the ppx shouldn't automatically pull the runtime library as a dependency

[Khady]

The code generated by the ppx does not depend on any lib. So this line could be removed. And consumers of the lib could add a dependency themselves if they wish to.

ppx_deriving_jsonschema/src/dune

Line 7 in 975e867

(ppx_runtime_libraries ppx_deriving_jsonschema.runtime))