Fix #8716 and fix #8717: Add missing extension span

Author: nicolasstucki

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3573,6 +3573,7 @@ object Parsers {
      */
     def extensionDef(start: Offset, mods: Modifiers): ModuleDef =
       in.nextToken()
+      val nameOffset = in.offset
       val name = if isIdent && !isIdent(nme.on) then ident() else EmptyTermName
       in.endMarkerScope(if name.isEmpty then nme.extension else name) {
         val (tparams, vparamss, extensionFlag) =
@@ -3588,7 +3589,7 @@ object Parsers {
         if !in.isNestedStart then syntaxError("Extension without extension methods")
         val templ = templateBodyOpt(makeConstructor(tparams, vparamss), Nil, Nil)
         templ.body.foreach(checkExtensionMethod(tparams, vparamss, _))
-        val edef = ModuleDef(name, templ)
+        val edef = atSpan(start, nameOffset, in.offset)(ModuleDef(name, templ))
         finalizeDef(edef, addFlag(mods, Given | extensionFlag), start)
       }
 

compiler/test-resources/repl/i8716_i8717

@@ -0,0 +1,14 @@
+scala>extension { }
+1 |extension { }
+  |^
+  |anonymous instance must implement a type or have at least one extension method
+scala> extension as on
+1 | extension as on
+  |                ^
+  |                '(' expected, but eof found
+scala> extension as on (s
+1 | extension as on (s
+  |                   ^
+  |                   ':' expected, but eof found
+scala> extension as on (s: String) { def expand = ??? }
+// defined object as