Don't include :code by default in storage proofs (#5060)

* Adds test to verify that the runtime currently is always contained in
the proof

* Start passing the runtime wasm code from the outside

* Fix compilation

* More build fixes

* Make the test work as expected now :)

* Last fixes

* Fixes benchmarks

* Review feedback

* Apply suggestions from code review

Co-Authored-By: Sergei Pepyakin <sergei@parity.io>

* Review feedback

* Fix compilation

Co-authored-by: Sergei Pepyakin <s.pepyakin@gmail.com>

substrate/primitives/state-machine/src/backend.rs

@@ -18,9 +18,9 @@
 
 use log::warn;
 use hash_db::Hasher;
-use codec::Encode;
+use codec::{Decode, Encode};
 
-use sp_core::storage::{ChildInfo, OwnedChildInfo};
+use sp_core::{traits::RuntimeCode, storage::{ChildInfo, OwnedChildInfo, well_known_keys}};
 use sp_trie::{TrieMut, MemoryDB, trie_types::TrieDBMut};
 
 use crate::{
@@ -359,3 +359,22 @@ pub(crate) fn insert_into_memory_db<H, I>(mdb: &mut MemoryDB<H>, input: I) -> Op
 
 	Some(root)
 }
+
+/// Get the runtime code from the given `backend`.
+///
+/// Returns an error if the `:code` could not be found.
+pub fn get_runtime_code<H: Hasher, B: Backend<H>>(backend: &B) -> Result<RuntimeCode, &'static str>
+	where H::Out: Encode,
+{
+	let code = backend.storage(well_known_keys::CODE)
+		.ok()
+		.flatten()
+		.ok_or("`:code` not found")?;
+	let hash = H::hash(&code).encode();
+	let heap_pages = backend.storage(well_known_keys::HEAP_PAGES)
+		.ok()
+		.flatten()
+		.and_then(|d| Decode::decode(&mut &d[..]).ok());
+
+	Ok(RuntimeCode { code, hash, heap_pages })
+}