Introduce original_storage and original_storage_hash (#2211)

Both functions will ignore any overlayed changes and access the backend
directly.

substrate/core/state-machine/src/basic.rs

@@ -111,6 +111,10 @@ impl<H: Hasher> Externalities<H> for BasicExternalities where H::Out: Ord + Heap
 		}
 	}
 
+	fn original_storage(&self, key: &[u8]) -> Option<Vec<u8>> {
+		Externalities::<H>::storage(self, key)
+	}
+
 	fn child_storage(&self, _storage_key: &[u8], _key: &[u8]) -> Option<Vec<u8>> {
 		None
 	}

substrate/core/state-machine/src/ext.rs

@@ -204,6 +204,16 @@ where
 			self.backend.storage_hash(key).expect(EXT_NOT_ALLOWED_TO_FAIL))
 	}
 
+	fn original_storage(&self, key: &[u8]) -> Option<Vec<u8>> {
+		let _guard = panic_handler::AbortGuard::new(true);
+		self.backend.storage(key).expect(EXT_NOT_ALLOWED_TO_FAIL)
+	}
+
+	fn original_storage_hash(&self, key: &[u8]) -> Option<H::Out> {
+		let _guard = panic_handler::AbortGuard::new(true);
+		self.backend.storage_hash(key).expect(EXT_NOT_ALLOWED_TO_FAIL)
+	}
+
 	fn child_storage(&self, storage_key: &[u8], key: &[u8]) -> Option<Vec<u8>> {
 		let _guard = panic_handler::AbortGuard::new(true);
 		self.overlay.child_storage(storage_key, key).map(|x| x.map(|x| x.to_vec())).unwrap_or_else(||

substrate/core/state-machine/src/lib.rs

@@ -95,6 +95,15 @@ pub trait Externalities<H: Hasher> {
 		self.storage(key).map(|v| H::hash(&v))
 	}
 
+	/// Read original runtime storage, ignoring any overlayed changes.
+	fn original_storage(&self, key: &[u8]) -> Option<Vec<u8>>;
+
+	/// Get original storage value hash, ignoring any overlayed changes.
+	/// This may be optimized for large values.
+	fn original_storage_hash(&self, key: &[u8]) -> Option<H::Out> {
+		self.original_storage(key).map(|v| H::hash(&v))
+	}
+
 	/// Read child runtime storage.
 	fn child_storage(&self, storage_key: &[u8], key: &[u8]) -> Option<Vec<u8>>;
 

substrate/core/state-machine/src/testing.rs

@@ -118,6 +118,10 @@ impl<H: Hasher> Externalities<H> for TestExternalities<H> where H::Out: Ord + He
 		}
 	}
 
+	fn original_storage(&self, key: &[u8]) -> Option<Vec<u8>> {
+		self.storage(key)
+	}
+
 	fn child_storage(&self, storage_key: &[u8], key: &[u8]) -> Option<Vec<u8>> {
 		self.changes.child_storage(storage_key, key)?.map(Vec::from)
 	}