It looks like pattern types need to be generalized at the same level …

…as the current execution. Fixes: #2773

src/lang/typechecking.ml

@@ -338,7 +338,7 @@ let rec check ?(print_toplevel = false) ~throw ~level ~(env : Typing.env) e =
           (* Printf.printf "generalize at %d: %B\n\n!" level (value_restriction def); *)
           if value_restriction def then fst (generalize ~level def.t) else []
         in
-        let penv, pa = type_of_pat ~level:(level + 1) ~pos pat in
+        let penv, pa = type_of_pat ~level ~pos pat in
         def.t <: pa;
         let penv =
           List.map

tests/language/type_errors.liq

@@ -231,6 +231,23 @@ def f() =
     end
   ")
 
+  incorrect('
+  def g() =
+    s = single("foo")
+
+    s = s
+
+    enc = %ffmpeg(
+      format="mkv",
+      %audio(codec="aac"),
+      %video(codec="aac")
+    )
+
+    output.file(fallible=true, enc, "/tmp/bla.mkv", s)
+
+    ignore(ffmpeg.decode.audio(s))
+  end')
+
   test.pass()
 end