotty/tools/dotc/tastyreflect/KernelImpl.scala

@@ -1310,6 +1310,9 @@ class KernelImpl(val rootContext: core.Contexts.Context, val rootPosition: util.
   def Position_sourceCode(self: Position): String =
     new String(self.source.content(), self.start, self.end - self.start)
 
+  def Position_withOffset(self: Position)(start: Int, end: Int): Position =
+    util.SourcePosition(self.source, util.Spans.Span(start, end))
+
   //
   // COMMENTS
   //

library/src/scala/tasty/reflect/Kernel.scala

@@ -1067,6 +1067,12 @@ trait Kernel {
   /** Source code within the position */
   def Position_sourceCode(self: Position): String
 
+  /** Create a position that ranges from start to end (exclusive) in the given source
+   *  @param start index of the start of the range (0 <= start < end)
+   *  @param end index of the end of the range (start < end <= sizeOf(pos.sourceFile))
+   */
+  def Position_withOffset(self: Position)(start: Int, end: Int): Position
+
   //
   // COMMENTS
   //

library/src/scala/tasty/reflect/PositionOps.scala

@@ -31,6 +31,13 @@ trait PositionOps extends Core {
     /** Source code within the position */
     def sourceCode: String = kernel.Position_sourceCode(pos)
 
+    /** Create a position that ranges from start to end (exclusive) in the given source
+     *  @param start index of the start of the range (0 <= start < end)
+     *  @param end index of the end of the range (start < end <= sizeOf(pos.sourceFile))
+     */
+    def withOffset(start: Int = pos.start, end: Int = pos.end): Position =
+      kernel.Position_withOffset(pos)(start, end)
+
   }
 
 }

tests/neg/tasty-macro-positions.check

@@ -0,0 +1,4 @@
+<122..125> in quoted_2.scala
+here (+5) is the the argument is foo
+[117..120] in quoted_2.scala
+here is the the argument is foo

tests/neg/tasty-macro-positions/quoted_1.scala

@@ -0,0 +1,17 @@
+import scala.quoted._
+
+import scala.tasty._
+
+object Macros {
+
+  inline def fun(x: Any): Unit = ${ impl('x) }
+
+  def impl(x: Expr[Any])(implicit reflect: Reflection): Expr[Unit] = {
+    import reflect._
+    val pos = x.unseal.underlyingArgument.pos
+    error("here is the the argument is " + x.unseal.underlyingArgument.showCode, pos)
+    error("here (+5) is the the argument is " + x.unseal.underlyingArgument.showCode, pos.withOffset(start = pos.start + 5, end = pos.end + 5))
+    '{}
+  }
+
+}

tests/neg/tasty-macro-positions/quoted_2.scala

@@ -0,0 +1,11 @@
+
+import Macros._
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    def foo: String = "abc"
+    fun(
+      foo // error // error
+    )
+  }
+}