Revive original test

Make another test to exercise the original large search behavior

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -183,6 +183,7 @@ class CompilationTests {
       compileFile("tests/neg-custom-args/feature-shadowing.scala", defaultOptions.and("-Xfatal-warnings", "-feature")),
       compileDir("tests/neg-custom-args/hidden-type-errors", defaultOptions.and("-explain")),
       compileFile("tests/neg-custom-args/i13026.scala", defaultOptions.and("-print-lines")),
+      compileFile("tests/neg-custom-args/i13838.scala", defaultOptions.and("-Ximplicit-search-limit", "1000")),
     ).checkExpectedErrors()
   }
 

tests/neg-custom-args/i13838.check

@@ -0,0 +1,26 @@
+-- Error: tests/neg-custom-args/i13838.scala:10:5 ----------------------------------------------------------------------
+10 |  foo  // error
+   |     ^
+   |no implicit argument of type Order[X] was found for parameter x$1 of method foo in object FooT
+   |
+   |where:    X is a type variable
+   |.
+   |I found:
+   |
+   |    FooT.OrderFFooA[F, A](FooT.OrderFFooA[F, A](/* missing */summon[Order[F[Foo[A]]]]))
+   |
+   |But given instance OrderFFooA in object FooT produces a diverging implicit search when trying to match type Order[F[Foo[A]]].
+-- [E168] Type Warning: tests/neg-custom-args/i13838.scala:10:5 --------------------------------------------------------
+10 |  foo  // error
+   |     ^
+   |     Implicit search problem too large.
+   |     an implicit search was terminated with failure after trying 1000 expressions.
+   |     The root candidate for the search was:
+   |
+   |       given instance OrderFFooA in object FooT  for  Order[Any]}
+   |
+   |     You can change the behavior by setting the `-Ximplicit-search-limit` value.
+   |     Smaller values cause the search to fail faster.
+   |     Larger values might make a very large search problem succeed.
+
+longer explanation available when compiling with `-explain`

tests/neg/i13838.scala → tests/neg-custom-args/i13838.scala

@@ -5,7 +5,9 @@ object Foo:
   given [A: Eq]: Eq[Foo[A]] = ???
 
 object FooT:
-  def liftF[F[_], A](fa: F[A]): F[Foo[A]] = map(fa)(???)  // error
+
+  def foo[X](using Order[X]): Unit = ???
+  foo  // error
 
   def map[F[_], A](ffa: F[Foo[A]])(f: A): Nothing = ???