Fix #7839: Improve error message for implicit parameters

Author: nicolasstucki

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

@@ -160,12 +160,12 @@ object Splicer {
           // OK
 
         case _ =>
+          val extra = if tree.span.isZeroExtent then ": " + tree.show else ""
           ctx.error(
-            """Malformed macro parameter
+            s"""Malformed macro parameter$extra
               |
-              |Parameters may be:
+              |Parameters may only be:
               | * Quoted parameters or fields
-              | * References to inline parameters
               | * Literal values of primitive types
               |""".stripMargin, tree.sourcePos)
       }

tests/neg-macros/i7839.check

@@ -0,0 +1,8 @@
+-- Error: tests/neg-macros/i7839.scala:4:18 ----------------------------------------------------------------------------
+4 |  ${ transformImpl } // error
+  |                  ^
+  |                  Malformed macro parameter: dummyImplicit
+  |
+  |                  Parameters may only be:
+  |                   * Quoted parameters or fields
+  |                   * Literal values of primitive types

tests/neg-macros/i7839.scala

@@ -0,0 +1,6 @@
+import scala.quoted._
+
+inline def transform(using dummyImplicit: DummyImplicit): Unit =
+  ${ transformImpl } // error
+
+def transformImpl(using dummyImplicit: DummyImplicit)(using QuoteContext): Expr[Unit] = ???