Try improving error

Author: Blaisorblade

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1478,10 +1478,10 @@ object messages {
     val explanation = ""
   }
 
-  case class DoesNotConformToBound(tpe: Type, which: String, bound: Type)(
+  case class DoesNotConformToBound(tpe: Type, which: String, bound: Type, inferred: Boolean)(
     err: typer.ErrorReporting.Errors)(implicit ctx: Context)
     extends Message(DoesNotConformToBoundID) {
-    val msg = hl"Type argument ${tpe} does not conform to $which bound $bound ${err.whyNoMatchStr(tpe, bound)}"
+    val msg = hl"${if (inferred) "Inferred type" else "Type"} argument $tpe does not conform to $which bound $bound ${err.whyNoMatchStr(tpe, bound)}"
     val kind = "Type Mismatch"
     val explanation = ""
   }

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -45,12 +45,10 @@ object Checking {
       }
     }
     for ((arg, which, bound) <- ctx.boundsViolations(args, boundss, instantiate)) {
-      if (arg.pos.isZeroExtent)
-        ctx.error(
-          DoesNotConformToBound(arg.tpe, which, bound)(err),
-          arg.pos.focus)
-      else
-        ctx.error(hl"inferred type ${arg.tpe} violates $which bound $bound", arg.pos.focus)
+      println(s"arg.pos ${arg.pos}, ${arg.pos.isSynthetic}")
+      ctx.error(
+        DoesNotConformToBound(arg.tpe, which, bound, arg.pos.isZeroExtent)(err),
+        arg.pos.focus)
     }
   }
 

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -629,10 +629,11 @@ class ErrorMessagesTests extends ErrorMessagesTest {
     .expect { (ictx, messages) =>
       implicit val ctx: Context = ictx
       assertMessageCount(1, messages)
-      val DoesNotConformToBound(tpe, which, bound) :: Nil = messages
+      val DoesNotConformToBound(tpe, which, bound, inferred) :: Nil = messages
       assertEquals("Int", tpe.show)
       assertEquals("upper", which)
       assertEquals("List[Int]", bound.show)
+      assertEquals(true, inferred)
     }
 
   @Test def doesNotConformToSelfType =