unikernel/duniverse/ppxlib/test/recursive_replacement/run.t

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+This test checks that an extension point or attribute that expands to another extension
+point or attribute will continue to be expanded recursively until it cannot be
+expanded anymore.
+
+It uses the extension and attribute defined in driver.ml which expands:
+- [%ext x ;; ["%ext", "@attr", ...]] into [%ext xx ;; ["@attr", ...]]
+- [%ext x ;; ["@attr", "%ext", ...]] into xx [@attr ["%ext", ...]]
+- [%ext x ;; []] into xx
+- x [@attr ["%ext", "@attr", ...]] into [%ext xx ;; ["@attr", ...]]
+- x [@attr ["@attr", "%ext", ...]] into xx [@attr ["%ext", ...]]
+- x [@attr []] into xx
+
+It adds an "x" to the ident to make it clear how many times the attribute has been applied.
+
+First check that an extension point is expanded recursively:
+  $ cat > test.ml << EOF
+  > let () = [%ext a ;; ["%ext"]];;
+  > EOF
+  $ ./driver.exe test.ml
+  let () = axx
+
+An attribute is also expanded recursively:
+  $ cat > test.ml << EOF
+  > let () = b [@attr ["@attr"]];;
+  > EOF
+  $ ./driver.exe test.ml
+  let () = bxx
+
+An extension that expands into an attribute and vice versa work:
+  $ cat > test.ml << EOF
+  > let () = [%ext c ;; ["@attr"]];;
+  > let () = d [@attr ["%ext"]];;
+  > EOF
+  $ ./driver.exe test.ml
+  let () = cxx
+  let () = dxx
+
+Something a bit silly to validate it carries on until it's done:
+  $ cat > test.ml << EOF
+  > let () = e [@attr ["%ext"; "@attr"; "@attr"; "%ext"; "%ext"]];;
+  > EOF
+  $ ./driver.exe test.ml
+  let () = exxxxxx