SI-8291 Fix implicitNotFound message with type aliases

This pattern of code is typically a bug:

    if (f(tp.typeSymbol)) {
       g(tp.typeArgs)
    }

Intead, one needs to take the base type of `tp` wrt `tp.typeSymbol`.

This commit does exactly that when formatting the `@implicitNotFound`
custom error message.

Patch found on the back of an envelope in the handwriting of @adriaanm

1 files changed, 7 insertions, 0 deletions

diff --git a/test/files/neg/t8291.scala b/test/files/neg/t8291.scala
new file mode 100644
index 0000000000..b344586a56
--- /dev/null
+++ b/test/files/neg/t8291.scala
@@ -0,0 +1,7 @@
+@scala.annotation.implicitNotFound("Could not find implicit for ${T} or ${U}") trait X[T, U]
+
+object Test {
+  type Z[U] = X[Int, U]
+  implicitly[X[Int, String]]
+  implicitly[Z[String]]
+}