Exclude runtime code from (at least wasm) light client bundle

[svyatonik]

Original problem description by @amaurymartiny: "the wasm light client has not 1 but 2 runtimes bundled in it: one in wasm and one in native (which is also wasm in our case)"

So the idea we have is to exclude both runtimes from (at least wasm) light client compilation. We have agreed that runtime code should still be included as storage entry in ChainSpec/GenesisConfig (we still need genesis runtime code for consensus modules initialization).

The main problem is that we need something similar to RuntimeApi, in order to compile Client (and its own clients - RPCs, consensus modules, ...). And RuntimeApi is provided by runtime, which we want to exclude from compilation. The simplest option is to generate that struct at the native node side, but then we need to sync apis that are implemented every time we add/remove something from runtime, which is unacceptable The other solution could be 3rd compilation mode for runtime (in addition to wasm and native) - light-native, which will only expose RuntimeApi implementation (that is something I've originally suggested in #3875 ).

[bkchr]

which will only expose RuntimeApi implementation (that is something I've originally suggested in #3875 )

This sounds like the best way IMHO. We could let the macros just generate the code that encodes the parameters and calls the appropriate function (which will be a remote call).

[EmmanuellNorbertTulbure]

Is this still relevant @svyatonik ? Asking to know if I should migrate it or not.