Wunused: only filter out non-zero span-length givens

Author: szymon-rd

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -478,7 +478,7 @@ object CheckUnused:
         if ctx.settings.WunusedHas.implicits then
           implicitParamInScope
             .filterNot(d => d.symbol.usedDefContains)
-            .filterNot(d => containsSyntheticSuffix(d.symbol) && !d.rawMods.is(Given))
+            .filterNot(d => containsSyntheticSuffix(d.symbol) && (!d.rawMods.is(Given) || hasZeroLengthSpan(d.symbol)))
             .map(d => d.namePos -> WarnTypes.ImplicitParams).toList
         else
           Nil
@@ -519,11 +519,18 @@ object CheckUnused:
         val importedMembers = qual.tpe.member(sel.name).alternatives.map(_.symbol)
         importedMembers.exists(s => s.is(Transparent) && s.is(Inline))
       }).exists(identity)
+
     /**
      * Heuristic to detect synthetic suffixes in names of symbols
      */
     private def containsSyntheticSuffix(symbol: Symbol)(using Context): Boolean =
       symbol.name.mangledString.contains("$")
+
+    /**
+     * Heuristic to detect generated symbols by checking if symbol has zero length span in source
+     */
+    private def hasZeroLengthSpan(symbol: Symbol)(using Context): Boolean =
+      symbol.span.end - symbol.span.start == 0
     /**
      * Is the the constructor of synthetic package object
      * Should be ignored as it is always imported/used in package