Reference key storage api (#447)

* codegen: Update polkadot.rs

polkadot commit-hash: d96d3bea85
polkadot tag: v0.9.16-rc2

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Reference key storage api

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Regenerate polkadot.rs with reference api

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Update tests with reference interface

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* cli: Fix polkadot.rs license check

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Update polkadot.rs with copyright

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Revert "codegen: Update polkadot.rs with copyright"

This reverts commit 2970d0573dc0b11d01072b270a525ad497992ddf.

Revert "cli: Fix polkadot.rs license check"

This reverts commit 6fe8818582ae39669c059c1ed0424b6606620295.

* codegen: Implement AccountData trait in the expected order

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Store implementation of StorageEntry

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Generate AccountDefaultData wrapper struct

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Allow `Account` references

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Update polkadot.rs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Utilize AccountDefaultData instead of Account

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Update polkadot.rs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Update tests to utilize `Account` reference

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Rename AccountDefaultData to AccountOwned

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Add comments for wrapper account

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Obtain vector type parameter for TypePath::Type

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Use slices instead of `& std::vec` in storage API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Update polkadot.rs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Fix documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Remove extra reference

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* examples: Add staking example to exercise storage API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Update polkadot.rs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Update storage tests

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Fix cargo clippy

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Simplify vec_type_param

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* examples: Rename staking_details.rs to fetch_staking_details.rs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Remove dummy variable

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* examples: Update polkadot version

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Apply rust-fmt

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* codegen: Regenerate polkadot.rs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* examples: Remove comment

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

codegen/src/types/type_path.rs

@@ -76,6 +76,21 @@ impl TypePath {
             Self::Substitute(sub) => sub.parent_type_params(acc),
         }
     }
+
+    /// Gets the vector type parameter if the data is represented as `TypeDef::Sequence`.
+    ///
+    /// **Note:** Utilized for transforming `std::vec::Vec<T>` into slices `&[T]` for the storage API.
+    pub fn vec_type_param(&self) -> Option<&TypePath> {
+        let ty = match self {
+            TypePath::Type(ty) => ty,
+            _ => return None,
+        };
+
+        match ty.ty.type_def() {
+            TypeDef::Sequence(_) => Some(&ty.params[0]),
+            _ => None,
+        }
+    }
 }
 
 #[derive(Clone, Debug)]