Create a Basic Proving Trie for the Runtime (#3881)

This PR will introduce a `BasicProvingTrie` type, which makes it easy to
construct and prove data in a base-16 merkle trie within the runtime.

Data into the merkle trie only require that they implement `Encode` /
`Decode`.

A FRAME compatible `TrieError` was created and added to `DispatchError`.

Expected usage is to construct the merkle trie with all data offline,
and then place only the merkle root of that trie on-chain.

Also offchain, a user is given a compact merkle proof of some data they
want to prove exists on the blockchain.

Then in the runtime, you can call `verify_single_value_proof` or
`verify_proof` with the root, proof, and the keys and values you want to
verify exists in the merkle trie.

Closes #3880

Contributes to #5400

---------

Co-authored-by: Ankan <[email protected]>
Co-authored-by: Oliver Tale-Yazdi <[email protected]>

prdoc/pr_3881.prdoc

@@ -0,0 +1,15 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Introduce a Generic Proving Trie
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      This PR introduces a Proving Trie object which can be used inside the runtime. This can allow
+      for things like airdrops where a single hash is stored on chain representing the whole airdrop
+      and individuals present a proof of their inclusion in the airdrop.
+
+crates:
+  - name: sp-runtime
+    bump: major

substrate/primitives/runtime/Cargo.toml

@@ -32,6 +32,7 @@ sp-arithmetic = { workspace = true }
 sp-core = { workspace = true }
 sp-io = { workspace = true }
 sp-std = { workspace = true }
+sp-trie = { workspace = true }
 sp-weights = { workspace = true }
 docify = { workspace = true }
 tracing = { workspace = true, features = ["log"], default-features = false }
@@ -69,6 +70,7 @@ std = [
 	"sp-state-machine/std",
 	"sp-std/std",
 	"sp-tracing/std",
+	"sp-trie/std",
 	"sp-weights/std",
 	"tracing/std",
 ]

substrate/primitives/runtime/src/lib.rs

@@ -90,6 +90,7 @@ pub mod generic;
 pub mod legacy;
 mod multiaddress;
 pub mod offchain;
+pub mod proving_trie;
 pub mod runtime_logger;
 mod runtime_string;
 #[cfg(feature = "std")]
@@ -103,6 +104,8 @@ pub use crate::runtime_string::*;
 // Re-export Multiaddress
 pub use multiaddress::MultiAddress;
 
+use proving_trie::TrieError;
+
 /// Re-export these since they're only "kind of" generic.
 pub use generic::{Digest, DigestItem};
 
@@ -592,6 +595,8 @@ pub enum DispatchError {
 	Unavailable,
 	/// Root origin is not allowed.
 	RootNotAllowed,
+	/// An error with tries.
+	Trie(TrieError),
 }
 
 /// Result of a `Dispatchable` which contains the `DispatchResult` and additional information about
@@ -697,6 +702,12 @@ impl From<ArithmeticError> for DispatchError {
 	}
 }
 
+impl From<TrieError> for DispatchError {
+	fn from(e: TrieError) -> DispatchError {
+		Self::Trie(e)
+	}
+}
+
 impl From<&'static str> for DispatchError {
 	fn from(err: &'static str) -> DispatchError {
 		Self::Other(err)
@@ -721,6 +732,7 @@ impl From<DispatchError> for &'static str {
 			Corruption => "State corrupt",
 			Unavailable => "Resource unavailable",
 			RootNotAllowed => "Root not allowed",
+			Trie(e) => e.into(),
 		}
 	}
 }
@@ -768,6 +780,10 @@ impl traits::Printable for DispatchError {
 			Corruption => "State corrupt".print(),
 			Unavailable => "Resource unavailable".print(),
 			RootNotAllowed => "Root not allowed".print(),
+			Trie(e) => {
+				"Trie error: ".print();
+				<&'static str>::from(*e).print();
+			},
 		}
 	}
 }